Hydrogels based on thiol-ene step-growth chemistry have gained increased attention due to their superior properties over the currently standard materials based on chain growth polymerization. In the thiol-ene reaction, a crosslinker with at least two thiol groups is necessary for network formation. Many currently used crosslinkers exhibit cytotoxic potential, are non-biodegradable, or involve toxic chemicals and relatively complicated procedures in their synthesis, thus hindering their broader application. As an alternative, the use of a protein (fibrinogen gamma chain, FGG) recombinantly expressed in Escherichia coli was investigated. The FGG is part of the multimeric fibrinogen involved in hemostasis. This protein complex is stabilized by disulfide crosslinking. This presence of cysteines in the sequence makes FGG a promising candidate as a thiol donor in thiol-ene reactions. It was shown for the first time, that a cysteine-containing protein expressed in E. coli was capable of forming hydrogels with norbornene functionalized gelatin. An increase in FGG concentration led to higher gel stiffness and a decrease in the swelling ratio. Furthermore, the material exhibited cell adhesive properties and biocompatibility. Overall, a proof-of-principle could be achieved, opening up the use of recombinant proteins without further modifications as crosslinkers in thiol-ene based hydrogels, providing a cost-effective, safe, and scalable material source.
Schlauch et al. (Fri,) studied this question.