1. Department of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058, China
2. Departments of Civil and Environmental Engineering and Mechanical Engineering; Center for Engineering and Health; Skin Disease Research Center, Northwestern University, Evanston, Illinois 60208, USA
3. Department of Materials Science and Engineering; Frederick Seitz Materials Research Laboratory; University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
4. Center for Mechanics and Materials, Tsinghua University, Beijing 100084, China