Prompt peripheral nerve regeneration induced by a hierarchically aligned fibrin nanofiber hydrogel

Fibrin plays a crucial role in peripheral nerve regeneration, which could occur spontaneously in the format of longitudinally oriented fibrin cables during the initial stage of nerve regeneration. This fibrin cable can direct migration and proliferation of Schwann cells and axonal regrowth, which is very important to nerve regeneration. In the present study, we prepared a three-dimensional hierarchically aligned fibrin nanofiber hydrogel (AFG) through electrospinning and molecular self-assembly to resemble the architecture and biological function of the native fibrin cable. The AFG displayed a hierarchically aligned topography as well as low elasticity (∼1.5kPa) that were similar to nerve extracellular matrix (ECM) and the native fibrin cable. Rapid, directional cell adhesion and migration of Schwann cells (SCs) and dorsal root ganglions were observed in vitro. The AFG was then used as a potential intraluminal substrate in a bioengineered chitosan tube to bridge a 10-mm-long sciatic nerve gap in rats. We found that the AFG served as a beneficial microenvironment to support SCs cable formation and axonal regrowth within 2weeks. Further histological and morphological analyses as well as electrophysiological and functional examinations were performed after AFG implantation for up to 12weeks. The results from morphological analysis and electrophysiological examination indicated that regenerative outcomes achieved by our developed graft were close to those by an autologous nerve graft, but superior to those by hollow chitosan tubes (hCST) and random fibrin nanofiber hydrogel (RFG). Our results demonstrate that the AFG creates an instructive microenvironment by mimicking the native fibrin cable as well as the oriented and soft features of nerve ECM to accelerate axonal regrowth, thus showing great promising potential for applications in neural regeneration.

In peripheral nervous system defect repair, a wide variety of strategies have been proposed for preparing functionalized nerve guidance conduits (NGC) with more complex configurations to obtain optimal repair effects. Longitudinally oriented fibrin cables were reported to form spontaneously during the initial stages of peripheral nerve regeneration in an empty NGC, which can direct the migration and proliferation of Schwann cells and promote axonal regrowth. Therefore, based on the biomimetic idea, we prepared a three-dimensional hierarchically aligned fibrin nanofiber hydrogel (AFG) through electrospinning and molecular self-assembly, resembling the architecture and biological function of the native fibrin cable and serving as an intraluminal filling to accelerate axon regeneration. We found that the AFG was a beneficial microenvironment to support SCs cable formation and accelerate axonal regrowth with improved motor functional recovery.