AFM and fluorescent microscopy of single cells with simultaneous mechanical stimulation via electrically stretchable soft substrates

We have developed a novel set-up to simultaneously 1) apply static and dynamic deformations to adherent cells in culture 2) optically image cells under fluorescence microscopy and 3) assay the near-membrane mechanical properties with atomic force microscopy. In this system, the cell culture substrate is formed by a dielectric elastomer film which that can be electro-actuated. The geometry and position of the actuating electrodes and the applied potential can be controlled by design in order to obtain specific strain fields over the cell culture chamber. We have modelled the electromechanical behaviour of the actuated elastomer film and by using optical markers we have established an experimental procedure to optimize and quantify the strain of adherent cells. This cell culture device has been integrated together with a commercial atomic force microscope coupled with an inverted optical microscope, equipped for fluorescence. This novel set-up allows us to temporally assess, with sub-micron spatial resolution, single cell topography and the elasticity, as well as ion fluxes, all during static or cyclic deformations. Preliminary results on fibroblast (3T3 NIH cell line) show a reproducible and reversible increase in cell elastic modulus as a response to 4% applied uni-axial stretch; additionally high resolution elasticity maps of an area 4x4 µm on a single fibroblast could be obtained while stretching a single cell. When measuring cardiomyocytes from mouse embryo, profiles of Ca2+ intracellular concentration could be also monitored while applying static and dynamic stretches. This study provides the proof-of-concept of a novel and flexible experimental platform to investigate mechano-transduction mechanisms at the single cell level.