1. Weldon School of Biomedical Engineering, Purdue University, 206 S. Martin Jischke Drive, West Lafayette, IN 47907 e-mail:
2. Department of Biomedical Engineering, Washington University, 1 Brookings Drive, St Louis, MO 63130;
3. Department of Orthopaedic Surgery, Columbia University, 116th Street and Broadway, New York, NY 10027 e-mail:
4. Mem. ASME Weldon School of Biomedical Engineering, Purdue University, 206 S. Martin Jischke Drive, West Lafayette, IN 47907 e-mail: