1. Beckman Laser Institute & Medical Clinic and Department of Biomedical Engineering, University of California - Irvine, Irvine, California 92612, USA
2. College of Material Science and Engineering, Sichuan University, Chengdu 610064, People's Republic of China
3. Department of Biomedical Engineering and NIH Transducer Resource Center, University of Southern California, Los Angeles, California 90089, USA