Improved nerve regeneration through piezoelectric vinylidenefluoride-trifluoroethylene copolymer guidance channels

Piezoelectric materials generating electrical charges in response to mechanical strain may be used to stimulate axonal regeneration following nerve injury. Tubular nerve guidance channels were extruded from a vinylidenefluoride-trifluoroethylene copolymer using a melt-extrusion process. Unlike vinylidenefluoride homopolymer, the copolymer does not need mechanical stretching to achieve a dipole-containing crystal structure, enabling the fabrication of complex piezoelectric devices. Selected tubes were rendered piezoelectric in a high voltage corona poling apparatus. Crystal structure changes induced by poling were evaluated with differential scanning calorimetry. In contrast to unpoled samples, poled ones displayed a sharp endothermic peak and a greater heat of transition at the Curie temperature, indicative of an increase in crystal order and size. The piezoelectric output of poled tubes was characterized using a laser-monitored deflection system interfaced with a charge amplifier and oscilloscope. Poled tubes generated significant voltages in response to slight mechanical deformations. The magnitude of electrical output was independent of the poling polarity. Unpoled tubes showed no electrical output. Positive, negative and unpoled vinylidenefluoride-trifluoroethylene copolymer tubes were used to repair a 10 mm gap in transected sciatic nerves of adult rats. Nerves regenerated in positively poled channels had a significantly greater number of myelinated axons than those regenerated in unpoled channels 4 wk post-implantation. Negatively poled channels contained an intermediate number of myelinated axons. We concluded that piezoelectrically active vinylidenefluoride-trifluoroethylene copolymer tubes significantly enhance nerve regeneration as compared to chemically identical, unpoled tubes and that the polarity of the corona poling procedure used to fabricate piezoelectric materials may play a role in determining biological responses.