3D micropatterned traction force microscopy: a technique to control three-dimensional cell shape while measuring cell-substrate force transmission.

Cell shape and function are intimately linked, in a way that is mediated by the forces exerted between cells and their environment. The relationship between cell shape and forces has been extensively studied for cells seeded on flat 2-dimensional (2D) substrates, but not for cells in more physiological three-dimensional (3D) settings. Here, we demonstrate a technique called 3D micropatterned traction force microscopy (3D-TFM) to confine cells in three-dimensional wells of defined shape, while simultaneously measuring the forces transmitted between cells and their microenvironment. This technique is based on the 3D micropatterning of polyacrylamide wells and on the calculation of 3D traction force from their deformation. With 3D-TFM, we show that MCF10A breast epithelial cells exert defined, reproducible patterns of forces on their microenvironment, which can be both contractile and extensile. We further show that cells switch from a global contractile to extensile behaviour as their volume is reduced. Our technique enables the quantitative study of cell mechanobiology with full access to 3D cellular forces while having accurate control over cell morphology and the mechanical conditions of the microenvironment.