Effects of nerve growth factor from genipin-crosslinked gelatin in polycaprolactone conduit on peripheral nerve regeneration--in vitro and in vivo

The gelatin solution crosslinked by genipin (0, 0.1, 0.5, 1.0, and 1.5% w/w) was studied as a nerve growth factor (NGF) carrier (GGp0, GGp0.1, GGp0.5, GGp1.0, and GGp1.5) in a polycaprolactone conduit in large-gap nerve regeneration. The GGp0 and GGp0.1 displayed the highest activity of PC12 cells and inhibited the reduction of 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl-tetrazolium bromide (MTT). No cytotoxicity was found in all groups by lactate dehydrogenase (LDH) release. The NGF-releasing characters were obtained by ELISA tests. A relatively fast release rate appeared during the first 10 days and then a subsequent slower release profile followed. NGF was higher in GGp0.1 than in GGp0 and GGp0.1 after 10 days. The bioactivity of the released NGF remains the same when measuring the neurite outgrowth of PC 12 cells. Finally, the controlled-release conduits were implanted into 12-mm long sciatic nerve gaps of rats. In addition, the best site of NGF carrier was determined either by filling carrier into the conduit lumen or by sucking carrier to the conduit wall. Four and 8 weeks after implantation, morphological analysis revealed that GGp0.1 conduits had markedly larger and more number of myelin axons in the midconduit and distal nerve. Further, sucking the carrier into the conduit wall was an efficient and convenient way to prevent the regeneration of axons and vessels from being impaired by the lumen's carrier. The genipin-crosslinked gelatin is a promising carrier in producing a high release concentration and a long release period of NGF to promote the regeneration over a large-gap nerve injury.