BIODEGRADABLE NERVE GRAFTS—PHYSIOLOGICALLY AND ENVIRONMENTALLY FRIENDLY?

Nerve grafting withautografts h as been used extensively to promote peripheral nerve regeneration, and these methods have been extended to autonomic nerves such as the cavernous nerve. The sural nerve has been used as a graft to promote cavernous nerve regeneration and has shown encouraging results in early clinical studies.1 However, autografts have several disadvantages, such as partial denervation of the donor site, painful neuroma formation and surgery at multiple locations. These problems can eventually be minimized by polymeric conduits that engineer an artificial environment to provide physical and chemical stimuli for promoting nerve regeneration. This alternative approach has shown great promise in peripheral nerve regeneration2 and is now being explored for cavernous nerve regeneration. Hisasue et al (page 286) are to be congratulated on their studies which represent an important advance in cavernous nerve regeneration, since only polymeric conduits are involved without the assistance of cells or tissues from the host animal or other sources. There are several advantages to using conduits for facilitating nerve regeneration. The conduit localizes neurotropic and neurotrophic factors between the nerve stumps and also provides physical guidance for the regenerating axons similar to nerve grafts. Neurotrophic agents stimulate growthand development wh ile neurotropic agents guide the growing neurons. Entubulization minimizes unregulated axonal growthat th e site of injury by providing a distinct environment, and the spatial cues also induce a change in tissue architecture, with the cabling of cells within the microconduit. 2 The conduits can also be environmentally enhanced with chemical stimulants and physical guidance cues. Current polymeric entubulization repair methods for peripheral nerve regeneration use nonbiodegradable and biodegradable materials of various gap lengths and chemical fillings. The most common nonbiodegradable material investigated has been silicone. Unfortunately, the nerve guide remains in the body and can incite a chronic immune response. Surgical removal may sometimes be required after regeneration to prevent nerve compression. 3 Biodegradable materials that completely degrade in the body have been used to make conduits for entubulization repairs but they can also swell and deform, causing compression of the regenerating nerve.4 Degradable polymers used to make conduits can be either synthetic or biological. The most commonly used synthetic degradable polymers for entubulization have been poly (Llactide), poly (glycolide), poly (epsilon-caprocalctone) and their copolymers,5, 6 and the most commonly used biological polymer has been collagen.7 Use of copolymers enables tailoring of polymer degradation rates to range from a few days to a few months. The degradation products are usually biocompatible and have been found to cause no adverse reactions. Biological polymers vary in their properties based on source and differ in immunogenicity from synthetic polymers. To exploit the advantages of both types, biological polymers suchas collagen h been used extensively in conjunction with the synthetic biodegradable as well as non