Factors influencing the mechanical properties of soft elastomer substrates for traction force microscopy

Abstract

Traction force microscopy (TFM) aims at determining the forces exerted by cells on their substrate. Traction quantification relieson the knowledge of the mechanical properties of the substrate, i.e., typically its Young’s modulus. Because of the challengesassociated with the mechanical analysis of very soft elastomers, a large range of modulus values are reported in literature for thesame materials. In order to provide a reliable characterization, a systematic study was performed, including a large number ofmicro-scale indentation experiments. The mechanical behavior of four elastomer configurations (Sylgard 184 40:1 and 60:1, andCY9:10 and 10:9), frequently used for TFM studies, was investigated. The good repeatability of the experimental procedureallowed characterizing the modulus variability within each material sample and between batches. The corresponding uncertaintyis in the range of 10%, consequently directly affecting the reliability of cell traction force values. Material aging, immersion in aliquid, and illumination were considered as specific factors potentially influencing the stiffness of TFM substrates. The resultsshow that stiffness changes significantly over the first 3 weeks following elastomer production, while immersion in a isoosmolarsolution and illumination have generally modest influence on micro-scale stiffness.