1. Department of Biomedical EngineeringCity University of Hong Kong Hong Kong 999077 P. R. China
2. Department of Mechanical and Automation EngineeringChinese University of Hong Kong Hong Kong 999077 P. R. China
3. Department of Mechanical EngineeringCity University of Hong Kong Hong Kong 999077 P. R. China
4. Department of Mechanical EngineeringMcCormick School of EngineeringNorthwestern University Evanston IL 60208 USA