* Corresponding authors

^a Center of Biomedical and Engineering and Regenerative Medicine, Frontier Institute of Science and Technology, Xi'an Jiaotong University, Xi'an 710054, China
E-mail: mapx@umich.edu
Fax: +(86)29-83395131
Tel: +(86)29-83395361

^b Key Laboratory of Flexible Electronics (KLOFE) and Institute of Advanced Materials (IAM), Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University, Nanjing 211816, China
E-mail: iampli@njtech.edu.cn
Fax: +(86) 25-83587982
Tel: +(86) 25-83587982

^c Center of Applied Chemical Research, Frontier Institute of Science and Technology, Xi'an Jiaotong University, Xi'an 710054, China

^d Key Laboratory of Applied Surface and Colloid Chemistry, School of Chemical and Chemical Engineering, Shaanxi Normal University, Xi'an 710119, China

^e Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA

^f Department of Biologic and Materials Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA

^g Macromolecular Science and Engineering Center, University of Michigan, Ann Arbor, Michigan 48109, USA

^h Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA