1. McKay Orthopaedic Research Laboratory, Department of Orthopaedic Surgery, University of Pennsylvania, Philadelphia, Pennsylvania.
2. Department of Bioengineering, University of Pennsylvania Philadelphia, Pennsylvania.
3. Department of Mechanical Engineering, University of Pennsylvania Philadelphia, Pennsylvania.
4. Department of Orthopaedics and Rehabilitation and Biomedical Engineering, University of Wisconsin–Madison, Madison, Wisconsin.
5. Department of Health and Human Services, Cartilage Biology and Orthopaedics Branch, National Institute of Musculoskeletal and Skin Disorders, National Institutes of Health, Bethesda, Maryland.