Preparation and evaluation of NGF-microsphere conduits for regeneration of defective nerves

To fabricate nerve growth factor (NGF) microsphere conduits and evaluate their promotional effects on regeneration of defective nerves.

NGF microspheres containing ovalbumin were prepared using a double-emulsion method. The total amount of NGF was determined by enzyme-linked immunosorbent assay, and bioactive NGF was quantified by the PC12 cell line method; the NGF bioactivity present during the release period was monitored. Conduits made of polylacticacid were added to the NGF microspheres to bridge and repair the nerve injury. The sciatic nerve of Wistar rats was used to evaluate nerve-regeneration efficacy.

NGF microspheres were spherical, with smooth and compact surfaces. The fabrication yield, encapsulation efficiency, and drug loading of the microspheres were 58.3, 29.72, and 0.003%, respectively. The monitoring of NGF bioactivity remaining during the release period showed that ~40% of the original bioactivity was kept on the twenty-eighth day and 10% left on the ninetieth day. Polylacticacid conduits are lowly antigenic, porous (facilitates oxygen diffusion), and able to prevent long-term compression. After 15 days, the length of nerve regenerated from NGF-microsphere conduits was statistically different from that of the control groups (P<0.05). NGF microspheres can accelerate the early nerve-regeneration rate, although the rate was not as good as that caused by autografts. Three months later, the recovery rate of the regenerated nerve collected from NGF-microsphere conduits showed lower values of nerve-conduction velocity, muscular tension, and muscle weight. However, poorer rates of regeneration were observed in the self-mutilation foot compared with those of the control group. The control group had no statistical difference from the sodium chloride and NGF-solution conduits, the best in the autograft group.

A long-term promoting effect of microsphere-bound exogenous NGF on the functional repair of peripheral nerves could not be confirmed, although the nerve-regeneration rate was rapid in the early stage. Better methods are needed to incorporate protein-release systems into nerve conduits to improve functional recovery in patients with injured nerves.