Modulating immune response inside biomaterial-based nerve conduits to stimulate endogenous peripheral nerve regeneration
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Injuries to the peripheral nervous system (PNS) are major and common source of disability, impairing the ability to move muscles and/or feel normal sensations, or resulting in painful neuropathies. Annually traumatic nerve injuries resulting from collisions, gunshot wounds, fractures, motor vehicle accidents, lacerations, and other forms of penetrating trauma, affected more than 250,000 patients just in the U.S. The clinical gold standard to bridge long non-healing nerve gaps is to use a nerve autograft- typically the patient’s own sural nerve. However, autografts are not ideal because of the need for secondary surgery to ‘source’ the nerve, loss of function at the donor site, lack of appropriate source nerve in diabetic patients, neuroma formation, and the need for multiple graft segments. Despite our best efforts, finding alternative ‘nerve bridges’ for peripheral nerve repair remains challenging – of the four nerve ‘tubes’ FDA approved for use in the clinic, none is typically used to bridge gaps longer than 10 mm due to poor outcomes. Hence, there is a compelling need to design alternatives that match or exceed the performance of autografts across critically sized nerve gaps. Here we demonstrate that early modulation of innate immune response at the site of peripheral nerve injury inside biomaterials-based conduit can favorably bias the endogenous regenerative potential after injury that obviates the need for the downstream modulation of multiple factors and has significant implications for the treatment of long peripheral nerve gaps. Moreover, our study strongly suggests that more than the extent of macrophage presence, their specific phenotype at the site of injury influence the regenerative outcomes. This research will advance our knowledge regarding peripheral nerve regeneration, and help developing technologies that are likely to improve clinical outcomes after peripheral nerve injury. The significant results presented here are complementary to a growing body of evidence showing the direct correlation between macrophage phenotype and the regeneration outcome of injured tissues.