Polypeptide Thermogel-Filled Silk Tube as a Bioactive Nerve Conduit

To repair nerve damages, nerve conduits are clinically used. However, when the gap distance is greater than 3 cm, nerve damages remain difficult to repair using current empty nerve conduits. To improve the nerve conduit, a silk nerve conduit (diameter = 5 mm and length = 3 cm) filled with a hydrogel matrix was prepared by injecting a thermogelling aqueous poly(ethylene glycol)-poly(l-alanine) (PEG-PA) solution containing stem cells and neurotropic factors into a silk tube at 37 °C. Successful differentiation of the incorporated stem cells into neuronal cells is a key factor for this system to be used as a nerve conduit. Therefore, neuronal differentiation of the incorporated stem cells in the thermogel-filled conduit system was investigated as a bioactive nerve conduit. The study found that the stem cells exhibited 20 to 60-fold increases in mRNA expression for the neuronal biomarkers of NFM and the glial biomarker of GFAP, in the PEG-PA thermogel-filled silk nerve conduit systems containing neurotropic factors of NGF and BDNF compared to control experiments. This article proved the potential of thermogel as an effective filler of a soft nerve conduit. The PEG-PA thermogel-filled silk conduit system incorporating stem cells and neurotropic factors can be promising as a bioactive nerve conduit system.