1. Bioengineering Laboratory, Department of Orthopaedics, The Warren Alpert Medical School, Brown University and Rhode Island Hospital, Providence, RI 02912
2. Center for Computation and Visualization, Brown University, Providence, RI 02912 e-mail:
3. Department of Ecology and Evolutionary Biology, Brown University, Providence, RI 02912 e-mail:
4. Bioengineering Laboratory, Department of Orthopaedics, The Warren Alpert Medical School, Brown University and Rhode Island Hospital, Providence, RI 02912; School of Engineering, Brown University, Providence, RI 02912