1. Department of Mechanical and Aerospace Engineering, University of Miami, Coral Gables, Florida 33146, United States
2. Department of Civil Engineering and Soft Matter Research Center, Zhejiang University, Hangzhou 310058, China
3. Department of Mechanical Engineering and Department of Civil and Environmental Engineering, Northwestern University, Evanston, Illinois 60208, United States
4. Center for Mechanics and Materials, Tsinghua University, Beijing 100084, People's Republic of China
5. Department of Electrical and Computer Engineering and Micro and Nanotechnology Laboratory, University of Illinois at Urbana—Champaign, Urbana, Illinois 61801, United States