1. Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455, USA.
2. Department of Biomedical Engineering, University of Minnesota, Minneapolis, MN 55455, USA.
3. Department of Surgery, University of Minnesota, Minneapolis, MN 55455, USA.
4. Medtronic, Mounds View, MN 55112, USA.
5. Institute for Engineering in Medicine, University of Minnesota, Minneapolis, MN 55455, USA.