1. Department of Materials Science and Engineering, National University of Singapore, Singapore 117574
2. Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117574
3. Biomedical Engineering Department, College of Design and Engineering, National University of Singapore, Singapore 117574
4. NUS Research Institute, No. 16 South Huashan Road, Liangjiang New Area, Chongqing 119077, China