Reversible hydrogels from self-assembling artificial proteins.

Recombinant DNA methods were used to create artificial proteins that undergo reversible gelation in response to changes in pH or temperature. The proteins consist of terminal leucine zipper domains flanking a central, flexible, water-soluble polyelectrolyte segment. Formation of coiled-coil aggregates of the terminal domains in near-neutral aqueous solutions triggers formation of a three-dimensional polymer network, with the polyelectrolyte segment retaining solvent and preventing precipitation of the chain. Dissociation of the coiled-coil aggregates through elevation of pH or temperature causes dissolution of the gel and a return to the viscous behavior that is characteristic of polymer solutions. The mild conditions under which gel formation can be controlled (near-neutral pH and near-ambient temperature) suggest that these materials have potential in bioengineering applications requiring encapsulation or controlled release of molecular and cellular species.