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20022 KiB

Open AccessArticle

Surface Morphology at the Microscopic Scale, Swelling/Deswelling, and the Magnetic Properties of PNIPAM/CMC and PNIPAM/CMC/Fe₃O₄ Hydrogels

by Marianna Uva and Andrea Atrei

Gels 2016, 2(4), 30; https://0-doi-org.brum.beds.ac.uk/10.3390/gels2040030 - 13 Dec 2016

Cited by 7 | Viewed by 5954

Abstract

Poly(N-isopropylacrylamide) (PNIPAM) hydrogels containing carboxymethylcellulose (CMC) and CMC/Fe₃O₄ nanoparticles were prepared. Free-radical polymerization with BIS as cross-linker was used to synthesize the hydrogels. The morphology at the microscopic scale of these materials was investigated using field emission scanning [...] Read more.

Poly(N-isopropylacrylamide) (PNIPAM) hydrogels containing carboxymethylcellulose (CMC) and CMC/Fe₃O₄ nanoparticles were prepared. Free-radical polymerization with BIS as cross-linker was used to synthesize the hydrogels. The morphology at the microscopic scale of these materials was investigated using field emission scanning electron microscopy (FESEM). The images show that CMC in the PNIPAM hydrogels induces the formation of a honeycomb structure. This surface morphology was not observed for pure PNIPAM hydrogels prepared under similar conditions. The equilibrium swelling degree of the PNIPAM/CMC hydrogels (5200%) is much larger than that of the pure PNIPAM hydrogels (2500%). The water retention of PNIPAM/CMC hydrogels above the volume phase transition temperature is strongly reduced compared to that of pure PNIPAM hydrogel. Both PNIPAM/Fe₃O₄ and PNIPAM/CMC/Fe₃O₄ hydrogels exhibit a superparamagnetic behavior, but the blocking temperature (104 K) of the former is higher than that of the latter (83 K). Full article

(This article belongs to the Special Issue Stimuli-Responsive Gels)

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3173 KiB

Open AccessArticle

Photo-Crosslinkable Colloids: From Fluid Structure and Dynamics of Spheres to Suspensions of Ellipsoids

by Avner P. Cohen, Maria Alesker, Andrew B. Schofield, David Zitoun and Eli Sloutskin

Gels 2016, 2(4), 29; https://0-doi-org.brum.beds.ac.uk/10.3390/gels2040029 - 16 Nov 2016

Cited by 4 | Viewed by 5496

Abstract

Recently-developed photo-crosslinkable PMMA (polymethylmethacrylate) colloidal spheres are a highly promising system for fundamental studies in colloidal physics and may have a wide range of future technological applications. We synthesize these colloids and characterize their size distribution. Their swelling in a density- and index- [...] Read more.

Recently-developed photo-crosslinkable PMMA (polymethylmethacrylate) colloidal spheres are a highly promising system for fundamental studies in colloidal physics and may have a wide range of future technological applications. We synthesize these colloids and characterize their size distribution. Their swelling in a density- and index- matching organic solvent system is demonstrated and we employ dynamic light scattering (DLS), as also the recently-developed confocal differential dynamic microscopy (ConDDM), to characterize the structure and the dynamics of a fluid bulk suspension of such colloids at different particle densities, detecting significant particle charging effects. We stretch these photo-crosslinkable spheres into ellipsoids. The fact that the ellipsoids are cross-linked allows them to be fluorescently stained, permitting a dense suspension of ellipsoids, a simple model of fluid matter, to be imaged by direct confocal microscopy. Full article

(This article belongs to the Special Issue Colloid Chemistry)

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3372 KiB

Open AccessFeature PaperReview

Bioresponsive Hydrogels: Chemical Strategies and Perspectives in Tissue Engineering

by Antonella Sgambato, Laura Cipolla and Laura Russo

Gels 2016, 2(4), 28; https://0-doi-org.brum.beds.ac.uk/10.3390/gels2040028 - 14 Oct 2016

Cited by 32 | Viewed by 7610

Abstract

Disease, trauma, and aging account for a significant number of clinical disorders. Regenerative medicine is emerging as a very promising therapeutic option. The design and development of new cell-customised biomaterials able to mimic extracellular matrix (ECM) functionalities represents one of the major strategies [...] Read more.

Disease, trauma, and aging account for a significant number of clinical disorders. Regenerative medicine is emerging as a very promising therapeutic option. The design and development of new cell-customised biomaterials able to mimic extracellular matrix (ECM) functionalities represents one of the major strategies to control the cell fate and stimulate tissue regeneration. Recently, hydrogels have received a considerable interest for their use in the modulation and control of cell fate during the regeneration processes. Several synthetic bioresponsive hydrogels are being developed in order to facilitate cell-matrix and cell-cell interactions. In this review, new strategies and future perspectives of such synthetic cell microenvironments will be highlighted. Full article

(This article belongs to the Special Issue Hydrogels in Tissue Engineering)

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4392 KiB

Open AccessFeature PaperArticle

Supramolecular Self-Assembly of a Model Hydrogelator: Characterization of Fiber Formation and Morphology

by Yuan Gao, Ryan Nieuwendaal, Emilios K. Dimitriadis, Boualem Hammouda, Jack F. Douglas, Bing Xu and Ferenc Horkay

Gels 2016, 2(4), 27; https://0-doi-org.brum.beds.ac.uk/10.3390/gels2040027 - 08 Oct 2016

Cited by 8 | Viewed by 6305

Abstract

Hydrogels are of intense recent interest in connection with biomedical applications ranging from 3-D cell cultures and stem cell differentiation to regenerative medicine, controlled drug delivery, and tissue engineering. This prototypical form of soft matter has many emerging material science applications outside the [...] Read more.

Hydrogels are of intense recent interest in connection with biomedical applications ranging from 3-D cell cultures and stem cell differentiation to regenerative medicine, controlled drug delivery, and tissue engineering. This prototypical form of soft matter has many emerging material science applications outside the medical field. The physical processes underlying this type of solidification are incompletely understood, and this limits design efforts aimed at optimizing these materials for applications. We address this general problem by applying multiple techniques (e.g., NMR, dynamic light scattering, small angle neutron scattering, rheological measurements) to the case of a peptide derivative hydrogelator (molecule 1, NapFFKYp) over a broad range of concentration and temperature to characterize both the formation of individual nanofibers and the fiber network. We believe that a better understanding of the hierarchical self-assembly process and control over the final morphology of this kind of material should have broad significance for biological and medicinal applications utilizing hydrogels. Full article

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9913 KiB

Open AccessTechnical Note

A Continuous Extraction and Pumpless Supercritical CO₂ Drying System for Laboratory-Scale Aerogel Production

by István Lázár and István Fábián

Gels 2016, 2(4), 26; https://0-doi-org.brum.beds.ac.uk/10.3390/gels2040026 - 01 Oct 2016

Cited by 44 | Viewed by 10525

Abstract

Production of aerogels starts with solution chemistry and may end with supercritical carbon dioxide drying, which both require a specialized system. Here we present a complete aerogel production system that was developed and used in our laboratory over the last nine years. Our [...] Read more.

Production of aerogels starts with solution chemistry and may end with supercritical carbon dioxide drying, which both require a specialized system. Here we present a complete aerogel production system that was developed and used in our laboratory over the last nine years. Our aim was to develop a supercritical dryer and a protocol, whereby the CO₂ pump can be left out, and the entire flow system is operated by the pressure of the CO₂ cylinder. Drying pressure and temperature are controlled by the combination of the filling and heating temperatures. A continuous-mode solvent exchange system has also been developed, in which the solvent consumption during the process can be reduced to one-third of the batch method. In the new medium temperature 1.5 L volume supercritical dryer, the temperature is set to a constant 80–82 °C, and the pressure can be in the 90–200 bar range, depending on the conditions. We have performed approximately 200 dryings thus far, and prepared a wide range of monolithic aerogels, from pristine silica aerogels to polysaccharides and collagen. In this paper, we have summarized not only the technical details, but also the work experiences, as well as advantages and disadvantages of the systems. Full article

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1947 KiB

Open AccessFeature PaperCommunication

Carbamate-Based Bolaamphiphile as Low-Molecular-Weight Hydrogelators

by Laurent Latxague, Alexandra Gaubert, David Maleville, Julie Baillet, Michael A. Ramin and Philippe Barthélémy

Gels 2016, 2(4), 25; https://0-doi-org.brum.beds.ac.uk/10.3390/gels2040025 - 28 Sep 2016

Cited by 18 | Viewed by 5706

Abstract

A new bolaamphiphile analog featuring carbamate moieties was synthesized in six steps starting from thymidine. The amphiphile structure exhibits nucleoside-sugar polar heads attached to a hydrophobic spacer via carbamate (urethane) functions. This molecular structure, which possesses additional H-bonding capabilities, induces the stabilization of [...] Read more.

A new bolaamphiphile analog featuring carbamate moieties was synthesized in six steps starting from thymidine. The amphiphile structure exhibits nucleoside-sugar polar heads attached to a hydrophobic spacer via carbamate (urethane) functions. This molecular structure, which possesses additional H-bonding capabilities, induces the stabilization of low-molecular-weight gels (LMWGs) in water. The rheological studies revealed that the new bolaamphiphile 7 stabilizes thixotropic hydrogels with a high elastic modulus (G′ > 50 kPa). Full article

(This article belongs to the Special Issue Colloid Chemistry)

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2724 KiB

Open AccessArticle

Polyelectrolyte Hydrogel Platforms for the Delivery of Antidepressant Drugs

by Mario Casolaro and Ilaria Casolaro

Gels 2016, 2(4), 24; https://0-doi-org.brum.beds.ac.uk/10.3390/gels2040024 - 27 Sep 2016

Cited by 13 | Viewed by 7446

Abstract

Some vinyl hydrogels containing α-amino acid residues (l-phenylalanine, l-valine) were used as polyelectrolyte platforms for the evaluation of the controlled release of two antidepressants (paroxetine and duloxetine). The closer acidity constant (pKa) values of the two drugs show a closer [...] Read more.

Some vinyl hydrogels containing α-amino acid residues (l-phenylalanine, l-valine) were used as polyelectrolyte platforms for the evaluation of the controlled release of two antidepressants (paroxetine and duloxetine). The closer acidity constant (pKa) values of the two drugs show a closer release profile in physiological phosphate buffered saline (PBS) buffer (pH 7.40) and for long periods of time. The great electrostatic interaction forces between the COO⁻ group of the hydrogel and the protonated secondary amino nitrogen of the drug are the main factor improving the release kinetics; this release was found to be slower compared to that of two structurally related drugs bearing the tertiary amino nitrogen atom (citalopram and trazodone). Moreover, at the lower value of pH 4.60, paroxetine showed a flatter release profile from the hydrogel containing the l-phenylalanine residues that, after six days, is half of that shown by duloxetine. Further effects due to steric and hydrophobic interactions may contribute to the different release profile. A further stimulation with alternating magnetic fields (AMF) of low frequency (20 kHz/50 W) enhanced the release of the drug at pH 7.40 from the hydrogel containing magnetic nanoparticles. Both AMF and PBS solution at pH 7.40 were used to trigger the ‘on-demand’ pulsatile paroxetine release from the nanocomposite hydrogel. Full article

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Gels, Volume 2, Issue 4 (December 2016) – 7 articles

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