1. McKay Orthopaedic Research Laboratory Department of Orthopaedic Surgery University of Pennsylvania 3450 Hamilton Walk, 371 Stemmler Hall Philadelphia PA 19104 USA
2. Translational Musculoskeletal Research Center Corporal Michael J Crescenz VA Medical Center 3900 Woodland Avenue Philadelphia PA 19104 USA
3. Department of Orthopaedics Emory University School of Medicine 201 Dowman Drive Atlanta GA 30322 USA
4. Department of Bioengineering University of Pennsylvania 210 South 33rd Street, Suite 240 Skirkanich Hall Philadelphia PA 19104‐6321 USA