Biocompatible Materials/therapeutic use; Intestinal Mucosa/physiology; Peripheral Nerves/physiology; Peripheral Nervous System Diseases/therapy; Schwann Cells/metabolism; Tissue Engineering/methods; Animals; Animals, Newborn; Brain-Derived Neurotrophic Factor/genetics; Brain-Derived Neurotrophic Factor/metabolism; Cell Adhesion/physiology; Cell Movement/physiology; Cell Proliferation; Cell Survival/physiology; Cells, Cultured; Graft Survival/physiology; Intestinal Mucosa/ultrastructure; Intestine, Small/physiology; Intestine, Small/ultrastructure; Microscopy, Electron, Scanning; Microscopy, Electron, Transmission; Nerve Growth Factor/genetics; Nerve Growth Factor/metabolism; Nerve Regeneration/physiology; Peripheral Nerves/cytology; Peripheral Nerves/surgery; RNA, Messenger/metabolism; Rats; Rats, Sprague-Dawley; Schwann Cells/ultrastructure; Sus scrofa