The controlled release of nerve growth factor protein from a chitosan matrix

Acidic, aqueous solutions of 37% N-acetylated chitosan and radioactively labeled, nerve growth factor (NGF) protein were cast into films and subsequently neutralized with ammonia vapors and washed with methanol. The films were immersed in aqueous solutions of lysozyme at a pH value of 7.4 and maintained at a temperature of 37 C. The films were periodically removed and measured for radioactivity. It was inferred from these measurements that 15 to 70% of the NGF protein in the films was eluted within the first 10 min, and the remainder was eluted from the films in a manner which could be explained with a simple diffusion model (D = 1.2 {dollar}times{dollar} 10{dollar}sp{lcub}-10{rcub}{dollar} cm{dollar}sp2{dollar}/s). Separate experiments showed that lysozyme in the steeping liquor substantially degraded the chitosan films. A gel electrophoresis experiment showed that the NGF was not degraded during the process, and the radioactive iodine tag remained bound to the NGF protein. Channels (6 mm in length) composed of a blend of chitosan (1 mg) and NGF protein (0.3 ug) were suitable as a guidance and NGF sustained delivery system for the regeneration of severed mouse sciatic nerves. The NGF protein had no statistically significant influence on the regeneration of myelinated axons, but did cause a 200% increase in the density of blood vessels within the regenerated nerves. The chitosan channels seemed to elicit an inflammatory response in the mice and were substantially eroded after 6 weeks. Silicone channels which contained an aqueous solution of NGF protein within the channel lumen were just as effective as the chitosan/NGF protein channels at promoting the regeneration of blood vessels in a healing nerve and were actually slightly superior to the chitosan channels in terms of promoting the regeneration of myelinated axons. The silicone channels elicited little inflammatory response, but were not bioerodible.