1. School of Materials Science and Engineering, Zhejiang University, Hangzhou, Zhejiang 310027, P. R. China
2. Department of Periodontology, The Second Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, 310009, P. R. China
3. Institute of Applied Bioresource Research, College of Animal Science, Zhejiang University, Yuhangtang Road 866, Hangzhou, Zhejiang 310058, P. R. China
4. Department of Chemistry and Biochemistry, University of Oklahoma, Norman, OK 73019, USA