CELLULAR FORCES AND MECHANICAL COUPLING USING MICROENGINEERED DEVICES
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The biological response of cells to mechanical forces is integral to both normal cell function and the progression of many diseases. Physical cues experienced by cells arise from internally generated contractile forces, as well as from external sources of force and strain in the local environment. We have used arrays of flexible micron-scale poly(dimethylsiloxane) (PDMS) cantilevers (posts) to probe the behavior of cell-generated contractile forces under varying chemical and mechanical conditions. The cells’ contractile forces displace the tops of the underlying posts, which are individually tracked through microscopy and image analysis, yielding a dynamic, micron-scale map of the cells’ mechanical activity. I have applied these techniques to study cell generated forces in two experimental systems. First, force generation by cardiac fibroblasts (CFs) in order to elucidate mechanical coupling between these cells and the myocytes responsible for the heart’s pumping action, which may contribute to certain types of cardiac arrhythmias. These experiments were part of a collaborative effort which demonstrated that modulation of both CF contractile forces, and the cellular structures on which these forces can act when coupled to cardiac myocytes, had direct influence on the electrical conduction mechanisms that are critical for the proper functioning of cardiac muscle tissue. The second experimental system studied the impact of force application through an applied global stretch on the traction force dynamics of arterial smooth muscle cells. These cells, resident within the inner walls of arteries, are constantly exposed to global stretching forces as a result of changes in blood pressure and flow. I developed an enhanced version of the micropost array that enabled the application of controlled global stretch to cells while the evolution of traction forces could be measured in real time. These measurements revealed a heterogeneous response to imposed strain, as a portion of the tested cells responded by increasing their force generation against the micropost substrate, while others underwent plastic deformation and exhibited relatively small changes in force generation. Upon reversal of stretch direction, all cells exhibited decreasing force generation that is characteristic of a viscoelastic response. Following stretch completion and left at rest, all cells demonstrated active recovery and re-establishment of contractile forces. I have also demonstrated the combined use of a laminar flow technique, micropipette “spritzing”, with both micropost arrays and microfabricated tissue gauges for application of local chemical stimulation to single cells or single tissues while observing contractile dynamics in real time.