Bioprinted fibrin-factor XIII-hyaluronate hydrogel scaffolds with encapsulated Schwann cells and their in vitro characterization for use in nerve regeneration

The blood clotting protein fibrin contains cell-binding domains, providing potential advantage for the fabrication of tissue repair scaffolds and for live cell encapsulation. However, fabrication of fibrin scaffolds with encapsulated cells using three dimensional (3D) printing has proven challenging due to the mechanical difficulties of fabricating protein hydrogel scaffolds with defined microstructure. For example, extrusion based 3D printing of fibrin is generally unfeasible because of the low viscosity of precursor fibrinogen solution. Here we describe a novel technique for bioprinting of fibrin scaffolds by extruding fibrinogen solution into thrombin solution, utilizing hyaluronic acid (HA) and polyvinyl alcohol (PVA) to increase the viscosities of the fibrinogen and thrombin solutions, respectively. Clotting factor XIII was also included to enhance fibrin crosslinking. This technique produced 3D fibrin-factor XIII-HA hydrogel scaffolds without the use of support structures. Living Schwann cells encapsulated within these scaffolds during fabrication were viable and proliferated in culture. Moreover, extrusion based bioprinting induced longitudinal alignment of fine fibrin fibers, which apparently provided haptotactic cues directing alignment of encapsulated Schwann cells and elongation of dorsal root ganglion neurites along the 3D printed strands. These aligned fibrin-factor XIII-HA scaffolds mimic the natural fibrin clot that forms between injured nerve ends, and the aligned, encapsulated Schwann cells may provide natural guidance of neurite growth. Bioprinted fibrin-factor XIII-HA scaffolds also have the potential to be applied towards regeneration of other aligned tissues.