1. Materials Science and Engineering, Texas A&M Univ., College Station, TX 77843-3123, US.
2. Dept. of Orthopedics, Shandong Provincial Hospital Affiliated to Shandong Univ., Jinan, Shangdong 250021, CN.
3. Dept. of Mechanical Engineering, Texas A&M Univ., College Station, TX 77843-3123, US (Corresponding author), e-mail: hliang@tamu.edu