(776d) Mechanical Stretching Induced Mesenchymal Stem Cell Orientation

Tissues and cells in the body are exposed to a complex mechanical microenvironment. Therefore, mechanical stimulation is important for cell proliferation and differentiation. Recent interest has grown on the impact of mechanical stimulation, such as stiffness, surface topography, and mechanical stretching, on cell fate decision. In this study, we created an anisotropic mechanical environment by stretching the substrate membrane in an uniaxial direction, and recorded mesenchymal stem cell orientation response accordingly.

We investigated the alignment behavior of cells on an anisotropic surface. The experimental results agreed with our "cell active sensing" model, and suggest that the cells can sense and respond to the surface anisotropy by orienting in the direction of maximal effective stiffness. We apply this model to a uniaxial pre-stretched surface to predict cell orientation. After stretching a substrate unidirectionally, we applied a thin poly-L-lysine coating (~0.8nm) and culture the MSCs, whereby the cells do not experience the actual stretching. By culturing cells on a pre-stretched PDMS substrate membrane, the effective stiffness the cells sense in the stretched direction is larger than in the unstretched direction. This resulted in the cells aligning in the stretched direction, and contributed to the regulation of the cell focal adhesion, and further modulated cell signaling and differentiation.

Currently, most of the prior studies that focused on mechanical stress attempted to measure the cytoskeletal changes after active stretching, whereby the cells are seeded prior to applying the external force or stretch. However, in our experiment we seed the cells after the membrane is stretched, such that the cells do not experience the stretch due to external changes in force. Nevertheless the cells are able to sense the differential effective stiffness in the two directions and changed their cytoskeleton accordingly to orient in the direction of maximum stiffness. These results support our model of "active mechanosensing".