1. Institute of Medical Research; Northwestern Polytechnical University; Xi'an 710072 P. R. China
2. School of Life Sciences; Northwestern Polytechnical University; Xi'an 710072 P. R. China
3. Second Department of General Surgery; Shaanxi Provincial People's Hospital; Xi'an 710068 P. R. China
4. Key Laboratory of Biorheological Science and Technology; Ministry of Education College of Bioengineering; Chongqing University; Chongqing 400044 P. R. China