1. State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics & Astronautics, Nanjing 210016, China
2. Department of Civil and Environmental Engineering, Northwestern University, Evanston, IL 60208
3. Department of Mechanical Engineering, Northwestern University, Evanston, IL 60208
4. Center for Engineering and Health, Northwestern University, Evanston, IL 60208
5. Skin Disease Research Center, Northwestern University, Evanston, IL 60208
6. Department of Materials Science and Engineering, Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801
7. Skin Disease Research Center, Northwestern University, Evanston, IL 60208 e-mail: