Ephemeral Gels: The Biological Example Applied to a New Type of Polymers

Abstract

In several biologicalprocesses, a solid gel phase due to both physical and chemical bonds isproduced which later dissolves. The relative influence of these two different kinds of links towards the gel properties were explored in a model system consisting of gelatin gels. Thermally reversible physical bonds, occurring with a coil to triple helix transition of gelatin chains, were obtained by cooling the protein solution. Covalent bonds were enzymatically catalyzed by a bacterial transglutaminase. Different temperature protocols were applied to gelatin solutions, with and without the enzyme, to vary the history of the gel so that different types of networks leading to various gel properties were obtained. Then, protease (thermolysin) and transglutaminase were considered as two antagonistic enzymes, one generating and the other cleaving covalent bonds. Alternate sol/gel and gel/sol transitions should occur within such a system, generating ephemeral gel phases. The various gels obtained were programmed to dissolve after a determined time, without any change in temperature or medium composition, and constitute a completely new type of material. Varying temperature, but also the ratio of the two antagonistic enzymes and the type of protease, we were able to generate a full range of ephemeral gels with controlled life times and mechanistic properties.