Cover Picture: UV‐Light‐Induced Swelling and Visible‐Light‐Induced Shrinking of a TiO2‐Containing Redox Gel (Adv. Mater. 9/2007)

Polyacrylate gels containing Ag⁺ and TiO₂ nanoparticles are shown to swell under UV light and shrink under visible light in water. In work reported by Tetsu Tatsuma and co‐workers on p. 1249, the TiO₂ absorbs UV light and reduces the Ag⁺, whereas the deposited Ag absorbs visible light and dissolves itself. These redox reactions change the interactions between the polymer chains and eventually the volume of the gel, as shown on the cover.     

High Mechanical Strength Double‐Network Hydrogel with Bacterial Cellulose

Double‐network (DN) hydrogels with high mechanical strength have been synthesized using the natural polymers bacterial cellulose (BC) and gelatin. As‐prepared BC contains 90 % water that can easily be squeezed out, with no more recovery in its swelling property. Gelatin gel is brittle and is easily broken into fragments under a modest compression. In contrast, the fracture strength and elastic modulus of a BC–gelatin DN gel under compressive stress are on the order of megapascals, which are several orders of magnitude higher than those of gelatin gel, and almost equivalent to those of articular cartilage. A similar enhancement in the mechanical strength was also observed for the combination of BC with polysaccharides, such as sodium alginate, gellan gum, and ι‐carrageenan.     

Inside Front Cover: Direct Printing of 3D and Curvilinear Micrometer‐Sized Architectures into Solid Substrates with Sub‐micrometer Resolution (Adv. Mater. 15/2006)

The inside cover shows a hexagonal array of convex microlenses etched directly into glass using a reaction‐diffusion process initiated from a hydrogel stamp. The technique, reported by Grzybowski and co‐workers on p. 2004, allows for direct printing of complex microarchitectures into a variety of materials with sub‐micrometer resolution. The images were generated by longtime exposure of slowly rotating patterns. Cover design by Christopher J. Campbell.     

PH敏感性水凝胶的分子热力学模型

本工作是在非离子凝胶的分子热力学模型基础，引入Ｄｏｎｎａｎ平衡项和大分子离子链的静电排斥项对凝胶自由能的贡献，建立了一个新的离子凝胶的分子热力学模型。该模型在解释离子凝胶的ＰＨ敏感性及其各种影响因素，以及预测ＰＨ溶胀曲线方面都取得了较好的效果。     

Injectable hydrogels of poly(?-caprolactone-co-glycolide)-poly(ethylene glycol)-poly(?-caprolactone-co-glycolide) triblock copolymer aqueous solutions

Thermogelling triblock copolymers of poly(?-caprolactone-co-glycolide)-poly(ethylene glycol)-poly(?-caprolactone-co-glycolide) [P(CL-GA)-PEG-P(CL-GA)] were successfully prepared by control of the hydrophilicity/hydrophobicity balance and chemical compositions of the copolymers. The aqueous solutions of the copolymers underwent sol-gel transition as the temperature was increased from 20 to 60 °C. The amphiphilic copolymer formed micelles in water and a gel was formed by aggregation of micelles. The structure parameters played a critical role in determining sol-gel transition behavior. Either increasing [GA]/[CL] ratio or decreasing P(CL-GA) block length could induce the increase of the lower sol-gel transition temperature. Glycolide (GA) was incorporated into the polymer chain to increase the polymer degradation rate. Sustained release of rifampicin for approximately 32 days was obtained from the gel. It is believed to have potential applications in drug delivery and tissue engineering.     

Swelling and mechanical properties of superporous hydrogels of poly(acrylamide-co-acrylic acid)/polyethylenimine interpenetrating polymer networks

Swelling and mechanical properties were investigated for superporous hydrogels (SPHs) of poly(acrylamide-co-acrylic acid)/polyethylenimine (P(AM-co-AA)/PEI) interpenetrating polymer networks (IPNs). Gelation kinetics of SPHs changed significantly according to the acidic condition of reactant. The compressive strength of neutralized SPHs decreased monotonically with AA concentration, while the maximum swelling was observed around the AA weight fraction of 0.4 for all PEI concentrations. The SPH samples composed of high concentrations of AA and PEI were easily cracked in water due to the swelling stress developed during water uptake. The swelling kinetics decreased with increasing PEI and PAA concentrations because of the high molecular entanglement and network density associated with ionic interaction between PAA and PEI molecules. For non-neutralized SPHs, the equilibrium water uptake decreased but the compressive strength increased with PEI and PAA concentrations by simple plasticization effect.