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Hydrogel Networks (hydrogel + network)
Selected AbstractsControllable Soluble Protein Concentration Gradients in Hydrogel Networks,ADVANCED FUNCTIONAL MATERIALS, Issue 21 2008Brian J. Peret Abstract Here, controlled formation of sustained, soluble protein concentration gradients within hydrated polymer networks is reported. The approach involves spatially localizing proteins or biodegradable, protein-loaded microspheres within hydrogels to form a protein-releasing "depot." Soluble protein concentration gradients are then formed as the released protein diffuses away from the localized source. Control over key gradient parameters, including maximum concentration, gradient magnitude, slope, and time dynamics, is achieved by controlling the release of protein from the depot and subsequent transport through the hydrogel. Results demonstrate a direct relationship between the amount of protein released from the depot and the source concentration, gradient magnitude, and slope of the concentration gradient. In addition, an inverse relationship exists between the diffusion coefficient of protein within the hydrogel and the slope of the concentration gradient. The time dynamics of the concentration gradient profile can be directly correlated to protein release from the localized source, providing a mechanism for temporarily controlling gradient characteristics. Therefore, each key biologically relevant parameter associated with the protein concentration gradient can be controlled by defining protein release and diffusion. It is anticipated that the resulting materials may be useful in 3D cell culture systems, and in emerging tissue engineering approaches that aim to regenerate complex, functional tissues. [source] Dynamically Restructuring Hydrogel Networks Formed with Reversible Covalent Crosslinks,ADVANCED MATERIALS, Issue 18 2007C. Roberts Dynamically restructuring hydrogel networks are formed from two water-soluble polymers by functionalization with phenylboronic acid (PBA) and salicylhydroxamic acid (SHA) moieties that interact through pH-sensitive and reversible covalent crosslinks (see figure). The networks can be tuned to display a wide range of pH-responsive properties, which can potentially be exploited for drug delivery systems in biological environments where similar acidic changes occur. [source] Fabrication of Silver Nanoparticles in Hydrogel Networks,MACROMOLECULAR RAPID COMMUNICATIONS, Issue 16 2006Y. Murali Mohan Abstract Summary: This paper describes a simple and facile approach to fabricate well dispersed silver nanoparticles (AgNPs) in poly[N -isopropylacrylamide- co -(sodium acrylate)] hydrogels. The silver nanoparticles formed are spherical in shape with a narrow size distribution in the hydrogel networks in which the nanoparticles are stabilized by the polymer network. Uniformly dispersed silver nanoparticles were obtained with poly[N -isopropylacrylamide- co -[sodium acrylate)] hydrogels, whereas a poly(N -isopropylacrylamide)/poly(sodium acrylate) IPN gel showed aggregated nanoparticles. It is demonstrated that the hydrogel network structure determines the size and shape of the nanoparticles. These particles are more stable in the gel networks compared to other reduction methods. The hydrogel/silver nanohybrids were well characterized by XRD, UV-vis spectrometry, scanning electron microscopy and transmission electron microscopy. Schematic representation of the preparation of Ag nanoparticles in hydrogel networks. [source] Photopolymerizable Hydrogels Made from Polymer-Conjugated Albumin for Affinity-Based Drug Delivery,ADVANCED ENGINEERING MATERIALS, Issue 1-2 2010Liat Oss-Ronen As a drug delivery vehicle, biodegradable albumin hydrogels can combine the high binding capacity of albumin with the structural stability of a polymeric hydrogel network to enable controlled release of small molecules based on both binding affinity and physical interactions. In the present study, we report on the development of a hybrid hydrogel composed of albumin conjugated to poly(ethylene glycol) (PEG) for drug delivery applications where controlled release is accomplished using the natural affinity of the drugs to the serum albumin. Bovine serum albumin was conjugated to PEG-diacrylate having a molecular weight of 1.5, 4, or 10,kDa to form a PEGylated albumin macromolecule (mono-PEGylated or multi-PEGylated). Biodegradable hydrogels were formed from the PEGylated albumin using photopolymerization. Two model drugs, Warfarin and Naproxen, were used for equilibrium dialysis and release experiments from the hydrogels, both having relatively low molecular weights and a known high affinity for albumin. Equilibrium dialysis experiments showed that multi-PEGylation of albumin significantly decreased the drug affinity to the protein compared to non-PEGylated controls, irrespective of the PEG molecular weight. However, the results from drug release experiments showed that mono-PEGylation of albumin did not change its natural affinity to the drug. Comparing the release profiles with a Fickian diffusion model provided strong evidence that hydrogels containing mono-PEGylated albumin exhibited sub-diffusive drug release properties based on the affinity of the drug to the tethered protein. [source] Controlling Affinity Binding with Peptide-Functionalized Poly(ethylene glycol) HydrogelsADVANCED FUNCTIONAL MATERIALS, Issue 14 2009Chien-Chi Lin Abstract Poly(ethylene glycol) (PEG) hydrogels functionalized with peptide moieties have been widely used in regenerative medicine applications. While many studies have suggested the importance of affinity binding within PEG hydrogels, the relationships between the structures of the peptide motifs and their binding to protein therapeutics remain largely unexplored, especially in the recently developed thiol-acrylate photopolymerization systems. Herein, Förster resonance energy transfer (FRET) and thiol-acrylate photopolymerizations are employed to investigate how the architectures of affinity peptides in crosslinked hydrogels affect their binding to diffusible proteins. The binding between diffusible streptavidin and biotinylated peptide immobilized to PEG hydrogel network was used as a model system to reveal the interplay between affinity binding and peptide sequences/architectures. In addition, peptides with different structures are designed to enhance affinity binding within PEG hydrogels and to provide tunable affinity-based controlled delivery of basic fibroblast growth factor (bFGF). This study demonstrates the importance of affinity binding in controlling the availability of hydrogel-encapsulated proteins and provides strategies for enhancing affinity binding of protein therapeutics to bound peptide moieties in thiol-acrylate photopolymerized PEG hydrogels. The results presented herein should be useful to the design and fabrication of hydrogels that retain and exhibit sustained release of growth factors for promoting tissue regeneration. [source] Dextran Microgels for Time-Controlled Delivery of siRNA,ADVANCED FUNCTIONAL MATERIALS, Issue 7 2008Koen Raemdonck Abstract To apply siRNA as a therapeutic agent, appropriate attention should be paid to the optimization of the siRNA gene silencing effect, both in terms of magnitude and duration. Intracellular time-controlled siRNA delivery could aid in tailoring the kinetics of siRNA gene knockdown. However, materials with easily tunable siRNA release properties have not been subjected to thorough investigation thus far. This report describes cationic biodegradable dextran microgels which can be loaded with siRNA posterior to gel formation. Even though the siRNAs are incorporated in the hydrogel network based on electrostatic interaction, still a time-controlled release can be achieved by varying the initial network density of the microgels. To demonstrate the biological functionality of the siRNA loaded gels, we studied their cellular internalization and enhanced green fluorescent protein (EGFP) gene silencing potential in HUH7 human hepatoma cells. [source] Synthesis of Polymerizable Superoxide Dismutase Mimetics to Reduce Reactive Oxygen Species Damage in Transplanted Biomedical Devices,ADVANCED FUNCTIONAL MATERIALS, Issue 20 2008Charles Y. Cheung Abstract A new polymerizable superoxide dismutase (SOD) mimetic metalloporphyrin macromer was synthesized to minimize inflammatory damage associated with tissue transplantation and biomaterial implantation, such as the use of encapsulated pancreatic islets for the treatment of type I diabetes mellitus (TIDM). This functional SOD mimetic, Mn(III) Tetrakis[1-(3-acryloxy-propyl)-4-pyridyl] porphyrin (MnTPPyP-Acryl), was copolymerized and crosslinked with poly(ethylene glycol) diacrylate (PEGDA) to form hydrogel networks that may actively reduce reactive oxygen species (ROS) damage associated with biomaterial implantation. Solution phase activity assays with MnTPPyP-Acryl macromers showed comparable SOD activity to MnTMPyP, a non-polymerizable commercially available SOD mimetic. This work also describes the development of a new, simple, and inexpensive solid phase assay system that was developed to assess the activity of MnTPPyP-Acryl macromers polymerized within PEGDA hydrogels, which has the potential to fulfill an existing void with the biochemical tools available for testing other immobilized ROS antagonists. With this new assay system, hydrogels containing up to 0.25,mol% MnTPPyP-Acryl showed significantly higher levels of SOD activity, whereas control hydrogels polymerized with inactive TPPyP-Acryl macromers showed only background levels of activity. The potential for repeated use of such hydrogel devices to consistently reduce superoxide anion concentrations was demonstrated upon retention of ,100% SOD activity for at least 72,h post-polymerization. These results demonstrate the potential that polymerizable SOD mimetics may have for integration into medical devices for the minimization of inflammatory damage upon transplantation, such as during the delivery of encapsulated pancreatic islets. [source] Bioinspired Design of Dynamic MaterialsADVANCED MATERIALS, Issue 23 2009Javeed Shaikh Mohammed Abstract An emerging approach for design of dynamic materials involves mimicking natural systems, which are adept at changing their structure and function in response to their environment. Biological systems possess a diverse range of dynamic mechanisms, including competitive ligand,protein binding, enzyme-catalyzed remodeling, and allosteric protein conformational changes. These dynamic mechanisms are now being exploited by materials scientists and engineers to design "bioinspired" synthetic materials that undergo responsive assembly and disassembly as well as dynamic volume and shape changes. The purpose of this review is to describe recent progress in design and development of bioinspired dynamic materials, with a particular emphasis on hydrogel networks. We specifically focus on emerging approaches that use biological phenomena as an inspiration for design of materials. [source] Dynamically Restructuring Hydrogel Networks Formed with Reversible Covalent Crosslinks,ADVANCED MATERIALS, Issue 18 2007C. Roberts Dynamically restructuring hydrogel networks are formed from two water-soluble polymers by functionalization with phenylboronic acid (PBA) and salicylhydroxamic acid (SHA) moieties that interact through pH-sensitive and reversible covalent crosslinks (see figure). The networks can be tuned to display a wide range of pH-responsive properties, which can potentially be exploited for drug delivery systems in biological environments where similar acidic changes occur. [source] Fabrication of Silver Nanoparticles in Hydrogel Networks,MACROMOLECULAR RAPID COMMUNICATIONS, Issue 16 2006Y. Murali Mohan Abstract Summary: This paper describes a simple and facile approach to fabricate well dispersed silver nanoparticles (AgNPs) in poly[N -isopropylacrylamide- co -(sodium acrylate)] hydrogels. The silver nanoparticles formed are spherical in shape with a narrow size distribution in the hydrogel networks in which the nanoparticles are stabilized by the polymer network. Uniformly dispersed silver nanoparticles were obtained with poly[N -isopropylacrylamide- co -[sodium acrylate)] hydrogels, whereas a poly(N -isopropylacrylamide)/poly(sodium acrylate) IPN gel showed aggregated nanoparticles. It is demonstrated that the hydrogel network structure determines the size and shape of the nanoparticles. These particles are more stable in the gel networks compared to other reduction methods. The hydrogel/silver nanohybrids were well characterized by XRD, UV-vis spectrometry, scanning electron microscopy and transmission electron microscopy. Schematic representation of the preparation of Ag nanoparticles in hydrogel networks. [source] In situ crosslinked hydrogels formed using Cu(I)-free Huisgen cycloaddition reactionPOLYMER INTERNATIONAL, Issue 10 2009Meredith Clark Abstract BACKGROUND: ,Click' chemistry, or the 1,3-dipolar cycloaddition of organic azides with alkynes, has been evaluated for many biomedical purposes; however, its utility in crosslinking hydrogels in situ is limited by the toxicity of the requisite copper(I) catalyst. We report the first use of catalyst-free Huisgen cycloaddition to generate crosslinked hydrogels under physiological conditions using multivalent azide-functionalized polymers and an electron-deficient dialkyne crosslinker. RESULTS: Water-soluble azide-functionalized polymers were crosslinked with an electron-deficient dialkyne crosslinker to form hydrogels at physiological temperature without the addition of copper(I) catalyst. Crosslinking was confirmed using scanning electron microscopy, Fourier transform infrared and 1H NMR analyses. Flow by vial inversion and dynamic rheological methodologies were implemented to evaluate gelation kinetics at 37 °C of variable polymer compositions, concentrations and stoichiometric ratios. Kinetic studies revealed gelation in as little as 12 h at 37 °C, although strong gels that withstand inversion were observed by 1,8 days. CONCLUSION: The ability to form hydrogel networks under mild conditions demonstrates the potential viability of the catalyst-free ,click' crosslinking chemistry for in situ gelling and other biological applications. Further chemical modifications in the crosslinking moieties, as well as polymer and crosslinker conformations, are expected to enhance gelation kinetics to a more biomedically practical rate. Copyright © 2009 Society of Chemical Industry [source] | ||||||||||||||||||||||