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Gels, Volume 3, Issue 1 (March 2017)

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Cover Story (view full-size image) Physically crosslinked polymer-based responsive hydrogels with tunable properties can be formed by [...] Read more.
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Open AccessCommunication
Self-Assembly of Colloidal Nanocomposite Hydrogels Using 1D Cellulose Nanocrystals and 2D Exfoliated Organoclay Layers
Gels 2017, 3(1), 11; https://doi.org/10.3390/gels3010011 - 17 Mar 2017
Cited by 2 | Viewed by 1976
Abstract
Stimuli-responsive colloidal nanocomposite hydrogels are prepared by exploiting non-covalent interactions between anionic cellulose nanocrystals and polycationic delaminated sheets of aminopropyl-functionalized magnesium phyllosilicate clays. Full article
(This article belongs to the Special Issue Stimuli-Responsive Gels) Printed Edition available
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Open AccessArticle
Mechanical, Swelling, and Structural Properties of Mechanically Tough Clay-Sodium Polyacrylate Blend Hydrogels
Gels 2017, 3(1), 10; https://doi.org/10.3390/gels3010010 - 25 Feb 2017
Cited by 7 | Viewed by 2895
Abstract
We investigated the mechanical, swelling, and structural properties of mechanically tough clay/sodium polyacrylate (PAAS) hydrogels prepared by simple mixing. The gels had large swelling ratios, reflecting the characteristics of the constituent polymer. The swelling ratios initially increased with the increase of the swelling [...] Read more.
We investigated the mechanical, swelling, and structural properties of mechanically tough clay/sodium polyacrylate (PAAS) hydrogels prepared by simple mixing. The gels had large swelling ratios, reflecting the characteristics of the constituent polymer. The swelling ratios initially increased with the increase of the swelling time, and then attained maximum values. Afterwards, they decreased with an increase of the swelling time and finally became constant. An increase in the clay concentration lead to a decrease in the swelling ratios, whereas an increase in the PAAS concentration lead to an increase in the swelling ratios. Tensile measurements indicated that the toughness for clay/PAAS (Mw = 3.50 × 106) gels was several hundred times larger than that of clay/PAAS (Mw = 5.07 × 105) gels, i.e., the use of ultra-high molecular weight PAAS is essential for fabricating mechanically tough clay/PAAS blend hydrogels. Synchrotron small-angle X-ray scattering (SAXS) results showed that the SAXS intensity measured at small scattering angles decreased with an increase in the clay concentration, indicating that the interparticle interactions were more repulsive at higher concentrations. The decrease of the scattering intensity at high clay concentrations was larger for the clay/PAAS (Mw = 5.07 × 105) gel system than for the clay/PAAS (Mw = 3.50 × 106) gel system. Full article
(This article belongs to the Special Issue Rheology of Gels)
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Open AccessFeature PaperArticle
Synthesis of Helical Phenolic Resin Bundles through a Sol-Gel Transcription Method
Gels 2017, 3(1), 9; https://doi.org/10.3390/gels3010009 - 23 Feb 2017
Cited by 4 | Viewed by 1917
Abstract
Chiral and helical polymers possess special helical structures and optical property, and may find applications in chiral catalysis and optical devices. This work presents the preparation and formation process of helical phenolic resins through a sol-gel transcription method. A pair of bola-type chiral [...] Read more.
Chiral and helical polymers possess special helical structures and optical property, and may find applications in chiral catalysis and optical devices. This work presents the preparation and formation process of helical phenolic resins through a sol-gel transcription method. A pair of bola-type chiral low-molecular-weight gelators (LMWGs) derived from valine are used as templates, while 2,4-dihydroxybenzoic acid and formaldehyde are used as precursors. The electron microscopy images show that the phenolic resins are single-handed helical bundles comprised of helical ultrafine nanofibers. The diffused reflection circular dichroism spectra indicate that the helical phenolic resins exhibit optical activity. A possible formation mechanism is proposed, which shows the co-assembly of the LMWGs and the precursors. Full article
(This article belongs to the Special Issue Gels as Templates for Transcription)
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Open AccessFeature PaperArticle
Carboxymethyl Cellulose-Grafted Mesoporous Silica Hybrid Nanogels for Enhanced Cellular Uptake and Release of Curcumin
Gels 2017, 3(1), 8; https://doi.org/10.3390/gels3010008 - 22 Feb 2017
Cited by 4 | Viewed by 3507
Abstract
Mesoporous silica nanoparticles (MSNs) with ordered pore structure have been synthesized and used as carriers for the anticancer drug curcumin. MSNs were functionalized with amine groups and further attached with carboxymethyl cellulose (CMC) using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) coupling chemistry, which increased the hydrophilicity and [...] Read more.
Mesoporous silica nanoparticles (MSNs) with ordered pore structure have been synthesized and used as carriers for the anticancer drug curcumin. MSNs were functionalized with amine groups and further attached with carboxymethyl cellulose (CMC) using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) coupling chemistry, which increased the hydrophilicity and biocompatibility of MSNs. The functionalized MSNs (MSN-NH2 and MSN-CMC) were characterized using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS), N2 adsorption, X-Ray Diffraction (XRD), Thermo Gravimetric Analysis (TGA) and Fourier Transform Infrared Spectroscopy (FT-IR). The in vitro release of curcumin from the –NH2 and CMC functionalized MSNs (MSN-cur-NH2 and MSN-cur-CMC) was performed in 0.5% aqueous solution of sodium lauryl sulphate (SLS). The effect of CMC functionalization of MSNs towards cellular uptake was studied in the human breast cancer cell line MDA-MB-231 and was compared with that of MSN-NH2 and free curcumin (cur). Both MSN-NH2 and MSN-CMC showed good biocompatibility with the breast cancer cell line. The MTT assay study revealed that curcumin-loaded MSN-cur-CMC showed better uptake as compared to curcumin-loaded MSN-cur-NH2. Free curcumin was used as a control and was shown to have much less internalization as compared to the curcumin-loaded functionalized MSNs due to poor bioavailability. Fluorescence microscopy was used to localize the fluorescent drug curcumin inside the cells. The work demonstrates that CMC-functionalized MSNs can be used as potential carriers for loading and release of hydrophobic drugs that otherwise cannot be used effectively in their free form for cancer therapy. Full article
(This article belongs to the Special Issue Micro- and Nanogels)
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Open AccessArticle
Hydrogel Micro-/Nanosphere Coated by a Lipid Bilayer: Preparation and Microscopic Probing
Gels 2017, 3(1), 7; https://doi.org/10.3390/gels3010007 - 15 Feb 2017
Cited by 1 | Viewed by 1925
Abstract
The result of polymeric nanogels and lipid vesicles interaction—lipobeads—can be considered as multipurpose containers for future therapeutic applications, such as targeted anticancer chemotherapy with superior tumor response and minimum side effects. In this work, micrometer sized lipobeads were synthesized by two methods: (i) [...] Read more.
The result of polymeric nanogels and lipid vesicles interaction—lipobeads—can be considered as multipurpose containers for future therapeutic applications, such as targeted anticancer chemotherapy with superior tumor response and minimum side effects. In this work, micrometer sized lipobeads were synthesized by two methods: (i) mixing separately prepared microgels made of poly(N-isopropylacrylamide) (PNIPA) and phospholipid vesicles of micrometer or nanometer size and (ii) polymerization within the lipid vesicles. For the first time, a high vacuum scanning electron microscopy was shown to be suitable for a quick validation of the structural organization of wet lipobeads and their constituents without special sample preparation. In particular, the structural difference of microgels prepared by thermal and UV-polymerization in different solvents was revealed and three types of giant liposomes were recognized under high vacuum in conjunction with their size, composition, and method of preparation. Importantly, the substructure of the hydrogel core and multi- and unilamellar constructions of the peripheral lipid part were explicitly distinguished on the SEM images of lipobeads, justifying the spontaneous formation of a lipid bilayer on the surface of microgels and evidencing an energetically favorable structural organization of the hydrogel/lipid bilayer assembly. This key property can facilitate lipobeads’ preparation and decrease technological expenses on their scaled production. The comparison of the SEM imaging with the scanning confocal and atomic force microscopies data are also presented in the discussion. Full article
(This article belongs to the Special Issue Micro- and Nanogels)
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Open AccessReview
Hydrogels for Biomedical Applications: Their Characteristics and the Mechanisms behind Them
Gels 2017, 3(1), 6; https://doi.org/10.3390/gels3010006 - 24 Jan 2017
Cited by 69 | Viewed by 4143
Abstract
Hydrogels are hydrophilic, three-dimensional networks that are able to absorb large quantities of water or biological fluids, and thus have the potential to be used as prime candidates for biosensors, drug delivery vectors, and carriers or matrices for cells in tissue engineering. In [...] Read more.
Hydrogels are hydrophilic, three-dimensional networks that are able to absorb large quantities of water or biological fluids, and thus have the potential to be used as prime candidates for biosensors, drug delivery vectors, and carriers or matrices for cells in tissue engineering. In this critical review article, advantages of the hydrogels that overcome the limitations from other types of biomaterials will be discussed. Hydrogels, depending on their chemical composition, are responsive to various stimuli including heating, pH, light, and chemicals. Two swelling mechanisms will be discussed to give a detailed understanding of how the structure parameters affect swelling properties, followed by the gelation mechanism and mesh size calculation. Hydrogels prepared from natural materials such as polysaccharides and polypeptides, along with different types of synthetic hydrogels from the recent reported literature, will be discussed in detail. Finally, attention will be given to biomedical applications of different kinds of hydrogels including cell culture, self-healing, and drug delivery. Full article
(This article belongs to the Special Issue Hydrogels in Tissue Engineering) Printed Edition available
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Open AccessEditorial
Acknowledgement to Reviewers of Gels in 2016
Gels 2017, 3(1), 5; https://doi.org/10.3390/gels3010005 - 11 Jan 2017
Viewed by 1011
Abstract
The editors of Gels would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2016.[...] Full article
Open AccessFeature PaperReview
Thermoresponsive Gels
Gels 2017, 3(1), 4; https://doi.org/10.3390/gels3010004 - 10 Jan 2017
Cited by 28 | Viewed by 3354
Abstract
Thermoresponsive gelling materials constructed from natural and synthetic polymers can be used to provide triggered action and therefore customised products such as drug delivery and regenerative medicine types as well as for other industries. Some materials give Arrhenius-type viscosity changes based on coil [...] Read more.
Thermoresponsive gelling materials constructed from natural and synthetic polymers can be used to provide triggered action and therefore customised products such as drug delivery and regenerative medicine types as well as for other industries. Some materials give Arrhenius-type viscosity changes based on coil to globule transitions. Others produce more counterintuitive responses to temperature change because of agglomeration induced by enthalpic or entropic drivers. Extensive covalent crosslinking superimposes complexity of response and the upper and lower critical solution temperatures can translate to critical volume temperatures for these swellable but insoluble gels. Their structure and volume response confer advantages for actuation though they lack robustness. Dynamic covalent bonding has created an intermediate category where shape moulding and self-healing variants are useful for several platforms. Developing synthesis methodology—for example, Reversible Addition Fragmentation chain Transfer (RAFT) and Atomic Transfer Radical Polymerisation (ATRP)—provides an almost infinite range of materials that can be used for many of these gelling systems. For those that self-assemble into micelle systems that can gel, the upper and lower critical solution temperatures (UCST and LCST) are analogous to those for simpler dispersible polymers. However, the tuned hydrophobic-hydrophilic balance plus the introduction of additional pH-sensitivity and, for instance, thermochromic response, open the potential for coupled mechanisms to create complex drug targeting effects at the cellular level. Full article
(This article belongs to the Special Issue Stimuli-Responsive Gels) Printed Edition available
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Open AccessFeature PaperReview
Responsive Hydrogels from Associative Block Copolymers: Physical Gelling through Polyion Complexation
Gels 2017, 3(1), 3; https://doi.org/10.3390/gels3010003 - 01 Jan 2017
Cited by 9 | Viewed by 2315
Abstract
The present review article highlights a specific class of responsive polymer-based hydrogels which are formed through association of oppositely charged polyion segments. The underpinning temporary three-dimensional network is constituted of hydrophilic chains (either ionic or neutral) physically crosslinked by ion pair formation arising [...] Read more.
The present review article highlights a specific class of responsive polymer-based hydrogels which are formed through association of oppositely charged polyion segments. The underpinning temporary three-dimensional network is constituted of hydrophilic chains (either ionic or neutral) physically crosslinked by ion pair formation arising from intermolecular polyionic complexation of oppositely charged repeating units (polyacid/polybase ionic interactions). Two types of hydrogels are presented: (i) hydrogels formed by triblock copolymers bearing oppositely charged blocks (block copolyampholytes), forming self-assembled networks; and (ii) hydrogels formed by co-assembly of oppositely charged polyelectrolyte segments belonging to different macromolecules (either block copolymers or homopolyelectrolytes). Due to the weak nature of the involved polyions, these hydrogels respond to pH and are sensitive to the presence of salts. Discussing and evaluating their solution, rheological and structural properties in dependence on pH and ionic strength, it comes out that the hydrogel properties are tunable towards potential applications. Full article
(This article belongs to the Special Issue Stimuli-Responsive Gels) Printed Edition available
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Open AccessFeature PaperReview
Single-Handed Helical Polybissilsesquioxane Nanotubes and Mesoporous Nanofibers Prepared by an External Templating Approach Using Low-Molecular-Weight Gelators
Gels 2017, 3(1), 2; https://doi.org/10.3390/gels3010002 - 01 Jan 2017
Cited by 3 | Viewed by 1514
Abstract
Chiral low-molecular-weight gelators (LMWGs) derived from amino acids can self-assemble into helical fibers and twisted/coiled nanoribbons by H-bonding and π–π interaction. Silica nanotubes with single-handed helices have been prepared using chiral LMWGs through sol–gel transcription. Molecular-scale chirality exists at the inner surfaces. Here, [...] Read more.
Chiral low-molecular-weight gelators (LMWGs) derived from amino acids can self-assemble into helical fibers and twisted/coiled nanoribbons by H-bonding and π–π interaction. Silica nanotubes with single-handed helices have been prepared using chiral LMWGs through sol–gel transcription. Molecular-scale chirality exists at the inner surfaces. Here, we discuss single-handed helical aromatic ring-bridged polybissilsesquioxane nanotubes and mesoporous nanofibers prepared using chiral LMWGs. This review aims at describing the formation mechanisms of the helical nanostructures, the origination of optical activity, and the applications for other helical nanomaterial preparation, mainly based on our group’s results. The morphology and handedness can be controlled by changing the chirality and kinds of LMWGs and tuning the reaction conditions. The aromatic rings arrange in a partially crystalline structure. The optical activity of the polybissilsesquioxane nanotubes and mesoporous nanofibers originates from chiral defects, including stacking and twisting of aromatic groups, on the inner surfaces. They can be used as the starting materials for preparation of silica, silicon, carbonaceous, silica/carbon, and silicon carbide nanotubes. Full article
(This article belongs to the Special Issue Gels as Templates for Transcription)
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Open AccessFeature PaperReview
Physicochemical Properties and the Gelation Process of Supramolecular Hydrogels: A Review
Gels 2017, 3(1), 1; https://doi.org/10.3390/gels3010001 - 01 Jan 2017
Cited by 15 | Viewed by 3280
Abstract
Supramolecular polysaccharide-based hydrogels have attracted considerable research interest recently due to their high structural functionality, low toxicity, and potential applications in foods, cosmetics, catalysis, drug delivery, tissue engineering and the environment. Modulation of the stability of hydrogels is of paramount importance, especially in [...] Read more.
Supramolecular polysaccharide-based hydrogels have attracted considerable research interest recently due to their high structural functionality, low toxicity, and potential applications in foods, cosmetics, catalysis, drug delivery, tissue engineering and the environment. Modulation of the stability of hydrogels is of paramount importance, especially in the case of stimuli-responsive systems. This review will update the recent progress related to the rational design of supramolecular hydrogels with the objective of understanding the gelation process and improving their physical gelation properties for tailored applications. Emphasis will be given to supramolecular host–guest systems with reference to conventional gels in describing general aspects of gel formation. A brief account of the structural characterization of various supramolecular hydrogels is also provided in order to gain a better understanding of the design of such materials relevant to the nature of the intermolecular interactions, thermodynamic properties of the gelation process, and the critical concentration values of the precursors and the solvent components. This mini-review contributes to greater knowledge of the rational design of supramolecular hydrogels with tailored applications in diverse fields ranging from the environment to biomedicine. Full article
(This article belongs to the Special Issue Colloid Chemistry) Printed Edition available
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