Silkworm silk fibers vs PEEK reinforced rubber luminescent strain gauge and stretchable composites

In the present study we demonstrate how the sensitive property of the constituent parts of silkworm silk fiber can be applied to the field of soft composite materials. It concerns the structural and intrinsic functional characteristics of silk vs. the macroscopic property and the realization of functional com- posites. Silk fiber reinforced silicone rubber (SR) composites have been fabricated with different fiber lengths. The key structural features of silk made of stiff nanocrystals, including hydrogen bonded b - strands and b -sheet nanocrystals, when embedded in a softer matrix demonstrate that the tensile strength as well as the stiffness of the composites are higher than those measured for SR reinforced with synthetic polyether-ether-ketone fibers. Moreover, the intrinsic luminescence of protein nanocrystals permits the direct observation of the deformation with accurate measurement of the strain in the composite. Based on the intrinsic properties of such natural hierarchical material, these findings will allow to transfer the engineering of composite materials, particularly, soft functional composites, to a new applications ranging from strain measurements in biological tissue to monitoring tool in structural composites.