1. Department of Materials Science and Engineering; Frederick Seitz Materials Research Laboratory; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA
2. Department of Biomedical Engineering; Washington University in Saint Louis; Saint Louis MO 63130 USA
3. Department of Civil Engineering and Soft Matter Research Center; Zhejiang University; Hangzhou 310058 China
4. Department of Mechanical Engineering and Civil and Environmental Engineering; Northwestern University; Evanston IL 60208 USA
5. Institute of Solid Mechanics; Beihang University; Beijing 100191 China
6. Department of Biomedical Engineering; George Washington University; Washington DC 20052 USA