Inducible Fibril Formation of Silk–Elastin Diblocks

[Image: see text] Silk–elastin block copolymers have such physical and biological properties that make them attractive biomaterials for applications ranging from tissue regeneration to drug delivery. Silk–elastin block copolymers that only assemble into fibrils at high concentrations can be used for a template-induced fibril assembly. This can be achieved by additionally including template-binding blocks that promote high local concentrations of polymers on the template, leading to a template-induced fibril assembly. We hypothesize that template-inducible silk-fibril formation, and hence high critical concentrations for fibril formation, requires careful tuning of the block lengths, to be close to a critical set of block lengths that separates fibril forming from nonfibril forming polymer architectures. Therefore, we explore herein the impact of tuning block lengths for silk–elastin diblock polypeptides on fibril formation. For silk–elastin diblocks E(S)(m)–S(Q)(n), in which the elastin pentamer repeat is E(S) = GSGVP and the crystallizable silk octamer repeat is S(Q) = GAGAGAGQ, we find that no fibril formation occurs for n = 6 but that the n = 10 and 14 diblocks do show concentration-dependent fibril formation. For n = 14 diblocks, no effect is observed of the length m (with m = 40, 60, 80) of the amorphous block on the lengths of the fibrils. In contrast, for the n = 10 diblocks that are closest to the critical boundary for fibril formation, we find that long amorphous blocks (m = 80) oppose the growth of fibrils at low concentrations, making them suitable for engineering template-inducible fibril formation.