GDNF and peripheral nerve injury: Nerve growth factor (NGF) [130–136], glial cell line-derived neurotrophic factor (GDNF) [137–142], brain derived neurotrophic factor (BDNF) [141, 143–145] and neurotrophin-3 (NT-3) [90, 135, 141, 146–148] have all been added to biomaterials to treat TBI as well as neurodegenerative disorders spinal cord injuries and peripheral nerve injuries.