1. Department of NanoEngineering University of California San Diego 9500 Gilman Drive La Jolla CA 92093 USA
2. Institute of Materials Research and Engineering A*STAR (Agency for Science, Technology and Research) Singapore 138634 Singapore
3. School of Materials Science and Engineering Nanyang Technological University Singapore 639798 Singapore
4. Department of Bioengineering University of California San Diego 9500 Gilman Drive La Jolla CA 92093 USA
5. Materials Science and Engineering Program University of California San Diego 9500 Gilman Drive La Jolla CA 92093 USA
6. Skaggs School of Pharmacy and Pharmaceutical Sciences University of California San Diego 9500 Gilman Drive La Jolla CA 92093 USA
7. Department of Radiology University of California San Diego 9500 Gilman Drive La Jolla CA 92093 USA