R S Potter1, S Y Tang2. 1. Department of Orthopedic Surgery, Washington University in St Louis, 660 S. Euclid, Campus Box 8233, St Louis, MO, 63103, USA; Department of Mechanical Engineering and Materials Science, Washington University in St Louis, St Louis, MO, USA. 2. Department of Orthopedic Surgery, Washington University in St Louis, 660 S. Euclid, Campus Box 8233, St Louis, MO, 63103, USA; Department of Biomedical Engineering, Washington University in St Louis, One Brookings Drive, Whitaker Hall, Campus Box 1097, St Louis, MO, 63130, USA; Department of Mechanical Engineering and Materials Science, Washington University in St Louis, St Louis, MO, USA. Electronic address: simon.tang@wustl.edu.