1. Department of Materials Science and Engineering and Frederick Seitz Materials Research Laboratory; University of Illinois at Urbana-Champaign; 1304 W. Green St. Urbana IL 61801 USA
2. Department of Biomedical Engineering; Washington University in Saint Louis; 360 Whitaker Hall, 1 Brookings Dr. Saint Louis MO 63130 USA
3. Center for Mechanics and Materials; Tsinghua University; Beijing 100084 China
4. Department of Civil and Environmental Engineering; Department of Mechanical Engineering; Center for Engineering and Health and Skin Disease Research Center; Northwestern University; 2145 Sheridan Road Evanston IL 60208 USA
5. Department of Chemical Engineering and Materials Science; Department of Ophthalmology; Department of Biomedical Engineering; University of Southern California; Los Angeles CA 90033 USA
6. Department of Electrical Engineering; Stanford University; 307 Spilker Building, 348 Via Pueblo Stanford CA 94305-4088 USA
7. Department of Materials Science and Engineering; Beckman Institute for Advanced Science and Technology and Frederick Seitz Materials Research Laboratory; University of Illinois at Urbana-Champaign; 1304 W. Green St. Urbana IL 61801 USA