• Ngo TT, Waggoner PJ, Romero AA, Nelson KD, Eberhart RC and Smith GM (2003). Poly(L-Lactide) microfilaments enhance peripheral nerve regeneration across extended nerve lesions. J Neurosci Res 72:227-38. Summary: After injury, axonal regeneration occurs across short gaps in the peripheral nervous system, but regeneration across larger gaps remains a challenge. To improve regeneration across extended nerve defects, we have fabricated novel microfilaments with the capability for drug release to support cellular migration and guide axonal growth across a lesion. In this study, we examine the nerve repair parameters of non-loaded filaments. To examine the influence of packing density on nerve repair, wet-spun poly(L-Lactide) (PLLA) microfilaments were bundled at densities of 3.75, 7.5, 15, and 30% to bridge a 1.0-cm gap lesion in the rat sciatic nerve. After 10 weeks, nerve cable formation increased significantly in the filament bundled groups when compared to empty-tube controls. At lower packing densities, the number of myelinated axons was more than twice that of controls or the highest packing density. In a consecutive experiment, PLLA bundles with lower filament-packing density were examined for nerve repair across 1.4- and 1.8-cm gaps. After 10 weeks, the number of successful regenerated nerves receiving filaments was more than twice that of controls. In addition, nerve cable areas for control groups were significantly less than those observed for filament groups. Axonal growth across 1.4- and 1.8-cm gaps was more consistent for the filament groups than for controls. These initial results demonstrate that PLLA microfilaments enhance nerve repair and regeneration across large nerve defects, even in the absence of drug release. Ongoing studies are examining nerve regeneration using microfilaments designed to release neurotrophins or cyclic AMP. Department of Physiology, Spinal Cord and Brain Injury Research Center, University of Kentucky, Albert B. Chandler Medical Center, Lexington, Kentucky.