pH值对壳聚糖/羧甲基壳聚糖水凝胶溶胀行为的影响

利用壳聚糖与羧甲基壳聚糖制备了一系列新型的水凝胶，研究了pH值对水凝胶溶胀度、微观结构和基团结构的影响．结果表明，壳聚糖与羧甲基壳聚糖水凝胶的溶胀行为和微观结构均表现出pH值敏感性，但随着羧基的引入，水凝胶的最低溶胀度从pH7．O移向pH3．O．红外光谱证明，水凝胶的pH敏感行为是由基团结构的变化引起的．     

Electric‐field‐controlled synthesis of HPMA hydrogels containing self‐organized arrays of micro‐channels

We report the synthesis of poly N‐(2‐hydroxypropyl)methacrylamide ordered arrays of fluid filled channels. The polymerization and crosslinking reactions are carried out under the influence of a constant electric field (60 V/cm). A charged comonomer, immobiline (pK 3.6), and porogen, polyethylene glycol (PEG) are added to the pregel solutions. Scanning electron microscopy reveals that the channels have a typical diameter of 2–25 μm and are oriented parallel to the electric field employed during synthesis. The self‐organization of channels occurs around an optimal PEG concentration of 8.6 wt/vol %, whereas significantly higher or lower concentrations yield random, isotropic pore structures. Moreover, tensile strength measurements show that the mechanical stability increases with decreasing concentration of PEG. Rheology experiments reveal that the swelling degree of these superabsorbant hydrogels increases with increasing PEG. Possible applications of these microstructured hydrogels as bidirectional scaffolds for regenerating neurons in the injured spinal cord are discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2593–2600, 2007     

Nanoporous Nanocomposite Hydrogels Composed of Polyvinyl Alcohol and Na-montmorillonite

Polyvinyl alcohol nanoporous nanocomposite hydrogels containing various levels of Na-montmorillonite were prepared by a cyclic freezing–thawing technique. An exfoliated morphology of silicate layers was observed for the nanocomposite hydrogels. The uniaxial tensile test indicated that the tensile modulus and tensile strength of the nanocomposite hydrogels increased with increasing Na-montmorillonite content, while their elongation-at-break values decreased. The results showed that by adding 15 wt% of montmorillonite to polyvinyl alcohol hydrogels, the molecular weight of polymer chains between two adjacent cross-links decreased to 56% and the effective cross-linking density increased up to 353%. It is also indicated that all nanocomposite hydrogel samples had nanoscale pore diameters and network mesh sizes less than 30 nm. The nanoporous structure of the nanocomposite hydrogels was confirmed by transmission electron microscopy observations and mercury intrusion porosimetry tests.     

Gelation and Swelling Behavior of Semi-Interpenetrating Polymer Network Hydrogels Based on Polyacrylamide and Poly(vinyl alcohol)

Novel semi-Interpenetrating Polymer Network (semi-IPN) hydrogels based on partially Hydrolyzed Polyacrylamide (HPAM) and Poly(Vinyl Alcohol) (PVA) were prepared by solution crosslinking using chromium triacetate. Effects of PVA content on the gelation process and swelling behavior in tap water and different electrolyte solutions were investigated. Study of the gelation behavior using dynamic rheometery showed that the limiting storage modulus of the semi-IPN gels decreased with increasing PVA content. It was also found that increasing the PVA content increases the loss factor, indicating that the viscous properties of this gelling system increase more strongly than the elastic properties. The swelling ratio of the semi-IPN gels in tap water decreased as the concentration of the PVA increased. However, the semi-IPN gels showed lower salt sensitivity factor in synthetic oil reservoir water as compared with HPAM gels. Therefore, they are potentially good candidates for enhanced oil recovery applications.     

Swelling and Gelation Time Behavior of Sulfonated Polyacrylamide/Chromium Triacetate Hydrogels

A hydrogel was prepared by crosslinking of aqueous solutions of sulfonated polyacrylamide/chromium triacetate for use in water shut-off operations in oil reservoirs. The effects of pH, salinity, retarder and temperature, as well as co-polymer and crosslinker concentration, on the gelation time were investigated. The results indicated that as temperature increased, gelation occurred more rapidly. The activation energy was measured as about 86 kJ/mol. The effects of initial pH and retarder on the gelation time were also examined. The results showed that addition of retarder and increasing of pH increased and decreased the gelation time, respectively. The increase of co-polymer concentration in solution increased the gel swelling. However, the increase of crosslinker concentration decreased the gel swelling. In the presence of electrolytes, the gel swelling decreased by about 80%. Finally, some usable practical recommendations are offered for the gelling systems in reservoirs.     

Fabrication and characterization of low-cost freeze-gelated chitosan/collagen/hydroxyapatite hydrogel nanocomposite scaffold

In the present research, chitosan/collagen and chitosan/collagen/nano-hydroxyapatite (nHAP) hydrogel nanocomposites were prepared using naturally extracted chitosan from Persian Gulf shrimp wastes and rat tail-tendon collagen. Freeze-gelation method was used to prepare highly porous scaffolds. The morphology, chemical structure, water retainability, and thermal properties were characterized using SEM, FTIR, water content experiment, simultaneous thermal analysis (STA), respectively. Atomic force microscopy (AFM) nanoindentation and unconfined compression test were used to assess different feature of the mechanical properties of the hydrogels. The obtained results were so promising that the prepared nanocomposites can be considered as a potential candidate for cartilage tissue engineering.     

Hybrid cross‐linked hydrogels as a technology platform for in vitro release of cephradine

Hydrogel‐based drug delivery systems can leverage therapeutically favorable upshots of drug release and found clinical uses. Hydrogels offer temporal and spatial control over the release of different therapeutic agents. Because of their tailor made controllable degradability, physical properties, and ability to prevent the labile drugs from degradation, hydrogels provide platform on which diverse physicochemical interactions with entrapped drugs cause to control drug release. Herein, we report the fabrication of novel vinyltrimethoxy silane (VTMS) cross‐linked chitosan/polyvinyl pyrrolidone hydrogels. Swelling in distilled water in conjunction with different buffer and electrolyte solutions was performed to assess the swellability of hydrogels. Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and X‐ray diffraction (XRD) analysis were further conducted to investigate the possible interactions between components, thermal stability, and crystallinity of as‐prepared hybrid hydrogels, respectively. In vitro time‐dependent biodegradability, antimicrobial study, and cytotoxicity were also carried out to evaluate their extensive biocompatibility and cytotoxic behavior. More interestingly, in vitro drug release study allowed for the controlled release of cephradine. Therefore, this facile strategy developed the novel biocompatible and biodegradable hybrid hydrogels, which could significantly expand the scope of these hydrogels in other biomedical applications like scaffolds, skin regeneration, tissue engineering, etc.     

Characterization and optimization of a positively charged poly (ethylene glycol)diacrylate hydrogel as an actuating muscle tissue engineering scaffold

Hydrogels have been used for many applications in tissue engineering and regenerative medicine due to their versatile material properties and similarities to the native extracellular matrix. Poly (ethylene glycol) diacrylate (PEGDA) is an ionic electroactive polymer (EAP), a material that responds to an electric field with a change in size or shape while in an ionic solution, that may be used in the development of hydrogels. In this study, we have investigated a positively charged EAP that can bend without the need of external ions. PEGDA was modified with the positively charged molecule 2‐(methacryloyloxy)ethyl‐trimethylammonium chloride (MAETAC) to provide its own positive ions. This hydrogel was then characterized and optimized for bending and cellular biocompatibility with C2C12 mouse myoblast cells. Studies show that the polymer responds to an electric field and supports C2C12 viability.