For whom the cells pull: Hydrogel and micropost devices for measuring traction forces

Abstract

While performing several functions, adherent cells deform their surrounding substrate via stable adhesions that connect the intracellular cytoskeleton to the extracellular matrix. The traction forces that deform the substrate are studied in mechanotrasduction because they are affected by the mechanics of the extracellular milieu. We review the development and application of two methods widely used to measure traction forces generated by cells on 2D substrates: i) traction force microscopy with polyacrylamide hydrogels and ii) calculation of traction forces with arrays of deformable microposts. Measuring forces with these methods relies on measuring substrate displacements and converting them into force. We describe approaches to determine force from displacements and elaborate on the necessary experimental conditions for this type of analysis. We emphasize device fabrication, mechanical calibration of substrates and covalent attachment of extracellular matrix proteins to substrates as key features in the design of experiments to measure cell traction forces with polyacrylamide hydrogels or microposts. We also report the challenges and achievements in integrating these methods with platforms for the mechanical stimulation of adherent cells. The approaches described here will enable new studies to understand cell mechanical outputs as a function of mechanical inputs and the understanding of mechanotransduction mechanisms.

Regulation of invadopodia by mechanical signaling

“…While studies with tunable rigidity substrates have been useful, more sophisticated methods to measure and manipulate force production at the subcellular level would allow closer investigation of local mechanical control of invadopodia. The standard method for measuring two-dimensional cellular forces is traction force microscopy in which stresses are calculated based on substrate deformations of elastic surfaces or pillars [75, 95, 96]. This method has been used to study podosomes; however, these structures can form large groups or rosettes which allows for easier measurements over a bigger area [68].…”

Quantifying single‐platelet biomechanics: An outsider’s guide to biophysical methods and recent advances

“…In principle, these techniques rely on quantitative light microscopy to measure substrate displacements, which are then converted into forces. However, substrate preparation methods, implementation, modeling and data analysis of TFM varies between different approaches . To measure traction forces produced by platelets, displacement tracking by TFM on hydrogel substrates and bending of elastomeric micropillar arrays are most commonly used.…”

Controlling cell shape on hydrogels using lift-off patterning

“…direct surface functionalization using UV-reactive sulfo-SANPAH crosslinkers 2 or polymerizing Nhydroxyacrylamide into the hydrogel surface 6 ) and ii) co-polymerization of ECM proteins into the gels during gelation through direct contact of the acrylamide precursor mix with a protein-patterned coverslip. The first method, direct surface functionalization, uses expensive functionalization reagents and also depends on reagent quality and reaction time as the chemicals are unstable in aqueous media and in the presence of oxygen 5 . The method of co-polymerizing ECM proteins relies on patterning glass coverslips with protein and placing them in direct contact with the hydrogel during polymerization.…”