1. Nanotechnology Research Laboratory, Research School of Engineering, The Australian National University, Canberra, Australian Capital Territory 2601, Australia.
2. Department of Mechanical and Biomedical Engineering, City University of Hong Kong, Hong Kong 999077, China.
3. Laboratory of Advanced Biomaterials, Research School of Engineering, The Australian National University, Canberra, Australian Capital Territory 2601, Australia.
4. Department of Applied Mathematics, Research School of Physics and Engineering, The Australian National University, Canberra, Australian Capital Territory 2601, Australia.