Fabrication of Elastomeric Silk Fibers.

Methods to generate fibers from hydrogels, with control over mechanical properties, fiber diameter and crystallinity, while retaining cytocompatibility and degradability, would expand options for biomaterials. Here we exploited features of silk fibroin protein for the formation of tunable silk hydrogel fibers. The biological, chemical, and morphological features inherent to silk were combined with elastomeric properties gained through enzymatic crosslinking of the protein. Post-processing via methanol and autoclaving provided tunable control of fiber features. Mechanical, optical, and chemical analyses demonstrated control of fiber properties by exploiting the physical cross-links, and generating double network hydrogels consisting of chemical and physical cross-links. Structure and chemical analysis revealed crystallinity from 30-50%, modulus from 0.5MPa to 4MPa, and ultimate strength 1 to 5 MPa depending on the processing method. Fabrication and post-processing combined provided fibers with extensibility from 100 to 400% ultimate strain. Fibers strained to 100% exhibited 4th order birefringence, revealing macroscopic orientation driven by chain mobility. The physical cross-links were influenced in part by the drying rate of fabricated materials, where bound water, packing density, and micro-structural homogeneity influenced cross-linking efficiency. The ability to generate robust and versatile hydrogel microfibers is desirable for bottom-up assembly of biological tissues and for broader biomaterial applications. This article is protected by copyright. All rights reserved.