Ultra-soft cantilevers and 3-D micro-patterned substrates for contractile bundle tension measurement in living cells.

Actin-myosin microfilament bundles or stress-fibers are the principal tension-generating structures in the cell. Their mechanical properties are critical for cell shape, motion, and interaction with other cells and extracellular matrix, but were so far difficult to access in a living cell. Here we propose a micro-fabricated two-component setup for direct tension measurement on a peripheral bundle within an intact cell. We used 3-D substrates made of silicon elastomer to elevate the cell making the filament bundle at its border accessible from the side, and employed an ultra-soft (spring constant 0.78 nN μm(-1)) epoxy-based cantilever for mechanical probing. With this setup we were able for the first time to measure the tension in peripheral actin bundles in living primary fibroblasts spread on a rigid substrate.