Cellular forces interfaced with an array of microneedles

Contractile forces exerted by cells play important roles in the formation of multicelluar tissues and in regulating their function. Although not widely appreciated, these forces regulate the adhesion of cells to the underlying substrate and to neighboring cells. Understanding of the mechanism by which these cell-generated forces affect cell behavior has been limited by the lack of methods to determine directly the nanonewton range of forces that cells exert. We created a system composed of an elastic array of microneedles to measure these forces. The needles are designed such that cells will adhere and spread on the tips of the needles. Local contractile forces generated by cells result in local bending of the needles, from which we calculate the magnitude and direction of forces. We used this system to study cellular forces important in the physiological functions of the vascular wall.; Using this system to study the forces that single arterial smooth muscle cells exert, we discovered two classes of force-supporting adhesions that exhibit distinct force-adhesion size relationships. Force increased with size of adhesions for those larger than 1 mum2, whereas no such correlation existed for smaller adhesions. By controlling cell adhesion on these micromechanical sensors, we showed that cell morphology regulates the magnitude of traction force generated by cells. Also, cells that were prevented from spreading and flattening against the substrate did not contract in response to stimulation by serum or lysophosphatidic acid, while spread cells did. Contractility in the unspread cells was rescued by expression of constitutively active RhoA. Together, these findings demonstrate a coordination of biochemical and mechanical signals to regulate cell adhesion and mechanics, and they introduce the use of arrays of mechanically isolated sensors to manipulate and measure the mechanical interactions of cells.; Subsequently, we used the microneedle array to directly measure innate cell-cell forces in the endothelium. Pairs of arterial endothelial cells were attached to the arrays of posts to form a bowtie configuration; the cells touched at the center of the bowtie and pulled on one another. Because the cells were attached to the posts while pulling on each other, the forces exerted between the cells could be detected by the deflection of the posts underneath each cell. Lastly, we explored how cell-cell and cell-ECM forces adjust as the integrity of the endothelial cell-cell junctions is altered. We discovered that the ratio of cell-cell forces to cell-ECM forces stays relatively constant. Soluble factors known to change the integrity of cell-cell junctions do so through modulation of cell-ECM forces directly rather than change the adhesive strength of the cell-cell junction. Our study begins to unravel how mechanical forces regulate cellular structures and are transduced within and across cells. (Abstract shortened by UMI.)...