Elastoplastic Deformation of Silk Micro- and Nanostructures

Excellent mechanical strength, programmable biodegradation, optical transparency, and extremely low surface roughness of reconstituted silk micro- and nanostructures makes them highly attractive for a broad range of applications in biophotonics, bioresorbable electronics, and targeted drug delivery. The mechanical behavior of reconstituted silk structures at micro- and nanometer length scales is not well understood because of the challenges associated with testing of silk structures at these length scales. In this study, we demonstrate the fabrication of low-dimensional patterned silk films and silk micro- and nanopillars and their transfer to stretchable substrates. The silk micro- and nanostructures exhibited extremely high ductility with large local deformation (up to ∼230% local strain) and the extent of local deformation before failure was found to be secondary structure-dependent. The successful transfer of the patterned silk films to stretchable substrates without the use of any organic solvent enabled us to probe the changes in the secondary structure of silk micro- and nanostructures upon mechanical deformation. Our results provide novel insight into the structure-function relationship of silk materials, and hold promise for applications in tissue engineering, controlled drug delivery, and electronic and optical devices.