Experimental and Computational Analysis of Cell Mechanics during Spreading and Migration

Thesis (Ph.D.)--University of Washington, 2012The processes of cell migration and spreading are critical for wound healing and cancer metastasis. Cells use their ability to generate mechanical forces to probe the mechanical resistance of their environment and move forward. Biomechanical explanations for how mechanical factors in their environment affect these forces and how cells use their forces to migrate are still unclear. Here, using patterned micropost arrays, the effects of substrate stiffness, cell adhesive area, and micropost density on contractile forces of endothelial cells were investigated. Each of these traits was found to play a fundamentally different role in contributing to overall cellular contractility. Substrate stiffness influenced the magnitude of traction force in a cell independently of its spread area whereas spread area affected it by regulating the number of available adhesions. By quantifying the size of individual focal adhesions on each post, it was also found that focal adhesion area responds to each parameter in the same way that traction forces do. A computational model (1) was then adopted to predict, using ordinary differential equations, the traction forces produced during cell migration. To validate the results from these simulations, NIH 3T3 fibroblasts were seeded onto arrays of posts, but allowed to migrate only in one dimension by patterning the tips of the posts with lines of extracellular matrix (ECM) proteins. Experimentally measured development of force at their leading edge and loss in force at their trailing edge matched closely with the computational simulations. Moreover, I found experimentally that the increase in force at the leading edge caused a decrease in force at the adjacent post, but did not affect the rest of the forces at the interior or trailing edge of the cell. Similarly, my experiments showed that when a cell detached from a post at its trailing edge, the decrease in force at the tail caused an increase in force at the adjacent post, but not at the interior or front of the cell. To match these experimental results, the model requires the elasticity of the cell to be lower than the elasticity of its substrate and the tension in the cell to be uniform across the whole cell. The significance of this dissertation work is that it provides biophysical relationship and mathematical model involoving mechanical properties of a substrate, a cell and traction force generation during spreading and migration