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Polymers, Volume 8, Issue 6 (June 2016)

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Cover Story A pH-responsive theranostic agent based on core cross-linked (CCL) micelles was constructed via [...] Read more.
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Open AccessArticle Polypeptide-Nanoparticle Interactions and Corona Formation Investigated by Monte Carlo Simulations
Polymers 2016, 8(6), 203; doi:10.3390/polym8060203
Received: 19 February 2016 / Revised: 11 May 2016 / Accepted: 12 May 2016 / Published: 25 May 2016
Cited by 1 | PDF Full-text (4349 KB) | HTML Full-text | XML Full-text
Abstract
Biomacromolecule activity is usually related to its ability to keep a specific structure. However, in solution, many parameters (pH, ionic strength) and external compounds (polyelectrolytes, nanoparticles) can modify biomacromolecule structure as well as acid/base properties, thus resulting in a loss of activity and
[...] Read more.
Biomacromolecule activity is usually related to its ability to keep a specific structure. However, in solution, many parameters (pH, ionic strength) and external compounds (polyelectrolytes, nanoparticles) can modify biomacromolecule structure as well as acid/base properties, thus resulting in a loss of activity and denaturation. In this paper, the impact of neutral and charged nanoparticles (NPs) is investigated by Monte Carlo simulations on polypeptide (PP) chains with primary structure based on bovine serum albumin. The influence of pH, salt valency, and NP surface charge density is systematically studied. It is found that the PP is extended at extreme pH, when no complex formation is observed, and folded at physiological pH. PP adsorption around oppositely-charged NPs strongly limits chain structural changes and modifies its acid/base properties. At physiological pH, the complex formation occurs only with positively-charged NPs. The presence of salts, in particular those with trivalent cations, introduces additional electrostatic interactions, resulting in a mitigation of the impact of negative NPs. Thus, the corona structure is less dense with locally-desorbed segments. On the contrary, very limited impact of salt cation valency is observed when NPs are positive, due to the absence of competitive effects between multivalent cations and NP. Full article
(This article belongs to the collection Polyelectrolytes)
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Open AccessArticle Spectroscopic, Physical and Topography of Photochemical Process of PVC Films in the Presence of Schiff Base Metal Complexes
Polymers 2016, 8(6), 204; doi:10.3390/polym8060204
Received: 22 April 2016 / Revised: 17 May 2016 / Accepted: 20 May 2016 / Published: 25 May 2016
Cited by 5 | PDF Full-text (5612 KB) | HTML Full-text | XML Full-text
Abstract
The photostability of poly(vinyl chloride), PVC, containing various Schiff base metal complexes (0.5% by weight) was investigated. Various indices corresponding to a number of functional groups were monitored with irradiation of polymeric films to determine their photostabilization activities. The quantum yield of the
[...] Read more.
The photostability of poly(vinyl chloride), PVC, containing various Schiff base metal complexes (0.5% by weight) was investigated. Various indices corresponding to a number of functional groups were monitored with irradiation of polymeric films to determine their photostabilization activities. The quantum yield of the chain scission (Φcs) of modified polymeric films was found to be (1.15–4.65) × 106. The surface morphology of a PVC sample was investigated by the use of atomic force microscope (AFM). The photostability of PVC films in the presence of Schiff base additives was found to follow the following order: PVC < PVC + CuL2 < PVC + CdL2 < PVC + ZnL2 < PVC + SnL2 < PVC + NiL2. Various mechanisms for PVC films photostability containing the Schiff base additives have been suggested. Full article
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Open AccessArticle Carbon Microparticles from Organosolv Lignin as Filler for Conducting Poly(Lactic Acid)
Polymers 2016, 8(6), 205; doi:10.3390/polym8060205
Received: 4 April 2016 / Revised: 18 May 2016 / Accepted: 20 May 2016 / Published: 26 May 2016
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Abstract
Carbon microparticles were produced from organosolv lignin at 2000 °C under argon atmosphere following oxidative thermostabilisation at 250 °C. Scanning electron microscopy, X-ray diffraction, small-angle X-ray scattering, and electro-conductivity measurements revealed that the obtained particles were electrically conductive and were composed of large
[...] Read more.
Carbon microparticles were produced from organosolv lignin at 2000 °C under argon atmosphere following oxidative thermostabilisation at 250 °C. Scanning electron microscopy, X-ray diffraction, small-angle X-ray scattering, and electro-conductivity measurements revealed that the obtained particles were electrically conductive and were composed of large graphitic domains. Poly(lactic acid) filled with various amounts of lignin-derived microparticles showed higher tensile stiffness increasing with particle load, whereas strength and extensibility decreased. Electric conductivity was measured at filler loads equal to and greater than 25% w/w. Full article
(This article belongs to the Special Issue Conductive Polymers 2016)
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Open AccessArticle Applications of Tris(4-(thiophen-2-yl)phenyl)amine- and Dithienylpyrrole-based Conjugated Copolymers in High-Contrast Electrochromic Devices
Polymers 2016, 8(6), 206; doi:10.3390/polym8060206
Received: 20 April 2016 / Revised: 18 May 2016 / Accepted: 19 May 2016 / Published: 27 May 2016
Cited by 5 | PDF Full-text (9132 KB) | HTML Full-text | XML Full-text
Abstract
Tris(4-(thiophen-2-yl)phenyl)amine- and dithienylpyrrole-based copolymers (P(TTPA-co-DIT) and P(TTPA-co-BDTA)) were electropolymerized on ITO electrode by applying constant potentials of 1.0, 1.1, and 1.2 V. Spectroelectrochemical investigations revealed that P(TTPA-co-DIT) film displayed more color changes than P(TTPA-co-BDTA) film.
[...] Read more.
Tris(4-(thiophen-2-yl)phenyl)amine- and dithienylpyrrole-based copolymers (P(TTPA-co-DIT) and P(TTPA-co-BDTA)) were electropolymerized on ITO electrode by applying constant potentials of 1.0, 1.1, and 1.2 V. Spectroelectrochemical investigations revealed that P(TTPA-co-DIT) film displayed more color changes than P(TTPA-co-BDTA) film. The P(TTPA-co-DIT) film is yellow in the neutral state, yellowish-green and green in the intermediate state, and blue (1.2 V) in highly oxidized state. The ∆Tmax of the P(TTPA-co-DIT) and P(TTPA-co-BDTA) films were measured as 60.3% at 1042 nm and 47.1% at 1096 nm, respectively, and the maximum coloration efficiency (η) of P(TTPA-co-DIT) and P(TTPA-co-BDTA) films were calculated to be 181.9 cm2·C1 at 1042 nm and 217.8 cm2·C1 at 1096 nm, respectively, in an ionic liquid solution. Dual type electrochromic devices (ECDs) consisting of P(TTPA-co-DIT) (or P(TTPA-co-BDTA)) anodic copolymer, ionic liquid-based electrolyte, and poly(3,4-(2,2-diethylpropylenedioxy)thiophene) (PProDOT-Et2) cathodic polymer were constructed. P(TTPA-co-BDTA)/PProDOT-Et2 ECD showed high ΔTmax (48.1%) and high coloration efficiency (649.4 cm2·C1) at 588 nm. Moreover, P(TTPA-co-DIT)/PProDOT-Et2 and P(TTPA-co-BDTA)/PProDOT-Et2 ECDs displayed satisfactory optical memory and long term switching stability. Full article
(This article belongs to the Special Issue Conjugated Polymers 2016)
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Open AccessArticle RAFT-Mediated Polymerization-Induced Self-Assembly of Poly(Acrylic Acid)-b-Poly(Hexafluorobutyl Acrylate): Effect of the pH on the Synthesis of Self-Stabilized Particles
Polymers 2016, 8(6), 207; doi:10.3390/polym8060207
Received: 26 March 2016 / Revised: 17 May 2016 / Accepted: 18 May 2016 / Published: 27 May 2016
Cited by 2 | PDF Full-text (3168 KB) | HTML Full-text | XML Full-text
Abstract
This paper describes a very simple strategy towards self-stabilized poly(acrylic acid)-block-poly(hexafluorobutyl acrylate) (PAA-b-PHFBA) block copolymer particles via reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization-induced self-assembly. Hexafluorobutyl acrylate (HFBA) monomer conversion and number-average molar mass of PAA-b-PHFBA increased gradually
[...] Read more.
This paper describes a very simple strategy towards self-stabilized poly(acrylic acid)-block-poly(hexafluorobutyl acrylate) (PAA-b-PHFBA) block copolymer particles via reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization-induced self-assembly. Hexafluorobutyl acrylate (HFBA) monomer conversion and number-average molar mass of PAA-b-PHFBA increased gradually with the increase in the pH value of the aqueous phase. When pH < 10, the molecular weight distributions of PAA-b-PHFBA were narrow, however, when the pH was raised to 11.55, PAA-b-PHFBA block copolymers had a broader distribution (ĐM = 1.82) with a serious trailing toward the low molecular weight. Furthermore, the morphology and size of PAA-b-PHFBA latex particles were measured by transmission electron microscopy and dynamic light scattering. The results indicated that the PAA-b-PHFBA latex particles had a clear spherical core-shell structure and the latex particles’ size increased with the increase of pH value. Full article
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Open AccessArticle Synthesis of New Polyether Ether Ketone Derivatives with Silver Binding Site and Coordination Compounds of Their Monomers with Different Silver Salts
Polymers 2016, 8(6), 208; doi:10.3390/polym8060208
Received: 15 March 2016 / Revised: 13 May 2016 / Accepted: 19 May 2016 / Published: 30 May 2016
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Abstract
Polyether ether ketone (PEEK) is a well-known polymer used for implants and devices, especially spinal ones. To overcome the biomaterial related infection risks, 4-4′-difluorobenzophenone, the famous PEEK monomer, was modified in order to introduce binding sites for silver ions, which are
[...] Read more.
Polyether ether ketone (PEEK) is a well-known polymer used for implants and devices, especially spinal ones. To overcome the biomaterial related infection risks, 4-4′-difluorobenzophenone, the famous PEEK monomer, was modified in order to introduce binding sites for silver ions, which are well known for their antimicrobial activity. The complexation of these new monomers with different silver salts was studied. Crystal structures of different intermediates were obtained with a linear coordination between two pyridine groups and the silver ions in all cases. The mechanical and thermal properties of different new polymers were characterized. The synthesized PEEKN5 polymers showed similar properties than the PEEK ones whereas the PEEKN7 polymers showed similar thermal properties but the mechanical properties are not as good as the ones of PEEK. To improve these properties, these polymers were complexed with silver nitrate in order to “cross-link” with silver ions. The presence of ionic silver in the polymer was then confirmed by thermogravimetric analysis (TGA) and X-ray powder diffraction (XRPD). Finally, a silver-based antimicrobial compound was successfully coated on the surface of PEEKN5. Full article
(This article belongs to the Special Issue Functional Polymers for Medical Applications)
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Open AccessArticle Demethylation of Wheat Straw Alkali Lignin for Application in Phenol Formaldehyde Adhesives
Polymers 2016, 8(6), 209; doi:10.3390/polym8060209
Received: 18 April 2016 / Revised: 13 May 2016 / Accepted: 24 May 2016 / Published: 30 May 2016
Cited by 2 | PDF Full-text (2623 KB) | HTML Full-text | XML Full-text
Abstract
Lignin is a natural biopolymer with a complex three-dimensional network. It is the second most abundant natural polymer on earth. Commercially, lignin is largely obtained from the waste liquors of pulping and bioethanol productions. In this study, wheat straw alkali lignin (WSAL) was
[...] Read more.
Lignin is a natural biopolymer with a complex three-dimensional network. It is the second most abundant natural polymer on earth. Commercially, lignin is largely obtained from the waste liquors of pulping and bioethanol productions. In this study, wheat straw alkali lignin (WSAL) was demethylated by using an in-situ generated Lewis acid under an optimized demethylation process. The demethylation process was monitored by a semi-quantitative Fourier Transform Infrared Spectroscopy (FTIR) method. The demethylated wheat straw alkali lignin (D-WSAL) was further characterized by Proton Nuclear Magnetic Resonance (1H NMR), Gel Permeation Chromatography (GPC), and titration methods. After the demethylation process, it was found that the relative value of the methoxy group decreased significantly from 0.82 to 0.17 and the phenolic hydroxyl group increased from 5.2% to 16.0%. Meanwhile, the hydroxyl content increased from 6.6% to 10.3%. GPC results suggested that the weighted averaged molecular weight of D-WSAL was lower than that of WSAL with a smaller polydispersity index. The D-WSAL was then used to replace 60 wt % of phenol to prepare lignin-based phenol formaldehyde adhesives (D-LPF). It was found that both the free formaldehyde content and the free phenol content in D-LPF were less than those of the lignin-based phenol formaldehyde adhesives without lignin demethylation (LPF). Gel time of D-LPF was shortened. Furthermore, the wet and dry bonding strengths of lap shear wood samples bonded using D-LPF were higher than those of the samples bonded using LPF. Therefore, D-WSAL has shown good potential for application in phenol formaldehyde adhesives. Full article
(This article belongs to the Special Issue Renewable Polymeric Adhesives)
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Open AccessArticle Correction of MHS Viscosimetric Constants upon Numerical Simulation of Temperature Induced Degradation Kinetic of Chitosan Solutions
Polymers 2016, 8(6), 210; doi:10.3390/polym8060210
Received: 10 March 2016 / Revised: 4 May 2016 / Accepted: 10 May 2016 / Published: 31 May 2016
Cited by 1 | PDF Full-text (2923 KB) | HTML Full-text | XML Full-text
Abstract
The Mark–Houwink–Sakurada (MHS) equation allows for estimation of rheological properties, if the molecular weight is known along with good understanding of the polymer conformation. The intrinsic viscosity of a polymer solution is related to the polymer molecular weight according to the MHS equation,
[...] Read more.
The Mark–Houwink–Sakurada (MHS) equation allows for estimation of rheological properties, if the molecular weight is known along with good understanding of the polymer conformation. The intrinsic viscosity of a polymer solution is related to the polymer molecular weight according to the MHS equation, where the value of the constants is related to the specific solvent and its concentration. However, MHS constants do not account for other characteristics of the polymeric solutions, i.e., Deacetilation Degree (DD) when the solute is chitosan. In this paper, the degradation of chitosan in different acidic environments by thermal treatment is addressed. In particular, two different solutions are investigated (used as solvent acetic or hydrochloric acid) with different concentrations used for the preparation of chitosan solutions. The samples were treated at different temperatures (4, 30, and 80 °C) and time points (3, 6 and 24 h). Rheological, Gel Permeation Chromatography (GPC), Fourier Transform Infrared Spectroscopy (FT-IR), Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analyses (TGA) were performed in order to assess the degradation rate of the polymer backbones. Measured values of molecular weight have been integrated in the simulation of the batch degradation of chitosan solutions for evaluating MHS coefficients to be compared with their corresponding experimental values. Evaluating the relationship between the different parameters used in the preparation of chitosan solutions (e.g., temperature, time, acid type and concentration), and their contribution to the degradation of chitosan backbone, it is important to have a mathematical frame that could account for phenomena involved in polymer degradation that go beyond the solvent-solute combination. Therefore, the goal of the present work is to propose an integration of MHS coefficients for chitosan solutions that contemplate a deacetylation degree for chitosan systems or a more general substitution degree for polymers in which viscosity depends not only on molecular weight and solvent combinations. Full article
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Open AccessArticle Monotonic and Cyclic Bond Behavior of Deformed CFRP Bars in High Strength Concrete
Polymers 2016, 8(6), 211; doi:10.3390/polym8060211
Received: 31 March 2016 / Revised: 8 May 2016 / Accepted: 19 May 2016 / Published: 31 May 2016
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Abstract
Composite reinforcing bars (rebars) that are used in concrete members with high performance (strength and durability) properties could have beneficial effects on the behavior of these members. This is especially vital when a building is constructed in an aggressive environment, for instance a
[...] Read more.
Composite reinforcing bars (rebars) that are used in concrete members with high performance (strength and durability) properties could have beneficial effects on the behavior of these members. This is especially vital when a building is constructed in an aggressive environment, for instance a corrosive environment. Although tension capacity/weight (or volume) ratios in composite rebars (carbon fiber reinforced polymer (CFRP), glass fiber reinforced polymer (GFRP), etc.) are very high when compared to steel rebars, major weaknesses in concrete members reinforced with these composite rebars may be the potential consequences of relatively poor bonding capacity. This may even be more crucial when the member is subjected to cyclic loading. Although monotonic bond tests are available in the literature, only limited experimental studies exist on bond characteristics under cyclic loading conditions. In order to fill this gap and propose preliminary design recommendations, 10 specimens of 10-mm-diameter ribbed CFRP rebars embedded in specially designed high strength concrete (fc = 70 MPa) blocks were subjected to monotonic and cyclic pullout tests. The experimental results showed that cyclically loaded CFRP rebars had less bond strength than those companion specimens loaded monotonically. Full article
(This article belongs to the Special Issue Selected Papers from “SMAR 2015”)
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Open AccessArticle Preparation, Characterization, and Biological Evaluation of Poly(Glutamic Acid)-b-Polyphenylalanine Polymersomes
Polymers 2016, 8(6), 212; doi:10.3390/polym8060212
Received: 18 March 2016 / Revised: 22 May 2016 / Accepted: 25 May 2016 / Published: 2 June 2016
Cited by 2 | PDF Full-text (2251 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Different types of amphiphilic macromolecular structures have been developed within recent decades to prepare the polymer particles considered as drug delivery systems. In the present research the series of amphiphilic block-copolymers containing poly(glutamatic acid) as hydrophilic, and polyphenylalanine as hydrophobic blocks was synthesized
[...] Read more.
Different types of amphiphilic macromolecular structures have been developed within recent decades to prepare the polymer particles considered as drug delivery systems. In the present research the series of amphiphilic block-copolymers containing poly(glutamatic acid) as hydrophilic, and polyphenylalanine as hydrophobic blocks was synthesized and characterized. Molecular weights for homo- and copolymers were determined by gel-permeation chromatography (GPC) and amino acid analysis, respectively. The copolymers obtained were applied for preparation of polymer particles. The specific morphology of prepared polymerosomes was proved using transmission electron microscopy (TEM). The influence on particle size of polymer concentration and pH used for self-assembly, as well as on the length of hydrophobic and hydrophilic blocks of applied copolymers, was studied by dynamic light scattering (DLS). Depending on different experimental conditions, the formation of nanoparticles with sizes from 60 to 350 nm was observed. The surface of polymersomes was modified with model protein (enzyme). No loss in biocatalytic activity was detected. Additionally, the process of encapsulation of model dyes was developed and the possibility of intracellular delivery of the dye-loaded nanoparticles was proved. Thus, the nanoparticles discussed can be considered for the creation of modern drug delivery systems. Full article
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Open AccessFeature PaperArticle Engineering Porous Poly(lactic acid) Scaffolds with High Mechanical Performance via a Solid State Extrusion/Porogen Leaching Approach
Polymers 2016, 8(6), 213; doi:10.3390/polym8060213
Received: 3 March 2016 / Revised: 18 May 2016 / Accepted: 26 May 2016 / Published: 31 May 2016
Cited by 1 | PDF Full-text (4153 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A knotty issue concerning the poor mechanical properties exists in the porogen leaching approach to porous scaffolds, despite its advantage in tuning pore structure. To address this hurdle, solid state extrusion (SSE) combined with porogen leaching was utilized to engineer porous scaffolds of
[...] Read more.
A knotty issue concerning the poor mechanical properties exists in the porogen leaching approach to porous scaffolds, despite its advantage in tuning pore structure. To address this hurdle, solid state extrusion (SSE) combined with porogen leaching was utilized to engineer porous scaffolds of poly(lactic acid) (PLA). Advances introduced by poly(ethylene glycol) (PEG) caused the PLA ductile to be processed and, on the other hand, enabled the formation of interconnected pores. Thus, a well-interconnected porous architecture with high connectivity exceeding 97% and elevated porosity over 60% was obtained in the as-prepared PLA scaffolds with the composition of NaCl higher than 75.00 wt % and PEG beyond 1.25 wt %. More strikingly, the pore walls of macropores encompassed countless micropores and rough surface topography, in favor of transporting nutrients and metabolites as well as cell attachment. The prominent compressive modulus of the PLA scaffolds was in the range of 85.7–207.4 MPa, matching the normal modulus of human trabecular bone (50–250 MPa). By means of alkaline modification to improve hydrophilicity, biocompatible porous PLA scaffolds exhibited good cell attachment. These results suggest that the SSE/porogen leaching approach provides an eligible clue for fabricating porous scaffolds with high mechanical performance for use as artificial extracellular matrices. Full article
(This article belongs to the Special Issue Functional Polymers for Medical Applications)
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Open AccessArticle High Temperature Epoxy Foam: Optimization of Process Parameters
Polymers 2016, 8(6), 215; doi:10.3390/polym8060215
Received: 5 May 2016 / Revised: 26 May 2016 / Accepted: 30 May 2016 / Published: 7 June 2016
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Abstract
For many years, reduction of fuel consumption has been a major aim in terms of both costs and environmental concerns. One option is to reduce the weight of fuel consumers. For this purpose, the use of a lightweight material based on rigid foams
[...] Read more.
For many years, reduction of fuel consumption has been a major aim in terms of both costs and environmental concerns. One option is to reduce the weight of fuel consumers. For this purpose, the use of a lightweight material based on rigid foams is a relevant choice. This paper deals with a new high temperature epoxy expanded material as substitution of phenolic resin, classified as potentially mutagenic by European directive Reach. The optimization of thermoset foam depends on two major parameters, the reticulation process and the expansion of the foaming agent. Controlling these two phenomena can lead to a fully expanded and cured material. The rheological behavior of epoxy resin is studied and gel time is determined at various temperatures. The expansion of foaming agent is investigated by thermomechanical analysis. Results are correlated and compared with samples foamed in the same temperature conditions. The ideal foaming/gelation temperature is then determined. The second part of this research concerns the optimization of curing cycle of a high temperature trifunctional epoxy resin. A two-step curing cycle was defined by considering the influence of different curing schedules on the glass transition temperature of the material. The final foamed material has a glass transition temperature of 270 °C. Full article
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Open AccessArticle Molecularly Imprinted Polymers for the Identification and Separation of Chiral Drugs and Biomolecules
Polymers 2016, 8(6), 216; doi:10.3390/polym8060216
Received: 31 March 2016 / Revised: 22 April 2016 / Accepted: 24 May 2016 / Published: 3 June 2016
Cited by 1 | PDF Full-text (3051 KB) | HTML Full-text | XML Full-text
Abstract
Molecularly imprinting polymers (MIPs) have been extensively applied in chromatography for the separation of chiral drugs. In this review, we mainly summarize recent developments of various MIPs used as chiral stationary phases (CSPs) in high performance liquid chromatography (HPLC), capillary electrochromatography (CEC), and
[...] Read more.
Molecularly imprinting polymers (MIPs) have been extensively applied in chromatography for the separation of chiral drugs. In this review, we mainly summarize recent developments of various MIPs used as chiral stationary phases (CSPs) in high performance liquid chromatography (HPLC), capillary electrochromatography (CEC), and supercritical fluid chromatography (SFC). Among them, HPLC has the advantages of straightforward operation and high selectivity. However, the low separation efficiency, due to slow interaction kinetics and heavy peak broadening, is the main challenge for the application of MIPs in HPLC. On the other hand, CEC possesses both the high selectivity of HPLC and the high efficiency of capillary electrophoresis. In CEC, electroosmotic flow is formed across the entire column and reduces the heavy peak broadening observed in HPLC mode. SFC can modify the low interaction kinetics in HPLC when supercritical fluids are utilized as mobile phases. If SFC and MIP-based CSPs can be well combined, better separation performance can be achieved. Particles, monoliths and membrane are typical formats of MIPs. Traditional MIP particles produced by bulk polymerization have been replaced by MIP particles by surface imprinting technology, which are highly consistent in size and shape. Monolithic MIPs are prepared by in situ method in a column, greatly shortening the pre-preparation time. Some novel materials, such as magnetic nanoparticles, are integrated into the MIPs to enhance the controllability and efficiency of the polymerization. This review will be helpful to guide the preparation, development, and application of MIPs in chromatographic and electrophoretic enantioseparation. Full article
(This article belongs to the Special Issue Functional Polymers for Medical Applications)
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Open AccessArticle Volume Phase Transitions of Slide-Ring Gels
Polymers 2016, 8(6), 217; doi:10.3390/polym8060217
Received: 27 March 2016 / Revised: 8 May 2016 / Accepted: 31 May 2016 / Published: 3 June 2016
PDF Full-text (4281 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The volume phase transition of slide-ring gels with freely-movable cross-linking junctions was investigated. Ionic chemical gels with fixed cross-linking junctions undergo volume phase transitions when they have higher than the critical degree of ionization. However, the experimentally-observed critical ionization value for slide-ring gels
[...] Read more.
The volume phase transition of slide-ring gels with freely-movable cross-linking junctions was investigated. Ionic chemical gels with fixed cross-linking junctions undergo volume phase transitions when they have higher than the critical degree of ionization. However, the experimentally-observed critical ionization value for slide-ring gels is much higher than theoretical values for chemical gels. This difference indicates that the volume phase transition is significantly suppressed in slide-ring gels. The mesoscale structure at various swollen or shrunken states was also investigated by small angle X-ray scattering. Changes in the scattering patterns with shrinking slide-ring gels suggest microphase separation due to the sliding of cyclic molecules threaded along the axis of the polymer chains, which may suppress the volume phase transition. In addition, slide-ring gels absorbed/desorbed greater than equilibrium volumes in the shrinking/swelling processes and showed slow dynamics; these observations are also related to their sliding properties. Full article
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Open AccessArticle Poly(lactide-co-glycolide)/Hydroxyapatite Porous Scaffold with Microchannels for Bone Regeneration
Polymers 2016, 8(6), 218; doi:10.3390/polym8060218
Received: 7 April 2016 / Revised: 6 May 2016 / Accepted: 30 May 2016 / Published: 7 June 2016
Cited by 5 | PDF Full-text (6968 KB) | HTML Full-text | XML Full-text
Abstract
Mass transfer restrictions of scaffolds are currently hindering the development of three-dimensional (3D), clinically viable, and tissue-engineered constructs. For this situation, a 3D poly(lactide-co-glycolide)/hydroxyapatite porous scaffold, which was very favorable for the transfer of nutrients to and waste products from the
[...] Read more.
Mass transfer restrictions of scaffolds are currently hindering the development of three-dimensional (3D), clinically viable, and tissue-engineered constructs. For this situation, a 3D poly(lactide-co-glycolide)/hydroxyapatite porous scaffold, which was very favorable for the transfer of nutrients to and waste products from the cells in the pores, was developed in this study. The 3D scaffold had an innovative structure, including macropores with diameters of 300–450 μm for cell ingrowth and microchannels with diameters of 2–4 μm for nutrition and waste exchange. The mechanical strength in wet state was strong enough to offer structural support. The typical structure was more beneficial for the attachment, proliferation, and differentiation of rabbit bone marrow mesenchymal stem cells (rBMSCs). The alkaline phosphatase (ALP) activity and calcium (Ca) deposition were evaluated on the differentiation of rBMSCs, and the results indicated that the microchannel structure was very favorable for differentiating rBMSCs into maturing osteoblasts. For repairing rabbit radius defects in vivo, there was rapid healing in the defects treated with the 3D porous scaffold with microchannels, where the bridging by a large bony callus was observed at 12 weeks post-surgery. Based on the results, the 3D porous scaffold with microchannels was a promising candidate for bone defect repair. Full article
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Open AccessArticle Multiphasic Reaction Modeling for Polypropylene Production in a Pilot-Scale Catalytic Reactor
Polymers 2016, 8(6), 220; doi:10.3390/polym8060220
Received: 19 March 2016 / Revised: 24 May 2016 / Accepted: 31 May 2016 / Published: 14 June 2016
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Abstract
In this study, a novel multiphasic model for the calculation of the polypropylene production in a complicated hydrodynamic and the physiochemical environments has been formulated, confirmed and validated. This is a first research attempt that describes the development of the dual-phasic phenomena, the
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In this study, a novel multiphasic model for the calculation of the polypropylene production in a complicated hydrodynamic and the physiochemical environments has been formulated, confirmed and validated. This is a first research attempt that describes the development of the dual-phasic phenomena, the impact of the optimal process conditions on the production rate of polypropylene and the fluidized bed dynamic details which could be concurrently obtained after solving the model coupled with the CFD (computational fluid dynamics) model, the basic mathematical model and the moment equations. Furthermore, we have established the quantitative relationship between the operational condition and the dynamic gas–solid behavior in actual reaction environments. Our results state that the proposed model could be applied for generalizing the production rate of the polymer from a chemical procedure to pilot-scale chemical reaction engineering. However, it was assumed that the solids present in the bubble phase and the reactant gas present in the emulsion phase improved the multiphasic model, thus taking into account that the polymerization took place mutually in the emulsion besides the bubble phase. It was observed that with respect to the experimental extent of the superficial gas velocity and the Ziegler-Natta feed rate, the ratio of the polymer produced as compared to the overall rate of production was approximately in the range of 9%–11%. This is a significant amount and it should not be ignored. We also carried out the simulation studies for comparing the data of the CFD-dependent dual-phasic model, the emulsion phase model, the dynamic bubble model and the experimental results. It was noted that the improved dual-phasic model and the CFD model were able to predict more constricted and safer windows at similar conditions as compared to the experimental results. Our work is unique, as the integrated developed model is able to offer clearer ideas related to the dynamic bed parameters for the separate phases and is also capable of computing the chemical reaction rate for every phase in the reaction. Our improved mutiphasic model revealed similar dynamic behaviour as the conventional model in the initial stages of the polymerization reaction; however, it diverged as time progressed. Full article
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Open AccessArticle Production and Characterization of a Novel, Electrospun, Tri-Layer Polycaprolactone Membrane for the Segregated Co-Culture of Bone and Soft Tissue
Polymers 2016, 8(6), 221; doi:10.3390/polym8060221
Received: 12 May 2016 / Revised: 31 May 2016 / Accepted: 1 June 2016 / Published: 7 June 2016
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Abstract
Composite tissue-engineered constructs combining bone and soft tissue have applications in regenerative medicine, particularly dentistry. This study generated a tri-layer, electrospun, poly-ε-caprolactone membrane, with two microfiber layers separated by a layer of nanofibers, for the spatially segregated culture of mesenchymal progenitor cells (MPCs)
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Composite tissue-engineered constructs combining bone and soft tissue have applications in regenerative medicine, particularly dentistry. This study generated a tri-layer, electrospun, poly-ε-caprolactone membrane, with two microfiber layers separated by a layer of nanofibers, for the spatially segregated culture of mesenchymal progenitor cells (MPCs) and fibroblasts. The two cell types were seeded on either side, and cell proliferation and spatial organization were investigated over several weeks. Calcium deposition by MPCs was detected using xylenol orange (XO) and the separation between fibroblasts and the calcified matrix was visualized by confocal laser scanning microscopy. SEM confirmed that the scaffold consisted of two layers of micron-diameter fibers with a thin layer of nano-diameter fibers in-between. Complete separation of cell types was maintained and calcified matrix was observed on only one side of the membrane. This novel tri-layer membrane is capable of supporting the formation of a bilayer of calcified and non-calcified connective tissue. Full article
(This article belongs to the Special Issue Functional Polymers for Medical Applications)
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Open AccessArticle Molecularly Imprinted Nanofiber Film for Sensitive Sensing 2,4,6-Tribromophenol
Polymers 2016, 8(6), 222; doi:10.3390/polym8060222
Received: 29 April 2016 / Revised: 30 May 2016 / Accepted: 2 June 2016 / Published: 22 June 2016
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Abstract
The determination of brominated flame retardants is of great importance, but remains a challenge. Particularly, universal and facile approaches are limited. Here we report a new general approach, combining molecular imprinting and electrospinning, for the efficient and facile imprinting sensor of 2,4,6-tribromophenol (TBP),
[...] Read more.
The determination of brominated flame retardants is of great importance, but remains a challenge. Particularly, universal and facile approaches are limited. Here we report a new general approach, combining molecular imprinting and electrospinning, for the efficient and facile imprinting sensor of 2,4,6-tribromophenol (TBP), which was used as a “novel” brominated flame retardant. With TBP as the template molecular, β-cyclodextrin (β-CD) as the functional monomer, and poly-vinylbutyral (PVB) as the electro-spinning matrix, the nanofiber film was deposited on the glassy carbon electrode (GCE) via electrospinning technique directly. The β-CD-PVB/GCE sensor system exhibited excellent TBP sensing performances, such as a low detection limit (6.29 × 10−10 mol·L−1) at room temperature, selective recognition to TBP/phenol/4-methyl-phenol, and good regeneration performance. The approach of fabricating a molecular imprinting nanofiber sensor may shed new light in the detection of other phenolic pollutants. Full article
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Open AccessArticle Design and Preparation of Nano-Lignin Peroxidase (NanoLiP) by Protein Block Copolymerization Approach
Polymers 2016, 8(6), 223; doi:10.3390/polym8060223
Received: 22 April 2016 / Revised: 9 May 2016 / Accepted: 1 June 2016 / Published: 6 June 2016
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Abstract
This study describes the preparation of nanoprotein particles having lignin peroxidase (LiP) using a photosensitive microemulsion polymerization technique. The protein-based nano block polymer was synthesized by cross-linking of ligninase enzyme with ruthenium-based aminoacid monomers. This type polymerization process brought stability in different reaction
[...] Read more.
This study describes the preparation of nanoprotein particles having lignin peroxidase (LiP) using a photosensitive microemulsion polymerization technique. The protein-based nano block polymer was synthesized by cross-linking of ligninase enzyme with ruthenium-based aminoacid monomers. This type polymerization process brought stability in different reaction conditions, reusability and functionality to the protein-based nano block polymer system when compared the traditional methods. After characterization of the prepared LiP copolymer nanoparticles, enzymatic activity studies of the nanoenzymes were carried out using tetramethylbenzidine (TMB) as the substrate. The parameters such as pH, temperature and initial enzyme concentration that affect the activity, were investigated by using prepared nanoLip particles and compared to free LiP. The reusability of the nano-LiP particles was also investigated and the obtained results showed that the nano-LiP particles exhibited admirable potential as a reusable catalyst. Full article
(This article belongs to the Special Issue Enzymatic Polymer Synthesis)
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Open AccessArticle Influence of Polyplex Formation on the Performance of Star-Shaped Polycationic Transfection Agents for Mammalian Cells
Polymers 2016, 8(6), 224; doi:10.3390/polym8060224
Received: 12 April 2016 / Revised: 30 May 2016 / Accepted: 1 June 2016 / Published: 6 June 2016
Cited by 3 | PDF Full-text (2023 KB) | HTML Full-text | XML Full-text
Abstract
Genetic modification (“transfection”) of mammalian cells using non-viral, synthetic agents such as polycations, is still a challenge. Polyplex formation between the DNA and the polycation is a decisive step in such experiments. Star-shaped polycations have been proposed as superior transfection agents, yet have
[...] Read more.
Genetic modification (“transfection”) of mammalian cells using non-viral, synthetic agents such as polycations, is still a challenge. Polyplex formation between the DNA and the polycation is a decisive step in such experiments. Star-shaped polycations have been proposed as superior transfection agents, yet have never before been compared side-by-side, e.g., in view of structural effects. Herein four star-shaped polycationic structures, all based on (2-dimethylamino) ethyl methacrylate (DMAEMA) building blocks, were investigated for their potential to deliver DNA to adherent (CHO, L929, HEK-293) and non-adherent (Jurkat, primary human T lymphocytes) mammalian cells. The investigated vectors included three structures where the PDMAEMA arms (different arm length and grafting densities) had been grown from a center silsesquioxane or silica-coated γ-Fe2O3-core and one micellar structure self-assembled from poly(1,2-butadiene)-block PDMAEMA polymers. All nano-stars combined high transfection potential with excellent biocompatibility. The micelles slightly outperformed the covalently linked agents. For method development and optimization, the absolute amount of polycation added to the cells was more important than the N/P-ratio (ratio between polycation nitrogen and DNA phosphate), provided a lower limit was passed and enough polycation was present to overcompensate the negative charge of the plasmid DNA. Finally, the matrix (NaCl vs. HEPES-buffered glucose solution), but also the concentrations adjusted during polyplex formation, affected the results. Full article
(This article belongs to the collection Polyelectrolytes)
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Open AccessArticle pH-Responsive Tumor-Targetable Theranostic Nanovectors Based on Core Crosslinked (CCL) Micelles with Fluorescence and Magnetic Resonance (MR) Dual Imaging Modalities and Drug Delivery Performance
Polymers 2016, 8(6), 226; doi:10.3390/polym8060226
Received: 18 April 2016 / Revised: 30 May 2016 / Accepted: 2 June 2016 / Published: 7 June 2016
Cited by 1 | PDF Full-text (3275 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The development of novel theranostic nanovectors is of particular interest in treating formidable diseases (e.g., cancers). Herein, we report a new tumor-targetable theranostic agent based on core crosslinked (CCL) micelles, possessing tumor targetable moieties and fluorescence and magnetic resonance (MR) dual imaging modalities.
[...] Read more.
The development of novel theranostic nanovectors is of particular interest in treating formidable diseases (e.g., cancers). Herein, we report a new tumor-targetable theranostic agent based on core crosslinked (CCL) micelles, possessing tumor targetable moieties and fluorescence and magnetic resonance (MR) dual imaging modalities. An azide-terminated diblock copolymer, N3-POEGMA-b-P(DPA-co-GMA), was synthesized via consecutive atom transfer radical polymerization (ATRP), where OEGMA, DPA, and GMA are oligo(ethylene glycol)methyl ether methacrylate, 2-(diisopropylamino)ethyl methacrylate, and glycidyl methacrylate, respectively. The resulting diblock copolymer was further functionalized with DOTA(Gd) (DOTA is 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakisacetic acid) or benzaldehyde moieties via copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC) chemistry, resulting in the formation of DOTA(Gd)-POEGMA-b-P(DPA-co-GMA) and benzaldehyde-POEGMA-b-P(DPA-co-GMA) copolymers. The resultant block copolymers co-assembled into mixed micelles at neutral pH in the presence of tetrakis[4-(2-mercaptoethoxy)phenyl]ethylene (TPE-4SH), which underwent spontaneous crosslinking reactions with GMA residues embedded within the micellar cores, simultaneously switching on TPE fluorescence due to the restriction of intramolecular rotation. Moreover, camptothecin (CPT) was encapsulated into the crosslinked cores at neutral pH, and tumor-targeting pH low insertion peptide (pHLIP, sequence: AEQNPIYWARYADWLFTTPLLLLDLALLVDADEGTCG) moieties were attached to the coronas through the Schiff base chemistry, yielding a theranostic nanovector with fluorescence and MR dual imaging modalities and tumor-targeting capability. The nanovectors can be efficiently taken up by A549 cells, as monitored by TPE fluorescence. After internalization, intracellular acidic pH triggered the release of loaded CPT, killing cancer cells in a selective manner. On the other hand, the nanovectors labeled with DOTA(Gd) contrast agents exhibited increased relaxivity (r1 = 16.97 mM−1·s−1) compared to alkynyl-DOTA(Gd) small molecule precursor (r1 = 3.16 mM−1·s−1). Moreover, in vivo MRI (magnetic resonance imaging) measurements revealed CCL micelles with pHLIP peptides exhibiting better tumor accumulation and MR imaging performance as well. Full article
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Open AccessArticle SANS from Salt-Free Aqueous Solutions of Hydrophilic and Highly Charged Star-Branched Polyelectrolytes
Polymers 2016, 8(6), 228; doi:10.3390/polym8060228
Received: 29 February 2016 / Revised: 14 May 2016 / Accepted: 23 May 2016 / Published: 8 June 2016
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Abstract
Scattering functions of sodium sulfonated polystyrene (NaPSS) star-branched polyelectrolytes with high sulfonation degrees were measured from their salt-free aqueous solutions, using the Small Angle Neutron Scattering (SANS) technique. Whatever the concentration c, they display two maxima. The first, of abscissa q1
[...] Read more.
Scattering functions of sodium sulfonated polystyrene (NaPSS) star-branched polyelectrolytes with high sulfonation degrees were measured from their salt-free aqueous solutions, using the Small Angle Neutron Scattering (SANS) technique. Whatever the concentration c, they display two maxima. The first, of abscissa q1*, is related to a position order between star cores and scales as q1* ∝ c1/3. The second, of abscissa q2*, is also observed in the scattering function of a semi-dilute solution of NaPSS linear polyelectrolytes. In the dilute regime (c < c*, non-overlapping stars), peak abscissa does not depend on concentration c and is just an intramolecular characteristic associated with the electrostatic repulsion between arms of the same star. In the semi-dilute regime, due to the star interpenetration, the scattering function – through the peak position, reflects repulsion between arms of the same star or of different stars. The c threshold between these distinct c-dependencies of q2* in the dilute and semi-dilute regimes is estimated as c*. Just as simple is the measurement of the geometrical radius R of the star obtained from the q1* value at c* through the relation 2R = 2π/q1*. By considering NaPSS stars of the same functionality with different degrees of polymerization per arm Na, we find R scaling linearly with Na, suggesting an elongated average conformation of the arms. This is in agreement with theoretical predictions and simulations. Meanwhile the value of q2* measured in the dilute regime does not allow any inhomogeneous counterion distribution inside the stars to be revealed. Full article
(This article belongs to the collection Polyelectrolytes)
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Open AccessArticle On the Orientation-Induced Crystallization of Polymers
Polymers 2016, 8(6), 229; doi:10.3390/polym8060229
Received: 1 April 2016 / Revised: 1 June 2016 / Accepted: 3 June 2016 / Published: 8 June 2016
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Abstract
In order to understand orientation-induced crystallization of polymers, we introduced an intermolecular interaction between polymer chains based on quantum mechanics. We therefore considered a pair of perfectly extended chains where the intermolecular interaction is assumed to be based on the hydrogen interaction with
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In order to understand orientation-induced crystallization of polymers, we introduced an intermolecular interaction between polymer chains based on quantum mechanics. We therefore considered a pair of perfectly extended chains where the intermolecular interaction is assumed to be based on the hydrogen interaction with a single chain. When two protons of each extended chain become closer together under tension, the attractive force between the extended chains is caused by the interaction between hydrogen atoms surrounding the main chains based on the hydrogen molecule ion H 2 + . The energy is split into the ground and excited states, and the spontaneous process leading to the ground state is the origin for orientation-induced crystallization. Full article
(This article belongs to the Special Issue Computational Modeling and Simulation in Polymer)
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Open AccessArticle A Phase Field Technique for Modeling and Predicting Flow Induced Crystallization Morphology of Semi-Crystalline Polymers
Polymers 2016, 8(6), 230; doi:10.3390/polym8060230
Received: 21 April 2016 / Revised: 27 May 2016 / Accepted: 2 June 2016 / Published: 8 June 2016
Cited by 2 | PDF Full-text (3681 KB) | HTML Full-text | XML Full-text
Abstract
Flow induced crystallization of semi-crystalline polymers is an important issue in polymer science and engineering because the changes in morphology strongly affect the properties of polymer materials. In this study, a phase field technique considering polymer characteristics was established for modeling and predicting
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Flow induced crystallization of semi-crystalline polymers is an important issue in polymer science and engineering because the changes in morphology strongly affect the properties of polymer materials. In this study, a phase field technique considering polymer characteristics was established for modeling and predicting the resulting morphologies. The considered crystallization process can be divided into two stages, which are nucleation upon the flow induced structures and subsequent crystal growth after the cessation of flow. Accordingly, the proposed technique consists of two parts which are a flow induced nucleation model based on the calculated information of molecular orientation and stretch, and a phase field crystal growth model upon the oriented nuclei. Two-dimensional simulations are carried out to predict the crystallization morphology of isotactic polystyrene under an injection molding process. The results of these simulations demonstrate that flow affects crystallization morphology mainly by producing oriented nuclei. Specifically, the typical skin-core structures along the thickness direction can be successfully predicted. More importantly, the results reveal that flow plays a dominant part in generating oriented crystal morphologies compared to other parameters, such as anisotropy strength, crystallization temperature, and physical noise. Full article
(This article belongs to the Special Issue Computational Modeling and Simulation in Polymer)
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Open AccessArticle Crystallization of Poly(3-hexylthiophene) Nanofiber in a Narrow Groove
Polymers 2016, 8(6), 231; doi:10.3390/polym8060231
Received: 22 April 2016 / Revised: 8 June 2016 / Accepted: 9 June 2016 / Published: 15 June 2016
Cited by 2 | PDF Full-text (9267 KB) | HTML Full-text | XML Full-text
Abstract
Whisker-type poly(3-hexylthiophene-2,5-diyl) (P3HT) nanofibers were aligned by restricting their growth direction using an approximately 100–1000 nm wide narrow groove fabricated by thermal nanoimprinting. In grooves made of an amorphous fluoropolymer (CYTOP™) with widths of less than 1500 nm, the nanofibers oriented uniaxially perpendicular
[...] Read more.
Whisker-type poly(3-hexylthiophene-2,5-diyl) (P3HT) nanofibers were aligned by restricting their growth direction using an approximately 100–1000 nm wide narrow groove fabricated by thermal nanoimprinting. In grooves made of an amorphous fluoropolymer (CYTOP™) with widths of less than 1500 nm, the nanofibers oriented uniaxially perpendicular to the groove and their length was limited to the width of the groove. This result indicates that the nucleation of nanofibers tends to be selectively promoted near the interface of CYTOP™ with fluoro-groups, and nanofiber growth perpendicular to the wall is promoted because P3HT molecules are supplied more frequently from the center of the groove. Furthermore, the orientation induced anisotropic conductivity, and the conductivity parallel to the oriented nanofibers was more than an order of magnitude higher than that perpendicular to the oriented nanofibers. Full article
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Open AccessArticle The Influence of Lyophilized EmuGel Silica Microspheres on the Physicomechanical Properties, In Vitro Bioactivity and Biodegradation of a Novel Ciprofloxacin-Loaded PCL/PAA Scaffold
Polymers 2016, 8(6), 232; doi:10.3390/polym8060232
Received: 11 May 2016 / Revised: 6 June 2016 / Accepted: 9 June 2016 / Published: 15 June 2016
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Abstract
A new composite poly(caprolactone) (PCL) and poly(acrylic acid) (PAA) (PCL:PAA 1:5) scaffold was synthesized via dispersion of PCL particles into a PAA network. Silica microspheres (Si) (2–12 μm) were then prepared by a lyophilized micro-emulsion/sol-gel (Emugel) system using varying weight ratios. The model
[...] Read more.
A new composite poly(caprolactone) (PCL) and poly(acrylic acid) (PAA) (PCL:PAA 1:5) scaffold was synthesized via dispersion of PCL particles into a PAA network. Silica microspheres (Si) (2–12 μm) were then prepared by a lyophilized micro-emulsion/sol-gel (Emugel) system using varying weight ratios. The model drug ciprofloxacin (CFX) was used for in situ incorporation into the scaffold. The physicochemical and thermal integrity, morphology and porosity of the system was analyzed by X-Ray Diffraction (XRD), Attenuated Total Refelctance Fourier Transform Infrared (ATR-FTIR), Differential Scanning Calorimetry (DSC), SEM, surface area analysis and liquid displacement, respectively. The mechanical properties of the scaffold were measured by textural analysis and in vitro bioactivity, biodegradation and pH variations were evaluated by XRD, FTIR and SEM after immersion in Simulated Body Fluid (SBF). The in vitro and in vivo studies of the prepared scaffold were considered as future aspects for this study. CFX release was determined in phosphate buffer saline (PBS) (pH 7.4; 37 °C). The incorporation of the Si microspheres and CFX into the scaffold was confirmed by XRD, FTIR, DSC and SEM, and the scaffold microstructure was dependent on the concentration of Si microspheres and the presence of CFX. The system displayed enhanced mechanical properties (4.5–14.73 MPa), in vitro bioactivity, biodegradation and controlled CFX release. Therefore, the PCL/PAA scaffolds loaded with Si microspheres and CFX with a porosity of up to 87% may be promising for bone tissue engineering. Full article
(This article belongs to the Special Issue Biodegradable Polymers)
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Open AccessArticle pH- and Metal Ion- Sensitive Hydrogels based on N-[2-(dimethylaminoethyl)acrylamide]
Polymers 2016, 8(6), 233; doi:10.3390/polym8060233
Received: 24 February 2016 / Revised: 12 May 2016 / Accepted: 6 June 2016 / Published: 15 June 2016
Cited by 2 | PDF Full-text (2076 KB) | HTML Full-text | XML Full-text
Abstract
Smart hydrogels are promising materials for actuators and sensors, as they can respond to small changes in their environment with a large property change. Hydrogels can respond to a variety of stimuli, for example temperature, pH, metal ions, etc. In this article,
[...] Read more.
Smart hydrogels are promising materials for actuators and sensors, as they can respond to small changes in their environment with a large property change. Hydrogels can respond to a variety of stimuli, for example temperature, pH, metal ions, etc. In this article, the synthesis and characterization of polyampholyte hydrogels based on open chain ligands showing pH and metal ion sensitivity are described. Copolymer and terpolymer gels using different mixtures of monomers i.e., N-[2-(dimethylaminoethyl)acrylamide] (DMAEAAm), N,N-dimethylacrylamide (DMAAm), acrylic acid (AA) and 2-acrylamido-2-methyl-1-propanesulphonic acid (AMPS), have been synthesized. The effect of copolymer composition, i.e., the ratio and amount of ionic monomers and the degree of crosslinking on the swelling characteristics, was evaluated as a function of pH. On this basis, metal ion sensitivity measurements were performed at selected pH values. The metal ion sensitivity was measured by varying the concentration of Cu2+, Zn2+ and Ag+ ions under acidic pH conditions. Full article
(This article belongs to the Special Issue Polymers for Aqueous Media)
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Open AccessArticle Effect of Very High Charge Density and Monomer Constitution on the Synthesis and Properties of Cationic Polyelectrolytes
Polymers 2016, 8(6), 234; doi:10.3390/polym8060234
Received: 8 March 2016 / Revised: 16 May 2016 / Accepted: 30 May 2016 / Published: 16 June 2016
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Abstract
The free-radical homopolymerization of 1,3-bis(N,N,N-trimethylammonium)-2-propylmethacrylate dichloride (di-M) and 1,3-bis(N,N,N-trimethylammonium)-2-propylacrylate dichloride (di-A) in aqueous solution yields cationic polyelectrolytes (PEL) with theoretical/structural charge spacing of only ≈0.12 nm. The high charge density causes condensation of ≈82% of the chloride counterions. The
[...] Read more.
The free-radical homopolymerization of 1,3-bis(N,N,N-trimethylammonium)-2-propylmethacrylate dichloride (di-M) and 1,3-bis(N,N,N-trimethylammonium)-2-propylacrylate dichloride (di-A) in aqueous solution yields cationic polyelectrolytes (PEL) with theoretical/structural charge spacing of only ≈0.12 nm. The high charge density causes condensation of ≈82% of the chloride counterions. The high level of counterion condensation reduces the ionic strength in the polymerizing batch when the monomer molecules connect to PEL chains. This has the consequence that the hydrodynamic and excluded volume of the PEL molecules will change. Studies of the free radical polymerization revealed non-ideal polymerization kinetics already at low conversion and additionally autoacceleration above a certain monomer concentration and conversion. Similar autoacceleration was not observed for monomers yielding PEL with charge spacing of 0.25 or 0.5 nm. Coulomb interactions, monomer association, steric effects, and specific features of the monomer constitution have been evaluated concerning their contributions to the concentration dependence and conversion dependence of kinetic parameters. The different backbone constitutions of di-M and di-A not only influence the polymerization kinetics but also equip poly(di-M) with higher hydrolytic stability. The experimental results confirm the impact of electrochemical parameters and the necessity to reconsider their inclusion in kinetic models. Full article
(This article belongs to the collection Polyelectrolytes)
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Open AccessArticle Spatial Rearrangement and Mobility Heterogeneity of an Anionic Lipid Monolayer Induced by the Anchoring of Cationic Semiflexible Polymer Chains
Polymers 2016, 8(6), 235; doi:10.3390/polym8060235
Received: 12 May 2016 / Revised: 8 June 2016 / Accepted: 13 June 2016 / Published: 17 June 2016
Cited by 2 | PDF Full-text (5574 KB) | HTML Full-text | XML Full-text
Abstract
We use Monte Carlo simulations to investigate the interactions between cationic semiflexible polymer chains and a model fluid lipid monolayer composed of charge-neutral phosphatidyl-choline (PC), tetravalent anionic phosphatidylinositol 4,5-bisphosphate (PIP2), and univalent anionic phosphatidylserine (PS) lipids. In particular, we explore how
[...] Read more.
We use Monte Carlo simulations to investigate the interactions between cationic semiflexible polymer chains and a model fluid lipid monolayer composed of charge-neutral phosphatidyl-choline (PC), tetravalent anionic phosphatidylinositol 4,5-bisphosphate (PIP2), and univalent anionic phosphatidylserine (PS) lipids. In particular, we explore how chain rigidity and polymer concentration influence the spatial rearrangement and mobility heterogeneity of the monolayer under the conditions where the cationic polymers anchor on the monolayer. We find that the anchored cationic polymers only sequester the tetravalent PIP2 lipids at low polymer concentrations, where the interaction strength between the polymers and the monolayer exhibits a non-monotonic dependence on the degree of chain rigidity. Specifically, maximal anchoring occurs at low polymer concentrations, when the polymer chains have an intermediate degree of rigidity, for which the PIP2 clustering becomes most enhanced and the mobility of the polymer/PIP2 complexes becomes most reduced. On the other hand, at sufficiently high polymer concentrations, the anchoring strength decreases monotonically as the chains stiffen—a result that arises from the pronounced competitions among polymer chains. In this case, the flexible polymers can confine all PIP2 lipids and further sequester the univalent PS lipids, whereas the stiffer polymers tend to partially dissociate from the monolayer and only sequester smaller PIP2 clusters with greater mobilities. We further illustrate that the mobility gradient of the single PIP2 lipids in the sequestered clusters is sensitively modulated by the cooperative effects between anchored segments of the polymers with different rigidities. Our work thus demonstrates that the rigidity and concentration of anchored polymers are both important parameters for tuning the regulation of anionic lipids. Full article
(This article belongs to the Special Issue Semiflexible Polymers)
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Open AccessArticle Exploring the Behavior of Bovine Serum Albumin in Response to Changes in the Chemical Composition of Responsive Polymers: Experimental and Simulation Studies
Polymers 2016, 8(6), 238; doi:10.3390/polym8060238
Received: 3 May 2016 / Revised: 13 June 2016 / Accepted: 13 June 2016 / Published: 18 June 2016
Cited by 1 | PDF Full-text (2223 KB) | HTML Full-text | XML Full-text
Abstract
Knowledge of the interactions between polymer and protein is very important to fabricate the potential materials for many bio-related applications. In this regard, the present work investigated the effect of copolymers on the conformation and thermal stability of bovine serum albumin (BSA) with
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Knowledge of the interactions between polymer and protein is very important to fabricate the potential materials for many bio-related applications. In this regard, the present work investigated the effect of copolymers on the conformation and thermal stability of bovine serum albumin (BSA) with the aid of biophysical techniques such as fluorescence spectroscopy, circular dichroism (CD) spectroscopy and differential scanning calorimetry (DSC). In comparison with that of copolymer PGA-1.5, our fluorescence spectroscopy results reveal that the copolymer PGA-1, which has a lower PEGMA/AA ratio, shows greater influence on the conformation of BSA. Copolymers induced unfolding of the polypeptide chain of BSA, which was confirmed from the loss in the negative ellipticity of CD spectra. DSC results showed that the addition of PGA-1 and PGA-1.5 (0.05% (w/v) decreased the transition temperature by 14.8 and 11.5 °C, respectively). The results from the present study on the behavior of protein in response to changes in the chemical composition of synthetic polymers are significant for various biological applications such as enzyme immobilization, protein separations, sensor development and stimuli-responsive systems. Full article
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Open AccessArticle New Statistical Models for Copolymerization
Polymers 2016, 8(6), 240; doi:10.3390/polym8060240
Received: 9 May 2016 / Revised: 7 June 2016 / Accepted: 15 June 2016 / Published: 22 June 2016
Cited by 1 | PDF Full-text (996 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
For many years, copolymerization has been studied using mathematical and statistical models. Here, we present new Markov chain models for copolymerization kinetics: the Bernoulli and Geometric models. They model copolymer synthesis as a random process and are based on a basic reaction scheme.
[...] Read more.
For many years, copolymerization has been studied using mathematical and statistical models. Here, we present new Markov chain models for copolymerization kinetics: the Bernoulli and Geometric models. They model copolymer synthesis as a random process and are based on a basic reaction scheme. In contrast to previous Markov chain approaches to copolymerization, both models take variable chain lengths and time-dependent monomer probabilities into account and allow for computing sequence likelihoods and copolymer fingerprints. Fingerprints can be computed from copolymer mass spectra, potentially allowing us to estimate the model parameters from measured fingerprints. We compare both models against Monte Carlo simulations. We find that computing the models is fast and memory efficient. Full article
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Open AccessFeature PaperArticle Predicting the Flory-Huggins χ Parameter for Polymers with Stiffness Mismatch from Molecular Dynamics Simulations
Polymers 2016, 8(6), 241; doi:10.3390/polym8060241
Received: 4 May 2016 / Revised: 13 June 2016 / Accepted: 16 June 2016 / Published: 22 June 2016
Cited by 2 | PDF Full-text (1770 KB) | HTML Full-text | XML Full-text
Abstract
The Flory–Huggins χ parameter describes the excess free energy of mixing and governs phase behavior for polymer blends and block copolymers. For chemically-distinct nonpolar polymers, the value of χ is dominated by the mismatch in cohesive energy densities of the monomers. For blends
[...] Read more.
The Flory–Huggins χ parameter describes the excess free energy of mixing and governs phase behavior for polymer blends and block copolymers. For chemically-distinct nonpolar polymers, the value of χ is dominated by the mismatch in cohesive energy densities of the monomers. For blends of chemically-similar polymers, the entropic portion of χ, arising from non-ideal local packing, becomes more significant. Using polymer field theory, Fredrickson et al. predicted that a difference in backbone stiffness can result in a positive χ for chains consisting of chemically-identical monomers. To quantitatively investigate this phenomenon, we perform molecular dynamic (MD) simulations for bead-spring chains, which differ only in stiffness. From the simulations, we apply a novel thermodynamic integration to extract χ as low as 10 - 4 per monomer for blends with stiffness mismatch. To compare with experiments, we introduce a standardized effective monomer to map real polymers onto our bead-spring chains. The predicted χ agrees well with experimental values for a wide variety of pairs of chemically-similar polymers. Full article
(This article belongs to the Special Issue Semiflexible Polymers)
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Open AccessArticle Quick Preparation of Moisture-Saturated Carbon Fiber-Reinforced Plastics and Their Accelerated Ageing Tests Using Heat and Moisture
Polymers 2016, 8(6), 242; doi:10.3390/polym8060242
Received: 27 April 2016 / Revised: 8 June 2016 / Accepted: 15 June 2016 / Published: 22 June 2016
PDF Full-text (13154 KB) | HTML Full-text | XML Full-text
Abstract
A quick method involving the control of heat and water vapor pressure for preparing moisture-saturated carbon fiber-reinforced plastics (CFRP, 8 unidirectional prepreg layers, 1.5 mm thickness, epoxy resin) has been developed. The moisture-saturated CFRP sample was obtained at 120 °C and 0.2 MPa
[...] Read more.
A quick method involving the control of heat and water vapor pressure for preparing moisture-saturated carbon fiber-reinforced plastics (CFRP, 8 unidirectional prepreg layers, 1.5 mm thickness, epoxy resin) has been developed. The moisture-saturated CFRP sample was obtained at 120 °C and 0.2 MPa water vapor in 72 h by this method using a sterilizer (autoclave). The bending strength and viscoelastic properties measured by a dynamic mechanical analysis (DMA) remained unchanged during repetitive saturation and drying steps. No degradation and molecular structural change occurred. Furthermore an accelerated ageing test with two ageing factors, i.e., heat and moisture was developed and performed at 140–160 °C and 0.36–0.62 MPa water vapor pressure by using a sealed pressure-proof stainless steel vessel (autoclave). The bending strength of the sample decreased from 1107 to 319 MPa at 160 °C and 0.63 MPa water vapor pressure in 9 days. Degraded samples were analyzed by DMA. The degree of degradation for samples was analyzed by DMA. CFRP and degraded CFRP samples were analyzed by using a surface and interfacial cutting analysis system (SAICAS) and an electron probe micro-analyzer (EPMA) equipped in a scanning electron microscope. Full article
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Open AccessReview Functionalized Polymers for Enhance Oral Bioavailability of Sensitive Molecules
Polymers 2016, 8(6), 214; doi:10.3390/polym8060214
Received: 16 March 2016 / Revised: 30 April 2016 / Accepted: 11 May 2016 / Published: 2 June 2016
Cited by 1 | PDF Full-text (1381 KB) | HTML Full-text | XML Full-text
Abstract
Currently, many sensitive molecules have been studied for effective oral administration. These substances are biologically active compounds that mainly suffer early degradation in the gastrointestinal tract (GIT) and physicochemical instability, inactivation and poor solubility and permeability. The sensibility of the biomolecules has limited
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Currently, many sensitive molecules have been studied for effective oral administration. These substances are biologically active compounds that mainly suffer early degradation in the gastrointestinal tract (GIT) and physicochemical instability, inactivation and poor solubility and permeability. The sensibility of the biomolecules has limited their oral administration in the body and today is an important research topic to achieve desired effects in medicine field. Under this perspective, various enhancement approaches have been studied as alternatives to increase their oral bioavailability. Some of these strategies include functionalized polymers to provide specific useful benefits as protection to the intestinal tract by preventing its degradation by stomach enzymes, to increase their absorption, permeability, stability, and to make a proper release in the GIT. Due to specific chemical groups, shapes and sizes, morphologies, mechanical properties, and degradation, recent advances in functionalized polymers have opened the door to great possibilities to improve the physicochemical characteristics of these biopharmaceuticals. Today, many biomolecules are found in basic studies, preclinical steps, and others are late stage clinical development. This review summarizes the contribution of functionalized polymers to enhance oral bioavailability of sensitive molecules and their application status in medicine for different diseases. Future trends of these polymers and their possible uses to achieve different formulation goals for oral delivery are also covered in this manuscript. Full article
(This article belongs to the Special Issue Functional Polymers for Medical Applications)
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Open AccessReview Polymers in Cartilage Defect Repair of the Knee: Current Status and Future Prospects
Polymers 2016, 8(6), 219; doi:10.3390/polym8060219
Received: 18 March 2016 / Revised: 26 May 2016 / Accepted: 31 May 2016 / Published: 4 June 2016
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Abstract
Cartilage defects in the knee are often seen in young and active patients. There is a need for effective joint preserving treatments in patients suffering from cartilage defects, as untreated defects often lead to osteoarthritis. Within the last two decades, tissue engineering based
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Cartilage defects in the knee are often seen in young and active patients. There is a need for effective joint preserving treatments in patients suffering from cartilage defects, as untreated defects often lead to osteoarthritis. Within the last two decades, tissue engineering based techniques using a wide variety of polymers, cell sources, and signaling molecules have been evaluated. We start this review with basic background information on cartilage structure, its intrinsic repair, and an overview of the cartilage repair treatments from a historical perspective. Next, we thoroughly discuss polymer construct components and their current use in commercially available constructs. Finally, we provide an in-depth discussion about construct considerations such as degradation rates, cell sources, mechanical properties, joint homeostasis, and non-degradable/hybrid resurfacing techniques. As future prospects in cartilage repair, we foresee developments in three areas: first, further optimization of degradable scaffolds towards more biomimetic grafts and improved joint environment. Second, we predict that patient-specific non-degradable resurfacing implants will become increasingly applied and will provide a feasible treatment for older patients or failed regenerative treatments. Third, we foresee an increase of interest in hybrid construct, which combines degradable with non-degradable materials. Full article
(This article belongs to the Special Issue Functional Polymers for Medical Applications)
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Open AccessReview Polybenzoxazine/Polyhedral Oligomeric Silsesquioxane (POSS) Nanocomposites
Polymers 2016, 8(6), 225; doi:10.3390/polym8060225
Received: 9 April 2016 / Revised: 26 May 2016 / Accepted: 2 June 2016 / Published: 7 June 2016
Cited by 2 | PDF Full-text (13335 KB) | HTML Full-text | XML Full-text
Abstract
The organic/inorganic hybrid materials from polyhedral oligomeric silsesquioxane (POSS, inorganic nanoparticles) and polybenzoxazine (PBZ) have received much interesting recently due to their excellent thermal and mechanical properties, flame retardance, low dielectric constant, well-defined inorganic framework at nanosized scale level, and higher performance relative
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The organic/inorganic hybrid materials from polyhedral oligomeric silsesquioxane (POSS, inorganic nanoparticles) and polybenzoxazine (PBZ) have received much interesting recently due to their excellent thermal and mechanical properties, flame retardance, low dielectric constant, well-defined inorganic framework at nanosized scale level, and higher performance relative to those of non-hybrid PBZs. This review describes the synthesis, dielectric constants, and thermal, rheological, and mechanical properties of covalently bonded mono- and multifunctionalized benzoxazine POSS hybrids, other functionalized benzoxazine POSS derivatives, and non-covalently (hydrogen) bonded benzoxazine POSS composites. Full article
(This article belongs to the collection Featured Mini Reviews in Polymer Science)
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Open AccessReview Polyglycidol, Its Derivatives, and Polyglycidol-Containing Copolymers—Synthesis and Medical Applications
Polymers 2016, 8(6), 227; doi:10.3390/polym8060227
Received: 9 May 2016 / Revised: 30 May 2016 / Accepted: 31 May 2016 / Published: 9 June 2016
Cited by 3 | PDF Full-text (8660 KB) | HTML Full-text | XML Full-text
Abstract
Polyglycidol (or polyglycerol) is a biocompatible polymer with a main chain structure similar to that of poly(ethylene oxide) but with a –CH2OH reactive side group in every structural unit. The hydroxyl groups in polyglycidol not only increase the hydrophilicity of this
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Polyglycidol (or polyglycerol) is a biocompatible polymer with a main chain structure similar to that of poly(ethylene oxide) but with a –CH2OH reactive side group in every structural unit. The hydroxyl groups in polyglycidol not only increase the hydrophilicity of this polymer but also allow for its modification, leading to polymers with carboxyl, amine, and vinyl groups, as well as to polymers with bonded aliphatic chains, sugar moieties, and covalently immobilized bioactive compounds in particular proteins. The paper describes the current state of knowledge on the synthesis of polyglycidols with various topology (linear, branched, and star-like) and with various molar masses. We provide information on polyglycidol-rich surfaces with protein-repelling properties. We also describe methods for the synthesis of polyglycidol-containing copolymers and the preparation of nano- and microparticles that could be derived from these copolymers. The paper summarizes recent advances in the application of polyglycidol and polyglycidol-containing polymers as drug carriers, reagents for diagnostic systems, and elements of biosensors. Full article
(This article belongs to the Special Issue Functional Polymers for Medical Applications)
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