1. Department of Materials Science and Engineering; The University of Tennessee; Knoxville TN 37996 USA
2. Department of Orthopedic Surgery; Mayo Clinic College of Medicine; Rochester MN 55905 USA
3. Department of Neurologic Surgery; Mayo Clinic College of Medicine; Rochester MN 55905 USA
4. Department of Neurology; Mayo Clinic College of Medicine; Rochester MN 55905 USA
5. Department of Physiology and Biomedical Engineering; Mayo Clinic College of Medicine; Rochester MN 55905 USA