First and foremost, I would like to thank my supervisor, Professor Jackie Y. Ying, for her close guidance, encouragement and scientific direction. This research would not have been possible without her help. Professor Ying was not only a supervisor, but also a mentor who gave me great support during the difficulties faced throughout my Ph.D. research. I am grateful to Ms Noreena AbuBakar; she provided me the privilege of working in a world-class research institute. Thanks also to Dr Mo-Huang Li for his ideas and suggestions during the course of my thesis research. The funding of Institute of Bioengineering and Nanotechnology (IBN) (Biomedical Research Council, Agency for Science and Technology and Research, Singapore) and the Ph.D. scholarship under the IBN Scientific Staff Development Scheme are much appreciated.