Modeling reconstituted silk fibroin gels during deformation

Silk from silkworms has been used in the textile industry for thousands of years. It consists of β-sheet structures formed from hydrophobic domains in the protein fibroin. Recently, a physical electrogel (e-gel) was made by reconstituting Bombyx mori silk into stable aqueous solutions and then applying small DC electric field [Tabatabai et al, Soft Matter 11 (2015) 756]. The e-gels exhibit distinctive strain hardening and are partially recoverable from strain.

We build a coarse-grained model of fibroin protein polymers, which comprise crystallizable domains and amorphous domains. To study the structural changes and nonlinear behavior of the gel during deformation, gels are tested by shearing, oscillating and stretching. We find that the kinetics of unfolding and refolding of crystallizable domains changes the number and functionality of crosslinks in the physical network, and thus causes the strain hardening of the gel and the non-recoverable strain. This model can also be useful in other associating polymer systems.