Double-twist elastomers: mechanical untwisting and chiral buckling

Motivated by collagen fibrils, we adapt the theory of nematic elastomers to cross-linked double-twist cylinders. We first derive a small angle approximation for the mechanical response, and we show that it provides a good fit to experimental untwisting observed for collagen fibrils under extension. We then explore the mechanics of twisted fibrils under axial compression, and find that phase-separation occurs between highly strained and twisted regions and lightly strained regions. We call this phenomenon ‘chiral buckling’.