1. College of Materials Science and Engineering Central South University of Forestry and Technology Changsha 410004 P. R. China
2. School of Biomedical Engineering The University of Sydney Sydney New South Wales 2006 Australia
3. Department of Hepatobiliary Surgery Hunan Provincial People's Hospital Changsha 410000 P. R. China
4. School of Material Science and Engineering Shanghai University Shanghai 200444 P. R. China