Magneto-Active Substrates for Local Mechanical Stimulation of Living Cells

Abstract

Cells can feel and react to the mechanical properties of their environment such as stiffness or geometry by translating mechanical cues into biochemical ones, inducing biochemical and mechanical responses. This process, called mechanotransduction, drives critical functions such as cell differentiation, proliferation and migration. In order to assess to which extend cellular response depends on the temporal and spatial characteristics of the stimulation, it is essential to control temporally and spatially the mechanical cues. Methods have been proposed to apply global and continuous deformations, or local deformations though discrete substrates. Here we propose a novel method to apply mechanical stimuli in a local and dynamic way to cells plated on the continuous surface of deformable substrates. These substrates are made of a soft elastomer (PDMS) in which iron micro-pillars are embedded and actuated by two electromagnets. The amplitude of the surface deformation is controlled by the input current in the coils, and monitored by tracking fluorescent particles underneath the surface. Traction Force Microscopy (TFM) allows us to estimate the stress generated by the pillars, and the cellular mechanical response. Cells adhering to the magneto-active substrates can be stimulated both in traction and compression in the range of contractile cell stresses. Thanks to the compatibility with standard fluorescence techniques, we can furthermore observe the biochemical response of cells with fluorescence techniques such as quantitative Fluorescence Resonance Energy Transfer (FRET).