Associate 2008-09

K Jimmy Hsia

Mechanical Science and Engineering


The living cell is an extremely complex system not only because of its complex dynamically evolving structures with multiple functionalities but also because of its dynamical interactions with the environment. A living cell’s cytoskeleton is a network of force-bearing filaments that provides structural integrity and determines the cell’s shape. These filaments are constantly lengthened (shortened) through polymerization (depolymerization) by the addition (removal) of proteins at their ends, giving rise to a continually changing shape. The process through which a cell attaches to and detaches from a substrate appears to involve both “feeling” biochemical signals at its adhesion points and responding through its filaments. Adherent cells probe elasticity as they anchor and pull on the extracellular matrix (ECM), and respond to topographic features of the ECM at all length-scales, from micron down to tens of nanometers, by adjusting their adhesion, cytoskeleton, and shape.

Carbon nanotubes (CNTs) are macromolecules consisting of pure carbon sheets rolled into a tube-like configuration. Among their extraordinary properties is an intrinsic biocompatibility, with a geometry resembling that of natural collagen fibers. CNTs physically interact with each other and often form bundles through van der Waals interaction. As with many nanoscale materials, CNTs also interact with living cells, resulting in beneficial or detrimental effects on the cells. It is of significant interest to study the interactions between living cells and CNTs, in particular, to determine whether such interactions can induce alignment of an initially random CNT network — a result with large implications for the field of regenerative medicine. During his Center appointment, Professor Hsia will explore the mechanics underlying cell-CNT interactions.

In Professor Hsia’s research project, cells’ behavior on a CNT-coated substrate will be studied. He will fabricate a biocompatible substrate coated with a uniform film of CNTs. The substrate will feature different surface patterns on its surface. The cells’ interactions with the CNTs will be observed through microscopy.

The project aims to answer several fundamental questions: Will the cells exert forces through their focal adhesion points onto the CNTs? Will the cell-CNT interaction induce reorganization and alignment of CNTs? Will the aligned CNTs act as preferred tracks that reorient and/or polarize cells to produce directed cell migration? And what are the underlying mechanisms for such an alignment or self-assembly process? The answers to these questions will help guide future applications of nanomaterials in bio- and health-related fields.