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Polymers, Volume 9, Issue 8 (August 2017)

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Cover Story Threadings are architecture-specific topological constraints that give rise to complex and [...] Read more.
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Open AccessArticle Synthesis of Novel Hyperbranched Polybenzo-Bisthiazole Amide with Donor–Acceptor (D-A) Architecture, High Fluorescent Quantum Yield and Large Stokes Shift
Polymers 2017, 9(8), 304; doi:10.3390/polym9080304
Received: 23 June 2017 / Revised: 16 July 2017 / Accepted: 21 July 2017 / Published: 25 July 2017
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Abstract
Two novel highly fluorescent hyperbranched polybenzobisthiazole amides with a donor–acceptor architecture and large Stokes shift were rationally designed and synthesized. The chemical structures of the prepared hyperbranched polymers were characterized using Fourier Transform Infrared Spectroscopy (FTIR) analysis, Hydrogen Nuclear Magnetic Resonance (1
[...] Read more.
Two novel highly fluorescent hyperbranched polybenzobisthiazole amides with a donor–acceptor architecture and large Stokes shift were rationally designed and synthesized. The chemical structures of the prepared hyperbranched polymers were characterized using Fourier Transform Infrared Spectroscopy (FTIR) analysis, Hydrogen Nuclear Magnetic Resonance (1H-NMR) analysis, and Gel Permeation Chromatography (GPC) analysis. These two polymers were soluble in dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF), and their DMSO and DMF solutions emitted strong green light (517–537 nm) with high quantum yields (QYs) and large Stokes shifts. Their relative fluorescence QYs in the DMSO solution were calculated as 77.75% and 81.14% with the Stokes shifts of 137 nm (0.86 eV) and 149 nm (0.92 eV) for HP–COOH and HP–NH2, respectively, using quinine sulfate as the standard. In the DMF solution, the QYs of HP–COOH and HP–NH2 were calculated as 104.65% and 118.72%, with the Stokes shifts of 128 nm (0.79 eV) and 147 nm (0.87 eV), respectively. Their films mainly emitted strong blue light with the maximum emission wavelengths of 436 nm and 480 nm for HP–COOH and HP–NH2, respectively. The Stokes shifts for HP–COOH and HP–NH2 films were 131 nm (0.42 eV) and 179 nm (0.86 eV), respectively. They are promising candidates for luminescent solar concentrators and blue light emitting materials. Full article
(This article belongs to the Special Issue Polymeric Materials for Optical Applications)
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Open AccessArticle Inducing β Phase Crystallinity in Block Copolymers of Vinylidene Fluoride with Methyl Methacrylate or Styrene
Polymers 2017, 9(8), 306; doi:10.3390/polym9080306
Received: 20 June 2017 / Revised: 19 July 2017 / Accepted: 20 July 2017 / Published: 26 July 2017
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Abstract
Block copolymers of poly(vinylidene fluoride) (PVDF) with either styrene or methyl methacrylate (MMA) were synthesized and analyzed with respect to the type of the crystalline phase occurring. PVDF with iodine end groups (PVDF-I) was prepared by iodine transfer polymerization either in solution with
[...] Read more.
Block copolymers of poly(vinylidene fluoride) (PVDF) with either styrene or methyl methacrylate (MMA) were synthesized and analyzed with respect to the type of the crystalline phase occurring. PVDF with iodine end groups (PVDF-I) was prepared by iodine transfer polymerization either in solution with supercritical CO2 or in emulsion. To activate all iodine end groups Mn2(CO)10 is employed. Upon UV irradiation Mn(CO)5 radicals are obtained, which abstract iodine from PVDF-I generating PVDF radicals. Subsequent polymerization with styrene or methyl methacrylate (MMA) yields block copolymers. Size exclusion chromatography and NMR results prove that the entire PVDF-I is converted. XRD, FT-IR, and differential scanning calorimetry (DSC) analyses allow for the identification of crystal phase transformation. It is clearly shown that the original α crystalline phase of PVDF-I is changed to the β crystalline phase in case of the block copolymers. For ratios of the VDF block length to the MMA block length ranging from 1.4 to 5 only β phase material was detected. Full article
(This article belongs to the Special Issue Fluorinated Polymers)
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Open AccessArticle Effects of RAFT Agent on the Chloromethylstyrene Polymerizations in a Simultaneous Radiation Grafting System
Polymers 2017, 9(8), 307; doi:10.3390/polym9080307
Received: 21 June 2017 / Revised: 20 July 2017 / Accepted: 21 July 2017 / Published: 26 July 2017
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Abstract
Reversible addition-fragmentation chain transfer (RAFT) agent was added into a simultaneous radiation grafting system and its effects on graft polymerization and homopolymerization were investigated. Chloromethylstyrene (CMS) was graft polymerized onto ethylene-tetrafluoroethylene copolymer (ETFE) films under γ-ray sources via simultaneous irradiation. The non-grafted poly(CMS)
[...] Read more.
Reversible addition-fragmentation chain transfer (RAFT) agent was added into a simultaneous radiation grafting system and its effects on graft polymerization and homopolymerization were investigated. Chloromethylstyrene (CMS) was graft polymerized onto ethylene-tetrafluoroethylene copolymer (ETFE) films under γ-ray sources via simultaneous irradiation. The non-grafted poly(CMS) in the grafted films were extracted by xylene at 120 °C. The poly(CMS) was characterized by NMR and GPC instruments. Addition of the RAFT agent suppressed both graft polymerization and homopolymerization. However, under a high concentration of RAFT agent, the homopolymerization in the monomer solution could occur through a typical RAFT polymerization while polymerization in the ETFE films proceeded via RAFT and conventional radical polymerization, resulting in poly(CMS) in the ETFE films with molecular weight dispersity higher than 1.0 but lower than that without RAFT agent. Furthermore, it was found that the molecular weight of the poly(CMS) in the ETFE films was several times higher than that of the poly(CMS) in the monomer solution. Full article
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Open AccessArticle Photooxidation Behavior of a LDPE/Clay Nanocomposite Monitored through Creep Measurements
Polymers 2017, 9(8), 308; doi:10.3390/polym9080308
Received: 26 June 2017 / Revised: 17 July 2017 / Accepted: 19 July 2017 / Published: 26 July 2017
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Abstract
Creep behavior of polymer nanocomposites has not been extensively investigated so far, especially when its effects are combined with those due to photooxidation, which are usually studied in completely independent ways. In this work, the photooxidation behavior of a low density polyethylene/organomodified clay
[...] Read more.
Creep behavior of polymer nanocomposites has not been extensively investigated so far, especially when its effects are combined with those due to photooxidation, which are usually studied in completely independent ways. In this work, the photooxidation behavior of a low density polyethylene/organomodified clay nanocomposite system was monitored by measuring the creep curves obtained while subjecting the sample to the combined action of temperature, tensile stress, and UV radiation. The creep curves of the irradiated samples were found to be lower than those of the non-irradiated ones and progressively diverging, because of the formation of branching and cross-linking due to photooxidation. This was further proved by the decrease of the melt index and the increase of the intrinsic viscosity; at the same time, the formation of carbonyl groups was observed. This behavior was more observable in the nanocomposite sample, because of its faster photooxidation kinetics. Full article
(This article belongs to the Special Issue Polymer Nanocomposites)
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Open AccessArticle Fabrication of Highly Crosslinked Gelatin Hydrogel and Its Influence on Chondrocyte Proliferation and Phenotype
Polymers 2017, 9(8), 309; doi:10.3390/polym9080309
Received: 24 May 2017 / Revised: 20 July 2017 / Accepted: 22 July 2017 / Published: 26 July 2017
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Abstract
Gelatin methacrylate (GelMA) hydrogels have been widely studied for biomedical applications, such as tissue engineering and drug delivery, because of their good biocompatibility and injectability. However, the quick degradation and low mechanical property of GelMA hydrogels need to be improved for further applications,
[...] Read more.
Gelatin methacrylate (GelMA) hydrogels have been widely studied for biomedical applications, such as tissue engineering and drug delivery, because of their good biocompatibility and injectability. However, the quick degradation and low mechanical property of GelMA hydrogels need to be improved for further applications, especially for long-term implantation. In this study, a sequential double modification of gelatin was used to achieve high density of photocrosslinkable double bonds in gelatin derivatives. The amino groups in gelatin were first reacted with methacrylic anhydride. After this, the hydroxyl and carboxyl groups in gelatin were reacted with glycidyl methacrylate to obtain the double modified gelatin macromer. The double modified gelatin macromer was used to prepare gelatin hydrogels with high crosslinking density. The hydrogels exhibited high storage modulus and low degradation. Culture of bovine articular chondrocytes in the gelatin hydrogels showed that chondrocytes had round morphology and maintained a cartilaginous phenotype while cell proliferation was hampered. This method for increasing crosslinking density should be useful for preparation of stable hydrogels for cartilage tissue engineering. Full article
(This article belongs to the Special Issue Hydrogels in Tissue Engineering and Regenerative Medicine)
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Open AccessArticle Flexible Polymer Device Based on Parylene-C with Memory and Temperature Sensing Functionalities
Polymers 2017, 9(8), 310; doi:10.3390/polym9080310
Received: 20 June 2017 / Revised: 18 July 2017 / Accepted: 25 July 2017 / Published: 26 July 2017
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Abstract
Polychloro-para-xylylene (parylene-C) is a flexible and transparent polymer material which has excellent chemical stability and high biocompatibility. Here we demonstrate a polymer device based on single-component parylene-C with memory and temperature sensing functionalities. The device shows stable bipolar resistive switching behavior, remarkable storage
[...] Read more.
Polychloro-para-xylylene (parylene-C) is a flexible and transparent polymer material which has excellent chemical stability and high biocompatibility. Here we demonstrate a polymer device based on single-component parylene-C with memory and temperature sensing functionalities. The device shows stable bipolar resistive switching behavior, remarkable storage window (>104), and low operation voltages, exhibiting great potential for flexible resistive random-access memory (RRAM) applications. The I-V curves and conductive atomic force microscopy (CAFM) results verify the metallic filamentary-type switching mechanism based on the formation and dissolution of a metal bridge related to the redox reaction of the active metal electrode. In addition, due to the metallic properties of the low-resistance state (LRS) in the polymer device, the resistance in the LRS exhibits a nearly linear relationship at the temperature regime between 25 °C and 100 °C. With a temperature coefficient of resistance (TCR) of 2.136 × 10−3/°C, the device is also promising for the flexible temperature sensor applications. Full article
(This article belongs to the Special Issue Wearable Sensor)
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Open AccessArticle Characterisation and Evaluation of Trimesic Acid Derivatives as Disulphide Cross-Linked Polymers for Potential Colon Targeted Drug Delivery
Polymers 2017, 9(8), 311; doi:10.3390/polym9080311
Received: 29 May 2017 / Revised: 14 July 2017 / Accepted: 20 July 2017 / Published: 27 July 2017
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Abstract
Discovery and use of biocompatible polymers offers great promise in the pharmaceutical field, particularly in drug delivery systems. Disulphide bonds, which commonly occur in peptides and proteins and have been used as drug-glutathione conjugates, are reductively cleaved in the colon. The intrinsic stability
[...] Read more.
Discovery and use of biocompatible polymers offers great promise in the pharmaceutical field, particularly in drug delivery systems. Disulphide bonds, which commonly occur in peptides and proteins and have been used as drug-glutathione conjugates, are reductively cleaved in the colon. The intrinsic stability of a disulphide relative to thiol groups is determined by the redox potential of the environment. The objective of this study was to synthesise a trimesic acid-based disulphide cross-linked polymer that could potentially be used for targeted delivery to the colon. The monomer was synthesised by an amide coupling reaction between trimesic acid and (triphenylmethyl) thioethylamine using a two-step synthesis method. The s-trityl group was removed using a cocktail of trifluoroacetic acid and triethylsilane to expose the thiols in preparation for further polymerisation. The resulting polymers (P10, P15, P21, P25, and P51, generated using different molar ratios) were reduced after 1.5 h of reduction time. Scanning electron microscopy images of the polymers showed spherical, loose, or tight patterns depending on the molar ratio of polymerisation. These polymers also exhibited efficient dissolution under various gastrointestinal conditions. Of the five polymers tested, P10 and P15 appeared to be promising drug delivery vehicles for poorly soluble drugs, due to the hydrophobic nature of the polymers. Full article
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Open AccessArticle Properties of Soy Protein Isolate Biopolymer Film Modified by Graphene
Polymers 2017, 9(8), 312; doi:10.3390/polym9080312
Received: 21 June 2017 / Revised: 22 July 2017 / Accepted: 25 July 2017 / Published: 27 July 2017
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Abstract
This study applied a facile and green approach to synthesize a stable graphene aqueous dispersion, and the graphene aqueous dispersion was employed to modify the renewable, compatible and biodegradable soy-protein-isolated (SPI) films to enhance their thermal stability, mechanical properties and water resistance. Atomic
[...] Read more.
This study applied a facile and green approach to synthesize a stable graphene aqueous dispersion, and the graphene aqueous dispersion was employed to modify the renewable, compatible and biodegradable soy-protein-isolated (SPI) films to enhance their thermal stability, mechanical properties and water resistance. Atomic force microscopy (AFM) images confirmed the monolayer structure of graphene. The hydrogen bonds and π–π interactions between graphene and the SPI molecules were showed with the attenuated total reflectance Fourier transform infrared (ATR FT-IR) spectroscopy, and X-ray diffraction (XRD). As expected, compared to the pure SPI film, the tensile strength (TS) of the film with 74% graphene increased by 27.22% and the total soluble matter (TSM) of the film with 93% graphene decreased by 11.30%. Full article
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Open AccessArticle Structural Behavior of a Semiflexible Polymer Chain in an Array of Nanoposts
Polymers 2017, 9(8), 313; doi:10.3390/polym9080313
Received: 2 July 2017 / Revised: 24 July 2017 / Accepted: 25 July 2017 / Published: 28 July 2017
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Abstract
The structural properties of a flexible and semiflexible circular chain confined in an array of parallel nanoposts with a square lattice cross-sectional projection were studied using coarse-grained molecular dynamics simulations. To address the effect of the circular topology, a comparison with linear analogs
[...] Read more.
The structural properties of a flexible and semiflexible circular chain confined in an array of parallel nanoposts with a square lattice cross-sectional projection were studied using coarse-grained molecular dynamics simulations. To address the effect of the circular topology, a comparison with linear analogs was also carried out. In the interpretation of the chain structural properties, the geometry of the post array is considered as a combination of a channel approximating the interstitial volume with the diameter dc and a slit approximating the passage aperture with the width wp. The number of interstitial volumes occupied by a chain monotonically increases with the decreasing ratio dc/wp regardless of the way the geometry of the post array is varied. However, depending on how the array geometry is modified, the chain span along the posts displays a monotonic (constant post separation) or a non-monotonic behavior (constant passage width) when plotted as a function of the post diameter. In the case of monotonic trend, the width of interstitial spaces increases with the increasing chain occupation number, while, in the case of non-monotonic trend, the width of interstitial spaces decreases with the increasing chain occupation number. In comparison with linear topology, for circular topology, the stiffness affects more significantly the relative chain extension along the posts and less significantly the occupation number. The geometrical parameters of the post arrays are stored in the single-chain structure factors. The characteristic humps are recognized in the structure factor which ensue from the local increase in the density of segments in the circular chains presented in an interstitial volume or from the correlation of parallel chain fragments separated by a row of posts. Although the orientation correlations provide qualitative information about the chain topology and the character of confinement within a single interstitial volume, information about the array periodicity is missing. Full article
(This article belongs to the Special Issue Knotted and Catenated Polymers)
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Open AccessArticle Biodegradation of Halloysite Nanotubes-Polyester Nanocomposites Exposed to Short Term Seawater Immersion
Polymers 2017, 9(8), 314; doi:10.3390/polym9080314
Received: 9 June 2017 / Revised: 6 July 2017 / Accepted: 25 July 2017 / Published: 28 July 2017
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Abstract
Halloysite nanotubes (HNTs)-polyester nanocomposites with four different concentrations were produced using solution casting technique and the biodegradation effect of short-term seawater exposure (120 h) was studied. Monolithic polyester was observed to have the highest seawater absorption with 1.37%. At 0.3 wt % HNTs
[...] Read more.
Halloysite nanotubes (HNTs)-polyester nanocomposites with four different concentrations were produced using solution casting technique and the biodegradation effect of short-term seawater exposure (120 h) was studied. Monolithic polyester was observed to have the highest seawater absorption with 1.37%. At 0.3 wt % HNTs reinforcement, the seawater absorption dropped significantly to the lowest value of 0.77% due to increase of liquid diffusion path. For samples tested in dry conditions, the Tg, storage modulus, tensile properties and flexural properties were improved. The highest improvement of Tg was from 79.3 to 82.4 °C (increase 3.1 °C) in the case of 0.3 wt % HNTs. This can be associated with the exfoliated HNTs particles, which restrict the mobility of polymer chains and thus raised the Tg. After seawater exposure, the Tg, storage modulus, tensile properties and flexural properties of polyester and its nanocomposites were decreased. The Young’s modulus of 0.3 wt % HNTs-polyester dropped 20% while monolithic polyester dropped up to 24% compared to their values in dry condition. Apart from that, 29% flexural modulus reduction was observed, which was 18% higher than monolithic polyester. In contrast, fracture toughness and surface roughness increased due to plasticization effect. The presence of various microbial communities caused gradual biodegradation on the microstructure of the polyester matrix as also evidently shown by SEM images. Full article
(This article belongs to the Special Issue Polymer Nanocomposites)
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Open AccessArticle Exceptionally High Negative Electro-Caloric Effects of Poly(VDF–co–TrFE) Based Nanocomposites Tuned by the Geometries of Barium Titanate Nanofillers
Polymers 2017, 9(8), 315; doi:10.3390/polym9080315
Received: 9 July 2017 / Revised: 25 July 2017 / Accepted: 26 July 2017 / Published: 28 July 2017
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Abstract
Exceptionally high electro-caloric effects (ECEs) are observed in nanocomposites consisting of poly(vinylidene fluoride-co-trifluoroethylene) (VDF–co–TrFE) copolymer and barium titanate (BT) nanoparticles and nanowires. The poly(VDF–co–TrFE) matrix nanocomposites containing 5% volume fraction of BT nanowires are found to exhibit
[...] Read more.
Exceptionally high electro-caloric effects (ECEs) are observed in nanocomposites consisting of poly(vinylidene fluoride-co-trifluoroethylene) (VDF–co–TrFE) copolymer and barium titanate (BT) nanoparticles and nanowires. The poly(VDF–co–TrFE) matrix nanocomposites containing 5% volume fraction of BT nanowires are found to exhibit a negative ECE temperature change as large as 12 °C or a refrigeration effect of 8.3 J/g, which is much larger than those reported to date. The mechanisms of negative ECE and the enhanced negative ECE in the nanocomposites consisting of poly(VDF–co–TrFE) and BT nanowires are explained by the Kauzmann theory on glassy polar states and the interaction between BT nanofillers and the copolymer matrix. The effects of geometries of BT nanofillers on the negative ECEs are elucidated by P-E loop measurements, and dielectric and dynamical mechanical analyses. The nanocomposites, with their enhanced negative ECE tuned by the geometries of BT nanofillers, provide us with promising ECE refrigerants for practical application to small-sized and environmentally-friendly ECE coolers in the heat management of electronic devices. Full article
(This article belongs to the Special Issue Fluorinated Polymers)
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Open AccessArticle Biodegradable Core–Multishell Nanocarriers: Influence of Inner Shell Structure on the Encapsulation Behavior of Dexamethasone and Tacrolimus
Polymers 2017, 9(8), 316; doi:10.3390/polym9080316
Received: 21 June 2017 / Revised: 18 July 2017 / Accepted: 25 July 2017 / Published: 29 July 2017
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Abstract
We here present the synthesis and characterization of a set of biodegradable core–multishell (CMS) nanocarriers. The CMS nanocarrier structure consists of hyperbranched polyglycerol (hPG) as core material, a hydrophobic (12, 15, 18, 19, and 36 C-atoms) inner and a polyethylene glycol monomethyl ether
[...] Read more.
We here present the synthesis and characterization of a set of biodegradable core–multishell (CMS) nanocarriers. The CMS nanocarrier structure consists of hyperbranched polyglycerol (hPG) as core material, a hydrophobic (12, 15, 18, 19, and 36 C-atoms) inner and a polyethylene glycol monomethyl ether (mPEG) outer shell that were conjugated by ester bonds only to reduce the toxicity of metabolites. The loading capacities (LC) of the drugs, dexamethasone and tacrolimus, and the aggregate formation, phase transitions, and degradation kinetics were determined. The intermediate inner shell length (C15) system had the best overall performance with good LCs for both drugs as well as a promising degradation and release kinetics, which are of interest for dermal delivery. Full article
(This article belongs to the Special Issue Polymers and Block Copolymers at Interfaces and Surfaces)
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Open AccessArticle Are There Knots in Chromosomes?
Polymers 2017, 9(8), 317; doi:10.3390/polym9080317
Received: 30 June 2017 / Revised: 24 July 2017 / Accepted: 25 July 2017 / Published: 2 August 2017
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Abstract
Recent developments have for the first time allowed the determination of three-dimensional structures of individual chromosomes and genomes in nuclei of single haploid mouse embryonic stem (ES) cells based on Hi–C chromosome conformation contact data. Although these first structures have a relatively low
[...] Read more.
Recent developments have for the first time allowed the determination of three-dimensional structures of individual chromosomes and genomes in nuclei of single haploid mouse embryonic stem (ES) cells based on Hi–C chromosome conformation contact data. Although these first structures have a relatively low resolution, they provide the first experimental data that can be used to study chromosome and intact genome folding. Here we further analyze these structures and provide the first evidence that G1 phase chromosomes are knotted, consistent with the fact that plots of contact probability vs sequence separation show a power law dependence that is intermediate between that of a fractal globule and an equilibrium structure. Full article
(This article belongs to the Special Issue Knotted and Catenated Polymers)
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Open AccessFeature PaperArticle In Vitro Evaluation of Essential Mechanical Properties and Cell Behaviors of a Novel Polylactic-co-Glycolic Acid (PLGA)-Based Tubular Scaffold for Small-Diameter Vascular Tissue Engineering
Polymers 2017, 9(8), 318; doi:10.3390/polym9080318
Received: 12 June 2017 / Revised: 23 July 2017 / Accepted: 27 July 2017 / Published: 30 July 2017
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Abstract
In this paper, we investigate essential mechanical properties and cell behaviors of the scaffolds fabricated by rolling polylactic-co-glycolic acid (PLGA) electrospinning (ES) films for small-diameter vascular grafts (inner diameter < 6 mm). The newly developed strategy can be used to fabricate
[...] Read more.
In this paper, we investigate essential mechanical properties and cell behaviors of the scaffolds fabricated by rolling polylactic-co-glycolic acid (PLGA) electrospinning (ES) films for small-diameter vascular grafts (inner diameter < 6 mm). The newly developed strategy can be used to fabricate small diameter vascular grafts with or without pre-seeded cells, which are two main branches for small diameter vascular engineering. We demonstrate that the mechanical properties of our rolling-based scaffolds can be tuned flexibly by the number of layers. For cell-free scaffolds, with the increase of layer number, burst pressure and suture retention increase, elastic tensile modulus maintains unchanged statistically, but compliance and liquid leakage decrease. For cell-containing scaffolds, seeding cells will significantly decrease the liquid leakage, but there are no statistical differences for other mechanical properties; moreover, cells live and proliferate well in the scaffold after a 6-day culture. Full article
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Open AccessArticle Manipulating Living Cells to Construct a 3D Single-Cell Assembly without an Artificial Scaffold
Polymers 2017, 9(8), 319; doi:10.3390/polym9080319
Received: 30 June 2017 / Revised: 24 July 2017 / Accepted: 25 July 2017 / Published: 30 July 2017
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Abstract
Artificial scaffolds such as synthetic gels or chemically-modified glass surfaces that have often been used to achieve cell adhesion are xenobiotic and may harm cells. To enhance the value of cell studies in the fields of regenerative medicine and tissue engineering, it is
[...] Read more.
Artificial scaffolds such as synthetic gels or chemically-modified glass surfaces that have often been used to achieve cell adhesion are xenobiotic and may harm cells. To enhance the value of cell studies in the fields of regenerative medicine and tissue engineering, it is becoming increasingly important to create a cell-friendly technique to promote cell–cell contact. In the present study, we developed a novel method for constructing stable cellular assemblies by using optical tweezers in a solution of a natural hydrophilic polymer, dextran. In this method, a target cell is transferred to another target cell to make cell–cell contact by optical tweezers in a culture medium containing dextran. When originally non-cohesive cells are held in contact with each other for a few minutes under laser trapping, stable cell–cell adhesion is accomplished. This method for creating cellular assemblies in the presence of a natural hydrophilic polymer may serve as a novel next-generation 3D single-cell assembly system with future applications in the growing field of regenerative medicine. Full article
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Open AccessArticle One-Pot Synthesis of Charged Amphiphilic Diblock and Triblock Copolymers Via High-Throughput Cu(0)-Mediated Polymerization
Polymers 2017, 9(8), 320; doi:10.3390/polym9080320
Received: 7 July 2017 / Revised: 23 July 2017 / Accepted: 26 July 2017 / Published: 30 July 2017
PDF Full-text (3823 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Block copolymers containing functionalized monomers, for example those containing charged groups, can be used for many purposes, one of which is the design of polymeric supramolecular materials based on electrostatic interactions. In this paper the synthesis of diblock copolymers and ABA-triblock copolymers containing
[...] Read more.
Block copolymers containing functionalized monomers, for example those containing charged groups, can be used for many purposes, one of which is the design of polymeric supramolecular materials based on electrostatic interactions. In this paper the synthesis of diblock copolymers and ABA-triblock copolymers containing poly(n-butyl acrylate) as a first or middle block and poly(2-(dimethylamino)ethyl acrylate), poly(1-ethoxyethyl acrylate) and poly(1-ethoxyethyl-2-carboxyethyl acrylate) as second or outer blocks, resulting in block copolymers that can contain positive or negative charges, is reported. The polymerizations were performed and optimized via one-pot sequential monomer addition reactions via Cu(0)-mediated polymerization using an automated parallel synthesizer. Different initiators, monomer concentrations and polymerization times were tested. While a bromide-containing initiator led to the best results for most monomers, when polymerizing 2-(dimethylamino)ethyl acrylate the use of a chloride-containing initiator was necessary. Due to the slower polymerization using this initiator, a longer polymerization time was needed before addition of the second monomer. Using the optimized conditions, the diblock and triblock copolymers could be synthesized with good control over molecular weight and dispersities around 1.1 were obtained. Full article
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Open AccessArticle Improvement in Functional Properties of Soy Protein Isolate-Based Film by Cellulose Nanocrystal–Graphene Artificial Nacre Nanocomposite
Polymers 2017, 9(8), 321; doi:10.3390/polym9080321
Received: 11 July 2017 / Revised: 23 July 2017 / Accepted: 25 July 2017 / Published: 30 July 2017
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Abstract
A facile, inexpensive, and green approach for the production of stable graphene dispersion was proposed in this study. We fabricated soy protein isolate (SPI)-based nanocomposite films with the combination of 2D negative charged graphene and 1D positive charged polyethyleneimine (PEI)-modified cellulose nanocrystals (CNC)
[...] Read more.
A facile, inexpensive, and green approach for the production of stable graphene dispersion was proposed in this study. We fabricated soy protein isolate (SPI)-based nanocomposite films with the combination of 2D negative charged graphene and 1D positive charged polyethyleneimine (PEI)-modified cellulose nanocrystals (CNC) via a layer-by-layer assembly method. The morphologies and surface charges of graphene sheets and CNC segments were characterized by atomic force microscopy and Zeta potential measurements. The hydrogen bonds and multiple interface interactions between the filler and SPI matrix were analyzed by Attenuated Total Reflectance–Fourier Transform Infrared spectra and X-ray diffraction patterns. Scanning electron microscopy demonstrated the cross-linked and laminated structures in the fracture surface of the films. In comparison with the unmodified SPI film, the tensile strength and surface contact angles of the SPI/graphene/PEI-CNC film were significantly improved, by 99.73% and 37.13% respectively. The UV–visible light barrier ability, water resistance, and thermal stability were also obviously enhanced. With these improved functional properties, this novel bio-nanocomposite film showed considerable potential for application for food packaging materials. Full article
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Open AccessArticle Preparation of Nanocomposites of Poly(ε-caprolactone) and Multi-Walled Carbon Nanotubes by Ultrasound Micro-Molding. Influence of Nanotubes on Melting and Crystallization
Polymers 2017, 9(8), 322; doi:10.3390/polym9080322
Received: 9 July 2017 / Revised: 24 July 2017 / Accepted: 25 July 2017 / Published: 30 July 2017
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Abstract
Ultrasound micro-molding technology was successfully applied to prepare nanocomposites based on a poly(ε-caprolactone) (PCL) matrix and multi-walled carbon nanotubes (MWCNTs). Optimization of processing parameters (i.e. amplitude, force and time) was crucial to obtain nanocomposites without any evidence of degradation, high material saving and
[...] Read more.
Ultrasound micro-molding technology was successfully applied to prepare nanocomposites based on a poly(ε-caprolactone) (PCL) matrix and multi-walled carbon nanotubes (MWCNTs). Optimization of processing parameters (i.e. amplitude, force and time) was crucial to obtain nanocomposites without any evidence of degradation, high material saving and short processing time (7–8 s). Good dispersion of nanotubes was achieved after processing previously formed solvent casting films. This dispersion was even partially detected in pieces directly obtained from powder mixtures of both components. Incorporation of MWCNTs had a remarkable influence on melting and crystallization processes, which were systematically studied by time resolved synchrotron experiments. Results indicated higher melting and crystallization temperatures for the nanocomposite, with temperature differences higher than 5 °C. Carbon nanotubes were effective nucleating agents and had an influence on crystallinity, crystallization rate and even on lamellar morphology, which was evaluated by analysis of the correlation function of small angle diffraction profiles. Crystallinity within lamellar stacks was lower for the solvent casting nanocomposite, but in this case lamellae underwent a thickening process during heating that accounted for the increase in the melting temperature. Crystallization from the melt rendered similar lamellar morphologies at the end of the process due to a lamellar insertion mechanism. Full article
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Open AccessArticle Effect of Bamboo Flour Grafted Lactide on the Interfacial Compatibility of Polylactic Acid/Bamboo Flour Composites
Polymers 2017, 9(8), 323; doi:10.3390/polym9080323
Received: 21 June 2017 / Revised: 20 July 2017 / Accepted: 25 July 2017 / Published: 30 July 2017
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Abstract
Bamboo flour (BF) was grafted onto lactide (LA) in the molten state using stannous octoate as a catalyst to form BF-g-LA. Then, polylactic acid (PLA) was blended with BF (PLA/BF, 85/15 wt %) to prepare PLA/BF/BF-g-LA composites using BF-g-LA as a compatibilizer. The
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Bamboo flour (BF) was grafted onto lactide (LA) in the molten state using stannous octoate as a catalyst to form BF-g-LA. Then, polylactic acid (PLA) was blended with BF (PLA/BF, 85/15 wt %) to prepare PLA/BF/BF-g-LA composites using BF-g-LA as a compatibilizer. The grafting rate of BF was characterized using infrared testing and elemental analysis. To investigate the effect of BF-g-LA on the performance of PLA/BF/BF-g-LA composites, the phase morphology, thermal stability, and mechanical properties of the composites were characterized using scanning electron microscopy, thermogravimetric analysis, and universal material testing, respectively. The addition of BF-g-LA improved the interface compatibility between PLA and BF. When the BF-g-LA content was 2 phr, the tensile and impact strengths of PLA/BF/BF-g-LA composites were 55.3 MPa and 9.56 kJ/m2, representing 30% and 27% increases, respectively, relative to corresponding values for PLA/BF composites. Full article
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Open AccessArticle Probing the Nanoscopic Thermodynamic Fingerprint of Paramagnetic Ligands Interacting with Amphiphilic Macromolecules
Polymers 2017, 9(8), 324; doi:10.3390/polym9080324
Received: 5 July 2017 / Revised: 24 July 2017 / Accepted: 24 July 2017 / Published: 31 July 2017
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Abstract
Self-assembly of macromolecules with ligands is an intricate dynamic process that depends on a wide variety of parameters and forms the basis of many essential biological processes. We elucidate the underlying energetic processes of self-assembly in a model system consisting of amphiphilic core-shell
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Self-assembly of macromolecules with ligands is an intricate dynamic process that depends on a wide variety of parameters and forms the basis of many essential biological processes. We elucidate the underlying energetic processes of self-assembly in a model system consisting of amphiphilic core-shell polymers interacting with paramagnetic, amphiphilic ligand molecules from temperature-dependent continuous wave electron paramagnetic resonance (CW EPR) spectroscopy subsequent to spectral simulation. The involved processes as observed from the ligands’ point of view are either based on temperature-dependent association constants (KA,j,k) or dynamic rotational regime interconversion (IC) constants (KIC,j,k). The interconversion process describes a transition from Brownian (b1) towards free (b2) diffusion of ligand. Both processes exhibit non-linear van’t Hoff (lnK vs. T−1) plots in the temperature range of liquid water and we retrieve decisive dynamic information of the system from the energetic fingerprints of ligands on the nanoscale, especially from the temperature-dependent interconversion heat capacity (∆C°P,IC). Full article
(This article belongs to the Special Issue From Amphiphilic to Polyphilic Polymers)
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Open AccessArticle Use of Vanadium Complexes Bearing Naphthalene-Bridged Nitrogen-Sulfonate Ligands as Catalysts for Copolymerization of Ethylene and Propylene
Polymers 2017, 9(8), 325; doi:10.3390/polym9080325
Received: 25 June 2017 / Revised: 19 July 2017 / Accepted: 24 July 2017 / Published: 31 July 2017
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Abstract
Vanadium complexes bearing naphthalene-bridged nitrogen-sulfonate ligand ([ê2(N,O)-8-(PhN)-1-naphthalenesulfonato]VOCl (1a) and [ê2(N,O)-8-(PhN)-1-naphthalenesulfonato]VCl2 (1b)) were synthesized. Activated by ethylaluminium sesquichloride (EASC) and in the presence of ethyl trichloroacetate (ETCA) as reactivator, complexes 1a and 1b showed activities
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Vanadium complexes bearing naphthalene-bridged nitrogen-sulfonate ligand ([ê2(N,O)-8-(PhN)-1-naphthalenesulfonato]VOCl (1a) and [ê2(N,O)-8-(PhN)-1-naphthalenesulfonato]VCl2 (1b)) were synthesized. Activated by ethylaluminium sesquichloride (EASC) and in the presence of ethyl trichloroacetate (ETCA) as reactivator, complexes 1a and 1b showed activities of up to 39.1 kg polymer (mol V)−1 h−1, affording the copolymers with high molecular weights (Mw up to 28 × 104) and narrow molecular weight distributions (Mw/Mn ~ 3.0) as well as high propylene incorporation of up to 49.4%. Compared to the traditional VOCl3 system, these complexes exhibited higher propylene incorporation ability and higher catalytic activities especially at high polymerization temperatures of 50 °C and above. Determined by DSC and 13C NMR, the copolymers obtained with 1a and 1b had more random structures than that with the VOCl3 system. Full article
(This article belongs to the Special Issue Olefin Polymerization and Polyolefin)
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Open AccessArticle Nanopaper Properties and Adhesive Performance of Microfibrillated Cellulose from Different (Ligno-)Cellulosic Raw Materials
Polymers 2017, 9(8), 326; doi:10.3390/polym9080326
Received: 10 July 2017 / Revised: 26 July 2017 / Accepted: 27 July 2017 / Published: 31 July 2017
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Abstract
The self-adhesive potential of nanocellulose from aqueous cellulosic suspensions is of interest with regard to a potential replacement of synthetic adhesives. In order to evaluate the performance of microfibrillated cellulose from different (ligno-)cellulosic raw materials for this purpose, softwood and hardwood powder were
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The self-adhesive potential of nanocellulose from aqueous cellulosic suspensions is of interest with regard to a potential replacement of synthetic adhesives. In order to evaluate the performance of microfibrillated cellulose from different (ligno-)cellulosic raw materials for this purpose, softwood and hardwood powder were fibrillated and compared to sugar beet pulp as a representative non-wood cellulose resource, and conventional microfibrillated cellulose produced from bleached pulp. An alkali pre-treatment of woody and sugar beet raw materials enhanced the degree of fibrillation achieved, same as TEMPO-mediated oxidation of microfibrillated cellulose. Nanopapers produced from fibrillated material showed highly variable density and mechanical performance, demonstrating that properties may be tuned by the choice of raw material. While nanopaper strength was highest for TEMPO-oxidated microfibrillated cellulose, fibrillated untreated sugar beet pulp showed the best adhesive performance. Different microscopic methods (AFM, SEM, light microscopy) examined the interface between wood and fibrillated material, showing particular distinctions to commercial adhesives. It is proposed that fibrillated material suspensions, which achieve bond strength up to 60% of commercial urea-formaldehyde adhesive, may provide a viable solution to bio-based adhesives in certain applications where wet-strength is not an issue. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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Open AccessArticle Mechanical Pulling of Linked Ring Polymers: Elastic Response and Link Localisation
Polymers 2017, 9(8), 327; doi:10.3390/polym9080327
Received: 30 June 2017 / Revised: 26 July 2017 / Accepted: 27 July 2017 / Published: 1 August 2017
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Abstract
By using Langevin dynamics simulations, we study how semiflexible rings that are topologically linked respond to mechanical stretching. We use both constant-force and constant-velocity pulling protocols and map out how the mechanical tension affects observables related to metric quantities such as the longitudinal
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By using Langevin dynamics simulations, we study how semiflexible rings that are topologically linked respond to mechanical stretching. We use both constant-force and constant-velocity pulling protocols and map out how the mechanical tension affects observables related to metric quantities such as the longitudinal extension or span, and topology-related ones such as the length of the linked portion. We find that the average extension of linked rings, once divided by that of a single equivalent ring, is nonmonotonic in the applied force. We show that this remarkable feature becomes more prominent as the link complexity is increased, and originates from the different stretching compliance of the linked portion and the rest of the rings’ contour. By comparing the results of different pulling protocols, we also establish the best one for telling apart different types of links from their tensile response. Full article
(This article belongs to the Special Issue Knotted and Catenated Polymers)
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Open AccessArticle Electrospinning PCL Scaffolds Manufacture for Three-Dimensional Breast Cancer Cell Culture
Polymers 2017, 9(8), 328; doi:10.3390/polym9080328
Received: 27 June 2017 / Revised: 23 July 2017 / Accepted: 27 July 2017 / Published: 1 August 2017
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Abstract
In vitro cell culture is traditionally performed within two-dimensional (2D) environments, providing a quick and cheap way to study cell properties in a laboratory. However, 2D systems differ from the in vivo environment and may not mimic the physiological cell behavior realistically. For
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In vitro cell culture is traditionally performed within two-dimensional (2D) environments, providing a quick and cheap way to study cell properties in a laboratory. However, 2D systems differ from the in vivo environment and may not mimic the physiological cell behavior realistically. For instance, 2D culture models are thought to induce cancer stem cells (CSCs) differentiation, a rare cancer cell subpopulation responsible for tumor initiation and relapse. This fact hinders the development of therapeutic strategies for tumors with a high relapse percentage, such as triple negative breast cancer (TNBC). Thus, three-dimensional (3D) scaffolds have emerged as an attractive alternative to monolayer culture, simulating the extracellular matrix structure and maintaining the differentiation state of cells. In this work, scaffolds were fabricated through electrospinning different poly(ε-caprolactone)-acetone solutions. Poly(ε-caprolactone) (PCL) meshes were seeded with triple negative breast cancer (TNBC) cells and 15% PCL scaffolds displayed significantly (p < 0.05) higher cell proliferation and elongation than the other culture systems. Moreover, cells cultured on PCL scaffolds exhibited higher mammosphere forming capacity and aldehyde dehydrogenase activity than 2D-cultured cells, indicating a breast CSCs enrichment. These results prove the powerful capability of electrospinning technology in terms of poly(ε-caprolactone) nanofibers fabrication. In addition, this study has demonstrated that electrospun 15% PCL scaffolds are suitable tools to culture breast cancer cells in a more physiological way and to expand the niche of breast CSCs. In conclusion, three-dimensional cell culture using PCL scaffolds could be useful to study cancer stem cell behavior and may also trigger the development of new specific targets against such malignant subpopulation. Full article
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Open AccessArticle The Influence of Calcium Glycerophosphate (GPCa) Modifier on Physicochemical, Mechanical, and Biological Performance of Polyurethanes Applicable as Biomaterials for Bone Tissue Scaffolds Fabrication
Polymers 2017, 9(8), 329; doi:10.3390/polym9080329
Received: 23 June 2017 / Revised: 13 July 2017 / Accepted: 28 July 2017 / Published: 1 August 2017
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Abstract
In this paper we describe the synthesis of poly(ester ether urethane)s (PEEURs) by using selected raw materials to reach a biocompatible polyurethane (PU) for biomedical applications. PEEURs were synthesized by using aliphatic 1,6-hexamethylene diisocyanate (HDI), poly(ethylene glycol) (PEG), α,ω-dihydroxy(ethylene-butylene adipate) (Polios), 1,4-butanediol (BDO)
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In this paper we describe the synthesis of poly(ester ether urethane)s (PEEURs) by using selected raw materials to reach a biocompatible polyurethane (PU) for biomedical applications. PEEURs were synthesized by using aliphatic 1,6-hexamethylene diisocyanate (HDI), poly(ethylene glycol) (PEG), α,ω-dihydroxy(ethylene-butylene adipate) (Polios), 1,4-butanediol (BDO) as a chain extender and calcium glycerolphosphate salt (GPCa) as a modifier used to stimulate bone tissue regeneration. The obtained unmodified (PURs) and modified with GPCa (PURs-M) PEEURs were studied by various techniques. It was confirmed that urethane prepolymer reacts with GPCa modifier. Further analysis of the obtained PURs and PURs-M by Fourier transform infrared (FTIR) and Raman spectroscopy revealed the chemical composition typical for PUs by the confirmed presence of urethane bonds. Moreover, the FTIR and Raman spectra indicated that GPCa was incorporated into the main PU chain at least at one-side. The scanning electron microscopy (SEM) analysis of the PURs-M surface was in good agreement with the FTIR and Raman analysis due to the fact that inclusions were observed only at 20% of its surface, which were related to the non-reacted GPCa enclosed in the PUR matrix as filler. Further studies of hydrophilicity, mechanical properties, biocompatibility, short term-interactions, and calcification study lead to the final conclusion that the obtained PURs-M may by suitable candidate material for further scaffold fabrication. Scaffolds were prepared by the solvent casting/particulate leaching technique (SC/PL) combined with thermally-induced phase separation (TIPS). Such porous scaffolds had satisfactory pore sizes (36–100 μm) and porosity (77–82%) so as to be considered as suitable templates for bone tissue regeneration. Full article
(This article belongs to the Special Issue Advance of Polymers Applied to Biomedical Applications: Biointerface)
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Open AccessArticle Development and In Vitro Evaluation of Lyotropic Liquid Crystals for the Controlled Release of Dexamethasone
Polymers 2017, 9(8), 330; doi:10.3390/polym9080330
Received: 20 June 2017 / Revised: 26 July 2017 / Accepted: 30 July 2017 / Published: 2 August 2017
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Abstract
In this study, amphiphilic polymers were investigated as biomaterials that can control dexamethasone (DXM) release. Such materials present interfacial properties in the presence of water and an oily phase that can result in lyotropic liquid crystalline systems (LLCS). In addition, they can form
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In this study, amphiphilic polymers were investigated as biomaterials that can control dexamethasone (DXM) release. Such materials present interfacial properties in the presence of water and an oily phase that can result in lyotropic liquid crystalline systems (LLCS). In addition, they can form colloidal nanostructures similar to those in living organisms, such as bilayers and hexagonal and cubic phases, which can be exploited to solubilize lipophilic drugs to sustain their release and enhance bioavailability. It was possible to obtain lamellar and hexagonal phases when combining polyoxyethylene (20) cetyl ether (CETETH-20) polymer with oleic acid (OA), N-methylpyrrolidone (P), isopropyl myristate (IM), and water. The phases were characterized by polarized light microscopy (PLM), small-angle X-ray scattering (SAXS), rheological, textural, and bioadhesion analyses followed by an in vitro release assay. All samples showed elastic behavior in the rheology studies and hexagonal samples containing P and IM showed the highest adhesiveness. The drug release profile of all LLCS presented an average lag time of 3 h and was best fitted to the Korsmeyer-Peppas and Weibull models, with controlled release governed by a combination of diffusion and erosion mechanisms. These systems are potential carriers for DXM and can be explored in several routes of administration, providing potential advantages over conventional pharmaceutical forms. Full article
(This article belongs to the Special Issue Advance of Polymers Applied to Biomedical Applications: Biointerface)
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Open AccessArticle Increased Surface Roughness in Polydimethylsiloxane Films by Physical and Chemical Methods
Polymers 2017, 9(8), 331; doi:10.3390/polym9080331
Received: 15 June 2017 / Revised: 20 July 2017 / Accepted: 25 July 2017 / Published: 2 August 2017
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Abstract
Two methods, the first physical and the other chemical, were investigated to modify the surface roughness of polydimethylsiloxane (PDMS) films. The physical method consisted of dispersing multi-walled carbon nanotubes (MWCNTs) and magnetic cobalt ferrites (CoFe2O4) prior to thermal cross-linking,
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Two methods, the first physical and the other chemical, were investigated to modify the surface roughness of polydimethylsiloxane (PDMS) films. The physical method consisted of dispersing multi-walled carbon nanotubes (MWCNTs) and magnetic cobalt ferrites (CoFe2O4) prior to thermal cross-linking, and curing the composite system in the presence of a uniform magnetic field H. The chemical method was based on exposing the films to bromine vapours and then UV-irradiating. The characterizing techniques included scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy, optical microscopy, atomic force microscopy (AFM) and magnetic force microscopy (MFM). The surface roughness was quantitatively analyzed by AFM. In the physical method, the random dispersion of MWCNTs (1% w/w) and magnetic nanoparticles (2% w/w) generated a roughness increase of about 200% (with respect to PDMS films without any treatment), but that change was 400% for films cured in the presence of H perpendicular to the surface. SEM, AFM and MFM showed that the magnetic particles always remained attached to the carbon nanotubes, and the effect on the roughness was interpreted as being due to a rupture of dispersion randomness and a possible induction of structuring in the direction of H. In the chemical method, the increase in roughness was even greater (1000%). Wells were generated with surface areas that were close to 100 μm2 and depths of up to 500 nm. The observations of AFM images and FTIR spectra were in agreement with the hypothesis of etching by Br radicals generated by UV on the polymer chains. Both methods induced important changes in the surface roughness (the chemical method generated the greatest changes due to the formation of surface wells), which are of great importance in superficial technological processes. Full article
(This article belongs to the Special Issue Polymer Nanocomposites)
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Open AccessArticle Effects of Amino-Functionalized Carbon Nanotubes on the Crystal Structure and Thermal Properties of Polyacrylonitrile Homopolymer Microspheres
Polymers 2017, 9(8), 332; doi:10.3390/polym9080332
Received: 18 June 2017 / Revised: 11 July 2017 / Accepted: 13 July 2017 / Published: 2 August 2017
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Abstract
Amino-functionalized multi-walled carbon nanotube (amino-CNT)/polyacrylonitrile (PAN) microspheres with diameter of about 300–400 nm were prepared by in situ polymerization under aqueous solution. The morphology, crystal structure, and thermal properties of amino-CNTs on a PAN homopolymer were investigated by scanning electron microscopy, transmission electron
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Amino-functionalized multi-walled carbon nanotube (amino-CNT)/polyacrylonitrile (PAN) microspheres with diameter of about 300–400 nm were prepared by in situ polymerization under aqueous solution. The morphology, crystal structure, and thermal properties of amino-CNTs on a PAN homopolymer were investigated by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectra, X-ray diffraction, and differential scanning calorimetry. The results showed that the amino-CNTs had a significant influence on the morphology of microspheres, and the PAN matrix were grafted onto the surface of amino-CNTs with interfacial bonding between them. The XRD studies showed that the crystal size of amino-CNT/PAN microspheres with lower crystallinity was bigger than in the control PAN homopolymer. The analysis of thermal properties indicated that the amino-CNT/PAN microspheres with lower glass transition temperature had a lower initial temperature and velocity of evolving heat during the exothermic processing as compared with the PAN homopolymer. These results suggested that the incorporation of amino-CNTs into the PAN homopolymer matrix was beneficial for controlling the heat released during the stabilization processing. Full article
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Open AccessArticle Thermally-Induced Self-Healing Behaviors and Properties of Four Epoxy Coatings with Different Network Architectures
Polymers 2017, 9(8), 333; doi:10.3390/polym9080333
Received: 27 June 2017 / Revised: 30 July 2017 / Accepted: 31 July 2017 / Published: 2 August 2017
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Abstract
The thermally-induced self-healing behavior of polymer coatings consists of two steps, i.e., gap closure and crack repair. In addition, the polymer coatings with thermally-induced self-healing capability are expected to show satisfied properties to ensure the application. Here, four epoxy coatings with dense irreversible
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The thermally-induced self-healing behavior of polymer coatings consists of two steps, i.e., gap closure and crack repair. In addition, the polymer coatings with thermally-induced self-healing capability are expected to show satisfied properties to ensure the application. Here, four epoxy coatings with dense irreversible Network I, dense reversible Network II based on a Diels–Alder (DA) reaction, loose irreversible Network III, as well as partially irreversible and partially reversible Network IV were prepared, respectively. The dense irreversible Network I showed an evident gap closure upon heating, while the crack still existed at the high temperature. The dense reversible Network II presented good self-healing upon direct heating at a high temperature of 150 °C, leading to the quick gap closure in 40 s and subsequent crack disappearance in 80 s. The loose irreversible Network III showed negligible crack variations upon heating, while the partially reversible and partially irreversible Network IV showed quick gap closure as well but only partial crack disappearance. Besides, the coating with the reversible Network II based on the DA reaction not only presented good self-healing capability but also possessed the satisfied mechanical properties and the best electrochemical corrosion property, ensuring its further exploitation and potential practical applications. Full article
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Open AccessArticle Cure Behavior and Thermomechanical Properties of Phthalonitrile–Polyhedral Oligomeric Silsesquioxane Copolymers
Polymers 2017, 9(8), 334; doi:10.3390/polym9080334
Received: 24 June 2017 / Revised: 27 July 2017 / Accepted: 27 July 2017 / Published: 3 August 2017
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Abstract
Phthalonitrile–polyhedral oligomeric silsesquioxane (POSS) copolymers were prepared by adding two different POSS cage mixtures: epoxycyclohexyl POSS (EP0408) and N-phenylaminopropyl POSS (AM0281). The cure behavior and properties of these polymers were analyzed and compared using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic
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Phthalonitrile–polyhedral oligomeric silsesquioxane (POSS) copolymers were prepared by adding two different POSS cage mixtures: epoxycyclohexyl POSS (EP0408) and N-phenylaminopropyl POSS (AM0281). The cure behavior and properties of these polymers were analyzed and compared using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), Fourier transform far infrared (FTIR) measurements, and rheometric studies. The POSS-containing polymers showed higher chemical reactivity, better thermal stability and better mechanical performance in comparison to their unmodified counterparts. All the polymers showed water absorption below 1.5%. As revealed by FTIR measurements, the polymerization products contained triazine ring structures that were responsible for the superior thermal properties exhibited by these POSS-containing polymers. Full article
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Open AccessArticle Membranes Based on Cellulose Nanofibers and Activated Carbon for Removal of Escherichia coli Bacteria from Water
Polymers 2017, 9(8), 335; doi:10.3390/polym9080335
Received: 3 July 2017 / Revised: 25 July 2017 / Accepted: 26 July 2017 / Published: 3 August 2017
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Abstract
Cellulosic nanomaterials are potential candidates in different areas, especially in water treatment. In the current work, palm fruit stalks cellulose nanofibers (CNF), TEMPO-oxidized CNF (OCNF), and activated carbon (AC) were used to make thin film membranes for removal of E. coli bacteria from
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Cellulosic nanomaterials are potential candidates in different areas, especially in water treatment. In the current work, palm fruit stalks cellulose nanofibers (CNF), TEMPO-oxidized CNF (OCNF), and activated carbon (AC) were used to make thin film membranes for removal of E. coli bacteria from water. Two types of layered membranes were produced: a single layer setup of crosslinked CNF and a two-layer setup of AC/OCNF (bottom) and crosslinked CNF (up) on hardened filter paper. The prepared membranes were evaluated regarding their microstructure and layers thickness using scanning electron microscopy (SEM). Water flux and rejection of E. coli bacteria was tested using dead end stirred cells at 1 MPa pressure. Thickness of the cosslinked CNF layer in both types of membranes was about 0.75 micron. The results showed that exchanging water by isopropyl alcohol before drying increased porosity of membranes, and thus resulted in increasing pure water flux and flux of bacteria suspension. The two-layer AC/OCNF/CNF membrane had much higher water flux than the single layer CNF due to higher porosity seen on the surface of the former. Both types of membranes showed high capability of removing E. coli bacteria (rejection ~96–99%) with slightly higher efficiency for the AC/OCNF/CNF membrane than CNF membrane. AC/OCNF/CNF membrane also showed resistance against growth of E. coli and S. aureus bacteria on the upper CNF surface while the single layer CNF membrane did not show resistance against growth of the aforementioned bacteria. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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Open AccessArticle New Eco-Friendly Phosphorus Organic Polymers as Gas Storage Media
Polymers 2017, 9(8), 336; doi:10.3390/polym9080336
Received: 12 July 2017 / Revised: 30 July 2017 / Accepted: 1 August 2017 / Published: 3 August 2017
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Abstract
Three phosphate esters 13 were successfully synthesized from the reaction of 2-, 3- and 4-hydroxybenzaldehyde with phosphoryl chloride. Reactions of 13 with benzidine in the presence of glacial acetic acid gave the corresponding novel phosphorus organic polymers 4
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Three phosphate esters 13 were successfully synthesized from the reaction of 2-, 3- and 4-hydroxybenzaldehyde with phosphoryl chloride. Reactions of 13 with benzidine in the presence of glacial acetic acid gave the corresponding novel phosphorus organic polymers 46 containing the azomethane linkage. The structures of the synthesized compounds were confirmed by Fourier transform infrared spectroscopy, nuclear magnetic resonance and elemental analysis. Interesting physiochemical properties for the polymeric materials 46 were observed using a combination of several techniques such as gel permeation chromatography, scanning electron microscopy, Brunauer–Emmett–Teller and nitrogen adsorption–desorption isotherm, Barrett–Joyner–Halenda and H-sorb 2600 analyzer. The mesoporous polymers 46 exhibit tunable porosity with Brunauer–Emmett–Teller surface area (SABET = 24.8–30 m2·g–1), pore volume (0.03–0.05 cm3·g–1) and narrow pore size distribution, in which the average pore size was 2.4–2.8 nm. Polymers 46 were found to have high gas storage capacity and physico-chemical stability, particularly at a high pressure. At 323 K and 50 bars, polymers 46 have remarkable carbon dioxide uptake (up to 82.1 cm3·g–1) and a low hydrogen uptake (up to 7.4 cm3·g–1). The adsorption capacity of gasses for polymer 5 was found to be higher than those for polymers 4 and 6. Full article
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Open AccessArticle Role of Ion Dissociation on DC Conductivity and Silver Nanoparticle Formation in PVA:AgNt Based Polymer Electrolytes: Deep Insights to Ion Transport Mechanism
Polymers 2017, 9(8), 338; doi:10.3390/polym9080338
Received: 23 June 2017 / Revised: 20 July 2017 / Accepted: 1 August 2017 / Published: 4 August 2017
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Abstract
In this study, the role of ion dissociation on formation of silver nanoparticle and DC conductivityin PVA:AgNO3 based solid polymer electrolyte has been discussed in detail. Samples of silver ion conducting solid polymer electrolyte were prepared by using solution cast technique. Absorption
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In this study, the role of ion dissociation on formation of silver nanoparticle and DC conductivityin PVA:AgNO3 based solid polymer electrolyte has been discussed in detail. Samples of silver ion conducting solid polymer electrolyte were prepared by using solution cast technique. Absorption spectroscopy in the ultraviolet–visible (UV–Vis) spectral region was used to investigate the formation of silver nanoparticles. Broad and sharp peaks due to plasmonic silver nanoparticles subjected to ion dissociation have been observed. The influence of dielectric constant on the intensity of surface plasmonic resonance (SPR) peaks attributed to silver nanoparticles was discussed. From impedance plots, the diameter of high frequency semicircle was found to be decreased with increasing salt concentration. The DC conductivity in relation to the dielectric constant was also explained. From the AC conductivity spectra, the dc conductivity was estimated to be close to that calculated from the bulk resistance. The temperature dependence of the DC conductivity was studied and found to follow Arrhenius equation within two distinguished regions. The AC conductivity at different temperatures has been studied to comprehend the ion conduction mechanism. The AC conductivity against frequency was found to obey the universal power law of Jonscher. Three distinct regions were recognized from the spectra of AC conductivity. The frequency exponent (S) was calculated for the dispersive region of the measured AC conductivity spectra. Various models were discussed to explain the behavior of S value with temperature. The behavior of S value with temperature was then used to interpret the DC conductivity pattern against 1000/T. Finally, from the comparison of calculated activation energy (Ea) and maximum barrier height (Wm), deep insights into ion conduction mechanism could be grasped. Full article
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Open AccessArticle Hyaluronic Acid Promotes the Osteogenesis of BMP-2 in an Absorbable Collagen Sponge
Polymers 2017, 9(8), 339; doi:10.3390/polym9080339
Received: 10 July 2017 / Revised: 24 July 2017 / Accepted: 31 July 2017 / Published: 4 August 2017
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Abstract
(1) Background: We tested the hypothesis that hyaluronic acid (HA) can significantly promote the osteogenic potential of BMP-2/ACS (absorbable collagen sponge), an efficacious product to heal large oral bone defects, thereby allowing its use at lower dosages and, thus, reducing its side-effects due
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(1) Background: We tested the hypothesis that hyaluronic acid (HA) can significantly promote the osteogenic potential of BMP-2/ACS (absorbable collagen sponge), an efficacious product to heal large oral bone defects, thereby allowing its use at lower dosages and, thus, reducing its side-effects due to the unphysiologically-high doses of BMP-2; (2) Methods: In a subcutaneous bone induction model in rats, we first sorted out the optimal HA-polymer size and concentration with micro CT. Thereafter, we histomorphometrically quantified the effect of HA on new bone formation, total construct volume, and densities of blood vessels and macrophages in ACS with 5, 10, and 20 μg of BMP-2; (3) Results: The screening experiments revealed that the 100 µg/mL HA polymer of 48 kDa molecular weight could yield the highest new bone formation. Eighteen days post-surgery, HA could significantly enhance the total volume of newly-formed bone by approximately 100%, and also the total construct volume in the 10 μg BMP-2 group. HA could also significantly enhance the numerical area density of blood vessels in 5 μg BMP-2 and 10 μg BMP-2 groups. HA did not influence the numerical density of macrophages; and (4) Conclusions: An optimal combined administration of HA could significantly promote osteogenic and angiogenic activity of BMP-2/ACS, thus potentially minimizing its potential side-effects. Full article
(This article belongs to the Special Issue Polymers from Renewable Resources)
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Open AccessArticle Preparation and Characterization of Thermo-Responsive Rod-Coil Diblock Copolymers
Polymers 2017, 9(8), 340; doi:10.3390/polym9080340
Received: 13 July 2017 / Revised: 31 July 2017 / Accepted: 1 August 2017 / Published: 4 August 2017
PDF Full-text (5643 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In this study, we synthesized amphiphilic poly(2,7–(9,9–dioctylfluorene))–block–N,N–(diisopropylamino)ethyl methacrylate (POF–b–PDPMAEMA) rod-coil diblock copolymers by atom transfer radical polymerization (ATRP). The structure and multifunctional sensing properties of these copolymers were also investigated. The POF rod segment length of 10
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In this study, we synthesized amphiphilic poly(2,7–(9,9–dioctylfluorene))–block–N,N–(diisopropylamino)ethyl methacrylate (POF–b–PDPMAEMA) rod-coil diblock copolymers by atom transfer radical polymerization (ATRP). The structure and multifunctional sensing properties of these copolymers were also investigated. The POF rod segment length of 10 was fixed and the PDPAEMA coil segment lengths of 90 and 197 were changed, respectively. The micellar aggregates of POF10b–PDPAEMA90 rod-coil diblock copolymer in water showed a reversible shape transition from cylinder bundles to spheres when the temperature was changed from 20 to 80 °C or the pH was changed from 11 to 2. The atomic force microscopy (AFM) and transmission electron microscopy (TEM) measurements indicated that the temperature had also an obvious influence on the micelle size. In addition, since POF10b–PDPAEMA90 had a lower critical solution temperature, its photoluminescence (PL) intensity in water is thermoreversible. The PL spectra showed that the POF–b–PDPAEMA copolymer had a reversible on/off profile at elevated temperatures, and thus could be used as an on/off fluorescent indicator for temperature or pH. The fluorescence intensity distribution of pH switched from “off–on” to “on–off” as the temperature increased. These results showed that the POF–b–PDPAEMA copolymer has a potential application for temperature and pH sensing materials. Full article
(This article belongs to the Special Issue Polymers and Block Copolymers at Interfaces and Surfaces)
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Open AccessArticle Theoretical Study on Decomposition Mechanism of Insulating Epoxy Resin Cured by Anhydride
Polymers 2017, 9(8), 341; doi:10.3390/polym9080341
Received: 11 July 2017 / Revised: 31 July 2017 / Accepted: 3 August 2017 / Published: 4 August 2017
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Abstract
High temperatures caused by partial discharge results in the decomposition of insulating epoxy resins in electrical equipment. In this paper, the ReaxFF force field is used to investigate the decomposition process of epoxy resins cured by anhydride and the formation mechanisms of small-molecule
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High temperatures caused by partial discharge results in the decomposition of insulating epoxy resins in electrical equipment. In this paper, the ReaxFF force field is used to investigate the decomposition process of epoxy resins cured by anhydride and the formation mechanisms of small-molecule gases. Results show that the initiation reaction is the cleavage of an ester bond linked with an epoxy resin. Produced by the decomposition of ester groups, CO2 is the first and most abundant product. Meanwhile, CH2O can be generated through three main ways, although the process still depends on the decomposition of epoxy functional groups. H2O is produced by free radical collision and dehydration. The production of small-molecule gases has the following sequence: CO2, CH2O, CO, and H2O. The produced gases have the following order according to amount: CO2, CH2O, H2O, and CO. Full article
(This article belongs to the collection Polymeric Adhesives)
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Open AccessArticle Crosslinked Polyarylene Ether Nitrile Interpenetrating with Zinc Ion Bridged Graphene Sheet and Carbon Nanotube Network
Polymers 2017, 9(8), 342; doi:10.3390/polym9080342
Received: 28 June 2017 / Revised: 30 July 2017 / Accepted: 2 August 2017 / Published: 4 August 2017
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Abstract
We report the fabrication and improved properties of crosslinked polyarylene ether nitrile (CPEN) interpenetrating with a zinc ion bridged graphene sheet (GS) and carbon nanotube (CNT) network (GS-Zn-CNT) (CPEN/GS-Zn-CNT). Graphene oxide (GO) and acidulated CNT were firstly prepared and then coordinated with zinc
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We report the fabrication and improved properties of crosslinked polyarylene ether nitrile (CPEN) interpenetrating with a zinc ion bridged graphene sheet (GS) and carbon nanotube (CNT) network (GS-Zn-CNT) (CPEN/GS-Zn-CNT). Graphene oxide (GO) and acidulated CNT were firstly prepared and then coordinated with zinc ions to form the zinc ion bridged GO and CNT network (GO-Zn-CNT). The mass ratio of GO and acidulated CNT in GO-Zn-CNT was controlled to be 1:3 and the optimized content of Zn2+ was Zn2+/C = 0.01 mmol/mg (mole of zinc acetate/total weight of GO and acidulated CNT). Phthalonitrile end-capped polyarylene ether nitrile (PEN-Ph) permeated into the GO-Zn-CNT in N-methyl-2-pyrrolidone (NMP) and the corresponding composite PEN/GO-Zn-CNT was fabricated through the solution-casting method. After thermal annealing at 230 °C for 1 h and further curing at 320 °C for 2 h, the GO in GO-Zn-CNT was partly reduced into GS, and PEN-Ph was crosslinked, offering the CPEN/GS-Zn-CNT. The mechanical, thermal, and electrical properties of the obtained CPEN/GS-Zn-CNT were investigated in detail. The glass transition temperature, relative permittivity, and tensile strength of CPEN/GS-Zn-CNT with 2.0 wt % GS-Zn-CNT, compared to that of PEN, were increased by 18%, 181%, and 27%, respectively. The CPEN/GS-Zn-CNT based composite is a potential candidate as material in high performance electronic devices. Full article
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Open AccessArticle Tuning the Density of Poly(ethylene glycol) Chains to Control Mammalian Cell and Bacterial Attachment
Polymers 2017, 9(8), 343; doi:10.3390/polym9080343
Received: 30 June 2017 / Revised: 1 August 2017 / Accepted: 2 August 2017 / Published: 5 August 2017
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Abstract
Surface modification of biomaterials with polymer chains has attracted great attention because of their ability to control biointerfacial interactions such as protein adsorption, cell attachment and bacterial biofilm formation. The aim of this study was to control the immobilisation of biomolecules on silicon
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Surface modification of biomaterials with polymer chains has attracted great attention because of their ability to control biointerfacial interactions such as protein adsorption, cell attachment and bacterial biofilm formation. The aim of this study was to control the immobilisation of biomolecules on silicon wafers using poly(ethylene glycol)(PEG) chains by a “grafting to” technique. In particular, to control the polymer chain graft density in order to capture proteins and preserve their activity in cell culture as well as find the optimal density that would totally prevent bacterial attachment. The PEG graft density was varied by changing the polymer solubility using an increasing salt concentration. The silicon substrates were initially modified with aminopropyl-triethoxysilane (APTES), where the surface density of amine groups was optimised using different concentrations. The results showed under specific conditions, the PEG density was highest with grafting under “cloud point” conditions. The modified surfaces were characterised with X-ray photoelectron spectroscopy (XPS), ellipsometry, atomic force microscopy (AFM) and water contact angle measurements. In addition, all modified surfaces were tested with protein solutions and in cell (mesenchymal stem cells and MG63 osteoblast-like cells) and bacterial (Pseudomonas aeruginosa) attachment assays. Overall, the lowest protein adsorption was observed on the highest polymer graft density, bacterial adhesion was very low on all modified surfaces, and it can be seen that the attachment of mammalian cells gradually increased as the PEG grafting density decreased, reaching the maximum attachment at medium PEG densities. The results demonstrate that, at certain PEG surface coverages, mammalian cell attachment can be tuned with the potential to optimise their behaviour with controlled serum protein adsorption. Full article
(This article belongs to the Special Issue Advance of Polymers Applied to Biomedical Applications: Biointerface)
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Open AccessArticle Combining Pickering Emulsion Polymerization with Molecular Imprinting to Prepare Polymer Microspheres for Selective Solid-Phase Extraction of Malachite Green
Polymers 2017, 9(8), 344; doi:10.3390/polym9080344
Received: 26 June 2017 / Revised: 28 July 2017 / Accepted: 1 August 2017 / Published: 6 August 2017
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Abstract
Malachite green (MG) is currently posing a carcinogenic threat to the safety of human lives; therefore, it is highly desirable to develop an effective method for fast trace detection of MG. Herein, for the first time, this paper presents a systematic study on
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Malachite green (MG) is currently posing a carcinogenic threat to the safety of human lives; therefore, it is highly desirable to develop an effective method for fast trace detection of MG. Herein, for the first time, this paper presents a systematic study on polymer microspheres, being prepared by combined Pickering emulsion polymerization and molecular imprinting, to detect and purify MG. The microspheres, molecularly imprinted with MG, show enhanced adsorption selectivity to MG, despite a somewhat lowered adsorption capacity, as compared to the counterpart without molecular imprinting. Structural features and adsorption performance of these microspheres are elucidated by different characterizations and kinetic and thermodynamic analyses. The surface of the molecularly imprinted polymer microspheres (M-PMs) exhibits regular pores of uniform pore size distribution, endowing M-PMs with impressive adsorption selectivity to MG. In contrast, the microspheres without molecular imprinting show a larger average particle diameter and an uneven porous surface (with roughness and a large pore size), causing a lower adsorption selectivity to MG despite a higher adsorption capacity. Various adsorption conditions are investigated, such as pH and initial concentration of the solution with MG, for optimizing the adsorption performance of M-PMs in selectively tackling MG. The adsorption kinetics and thermodynamics are deeply discussed and analyzed, so as to provide a full picture of the adsorption behaviors of the polymer microspheres with and without the molecular imprinting. Significantly, M-PMs show promising solid-phase extraction column applications for recovering MG in a continuous extraction manner. Full article
(This article belongs to the Special Issue Emulsion Polymerization)
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Open AccessArticle Organic Catalysis for Ring-Opening Graft Polymerization of p-Dioxanone with Xylan in Ionic liquid
Polymers 2017, 9(8), 345; doi:10.3390/polym9080345
Received: 16 June 2017 / Revised: 1 August 2017 / Accepted: 4 August 2017 / Published: 6 August 2017
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Abstract
Recently, organic catalysis has become a powerful alternative to the use of more traditional metal-based catalysts. In this study, 4-dimethylaminopyridine (DMAP), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) were applied to mediate the ring-opening graft polymerization (ROGP) of p-dioxanone (PDO) with xylan-based hemicelluloses in
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Recently, organic catalysis has become a powerful alternative to the use of more traditional metal-based catalysts. In this study, 4-dimethylaminopyridine (DMAP), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) were applied to mediate the ring-opening graft polymerization (ROGP) of p-dioxanone (PDO) with xylan-based hemicelluloses in ionic liquid 1-butyl-3-methylimidazolium chloride ([Bmim]Cl). Excellent control of the molar ratio of the catalyst to anhydroxylose units (AXU) in xylan was found for a good tuning of the weight percent gain (WPG) of xylan-graft-poly(p-dioxanone) (xylan-g-PPDO) copolymers. As a result, the maximum WPG of xylan-g-PPDO copolymers was 431.07% (DMAP/AXU of 2/1), 316.72% (DBU/AXU of 0.2/1), and 323.15% (TBD/AXU of 0.2/1), respectively. The structure of xylan-g-PPDO copolymers was characterized with FT-IR and NMR. The thermal properties of copolymers were investigated using thermogravimetric analysis (TGA/DTG) and differential scanning calorimetry (DSC), and a significant difference was observed regarding the transition temperature (Tg), melting temperature (Tm), and crystallization temperature (Tc). Full article
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Open AccessArticle Characterization of Type-II Acetylated Cellulose Nanocrystals with Various Degree of Substitution and Its Compatibility in PLA Films
Polymers 2017, 9(8), 346; doi:10.3390/polym9080346
Received: 2 July 2017 / Revised: 23 July 2017 / Accepted: 4 August 2017 / Published: 6 August 2017
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Abstract
In order to decrease the self-agglomeration and improve the hydrophobic properties of type-II acetylated cellulose nanocrystals (ACNC II), various degree of substitution (DS) values of ACNCs were successfully prepared by a single-step method from microcrystalline cellulose with anhydrous phosphoric acid as the solvent,
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In order to decrease the self-agglomeration and improve the hydrophobic properties of type-II acetylated cellulose nanocrystals (ACNC II), various degree of substitution (DS) values of ACNCs were successfully prepared by a single-step method from microcrystalline cellulose with anhydrous phosphoric acid as the solvent, and acetic anhydride as the acetylation reagent, under different reaction temperatures (20–40 °C). To thoroughly investigate the DS values of ACNC II, analyses were performed using Fourier transform infrared spectroscopy (FT-IR), 13C cross polarization-magic angle spinning (CP-MAS) nuclear magnetic resonance (NMR), and X-ray photoelectron spectroscopy (XPS). At a reaction temperature of 40°C, the highest DS value was successfully obtained. XRD proved that the crystal structure of ACNC II with various DS values was maintained after acetylation. TEM showed the threadlike shape for ACNC II with various DS values. The ACNC II with various DS values was introduced into a polylactic acid (PLA) matrix to produce PLA/ACNC composite films, which showed improved rheological and thermal properties. This improvement was primarily attributed to good dispersion of the ACNC II, and the interfacial compatibility between ACNC II and the PLA matrix. This study aims to analyze the compatibility of ACNC II with various DS values in the PLA matrix by microstructure, crystallization, and rheological and thermal tests. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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Open AccessArticle Coordination-Driven Controlled Assembly of Polyphenol-Metal Green Coating on Wood Micro-Grooved Surfaces: A Novel Approach to Stable Superhydrophobicity
Polymers 2017, 9(8), 347; doi:10.3390/polym9080347
Received: 18 June 2017 / Revised: 26 July 2017 / Accepted: 1 August 2017 / Published: 7 August 2017
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Abstract
A versatile, fast, and nature-inspired polyphenol chemistry surface modification was applied to prepare superhydrophobic surfaces with micro-grooved structures in this study. Tannic acid and iron ion (TA–FeIII) complexes were employed as a molecular building block for anchoring biomimetic coating onto the
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A versatile, fast, and nature-inspired polyphenol chemistry surface modification was applied to prepare superhydrophobic surfaces with micro-grooved structures in this study. Tannic acid and iron ion (TA–FeIII) complexes were employed as a molecular building block for anchoring biomimetic coating onto the wood substrate with catalytically reducing formative Ag ions as the rough surface to ensure well-developed micro/nanostructure hierarchical roughness. TA–FeIII complexes also acted as stable bridges between the substrate and hydrophobic groups. The thickness and architecture of TA–FeIII complex coatings can be tailored by coordination-driven multistep assembly. The results indicated that the micro/nano hierarchical roughness structure was well-developed with increased coating times and increased deposition of reduced Ag nanoparticles, resulting in excellent superhydrophobic properties (e.g., water CA (contact angle) of about 156° and a rolling angle of about 4°). The superhydrophobic material exhibited outstanding stability and durability in harsh conditions, including strong acid/base or organic solvent, high-temperature water boiling, ultrasonic cleaning, and ultraviolet aging. A series of superhydrophobic models are proposed to clarify the effect of the micro/nano hierarchical structure on these superhydrophobic properties. Full article
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Open AccessArticle Enhanced Cartilaginous Tissue Formation with a Cell Aggregate-Fibrin-Polymer Scaffold Complex
Polymers 2017, 9(8), 348; doi:10.3390/polym9080348
Received: 28 June 2017 / Revised: 3 August 2017 / Accepted: 3 August 2017 / Published: 8 August 2017
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Abstract
Cell density is one of the factors required in the preparation of engineered cartilage from mesenchymal stem cells (MSCs). Additionally, it is well known for having a significant role in chemical and physical stimulations when stem cells undergo chondrogenic differentiation. Here, we developed
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Cell density is one of the factors required in the preparation of engineered cartilage from mesenchymal stem cells (MSCs). Additionally, it is well known for having a significant role in chemical and physical stimulations when stem cells undergo chondrogenic differentiation. Here, we developed an engineered cartilage with a cell aggregate-hydrogel-polymer scaffold complex capable of inducing the effective regeneration of cartilage tissue similar to natural cartilage while retaining a high mechanical strength, flexibility, and morphology. Cell aggregates were generated by the hanging drop method with rabbit bone marrow stromal cells (BMSCs), and poly (lactide-co-caprolactone) (PLCL) scaffolds were fabricated with 78.3 ± 5.3% porosity and a 300–500 μm pore size with a gel-pressing method. We prepared the cell aggregate-fibrin-poly (lactide-co-caprolactone) (PLCL) scaffold complex, in which the cell aggregates were evenly dispersed in the fibrin, and they were immobilized onto the surface of the polymer scaffold while filling up the pores. To examine the chondrogenic differentiation of seeded BMSCs and the formation of chondral extracellular matrix onto the complexes, they were cultured in vitro or subcutaneously implanted into nude mice for up to eight weeks. The results of the in vitro and in vivo studies revealed that the accumulation of the chondral extracellular matrices was increased on the cell aggregate-fibrin-PLCL scaffold complexes (CAPs) compared to the single cell-fibrin-PLCL scaffold complexes (SCPs). Additionally, we examined whether the mature and well-developed cartilaginous tissues and lacunae structures typical of mature cartilage were evenly distributed in the CAPs. Consequently, the cell aggregates in the hybrid scaffolds of fibrin gels and elastic PLCL scaffolds can induce themselves to differentiate into chondrocytes, maintain their phenotypes, enhance glycosaminoglycan (GAG) production, and improve the quality of cartilaginous tissue formed in vitro and in vivo. Full article
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Open AccessFeature PaperArticle The Distribution of Nanoclay Particles at the Interface and Their Influence on the Microstructure Development and Rheological Properties of Reactively Processed Biodegradable Polylactide/Poly(butylene succinate) Blend Nanocomposites
Polymers 2017, 9(8), 350; doi:10.3390/polym9080350
Received: 6 July 2017 / Revised: 4 August 2017 / Accepted: 7 August 2017 / Published: 9 August 2017
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Abstract
The present work investigates the distribution of nanoclay particles at the interface and their influence on the microstructure development and non-linear rheological properties of reactively processed biodegradable polylactide/poly(butylene succinate) blend nanocomposites. Two types of organoclays, one is more hydrophilic (Cloisite®30B (C30B))
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The present work investigates the distribution of nanoclay particles at the interface and their influence on the microstructure development and non-linear rheological properties of reactively processed biodegradable polylactide/poly(butylene succinate) blend nanocomposites. Two types of organoclays, one is more hydrophilic (Cloisite®30B (C30B)) and another one is more hydrophobic (BetsopaTM (BET)), were used at different concentrations. Surface and transmission electron microscopies were respectively used to study the blend morphology evolution and for probing the dispersion and distribution of nanoclay platelets within the blend matrix and at the interface. The results suggested that both organoclays tended to localize at the interface between the blend’s two phases and encapsulate the dispersed poly(butylene succinate) phase, thereby suppressing coalescence. Using small angle X-ray scattering the probability of finding neighboring nanoclay particles in the blend matrix was calculated using the Generalized Indirect Fourier Transformation technique. Fourier Transform-rheology was utilized for quantifying nonlinear rheological responses and for correlating the extent of dispersion as well as the blend morphological evolution, for different organoclay loadings. The rheological responses were in good agreement with the X-ray scattering and electron microscopic results. It was revealed that C30B nanoparticles were more efficient in stabilizing the morphologies by evenly distributing at the interface. Nonlinear coefficient from FT-rheology was found to be more pronounced in case of blends filled with C30B, indicating better dispersion of C30B compare with BET which was in agreement with the SAXS results. Full article
(This article belongs to the Special Issue Polymer Nanocomposites)
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Open AccessArticle Silane-Treated Basalt Fiber–Reinforced Poly(butylene succinate) Biocomposites: Interfacial Crystallization and Tensile Properties
Polymers 2017, 9(8), 351; doi:10.3390/polym9080351
Received: 12 July 2017 / Revised: 6 August 2017 / Accepted: 7 August 2017 / Published: 9 August 2017
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Abstract
In this work, an economical modifier silane agent—KH550—was used for surface treatment of basalt fiber. Then, a biodegradable poly(butylene succinate) (PBS)/modified basalt fiber (MBF) biocomposite was successfully developed. The effects of silane treatment and fiber mass content on crystalline structure, isothermal crystallization process
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In this work, an economical modifier silane agent—KH550—was used for surface treatment of basalt fiber. Then, a biodegradable poly(butylene succinate) (PBS)/modified basalt fiber (MBF) biocomposite was successfully developed. The effects of silane treatment and fiber mass content on crystalline structure, isothermal crystallization process and mechanical performance of composites were evaluated. The interfacial crystallization of PBS on the surface of MBF was investigated by using a polarized optical microscope (POM). The transcrystalline (TC) structure could be clearly observed and it grew perpendicular to the surface of MBF, which boosted the nucleation ability on PBS crystallization and the strong interfacial interaction between PBS and silane-treated basalt fiber. Under isothermal crystallization kinetics, the incorporation of basalt fiber enhanced the crystallization rate and reduced the crystallization half-time values of composites compared with that of neat PBS due to a heterogeneous nucleation effect. Furthermore, tensile results confirmed that the presence of MBF could greatly improve the tensile strength and modulus. The predicted interfacial shear strength (IFSS) suggested that an enhancement of interfacial bonding could be realized via interfacial crystallization, which was also verified by SEM images. The PBS/MBF biocomposites can be applied in many fields as a low-cost, lightweight, and biodegradable composite material. Full article
(This article belongs to the Special Issue Biodegradable and Biobased Polyesters)
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Open AccessArticle Long Lived Photoexcitation Dynamics in π-Conjugated Polymer/PbS Quantum Dot Blended Films for Photovoltaic Application
Polymers 2017, 9(8), 352; doi:10.3390/polym9080352
Received: 3 July 2017 / Revised: 26 July 2017 / Accepted: 9 August 2017 / Published: 10 August 2017
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Abstract
We used continuous wave photoinduced absorption (PIA) spectroscopy to investigate long-lived polarons in a blend of PbS quantum dot and regio-regular poly (3-hexylthiophene) (RR-P3HT). The charge transfer from RR-P3HT to PbS as well as from PbS to RR-P3HT were observed after changing the
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We used continuous wave photoinduced absorption (PIA) spectroscopy to investigate long-lived polarons in a blend of PbS quantum dot and regio-regular poly (3-hexylthiophene) (RR-P3HT). The charge transfer from RR-P3HT to PbS as well as from PbS to RR-P3HT were observed after changing the capping ligand of PbS from a long chain molecular to a short one. Therefore, PbS could be used to extend the working spectral range in hybrid solar cells with a proper capping ligand. However, we found that the recombination mechanism in the millisecond time region is dominated by the trap/defects in blended films, while it improves to a bimolecular recombination partially after ligand exchange. Our results suggest that passivating traps of nanocrystals by improving surface ligands will be crucial for relevant solar cell applications. Full article
(This article belongs to the Special Issue Polymeric Materials for Optical Applications)
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Open AccessArticle Facile, Efficient Copolymerization of Ethylene with Norbornene-Containing Dienes Promoted by Single Site Non-Metallocene Oxovanadium(V) Catalytic System
Polymers 2017, 9(8), 353; doi:10.3390/polym9080353
Received: 23 July 2017 / Revised: 8 August 2017 / Accepted: 8 August 2017 / Published: 11 August 2017
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Abstract
Non-metallocene oxovanadium(V) complexes bearing either [ONNO]-type amine pyridine bis(phenolate) ligands or [ONN]-type amine pyridine phenolate ligands were employed as efficient catalysts to copolymerize ethylene with several unsymmetrical norbornene-containing dienes, such as 5-vinyl-2-norbornene (VNB), 5-ethylidene-2-norbornene (ENB) or dicyclopentadiene (DCPD), producing copolymers with high comonomer
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Non-metallocene oxovanadium(V) complexes bearing either [ONNO]-type amine pyridine bis(phenolate) ligands or [ONN]-type amine pyridine phenolate ligands were employed as efficient catalysts to copolymerize ethylene with several unsymmetrical norbornene-containing dienes, such as 5-vinyl-2-norbornene (VNB), 5-ethylidene-2-norbornene (ENB) or dicyclopentadiene (DCPD), producing copolymers with high comonomer incorporations (VNB: 33.0 mol %; ENB: 30.4 mol %; DCPD: 31.6 mol %, respectively) and high molecular weight (VNB: 86.4 kDa; ENB: 256 kDa; DCPD: 86.4 kDa, respectively). The enchainment of the dienes was proven to be exclusive of vinyl-addition via the C=C double bond of the norbornene ring while the other double bond was retained near the backbone without crosslinking. During the copolymerization of ethylene with ENB, a positive ‘comonomer effect’ was observed. The catalytic activities of the catalysts as well as the molecular weights and comonomer incorporations of the resultant copolymers could be tuned within a wide range by varying the structures of the catalysts and copolymerization conditions. The [ONN]-type oxovanadium(V) complexes showed higher catalytic activities than those of [ONNO]-type oxovanadium(V) complexes, irrespective of the structure of the dienes. In addition, the dominant chain transfer pathway of the non-metallocene oxovanadium(V) catalytic system promoted copolymerization was proven to be transfer to aluminum compounds. Full article
(This article belongs to the Special Issue Olefin Polymerization and Polyolefin)
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Open AccessArticle Isolation and Characterization of Cellulose Nanocrystals from Oil Palm Mesocarp Fiber
Polymers 2017, 9(8), 355; doi:10.3390/polym9080355
Received: 12 July 2017 / Revised: 9 August 2017 / Accepted: 9 August 2017 / Published: 11 August 2017
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Abstract
The aim was to explore the utilization of oil palm mesocarp fiber (OPMF) as a source for the production of cellulose nanocrystals (CNC). OPMF was first treated with alkali and then bleached before the production of CNC by acid hydrolysis (H2SO
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The aim was to explore the utilization of oil palm mesocarp fiber (OPMF) as a source for the production of cellulose nanocrystals (CNC). OPMF was first treated with alkali and then bleached before the production of CNC by acid hydrolysis (H2SO4). The produced materials were characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), a scanning electron microscope (SEM) and a transmission electron microscope (TEM). It was proven that acid hydrolysis can increase the crystallinity of bleached OPMF and reduce the dimension of cellulose to nano scale. Changes in the peaks of the FTIR spectrum at 2852 (C-H stretching), 1732 (C=O stretching) and 1234 cm−1 (C-O stretching) indicated that the alkali treatment completely removed hemicelluloses and lignin from the fiber surface. This can be seen from the thermogram obtained from the TGA characterization. Morphological characterization clearly showed the formation of rod-shaped CNCs. The promising results prove that OPMF is a valuable source for the production of CNC. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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Open AccessArticle Directional Alignment of Polyfluorene Copolymers at Patterned Solid-Liquid Interfaces
Polymers 2017, 9(8), 356; doi:10.3390/polym9080356
Received: 26 June 2017 / Revised: 2 August 2017 / Accepted: 3 August 2017 / Published: 11 August 2017
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Abstract
Polyfluorene and its derivatives have been recognized as efficient light-emitting semiconductors. However, directional alignment of polyfluorene copolymers at a large scale has rarely been observed, in particular for the two relatively more amorphous members of poly-9,9-dioctylfluorene-co-bethiadisazole (F8BT) and poly-(9,9-dioctylfluorenyl-2,7-diyl)-co-(N,
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Polyfluorene and its derivatives have been recognized as efficient light-emitting semiconductors. However, directional alignment of polyfluorene copolymers at a large scale has rarely been observed, in particular for the two relatively more amorphous members of poly-9,9-dioctylfluorene-co-bethiadisazole (F8BT) and poly-(9,9-dioctylfluorenyl-2,7-diyl)-co-(N,N0-diphenyl)-N,N′di(p-butyl-oxy-pheyl)-1,4-diamino-benzene) (PFB) molecules. Furthermore, the directional alignment of PFB has not been observed so far due to the triphenylamine units in its molecular structures. We present, in this work, a solution-processible method to achieve large-scale alignment of F8BT and PFB molecules into fibers as long as millimeters in a defined direction. Spin-coating the polymer film on to a glass substrate patterned by one-dimensional dielectric nano-grating structures through interference lithography and subsequent modification using 1,5-pentanediol have been used in all of the preparation procedures. Polymer fibers have been obtained in an arrangement parallel to the grating lines. The microscopic, spectroscopic, and photoconductive performances verified the formation and the quality of these directionally-aligned polymeric fibers. Full article
(This article belongs to the Special Issue Host-Guest Polymer Complexes)
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Open AccessArticle Development of Synergistic Antimicrobial Coating of p-Aramid Fibers Using Ag Nanoparticles and Glycidyltrimethylammonium Chloride (GTAC) without the Aid of a Cross-Linking Agent
Polymers 2017, 9(8), 357; doi:10.3390/polym9080357
Received: 5 July 2017 / Revised: 3 August 2017 / Accepted: 6 August 2017 / Published: 11 August 2017
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Abstract
Functional p-aramid fibers that can express antimicrobial activity were produced by simple processing of silver nanoparticles (AgNPs), which are well known as antimicrobial agents, by using glycidyltrimethylammonium chloride (GTAC), a quaternary ammonium salt. P-aramid fibers were treated with GTAC by the pad-dry-cure process
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Functional p-aramid fibers that can express antimicrobial activity were produced by simple processing of silver nanoparticles (AgNPs), which are well known as antimicrobial agents, by using glycidyltrimethylammonium chloride (GTAC), a quaternary ammonium salt. P-aramid fibers were treated with GTAC by the pad-dry-cure process and put into an Ag colloid solution for reactions at 40 °C for 90 min to prepare GTAC/AgNPs-treated p-aramid fibers. Through these processes, GTAC was used as a substitute for existing cross-linking agents. The changes in the degree of attachment of AgNPs to the surface of p-aramid fibers were determined using a scanning electron microscope according to parameters such as GTAC concentration, Ag colloid concentration, and reaction temperature. Through this study, the following results were obtained: (i) The tensile strength of AgNPs/GTAC-treated p-aramid fibers was found to be about 80% of that of untreated p-aramid fibers; (ii) Thermogravimetric analysis showed that the thermal stability of p-aramid fibers did not change much after GTAC/AgNPs treatment and (iii) Antimicrobial activity analysis showed that AgNPs/GTAC-treated p-aramid fibers exhibited superior antibacterial properties compared to untreated p-aramid fibers, which may or may not be the effect of GTAC or AgNPs, or both. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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Open AccessArticle Influence of Temperature on the Electromechanical Properties of Ionic Liquid-Doped Ionic Polymer-Metal Composite Actuators
Polymers 2017, 9(8), 358; doi:10.3390/polym9080358
Received: 28 July 2017 / Revised: 8 August 2017 / Accepted: 9 August 2017 / Published: 12 August 2017
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Abstract
Ionic polymer-metal composite (IPMC) actuators have considerable potential for a wide range of applications. Although IPMC actuators are widely studied for their electromechanical properties, most studies have been conducted at the ambient conditions. The electromechanical performance of IPMC actuators at higher temperature is
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Ionic polymer-metal composite (IPMC) actuators have considerable potential for a wide range of applications. Although IPMC actuators are widely studied for their electromechanical properties, most studies have been conducted at the ambient conditions. The electromechanical performance of IPMC actuators at higher temperature is still far from understood. In this study, the effect of temperature on the electromechanical behavior (the rate of deformation and curvature) and electrochemical behavior (current flow) of ionic liquid doped IPMC actuators are examined and reported. Both electromechanical and electrochemical studies were conducted in air at temperatures ranging from 25 °C to 90 °C. Electromechanically, the actuators showed lower cationic curvature with increasing temperature up to 70 °C and a slower rate of deformation with increasing temperature up to 50 °C. A faster rate of deformation was recorded at temperatures higher than 50 °C, with a maximum rate at 60 °C. The anionic response showed a lower rate of deformation and a higher anionic curvature with increasing temperatures up to 50 °C with an abrupt increase in the rate of deformation and decrease of curvature at 60 °C. In both cationic and anionic responses, actuators started to lose functionality and show unpredictable performance for temperatures greater than 60 °C, with considerable fluctuations at 70 °C. Electrochemically, the current flow across the actuators was increased gradually with increasing temperature up to 80 °C during the charging and discharging cycles. A sudden increase in current flow was recorded at 90 °C indicating a shorted circuit and actuator failure. Full article
(This article belongs to the Special Issue Electroactive Polymers and Gels)
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Open AccessArticle Surface Molecularly Imprinted Polymer Film with Poly(p-aminothiophenol) Outer Layer Coated on Gold Nanoparticles Inner Layer for Highly Sensitive and Selective Sensing Paraoxon
Polymers 2017, 9(8), 359; doi:10.3390/polym9080359
Received: 19 July 2017 / Revised: 9 August 2017 / Accepted: 10 August 2017 / Published: 12 August 2017
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Abstract
This paper presents the fabrication of a molecularly imprinted, polymer-based disposable electrochemical sensor for paraoxon (PO) determination. The sensor was based on a screen-printed carbon electrode (SPCE) modified with a surface molecularly imprinted poly (p-aminothiophenol) (PATP)/gold nanoparticles (AuNPs) composite film, which
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This paper presents the fabrication of a molecularly imprinted, polymer-based disposable electrochemical sensor for paraoxon (PO) determination. The sensor was based on a screen-printed carbon electrode (SPCE) modified with a surface molecularly imprinted poly (p-aminothiophenol) (PATP)/gold nanoparticles (AuNPs) composite film, which consisted of a PATP outer layer and an AuNPs inner layer. We report a novel strategy, combining surface molecularly imprinting and self-assembly directed electro-polymerization with high densely imprinting PO molecules in the PATP/AuNPs film. Firstly, AuNPs were in situ electrodeposited at the electrode surface, and then assembled with electropolmerizable functional monomer p-aminothiophenol (ATP). Subsequently, PO molecules were assembled onto the ATP monolayer-modified AuNPs, forming a basis of surface molecular imprinting. After that, replenished PO molecules were embedded in the PATP/AuNPs film by PO and the ATP molecular self-assembly directed electro-polymerization in the polymerization precursor mixture. The resulting imprinted PATP/AuNPs/SPCE possesses high sensitivity, affinity, and selectivity toward PO, with a low detection limit of 1 × 10−9 M. The proposed sensor was successfully applied for the determination of PO in fruit and vegetables, giving satisfactory recoveries. The strategy reported herein can be further expected to fabricate various molecular imprinted sensors for the determination of other pesticide residuals. Full article
(This article belongs to the Special Issue Polymer Based Bio-Sensors)
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Open AccessArticle Synthesis and Application of Novel Magnetic Ion-Imprinted Polymers for Selective Solid Phase Extraction of Cadmium (II)
Polymers 2017, 9(8), 360; doi:10.3390/polym9080360
Received: 4 July 2017 / Revised: 10 August 2017 / Accepted: 10 August 2017 / Published: 14 August 2017
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Abstract
Ion-imprinted polymers (IIPs) have received much attention in the fields of separation and purification. Nevertheless, selectivity of IIPs for trace target ions in complicated matrix remains a challenge. In this work, a cadmium magnetic ion-imprinted polymer (MIIP) was synthesized via surface imprinting, using
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Ion-imprinted polymers (IIPs) have received much attention in the fields of separation and purification. Nevertheless, selectivity of IIPs for trace target ions in complicated matrix remains a challenge. In this work, a cadmium magnetic ion-imprinted polymer (MIIP) was synthesized via surface imprinting, using methacrylic acid and acrylamide as dual functional monomers, vinyltrimethoxysilane as ligand, Fe3O4@SiO2 as support, azodiisobutyronitrile as initiator, and ethylene glycol dimethacrylate as crosslinker. The MIIP was characterized by transmission electron microscopy, infrared spectroscopy, thermal gravimetric analysis, and a vibrating sample magnetometer. The maximum adsorption capacities of the MIIP and magnetic non-imprinted polymer for Cd(II) were 46.8 and 14.7 mg·g−1, respectively. The selectivity factors of Pb(II), Cu(II), and Ni(II) were 3.17, 2.97, and 2.57, respectively, which were greater than 1. The adsorption behavior of Cd(II) followed the Freundlich isotherm and a pseudo second order model. The MIIP was successfully used for the selective extraction and determination of trace Cd(II) in representative rice samples. The limit of detection and recovery of the method was 0.05 µg·L−1 and 80–103%, respectively, with a relative standard deviation less than 4.8%. This study shows that MIIP provides an attractive strategy for heavy metal detection. Full article
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Open AccessArticle Aromatic Modification of Low Molecular Weight PEI for Enhanced Gene Delivery
Polymers 2017, 9(8), 362; doi:10.3390/polym9080362
Received: 17 July 2017 / Revised: 3 August 2017 / Accepted: 3 August 2017 / Published: 15 August 2017
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Abstract
Low molecular weight polyethylenimine (1800 Da, also referred to as oligoethylenimines, OEI) was modified with amino acids, including two aromatic amino acids (tryptophan, phenylalanine) and an aliphatic amino acid (leucine). The substitution degree of amino acids could be controlled by adjusting the feeding
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Low molecular weight polyethylenimine (1800 Da, also referred to as oligoethylenimines, OEI) was modified with amino acids, including two aromatic amino acids (tryptophan, phenylalanine) and an aliphatic amino acid (leucine). The substitution degree of amino acids could be controlled by adjusting the feeding mole ratio of the reactants. Fluorescence spectroscopy and circular dichroism experiments demonstrated that the indole ring of tryptophan may intercalate into the DNA base pairs and contribute to efficient DNA condensation. In vitro gene expression results revealed that the modified OEIs (OEI-AAs) may provide higher transfection efficiency even than high molecular weight polyethylenimine (25 kDa, PEI), especially the aromatic tryptophan substituted OEI. Moreover, OEI-AAs exhibited excellent serum tolerance, and up to 137 times higher transfection efficiency than PEI 25 kDa that was obtained in the presence of serum. The cytotoxicity of OEI-AAs is much lower than PEI 25 kDa. This study may afford a new method for the development of low molecular weight oligomeric non-viral gene vectors with both high efficiency and biocompatibility. Full article
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Open AccessArticle Hydrogen-Bonded Polymer Complex Thin Film of Poly(2-oxazoline) and Poly(acrylic acid)
Polymers 2017, 9(8), 363; doi:10.3390/polym9080363
Received: 7 July 2017 / Revised: 9 August 2017 / Accepted: 11 August 2017 / Published: 15 August 2017
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Abstract
The hydrogen-bonded polymer complex thin film of poly(2-ethyl-2-oxazoline) (PEOX) and poly(acrylic acid) (PAA) was fabricated with layer-by-layer (LbL) assembly. The film shows exponential growth at early stage and transfers to linear growth after 10 assembling cycles, and the stable thickness increment per assembling
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The hydrogen-bonded polymer complex thin film of poly(2-ethyl-2-oxazoline) (PEOX) and poly(acrylic acid) (PAA) was fabricated with layer-by-layer (LbL) assembly. The film shows exponential growth at early stage and transfers to linear growth after 10 assembling cycles, and the stable thickness increment per assembling cycle in the linear region could be higher than 100 nm. The film growth should be related with polymer chain diffusion during LbL assembly. The effects of assembling time, rinsing time, temperature, pH value, concentration and molecular weight on the thin film growth were investigated. Increasing the assembly time, the temperature and the concentration is favorable to produce the thick film. Prolonging rinsing time is good for preparing smooth film. The film can be constructed below pH 4.5 while the prepared film will not completely dissolve until pH value elevates to 7.0. Molecular weight has a subtle effect on the PEOX/PAA film growth. The PEOX-PAA pair that has a big molecular weight contrast shows fast film growth in the linear region. Full article
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Open AccessArticle Biodegradation Studies of Novel Fluorinated Di-Vinyl Urethane Monomers and Interaction of Biological Elements with Their Polymerized Films
Polymers 2017, 9(8), 365; doi:10.3390/polym9080365
Received: 21 June 2017 / Revised: 1 August 2017 / Accepted: 11 August 2017 / Published: 17 August 2017
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Abstract
The monomeric components of resin composites in dental restorative materials are susceptible to hydrolysis in the oral cavity. The main objective of this study was to assess the bio-stability of fluorinated urethane dimethacrylates and determine the nature of fluoro-chemistry interactions with protein and
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The monomeric components of resin composites in dental restorative materials are susceptible to hydrolysis in the oral cavity. The main objective of this study was to assess the bio-stability of fluorinated urethane dimethacrylates and determine the nature of fluoro-chemistry interactions with protein and bacterial adhesion (both sources of hydrolytic activity) onto cured resin. Degradation studies were performed in the presence of either albumin (in a mildly alkaline pH) or cholesterol esterase (CE). The surface chemistry of the polymers was assessed by water contact angle measurements, pre- and post- incubation with albumin. Adhesion of Streptococcus mutans to cured resin was investigated. The fluorinated monomers were more stable against degradation when compared to the commercial monomer bisphenol A-diglycidyl methacrylate (BisGMA). While fluorinated monomers showed hydrolytic stability with respect to CE, all fluorinated monomers underwent some degree of degradation with albumin. The fluoro-chemistry did not reduce protein and/or bacterial adhesion onto the surface, however post incubation with albumin, the fluorinated surfaces still presented hydrophobic character as determined by the high contact angle values ranging from 79° to 86°. These monomers could potentially be used to increase the hydrophobicity of polymeric composites and provide a means to moderate esterolytic degradation associated with the monomeric component of the polymers within the oral cavity. Full article
(This article belongs to the Special Issue Advance of Polymers Applied to Biomedical Applications: Biointerface)
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Open AccessArticle Pulp Fines—Characterization, Sheet Formation, and Comparison to Microfibrillated Cellulose
Polymers 2017, 9(8), 366; doi:10.3390/polym9080366
Received: 28 July 2017 / Revised: 13 August 2017 / Accepted: 13 August 2017 / Published: 17 August 2017
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Abstract
In the pulp and paper industry different types of pulp or fiber fines are generated during the pulping (primary fines, mechanical fines), and/or the refining process (secondary fines). Besides fibers, these cellulosic microparticles are a further component of the paper network. Fines, which
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In the pulp and paper industry different types of pulp or fiber fines are generated during the pulping (primary fines, mechanical fines), and/or the refining process (secondary fines). Besides fibers, these cellulosic microparticles are a further component of the paper network. Fines, which are defined as the fraction of pulp that is able to pass through a mesh screen or a perforated plate having a hole diameter of 76 μm, are known to influence the properties of the final paper product. To better understand the effect and properties of this material, fines have to be separated from the pulp and investigated as an independent material. In the present study, fines are isolated from the pulp fraction by means of a laboratory pressure screen. To allow for further processing, the solids content of the produced fines suspension was increased using dissolved air flotation. Morphological properties of different types of fines and other cellulosic microparticles, such as microfibrillated celluloses (MFC) are determined and compared to each other. Furthermore, handsheets are prepared from these materials and properties, such as apparent density, contact angle, modulus of elasticity, and strain are measured giving similar results for the analyzed types of fines in comparison to the tested MFC grades. The analysis of the properties of fiber fines contributes on the one hand to a better understanding of how these materials influences the final paper products, and on the other hand, helps in identifying other potential applications of this material. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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Open AccessArticle pH-Induced Association and Dissociation of Intermolecular Complexes Formed by Hydrogen Bonding between Diblock Copolymers
Polymers 2017, 9(8), 367; doi:10.3390/polym9080367
Received: 26 July 2017 / Revised: 12 August 2017 / Accepted: 15 August 2017 / Published: 17 August 2017
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Abstract
Poly(sodium styrenesulfonate)–block–poly(acrylic acid) (PNaSS–b–PAA) and poly(sodium styrenesulfonate)–blockpoly(N-isopropylacrylamide) (PNaSS–bPNIPAM) were prepared via reversible addition–fragmentation chain transfer (RAFT) radical polymerization using a PNaSS-based macro-chain transfer agent. The molecular weight distributions (Mw/M
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Poly(sodium styrenesulfonate)–block–poly(acrylic acid) (PNaSS–b–PAA) and poly(sodium styrenesulfonate)–blockpoly(N-isopropylacrylamide) (PNaSS–bPNIPAM) were prepared via reversible addition–fragmentation chain transfer (RAFT) radical polymerization using a PNaSS-based macro-chain transfer agent. The molecular weight distributions (Mw/Mn) of PNaSS–b–PAA and PNaSS–bPNIPAM were 1.18 and 1.39, respectively, suggesting that these polymers have controlled structures. When aqueous solutions of PNaSS–b–PAA and PNaSS–bPNIPAM were mixed under acidic conditions, water-soluble PNaSS–bPAA/PNaSS–bPNIPAM complexes were formed as a result of hydrogen bonding interactions between the pendant carboxylic acids in the PAA block and the pendant amide groups in the PNIPAM block. The complex was characterized by 1H NMR, dynamic light scattering, static light scattering, and transmission electron microscope measurements. The light scattering intensity of the complex depended on the mixing ratio of PNaSS–b–PAA and PNaSS–bPNIPAM. When the molar ratio of the N-isopropylacrylamide (NIPAM) and acrylic acid (AA) units was near unity, the light scattering intensity reached a maximum, indicating stoichiometric complex formation. The complex dissociated at a pH higher than 4.0 because the hydrogen bonding interactions disappeared due to deprotonation of the pendant carboxylic acids in the PAA block. Full article
(This article belongs to the Special Issue Polymer Micelles)
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Open AccessFeature PaperArticle The Effect of Hydrogen Bonding on Radical Semi-Batch Copolymerization of Butyl Acrylate and 2-Hydroxyethyl Acrylate
Polymers 2017, 9(8), 368; doi:10.3390/polym9080368
Received: 24 July 2017 / Revised: 12 August 2017 / Accepted: 15 August 2017 / Published: 17 August 2017
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Abstract
The radical copolymerization of butyl acrylate (BA) and 2-hydroxyethyl acrylate (HEA) was investigated under batch and semi-batch operations, with a focus on the influence of hydrogen-bonding on acrylate backbiting. The effect of hydrogen bonding on HEA to BA relative incorporation rates during copolymerization,
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The radical copolymerization of butyl acrylate (BA) and 2-hydroxyethyl acrylate (HEA) was investigated under batch and semi-batch operations, with a focus on the influence of hydrogen-bonding on acrylate backbiting. The effect of hydrogen bonding on HEA to BA relative incorporation rates during copolymerization, previously seen in low-conversion kinetic studies, was also observed under high-conversion semi-batch conditions. However, overall reaction rates (as indicated by free monomer concentrations), polymer molar masses, and branching levels did not vary as copolymer HEA content was increased from 0 to 40 wt % in the semi-batch system. In contrast, introduction of a H-bonding solvent, n-pentanol, led to an observable decrease in branching levels, and branching levels were also reduced in batch (co)polymerizations with HEA. These differences can be attributed to the low levels of unreacted HEA in the starved-feed semi-batch system. Full article
(This article belongs to the Special Issue Tailored Polymer Synthesis by Advanced Polymerization Techniques)
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Open AccessArticle Constraining Polymers into β-Turns: Miscibility and Phase Segregation Effects in Lipid Monolayers
Polymers 2017, 9(8), 369; doi:10.3390/polym9080369
Received: 28 July 2017 / Revised: 11 August 2017 / Accepted: 13 August 2017 / Published: 17 August 2017
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Abstract
Abstract: Investigation of model biomembranes and their interactions with natural or synthetic macromolecules are of great interest to design membrane systems with specific properties such as drug-delivery. Here we study the behavior of amphiphilic β-turn mimetic polymer conjugates at the air–water interface
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Abstract: Investigation of model biomembranes and their interactions with natural or synthetic macromolecules are of great interest to design membrane systems with specific properties such as drug-delivery. Here we study the behavior of amphiphilic β-turn mimetic polymer conjugates at the air–water interface and their interactions with lipid model membranes. For this endeavor we synthesized two different types of conjugates containing either hydrophobic polyisobutylene (PIB, Mn = 5000 g·mol−1) or helical poly(n-hexyl isocyanate) (PHIC, Mn = 4000 g·mol−1), both polymers being immiscible, whereas polyisobutylene as a hydrophobic polymer can incorporate into lipid membranes. The conjugates were investigated using Langmuir-film techniques coupled with epifluorescence microscopy and AFM (Atomic Force Microscopy), in addition to their phase behavior in mixed lipid/polymer membranes composed of DPPC (dipalmitoyl-sn-glycero-3-phosphocholine). It was found that the DPPC monolayers are strongly disturbed by the presence of the polymer conjugates and that domain formation of the polymer conjugates occurs at high surface pressures (π > 30 mN·m−1). Full article
(This article belongs to the Special Issue From Amphiphilic to Polyphilic Polymers)
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Open AccessArticle Molecular Dynamics Study on the Effect of Surface Hydroxyl Groups on Three-Phase Wettability in Oil-Water-Graphite Systems
Polymers 2017, 9(8), 370; doi:10.3390/polym9080370
Received: 30 June 2017 / Revised: 15 August 2017 / Accepted: 15 August 2017 / Published: 18 August 2017
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Abstract
In this paper, a hydroxylated graphite surface is generated as a hydrophilic oleophobic material for the application of oil-water separation, and the effects of hydroxyl density on the three-phase wettability are studied in oil-water-graphite systems. We analyze the adsorption of water molecules on
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In this paper, a hydroxylated graphite surface is generated as a hydrophilic oleophobic material for the application of oil-water separation, and the effects of hydroxyl density on the three-phase wettability are studied in oil-water-graphite systems. We analyze the adsorption of water molecules on the hydroxylated surfaces and obtain the relationship between water-oil-solid interfacial properties and the hydroxyl density, which results from the synthetic effects of the orientation of molecules and hydrogen bonds. With the increase of hydroxyl density, the water-solid contact angle first decreases rapidly, and then remains constant. The density of the hydrogen bond formed between hydroxyls and water molecules in the adsorption layer can explain the regularity of the three-phase wettability. The orientation of the water molecules in the adsorption layer shows insignificant variation, owing to the hydrogen bond network formed between the water molecules; thus, little change is observed in the hydrogen bond density in the adsorption layer. Full article
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Open AccessArticle Surface Modification of Poly(lactic acid) Fabrics with Plasma Pretreatment and Chitosan/Siloxane Polyesters Coating for Color Strength Improvement
Polymers 2017, 9(8), 371; doi:10.3390/polym9080371
Received: 12 July 2017 / Revised: 3 August 2017 / Accepted: 16 August 2017 / Published: 18 August 2017
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Abstract
As people in the 21st century become increasingly environmentally aware, environmentally friendly products have come into focus. As such, environmentally friendly textiles and eco-textiles have become an international trend in research and development. Poly(lactic acid) fiber, which is biodegradable, holds much promise, but
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As people in the 21st century become increasingly environmentally aware, environmentally friendly products have come into focus. As such, environmentally friendly textiles and eco-textiles have become an international trend in research and development. Poly(lactic acid) fiber, which is biodegradable, holds much promise, but it is difficult to deep dye. This study used chitosan, succine anhydride, siloxane, and polyethylene glycol to produce a series of chitosan/siloxane polyesters that have a hydrophilic component (chitosan) and a hydrophobic component (siloxane), and this chitosan/siloxane polyester can be coated on poly(lactic acid) fiber, which we had subjected to Argon plasma treatment to increase their antimicrobial properties and to increase the fibers dyeing efficiency. The study shows that, after the surface plasma treatment, longer PEG chain lengths resulted in higher K/S values. This result suggests that the surface plasma pretreatment and chitosan/siloxane polyesters coating showed that lower ∆E values result in more leveling dyeing of poly(lactic acid) fiber. Full article
(This article belongs to the Special Issue Biodegradable and Biobased Polyesters)
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Open AccessArticle Microstructural and Mechanical Implications of Microscaled Assembly in Droplet-based Multi-Material Additive Manufacturing
Polymers 2017, 9(8), 372; doi:10.3390/polym9080372
Received: 30 June 2017 / Revised: 15 August 2017 / Accepted: 16 August 2017 / Published: 18 August 2017
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Abstract
To reveal the potential and limits of multi-material three-dimensional (3D) printed parts in droplet-based additive manufacturing, a study combining tensile experiments and 3D imaging technique is proposed. A polymeric composite structure made of acrylonitrile butadiene styrene and thermoplastic polyurethane is manufactured using a
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To reveal the potential and limits of multi-material three-dimensional (3D) printed parts in droplet-based additive manufacturing, a study combining tensile experiments and 3D imaging technique is proposed. A polymeric composite structure made of acrylonitrile butadiene styrene and thermoplastic polyurethane is manufactured using a two extrusion head printer. The quality of the interface between the two thermoplastics is quantified by adjusting the number of intertwining droplets at the interface. Tensile experiments assisted with digital image correlation are performed with two-interface orientation to discriminate shearing and traction at the interface. The 3D imaging results, which are based on X-ray micro-tomography, show the distinct features of droplet-based additive manufacturing in terms of porosity content and connectivity. Interface properties are found to control, in an incomparable way, the mechanical response. It is found that the interface quality is determinant for enhancing the ultimate performance whereas the interface orientation is found to be the perfect leverage for varying the slope of the linear part. Full article
(This article belongs to the Special Issue Three-Dimensional Structures: Fabrication and Application)
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Open AccessCommunication Synthesis of Humin-Phenol-Formaldehyde Adhesive
Polymers 2017, 9(8), 373; doi:10.3390/polym9080373
Received: 27 May 2017 / Revised: 11 August 2017 / Accepted: 14 August 2017 / Published: 18 August 2017
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Abstract
Humins are low-value-added byproducts from the biomass acid hydrolysis process. In the present work, humins were first employed as a phenol replacement for synthesis of modified phenol-formaldehyde adhesives through a two-step process. In this process, humins were first utilized to obtain alkaline soluble
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Humins are low-value-added byproducts from the biomass acid hydrolysis process. In the present work, humins were first employed as a phenol replacement for synthesis of modified phenol-formaldehyde adhesives through a two-step process. In this process, humins were first utilized to obtain alkaline soluble products, mainly consisting of phenolics, through a hydrothermal process. The obtained alkaline soluble products then reacted with phenol and formaldehyde to produce humin-phenol-formaldehyde adhesive (HPFA). The physicochemical properties of HPFA, including viscosity, bonding strength, pH, free formaldehyde level, free phenol level and solid content, met the requirements of the GB/T 14732-2006 Chinese National Standard. Full article
(This article belongs to the collection Polymeric Adhesives)
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Open AccessArticle Bacterial Nanocellulose from Side-Streams of Kombucha Beverages Production: Preparation and Physical-Chemical Properties
Polymers 2017, 9(8), 374; doi:10.3390/polym9080374
Received: 15 July 2017 / Revised: 11 August 2017 / Accepted: 14 August 2017 / Published: 18 August 2017
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Abstract
We focused on preparing cellulose nanofibrils by purification, separation, and mechanical treatment of Kombucha membranes (KM) resulted as secondary product from beverage production by fermentation of tea broth with symbiotic culture of bacteria and yeast (SCOBY). We purified KM using two alkaline solutions,
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We focused on preparing cellulose nanofibrils by purification, separation, and mechanical treatment of Kombucha membranes (KM) resulted as secondary product from beverage production by fermentation of tea broth with symbiotic culture of bacteria and yeast (SCOBY). We purified KM using two alkaline solutions, 1 and 4 M NaOH, which afterwards were subjected to various mechanical treatments. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), dynamic light scattering (DLS), X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) were employed to evaluate the purification degree, the size and aspect of cellulose fibrils after each treatment step, the physical-chemical properties of intermediary and final product, and for comparison with micro-crystalline cellulose from wooden sources. We determined that 1 M NaOH solution leads to approx. 85% purification, while a higher concentration assures almost 97% impurities removal. XRD analysis evidenced an increase in crystallinity from 37% to 87% after purification, the characteristic diffractograms of Iα and Iβ cellulose allomorphs, and a further decrease in crystallinity to 46% after microfluidization, fact correlated with a drastically decrease in fibrils’ size. FTIR analysis evidenced the appearance of new chain ends by specific transmission bands at 2941 and 2843cm−1. Full article
(This article belongs to the Special Issue Cellulose Nanomaterials)
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Open AccessArticle Correlation-Based Multiplexing of Complex Amplitude Data Pages in a Holographic Storage System Using Digital Holographic Techniques
Polymers 2017, 9(8), 375; doi:10.3390/polym9080375
Received: 30 June 2017 / Revised: 9 August 2017 / Accepted: 15 August 2017 / Published: 18 August 2017
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Abstract
Holographic recording media can store the amplitude and the phase, or the complex amplitude, of a beam on the basis of holography. Owing to this characteristic, digital data can be encoded onto the complex amplitude of a signal beam in holographic data storage.
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Holographic recording media can store the amplitude and the phase, or the complex amplitude, of a beam on the basis of holography. Owing to this characteristic, digital data can be encoded onto the complex amplitude of a signal beam in holographic data storage. However, most of conventional holographic storage systems encode digital data onto the amplitude alone because there are difficulties for modulating and detecting the phase. To solve the difficulties, a holographic storage system using digital holographic techniques has been proposed. With the help of digital holographic techniques, it is possible to modulate and detect the complex amplitude of a signal beam. Moreover, the proposed system can modulate the complex amplitude of a reference beam. In this paper, by making use of the capability, a correlation-based multiplexing with uncorrelated reference beams is demonstrated in the proposed system. Multiple holograms can be recorded in the same volume of a recording medium with no need for mechanical movements. Experimental results show that the proposed system with a correlation-based multiplexing can improve the storage capacity and can utilize the full potential of a recording medium without crosstalk noise stem from the optical setup. Full article
(This article belongs to the Special Issue Photo-Responsive Polymers)
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Open AccessArticle Effect of Catechol Content in Catechol-Conjugated Dextrans on Antiplatelet Performance
Polymers 2017, 9(8), 376; doi:10.3390/polym9080376
Received: 26 June 2017 / Revised: 17 August 2017 / Accepted: 17 August 2017 / Published: 19 August 2017
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Abstract
The surface coating of solid substrates using dextrans has gained a great deal of attention, because dextran-coated surfaces show excellent anti-fouling property as well as biocompatibility behavior. Much effort has been made to develop efficient methods for grafting dextrans on solid surfaces. This
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The surface coating of solid substrates using dextrans has gained a great deal of attention, because dextran-coated surfaces show excellent anti-fouling property as well as biocompatibility behavior. Much effort has been made to develop efficient methods for grafting dextrans on solid surfaces. This led to the development of catechol-conjugated dextrans (Dex-C) which can adhere to a number of solid surfaces, inspired by the underwater adhesion behavior of marine mussels. The present study is a systematic investigation of the characteristics of surface coatings developed with Dex-C. Various Dex-C with different catechol contents were synthesized and used as a surface coating material. The effect of catechol content on surface coating and antiplatelet performance was investigated. Full article
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Open AccessArticle Effect of Sodium Hydroxide Treatments on the Tensile Strength and the Interphase Quality of Hemp Core Fiber-Reinforced Polypropylene Composites
Polymers 2017, 9(8), 377; doi:10.3390/polym9080377
Received: 21 July 2017 / Revised: 11 August 2017 / Accepted: 14 August 2017 / Published: 19 August 2017
PDF Full-text (3144 KB) | HTML Full-text | XML Full-text
Abstract
The formulation of greener composite materials by substituting glass fibers with natural fibers is a current field of research. If such natural fiber reinforcements come from industrial side streams, as hemp core fibers (HCFs) come from the extraction of hemp strands for the
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The formulation of greener composite materials by substituting glass fibers with natural fibers is a current field of research. If such natural fiber reinforcements come from industrial side streams, as hemp core fibers (HCFs) come from the extraction of hemp strands for the textile industry, an additional advantage can be identified. Nonetheless, such by-product fibers show some drawbacks, such as high lignin contents, which can make it difficult to obtain a good interphase between the fibers and the matrix and to obtain a good fiber individualization. A digestion treatment at different NaOH contents is proposed to eliminate soluble lignin and extractives from the surface of the fibers. At the same time, the use of a coupling agent solves incompatibilities between the fibers and the matrix. The composites were tensile tested and the impact of the proposed treatments is evaluated and discussed. Later, the Kelly-Tyson modified equation and a modified rule of mixtures—the micro-mechanic models—is used to study the impact of such treatments on the quality of the interphase between the polymer and the reinforcement. Both treatments showed a high impact on the tensile strength and the quality of the interphase, obtaining competitive composite materials reinforced with HCFs derived from a by-product. Full article
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Open AccessArticle Mechanical Properties of Composite Hydrogels of Alginate and Cellulose Nanofibrils
Polymers 2017, 9(8), 378; doi:10.3390/polym9080378
Received: 27 June 2017 / Revised: 10 August 2017 / Accepted: 17 August 2017 / Published: 19 August 2017
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Abstract
Alginate and cellulose nanofibrils (CNF) are attractive materials for tissue engineering and regenerative medicine. CNF gels are generally weaker and more brittle than alginate gels, while alginate gels are elastic and have high rupture strength. Alginate properties depend on their guluronan and mannuronan
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Alginate and cellulose nanofibrils (CNF) are attractive materials for tissue engineering and regenerative medicine. CNF gels are generally weaker and more brittle than alginate gels, while alginate gels are elastic and have high rupture strength. Alginate properties depend on their guluronan and mannuronan content and their sequence pattern and molecular weight. Likewise, CNF exists in various qualities with properties depending on, e.g., morphology and charge density. In this study combinations of three types of alginate with different composition and two types of CNF with different charge and degree of fibrillation have been studied. Assessments of the composite gels revealed that attractive properties like high rupture strength, high compressibility, high gel rigidity at small deformations (Young’s modulus), and low syneresis was obtained compared to the pure gels. The effects varied with relative amounts of CNF and alginate, alginate type, and CNF quality. The largest effects were obtained by combining oxidized CNF with the alginates. Hence, by combining the two biopolymers in composite gels, it is possible to tune the rupture strength, Young’s modulus, syneresis, as well as stability in physiological saline solution, which are all important properties for the use as scaffolds in tissue engineering. Full article
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Open AccessArticle The Effect of Network Solvation on the Viscoelastic Response of Polymer Hydrogels
Polymers 2017, 9(8), 379; doi:10.3390/polym9080379
Received: 29 June 2017 / Revised: 11 August 2017 / Accepted: 15 August 2017 / Published: 19 August 2017
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Abstract
The majority of investigations consider the deformation response of hydrogels, fully controlled by the deformation behavior of their polymer network, neglecting the contribution caused by the presence of water. Here, we use molecular dynamics simulation in an attempt to include the effect of
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The majority of investigations consider the deformation response of hydrogels, fully controlled by the deformation behavior of their polymer network, neglecting the contribution caused by the presence of water. Here, we use molecular dynamics simulation in an attempt to include the effect of physically bound water via polymer chain solvation on the viscoelastic response of hydrogels. Our model allows us to control the solvation of chains as an independent variable. The solvation of the chain is independent of other factors, mainly the effect (pH) which interferes significantly in experiments. The solvation of hydrophilic chains was controlled by setting a partial charge on the chains and quantified by the Bjerrum length (BL). The BL was calculated from the partial electric charge of the solvent and macromolecular network. When the BL is short, the repulsive Van der Waals interactions are predominant in the vicinity of macromolecules and solvation is not observed. For a long BL, the water molecules in the solvation zone of network are in the same range as attractive intermolecular forces and the solvation occurs. The model also allows the consideration of molecules of water attached to two chains simultaneously, forming a temporary bridging. By elucidating the relations between solvation of the network and structural changes during the network deformation, one may predict the viscoelastic properties of hydrogels knowing the molecular structure of its polymer chains. Full article
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Open AccessArticle Light-Driven Liquid Crystal Circular Dammann Grating Fabricated by a Micro-Patterned Liquid Crystal Polymer Phase Mask
Polymers 2017, 9(8), 380; doi:10.3390/polym9080380
Received: 27 June 2017 / Revised: 11 August 2017 / Accepted: 17 August 2017 / Published: 21 August 2017
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Abstract
As one of the diffractive optical elements, circular Dammann grating has shown its excellent versatility in practical applications. The electrically switchable Dammann grating has been extensively investigated; however, the research on the optically tunable circular Dammann grating has received less attention and reports
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As one of the diffractive optical elements, circular Dammann grating has shown its excellent versatility in practical applications. The electrically switchable Dammann grating has been extensively investigated; however, the research on the optically tunable circular Dammann grating has received less attention and reports on this subject have been insufficient in the past decade. In this paper, three-order and eight-order binary-phase liquid crystal circular Dammann gratings with two mutually orthogonal photo-induced alignments in every two adjacent alignment domains, fabricated by a micro-patterned liquid crystal polymer phase mask, are proposed to generate annular uniform-intensity patterns in the far field. A simple maskless optical tuning of an eight-order liquid crystal circular Dammann grating is demonstrated by controlling the polarization of an ultraviolet light as well as the energy dose. The proposed liquid crystal circular Dammann gratings with high efficiencies and desirable uniformities exhibit outstanding optical as well as electrical tunabilities, enabling the widespread prospective applications in adaptive photonic chips stimulated flexibly by only light or by the combination of light and electric field. Full article
(This article belongs to the Special Issue Photo-Responsive Polymers)
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Open AccessArticle Increased X-ray Visualization of Shape Memory Polymer Foams by Chemical Incorporation of Iodine Motifs
Polymers 2017, 9(8), 381; doi:10.3390/polym9080381
Received: 3 August 2017 / Revised: 18 August 2017 / Accepted: 18 August 2017 / Published: 20 August 2017
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Abstract
Shape memory polymers can be programmed into a secondary geometry and recovered to their primary geometry with the application of a controlled stimulus. Porous shape memory polymer foam scaffolds that respond to body temperature show particular promise for embolic medical applications. A limitation
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Shape memory polymers can be programmed into a secondary geometry and recovered to their primary geometry with the application of a controlled stimulus. Porous shape memory polymer foam scaffolds that respond to body temperature show particular promise for embolic medical applications. A limitation for the minimally invasive delivery of these materials is an inherent lack of X-ray contrast. In this work, a triiodobenzene containing a monomer was incorporated into a shape memory polymer foam material system to chemically impart X-ray visibility and increase material toughness. Composition and process changes enabled further control over material density and thermomechanical properties. The proposed material system demonstrates a wide range of tailorable functional properties for the design of embolic medical devices, including X-ray visibility, expansion rate, and porosity. Enhanced visualization of these materials can improve the acute performance of medical devices used to treat vascular malformations, and the material porosity provides a healing scaffold for durable occlusion. Full article
(This article belongs to the Special Issue Shape Memory Polymers)
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Review

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Open AccessReview Smart Sensor Systems for Wearable Electronic Devices
Polymers 2017, 9(8), 303; doi:10.3390/polym9080303
Received: 13 June 2017 / Revised: 20 July 2017 / Accepted: 22 July 2017 / Published: 25 July 2017
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Abstract
Wearable human interaction devices are technologies with various applications for improving human comfort, convenience and security and for monitoring health conditions. Healthcare monitoring includes caring for the welfare of every person, which includes early diagnosis of diseases, real-time monitoring of the effects of
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Wearable human interaction devices are technologies with various applications for improving human comfort, convenience and security and for monitoring health conditions. Healthcare monitoring includes caring for the welfare of every person, which includes early diagnosis of diseases, real-time monitoring of the effects of treatment, therapy, and the general monitoring of the conditions of people’s health. As a result, wearable electronic devices are receiving greater attention because of their facile interaction with the human body, such as monitoring heart rate, wrist pulse, motion, blood pressure, intraocular pressure, and other health-related conditions. In this paper, various smart sensors and wireless systems are reviewed, the current state of research related to such systems is reported, and their detection mechanisms are compared. Our focus was limited to wearable and attachable sensors. Section 1 presents the various smart sensors. In Section 2, we describe multiplexed sensors that can monitor several physiological signals simultaneously. Section 3 provides a discussion about short-range wireless systems including bluetooth, near field communication (NFC), and resonance antenna systems for wearable electronic devices. Full article
(This article belongs to the Special Issue Wearable Sensor)
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Open AccessReview A Review of Hologram Storage and Self-Written Waveguides Formation in Photopolymer Media
Polymers 2017, 9(8), 337; doi:10.3390/polym9080337
Received: 28 June 2017 / Revised: 28 July 2017 / Accepted: 1 August 2017 / Published: 3 August 2017
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Abstract
Photopolymer materials have received a great deal of attention because they are inexpensive, self-processing materials that are extremely versatile, offering many advantages over more traditional materials. To achieve their full potential, there is significant value in understanding the photophysical and photochemical processes taking
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Photopolymer materials have received a great deal of attention because they are inexpensive, self-processing materials that are extremely versatile, offering many advantages over more traditional materials. To achieve their full potential, there is significant value in understanding the photophysical and photochemical processes taking place within such materials. This paper includes a brief review of recent attempts to more fully understand what is needed to optimize the performance of photopolymer materials for Holographic Data Storage (HDS) and Self-Written Waveguides (SWWs) applications. Specifically, we aim to discuss the evolution of our understanding of what takes place inside these materials and what happens during photopolymerization process, with the objective of further improving the performance of such materials. Starting with a review of the photosensitizer absorptivity, a dye model combining the associated electromagnetics and photochemical kinetics is presented. Thereafter, the optimization of photopolymer materials for HDS and SWWs applications is reviewed. It is clear that many promising materials are being developed for the next generation optical applications media. Full article
(This article belongs to the Special Issue Photo-Responsive Polymers)
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Open AccessReview Ring Polymers: Threadings, Knot Electrophoresis and Topological Glasses
Polymers 2017, 9(8), 349; doi:10.3390/polym9080349
Received: 5 July 2017 / Revised: 4 August 2017 / Accepted: 5 August 2017 / Published: 8 August 2017
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Abstract
Elucidating the physics of a concentrated suspension of ring polymers, or of an ensemble of ring polymers in a complex environment, is an important outstanding question in polymer physics. Many of the characteristic features of these systems arise due to topological interactions between
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Elucidating the physics of a concentrated suspension of ring polymers, or of an ensemble of ring polymers in a complex environment, is an important outstanding question in polymer physics. Many of the characteristic features of these systems arise due to topological interactions between polymers, or between the polymers and the environment, and it is often challenging to describe this quantitatively. Here we review recent research which suggests that a key role is played by inter-ring threadings (or penetrations), which become more abundant as the ring size increases. As we discuss, the physical consequences of such threadings are far-reaching: for instance, they lead to a topologically-driven glassy behaviour of ring polymer melts under pinning perturbations, while they can also account for the shape of experimentally observed patterns in two-dimensional gel electrophoresis of DNA knots. Full article
(This article belongs to the Special Issue Knotted and Catenated Polymers)
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Open AccessFeature PaperReview Poly(3,4-ethylenedioxythiophene) (PEDOT) Derivatives: Innovative Conductive Polymers for Bioelectronics
Polymers 2017, 9(8), 354; doi:10.3390/polym9080354
Received: 26 June 2017 / Revised: 7 August 2017 / Accepted: 8 August 2017 / Published: 11 August 2017
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Abstract
Poly(3,4-ethylenedioxythiophene)s are the conducting polymers (CP) with the biggest prospects in the field of bioelectronics due to their combination of characteristics (conductivity, stability, transparency and biocompatibility). The gold standard material is the commercially available poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). However, in order to well connect
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Poly(3,4-ethylenedioxythiophene)s are the conducting polymers (CP) with the biggest prospects in the field of bioelectronics due to their combination of characteristics (conductivity, stability, transparency and biocompatibility). The gold standard material is the commercially available poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). However, in order to well connect the two fields of biology and electronics, PEDOT:PSS presents some limitations associated with its low (bio)functionality. In this review, we provide an insight into the synthesis and applications of innovative poly(ethylenedioxythiophene)-type materials for bioelectronics. First, we present a detailed analysis of the different synthetic routes to (bio)functional dioxythiophene monomer/polymer derivatives. Second, we focus on the preparation of PEDOT dispersions using different biopolymers and biomolecules as dopants and stabilizers. To finish, we review the applications of innovative PEDOT-type materials such as biocompatible conducting polymer layers, conducting hydrogels, biosensors, selective detachment of cells, scaffolds for tissue engineering, electrodes for electrophysiology, implantable electrodes, stimulation of neuronal cells or pan-bio electronics. Full article
(This article belongs to the Special Issue Conductive Polymers 2017)
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Open AccessFeature PaperReview Hydrogel Based Sensors for Biomedical Applications: An Updated Review
Polymers 2017, 9(8), 364; doi:10.3390/polym9080364
Received: 20 July 2017 / Revised: 10 August 2017 / Accepted: 12 August 2017 / Published: 16 August 2017
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Abstract
Biosensors that detect and convert biological reactions to a measurable signal have gained much attention in recent years. Between 1950 and 2017, more than 150,000 papers have been published addressing the applications of biosensors in different industries, but to the best of our
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Biosensors that detect and convert biological reactions to a measurable signal have gained much attention in recent years. Between 1950 and 2017, more than 150,000 papers have been published addressing the applications of biosensors in different industries, but to the best of our knowledge and through careful screening, critical reviews that describe hydrogel based biosensors for biomedical applications are rare. This review discusses the biomedical application of hydrogel based biosensors, based on a search performed through Web of Science Core, PubMed (NLM), and Science Direct online databases for the years 2000–2017. In this review, we consider bioreceptors to be immobilized on hydrogel based biosensors, their advantages and disadvantages, and immobilization techniques. We identify the hydrogels that are most favored for this type of biosensor, as well as the predominant transduction strategies. We explain biomedical applications of hydrogel based biosensors including cell metabolite and pathogen detection, tissue engineering, wound healing, and cancer monitoring, and strategies for small biomolecules such as glucose, lactate, urea, and cholesterol detection are identified. Full article
(This article belongs to the Special Issue Hydrogels in Tissue Engineering and Regenerative Medicine)
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Open AccessReview Characterization of Cell Scaffolds by Atomic Force Microscopy
Polymers 2017, 9(8), 383; doi:10.3390/polym9080383
Received: 30 July 2017 / Revised: 13 August 2017 / Accepted: 16 August 2017 / Published: 21 August 2017
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Abstract
This review reports on the use of the atomic force microscopy (AFM) in the investigation of cell scaffolds in recent years. It is shown how the technique is able to deliver information about the scaffold surface properties (e.g., topography), as well as about
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This review reports on the use of the atomic force microscopy (AFM) in the investigation of cell scaffolds in recent years. It is shown how the technique is able to deliver information about the scaffold surface properties (e.g., topography), as well as about its mechanical behavior (Young’s modulus, viscosity, and adhesion). In addition, this short review also points out the utilization of the atomic force microscope technique beyond its usual employment in order to investigate another type of basic questions related to materials physics, chemistry, and biology. The final section discusses in detail the novel uses that those alternative measuring modes can bring to this field in the future. Full article
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Other

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Open AccessRetraction Retraction: Abdalla, S., et al. A Bio Polymeric Adhesive Produced by Photo Cross-Linkable Technique. Polymers 2016, 8, 292, doi:10.3390/polym8080292 and Abdalla, S., et al. Controlled Light Cross-Linking Technique to Prepare Healable Materials. Polymers 2017, 9, 241, doi:10.3390/polym9060241
Polymers 2017, 9(8), 382; doi:10.3390/polym9080382
Received: 17 August 2017 / Revised: 17 August 2017 / Accepted: 17 August 2017 / Published: 21 August 2017
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Abstract
These two articles [1,2] published in Polymers will be marked as retracted.[...] Full article