Medical devices employing semipermeable materials, such as acrylic copolymers, polyurethane isocyanate, and other biocompatible semipermeable polymers, are disclosed for use as guidance channels in regenerating nerves. The devices can be formed by tubular semipermeable conduits adapted to receive the ends of a severed or damaged nerve. The tubular conduits define lumens through which axons can regenerate to restore motor and/or sensory functions. The guidance materials are chosen such that they are capable of allowing the diffusion of nutrients and other metabolites to the regenerating nerve site while excluding fibroblasts and other scar-forming cells. In particular, tubular channels which have a smooth inner surface and longitudinally oriented trabeculae result in significantly larger regenerated nerve cables and higher numbers of regenerated myelinated axons.