1. Tissue Engineering and Biomaterials Laboratory, Department of Orthopaedic Surgery, Department of Physiology and Biomedical Engineering, and Department of Neurology, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, Minnesota 55905, Department of Materials Science and Engineering, The University of Tennessee, Knoxville, Tennessee 37996, and Department of Orthopaedic Surgery, University of Minnesota, Minneapolis, Minnesota 55455