Gels | December 2015 - Browse Articles

23 pages, 2845 KiB

Open AccessFeature PaperArticle

On the Road to Biopolymer Aerogels—Dealing with the Solvent

by Raman Subrahmanyam, Pavel Gurikov, Paul Dieringer, Miaotian Sun and Irina Smirnova

Gels 2015, 1(2), 291-313; https://doi.org/10.3390/gels1020291 (registering DOI) - 21 Dec 2015

Cited by 112 | Viewed by 13829 | Correction

Aerogels are three-dimensional ultra-light porous structures whose characteristics make them exciting candidates for research, development and commercialization leading to a broad scope of applications ranging from insulation and catalysis to regenerative medicine and pharmaceuticals. Biopolymers have recently entered the aerogel foray. In order [...] Read more.

Aerogels are three-dimensional ultra-light porous structures whose characteristics make them exciting candidates for research, development and commercialization leading to a broad scope of applications ranging from insulation and catalysis to regenerative medicine and pharmaceuticals. Biopolymers have recently entered the aerogel foray. In order to fully realize their potential, progressive strategies dealing with production times and costs reduction must be put in place to facilitate the scale up of aerogel production from lab to commercial scale. The necessity of studying solvent/matrix interactions during solvent exchange and supercritical CO₂ drying is presented in this study using calcium alginate as a model system. Four frameworks, namely (a) solvent selection methodology based on solvent/polymer interaction; (b) concentration gradient influence during solvent exchange; (c) solvent exchange kinetics based on pseudo second order model; and (d) minimum solvent concentration requirements for supercritical CO₂ drying, are suggested that could help assess the role of the solvent in biopolymer aerogel production. Full article

(This article belongs to the Special Issue Aerogels)

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15 pages, 4123 KiB

Open AccessArticle

On the Size Effect of Gelation Kinetics in RF Aerogels

by Lorenz Ratke and Anna Hajduk

Gels 2015, 1(2), 276-290; https://doi.org/10.3390/gels1020276 - 10 Dec 2015

Cited by 8 | Viewed by 4852

Abstract

We experimentally and theoretically investigate the size effect of gelation using Resorcinol-Formaldehyde aerogels. We find a clear dependence of gelation time on the sample size under mild shear conditions. We developed a theoretical model based on Smoluchowski’s aggregation model adding, however, a growth [...] Read more.

We experimentally and theoretically investigate the size effect of gelation using Resorcinol-Formaldehyde aerogels. We find a clear dependence of gelation time on the sample size under mild shear conditions. We developed a theoretical model based on Smoluchowski’s aggregation model adding, however, a growth term which accounts for the continuous growth of the colloidal particles while clustering happens. The model is solved analytically and agrees with our experimental observations for base catalyzed RF-gels. Full article

(This article belongs to the Special Issue Aerogels)

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20 pages, 1039 KiB

Open AccessFeature PaperReview

Mechanical Properties and Brittle Behavior of Silica Aerogels

by Thierry Woignier, Juan Primera, Adil Alaoui, Pascal Etienne, Florence Despestis and Sylvie Calas-Etienne

Gels 2015, 1(2), 256-275; https://doi.org/10.3390/gels1020256 - 10 Dec 2015

Cited by 83 | Viewed by 13948

Abstract

Sets of silica gels: aerogels, xerogels and sintered aerogels, have been studied in the objective to understand the mechanical behavior of these highly porous solids. The mechanical behaviour of gels is described in terms of elastic and brittle materials, like glasses or ceramics. [...] Read more.

Sets of silica gels: aerogels, xerogels and sintered aerogels, have been studied in the objective to understand the mechanical behavior of these highly porous solids. The mechanical behaviour of gels is described in terms of elastic and brittle materials, like glasses or ceramics. The magnitude of the elastic and rupture modulus is several orders of magnitude lower compared to dense glass. The mechanical behaviours (elastic and brittle) are related to the same kinds of gel characteristics: pore volume, silanol content and pore size. Elastic modulus depends strongly on the volume fraction of pores and on the condensation reaction between silanols. Concerning the brittleness features: rupture modulus and toughness, it is shown that pores size plays an important role. Pores can be considered as flaws in the terms of fracture mechanics and the flaw size is related to the pore size. Weibull’s theory is used to show the statistical nature of flaw. Moreover, stress corrosion behaviour is studied as a function of environmental conditions (water and alcoholic atmosphere) and temperature. Full article

(This article belongs to the Special Issue Aerogels)

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21 pages, 3123 KiB

Open AccessArticle

Precise Control over the Rheological Behavior of Associating Stimuli-Responsive Block Copolymer Gels

by Jérémy Brassinne, Flanco Zhuge, Charles-André Fustin and Jean-François Gohy

Gels 2015, 1(2), 235-255; https://doi.org/10.3390/gels1020235 - 7 Dec 2015

Cited by 13 | Viewed by 7282

Abstract

“Smart” materials have considerably evolved over the last few years for specific applications. They rely on intelligent macromolecules or (supra-)molecular motifs to adapt their structure and properties in response to external triggers. Here, a supramolecular stimuli-responsive polymer gel is constructed from heterotelechelic double [...] Read more.

“Smart” materials have considerably evolved over the last few years for specific applications. They rely on intelligent macromolecules or (supra-)molecular motifs to adapt their structure and properties in response to external triggers. Here, a supramolecular stimuli-responsive polymer gel is constructed from heterotelechelic double hydrophilic block copolymers that incorporate thermo-responsive sequences. These macromolecular building units are synthesized via a three-step controlled radical copolymerization and then hierarchically assembled to yield coordination micellar hydrogels. The dynamic mechanical properties of this particular class of materials are studied in shear flow and finely tuned via temperature changes. Notably, rheological experiments show that structurally reinforcing the micellar network nodes leads to precise tuning of the viscoelastic response and yield behavior of the material. Hence, they constitute promising candidates for specific applications, such as mechano-sensors. Full article

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

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16 pages, 4303 KiB

Open AccessArticle

Swelling Dynamics of a DNA-Polymer Hybrid Hydrogel Prepared Using Polyethylene Glycol as a Porogen

by Ming Gao, Kamila Gawel and Bjørn Torger Stokke

Gels 2015, 1(2), 219-234; https://doi.org/10.3390/gels1020219 - 18 Nov 2015

Cited by 9 | Viewed by 9966

Abstract

DNA-polyacrylamide hybrid hydrogels designed with covalent and double-stranded (dsDNA) crosslinks respond to specific single-stranded DNA (ssDNA) probes by adapting new equilibrium swelling volume. The ssDNA probes need to be designed with a base pair sequence that is complementary to one of the strands [...] Read more.

DNA-polyacrylamide hybrid hydrogels designed with covalent and double-stranded (dsDNA) crosslinks respond to specific single-stranded DNA (ssDNA) probes by adapting new equilibrium swelling volume. The ssDNA probes need to be designed with a base pair sequence that is complementary to one of the strands in a dsDNA supported network junction. This work focuses on tuning the hydrogel swelling kinetics by introducing polyethylene glycol (PEG) as a pore-forming agent. Adding PEG during the preparation of hydrogels, followed by removal after polymerization, has been shown to improve the swelling dynamics of DNA hybrid hydrogels upon specific ssDNA probe recognition. The presence of porogen did not influence the kinetics of osmotic pressure-driven (2-acrylamido-2-methylpropane sulfonic acid)-co-acrylamide (AMPSA-co-AAm) hydrogels’ swelling, which is in contrast to the DNA-sensitive hydrogels. The difference in the effect of using PEG as a porogen in these two cases is discussed in view of processes leading to the swelling of the gels. Full article

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

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25 pages, 877 KiB

Open AccessReview

Grafting Techniques towards Production of Peptide-Tethered Hydrogels, a Novel Class of Materials with Biomedical Interest

by Mariana Barbosa, M. Cristina L. Martins and Paula Gomes

Gels 2015, 1(2), 194-218; https://doi.org/10.3390/gels1020194 - 21 Oct 2015

Cited by 17 | Viewed by 7813

Abstract

In recent years, new highly functional polymeric biomaterials are being developed to increase the therapeutic efficacy in tissue regeneration approaches. Peptides regulate most physiological processes and display several other biological activities. Therefore, their importance in the field of biomedical research and drug development [...] Read more.

In recent years, new highly functional polymeric biomaterials are being developed to increase the therapeutic efficacy in tissue regeneration approaches. Peptides regulate most physiological processes and display several other biological activities. Therefore, their importance in the field of biomedical research and drug development is rapidly increasing. However, the use of peptides as therapeutic agents is restricted by some of their physicochemical properties. The development of improved routes of delivery of peptide-based therapeutics is crucial and is crucial and its biomedical value is expected to increase in the near future. The unique properties of hydrogels triggered their spreading as localized drug depots. Several strategies, such as the carbodiimide chemistry, have been used to successfully immobilize bioactive peptide sequences into the hydrogels backbone. Peptide tethering through the so-called “click” chemistry reactions is also a highly promising, yet underexplored, approach to the synthesis of hydrogels with varying dimensions and patterns. The present review focus on the approaches that are being used for the establishment of chemical bonds between peptides and non-peptidic hydrogels throughout the last decade. Full article

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15 pages, 3484 KiB

Open AccessArticle

Biosynthesis and Characterization of Cross-Linked Fmoc Peptide-Based Hydrogels for Drug Delivery Applications

by Laura Chronopoulou, Silvia Margheritelli, Yosra Toumia, Gaio Paradossi, Federico Bordi, Simona Sennato and Cleofe Palocci

Gels 2015, 1(2), 179-193; https://doi.org/10.3390/gels1020179 - 16 Oct 2015

Cited by 25 | Viewed by 8857

Abstract

Recently, scientific and technological interest in the synthesis of novel peptide-based hydrogel materials have grown dramatically. Applications of such materials mostly concern the biomedical field with examples covering sectors such as drug delivery, tissue engineering, and production of scaffolds for cell growth, thanks [...] Read more.

Recently, scientific and technological interest in the synthesis of novel peptide-based hydrogel materials have grown dramatically. Applications of such materials mostly concern the biomedical field with examples covering sectors such as drug delivery, tissue engineering, and production of scaffolds for cell growth, thanks to their biocompatibility and biodegradability. In this work we synthesized Fmoc-Phe₃ based hydrogels of different chirality by using a biocatalytic approach. Moreover, we investigated the possibility of employing a crosslinker during the biosynthetic process and we studied and compared some chemico-physical features of both crosslinked and non-crosslinked hydrogels. In particular, we investigated the rheological properties of such materials, as well as their swelling ability, stability in aqueous medium, and their structure by SEM and AFM analysis. Crosslinked and non-crosslinked hydrogels could be formed by this procedure with comparable yields but distinct chemico-physical features. We entrapped dexamethasone within nanopolymeric particles based on PLGA coated or not with chitosan and we embedded these nanoparticles into the hydrogels. Dexamethasone release from such a nanopolymer/hydrogel system was controlled and sustained and dependent on genipin crosslinking degree. The possibility of efficiently coupling a drug delivery system to hydrogel materials seem particularly promising for tissue engineering applications, where the hydrogel could provide cells the necessary support for their growth, while nanoparticles could favor cell growth or differentiation by providing them the necessary bioactive molecules. Full article

(This article belongs to the Special Issue Nanoparticle-Hydrogel Composites for Biomedical Applications)

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17 pages, 1959 KiB

Open AccessReview

Nanoparticle-Integrated Hydrogels as Multifunctional Composite Materials for Biomedical Applications

by Marco Biondi, Assunta Borzacchiello, Laura Mayol and Luigi Ambrosio

Gels 2015, 1(2), 162-178; https://doi.org/10.3390/gels1020162 - 14 Oct 2015

Cited by 116 | Viewed by 13977

Abstract

This review focuses on the most recent developments in the field of nanocomposite hydrogels intended for biomedical applications. Nanocomposite hydrogels are hydrated polymeric networks with a physically or covalently crosslinked three-dimensional (3D) structure swollen with water, in the presence of nanoparticles or nanostructures. [...] Read more.

This review focuses on the most recent developments in the field of nanocomposite hydrogels intended for biomedical applications. Nanocomposite hydrogels are hydrated polymeric networks with a physically or covalently crosslinked three-dimensional (3D) structure swollen with water, in the presence of nanoparticles or nanostructures. A wide array of nanomaterials (polymeric, carbon-based, metallic, ceramic) can be incorporated within the hydrogel network to obtain reinforced nanocomposite hydrogels. Nanocomposites represent a new class of materials with properties absent in the individual components. In particular, the incorporation of nanomaterials within a polymeric hydrogel network is an attractive approach to tailor the mechanical properties of the hydrogels and/or to provide the nanocomposite with responsiveness to external stimuli. Full article

(This article belongs to the Special Issue Nanoparticle-Hydrogel Composites for Biomedical Applications)

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27 pages, 7995 KiB

Open AccessReview

Magnetic Gel Composites for Hyperthermia Cancer Therapy

by Marleen Häring, Jana Schiller, Judith Mayr, Santiago Grijalvo, Ramon Eritja and David Díaz Díaz

Gels 2015, 1(2), 135-161; https://doi.org/10.3390/gels1020135 - 30 Sep 2015

Cited by 57 | Viewed by 16729

Abstract

Hyperthermia therapy is a medical treatment based on the exposition of body tissue to slightly higher temperatures than physiological (i.e., between 41 and 46 °C) to damage and kill cancer cells or to make them more susceptible to the effects of [...] Read more.

Hyperthermia therapy is a medical treatment based on the exposition of body tissue to slightly higher temperatures than physiological (i.e., between 41 and 46 °C) to damage and kill cancer cells or to make them more susceptible to the effects of radiation and anti-cancer drugs. Among several methods suitable for heating tumor areas, magnetic hyperthermia involves the introduction of magnetic micro/nanoparticles into the tumor tissue, followed by the application of an external magnetic field at fixed frequency and amplitude. A very interesting approach for magnetic hyperthermia is the use of biocompatible thermo-responsive magnetic gels made by the incorporation of the magnetic particles into cross-linked polymer gels. Mainly because of the hysteresis loss from the magnetic particles subjected to a magnetic field, the temperature of the system goes up and, once the temperature crosses the lower critical solution temperature, thermo-responsive gels undergo large volume changes and may deliver anti-cancer drug molecules that have been previously entrapped in their networks. This tutorial review describes the main properties and formulations of magnetic gel composites conceived for magnetic hyperthermia therapy. Full article

(This article belongs to the Special Issue Nanoparticle-Hydrogel Composites for Biomedical Applications)

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Gels, Volume 1, Issue 2 (December 2015) – 9 articles , Pages 135-313

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