1. Department of Mechanical and Aerospace Engineering; University of Virginia; Charlottesville VA 22904 USA
2. Department of Materials Science and Engineering; Beckman Institute, and Frederick Seitz Materials Research Laboratory; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA
3. Neuroscience Program; Medical Scholars Program; Beckman Institute, and Coordinated Science Laboratory; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA
4. Department of Engineering Mechanics and Center for Mechanics and Materials; Tsinghua University; Beijing 100084 China
5. Department of Mechanical Engineering and Department of Civil and Environmental Engineering; Center for Engineering and Healthand Skin Disease Research Center; Northwestern University; Evanston IL 60208 USA
6. Department of Mechanical and Nuclear Engineering; Center for Rehabilitation Science and Engineering; Virginia Commonwealth University; Richmond VA 23284 USA
7. Department of Aerospace Engineering; Beckman Institute, and Coordinated Science Laboratory; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA