1. Department of Bioengineering School of Engineering and Applied Science University of Pennsylvania Philadelphia PA 19104 USA
2. McKay Orthopaedic Research Laboratory Department of Orthopaedic Surgery Perelman School of Medicine University of Pennsylvania Philadelphia PA 19104 USA
3. Translational Musculoskeletal Research Center Corporal Michael J. Crescenz Veterans Affairs Medical Center Philadelphia PA 19104 USA
4. Department of Chemical and Biomolecular Engineering School of Engineering and Applied Science University of Pennsylvania Philadelphia PA 19104 USA