Rapid-response hydrogels

Water-swelled polymers that quickly change their properties when triggered by the right stimulus, have been created. A hydrogel is a 3D cagelike polymer that is relatively sluggish in responding to the application or removal of stress, light, or a change in acidity. Using a novel design based on artificial protein polymers, a collaboration of scientists from the University of California, Santa Barbara, and the University of Delaware has now developed a hydrogel that can recover quickly after the removal of mechanical stress. The novel hydrogel contains two chemical building blocks: one that is highly charged and hydrophilic and another that is hydrophobic and has a special shape that causes the polymers to link and form a porous hydrogel at very low concentrations in solution. After the gels were shaken vigorously to break down their structure, they recovered 80% of their strength in a matter of seconds, even at 90°C. The rapid response and highly porous nature of the new hydrogel potentially opens up new biotechnological uses for the compound. Possibilities include an organic scaffolding to hold regenerating tissue within the body and a drug-delivery capsule to hold large proteins and release them when given the right stimulus. (A. P. Nowak et al., Nature 417, 424, 2002 http://dx.doi.org/10.1038/417424a .)