1. New Jersey Center for Biomaterials, Rutgers University, Piscataway, New Jersey, U.S.A.
2. Department of Mechanical Engineering, Colorado State University, Fort Collins, Colorado, U.S.A.
3. Department of Chemistry and School of Biomedical Engineering, Colorado State University, Fort Collins, Colorado, U.S.A.
4. Department of Mechanical Engineering and School of Biomedical Engineering, Colorado State University, Fort Collins, Colorado, U.S.A.