1. Key Laboratory for Biomechanics and Mechanobiology of Ministry of EducationSchool of Biological Science and Medical EngineeringBeihang University Beijing 100191 P. R. China
2. School of Pharmaceutical SciencesTsinghua University Beijing 100084 P. R. China
3. Beijing Advanced Innovation Centre for Biomedical EngineeringBeihang University Beijing 100191 P. R. China
4. National Research Center for Rehabilitation Technical Aids Beijing 100176 P. R. China