1. Division of Applied Mathematics, Brown University, Providence, RI 02912, USA
2. Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
3. Computational Sciences and Mathematics Division, Pacific Northwest National Laboratory, Richland, WA 99354, USA
4. Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA
5. Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA