1. Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan.
2. Section of Plastic and Reconstructive Surgery, University of Michigan, Ann Arbor, Michigan.
3. Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan.
4. Institute of Gerontology, University of Michigan, Ann Arbor, Michigan.
5. Harvard-MIT Division of Health Sciences & Technology, Cambridge, Massachusetts.