Measurement of cellular contractile forces using patterned elastomer

The chapter describes the technique used for the preparation of the patterned elastomeric substrate and for measuring the cellular forces. Calibration of elastic properties of the elastomer involves determining whether the cured patterned polydimethylsiloxane (PDMS) is an elastomer and to obtain the two parameters that characterize its elasticity, namely the Young modulus (Y) and the Poisson ratio. In order to verify that the plating of cells does not modify the elastic characteristics of the surface, in situ calibration of the elasticity of the patterned substrate is performed under a microscope. The force exerted by the micropipette is measured directly by quantifying the deflexion of the pipette in the image. One needs to verify that the calculation of force using the bulk Young modulus agrees with the known force exerted by the calibrated micropipette. Substrates with low resolution patterns such as the 30-?m grid can provide semi-quantitative estimates of the mechanical perturbation due to cells and is useful for the rapid comparison between different cell types or conditions.