Microfluidic Silk Fibers with Aligned Hierarchical Microstructures.

The hierarchical structure of the ECM provides specific niches for tissues to regulate cell behavior, yet the challenge remains to design biomaterial systems for tissue regeneration to recreate such features in vitro. Here, we achieved this goal through the use of aligned hierarchical structures of native silk fibers, generated through the integration of "bottom-up" and "top-down" strategies to generate regenerated silk fibers with aligned nano- to micro-hierarchical structures. To achieve these designs, we assembled and dispersed silk nanofibers (SNF) in formic acid and spun them into fibers using bioinspired microfluidic chips with a geometry mimicking the native silk gland. The fibers generated using this device exhibited aligned hierarchical structure with fiber mechanical properties superior to fibers derived from more traditional spinning approaches with regenerated silk solutions. Besides the improved mechanical properties, Raman spectroscopic results indicated similarly aligned structures to native fibers and active control of cell proliferation, migration, and aggregate orientation. The results indicate the feasibility of developing bioactive silk fiber materials with hierarchical structures to facilitate utility in a range of cell and tissue regeneration scenarios.