Development of Electrospun Nerve Guidance Conduits by a Milk-Derived Protein with Biodegradable Polymers for Peripheral Nerve Regeneration

Bioactive and biodegradable fibrous conduits consisting of well-organized microfibers with longitudinal grooves on the fiber surface were prepared by electrospinning for nerve guidance conduit (NGC) application. Tubular constructs with uniaxially aligned topographical cues have great potential to enhance axonal regeneration and are needed to bridge large gaps between proximal and distal nerves. In this study, we developed electrospun NGCs using milk-derived casein protein (MDP) with biodegradable polycaprolactone and polylactic-<i>co</i>-glycolic acid. We designed and fabricated a biodegradable polymer for random fiber (RF), aligned fiber (AF), random fiber with MDP (MDP-RF), and aligned the fiber with MDP (MDP-AF) by using electrospinning. We hypothesized that topographically defined NGC as MDP-AF NGC would enhance axonal outgrowth by topographical cues and chemoattraction of the bioactive peptide in MDP for macrophage migration. The in vitro MDP-AF NGC results showed not only the promotion of a guidance effect on Schwann cell migration and macrophage polarization but also the enhancement of PC12 cell neurite outgrowth. Additionally, we demonstrated that the synergetic effects of the MDP-AF NGC enhanced the regeneration of injured sciatic nerves. To confirm the effect of MDP-AF NGC, we implanted it into a rat sciatic nerve (10 mm defect). The walking track analysis for sciatic function, electrophysiological test, gastrocnemius muscle weight, and histological and immunohistological analyses indicated that MDP-AF NGC effectively improved sciatic nerve regeneration compared with other groups at 4 and 8 weeks. Herein, we evolutionally developed MDP-AF NGC with geometric and chemotactic stimuli using an electrospinning method combined with a biocompatible synthetic polymer and bioactive casein protein.