Tissue mechanics are important during development: forces generated by collective cell behaviours drive tissue deformations and determine the organism's form and function. Several techniques have been developed to measure mechanical stresses, but embryonic tissues are soft, and the stresses produced are small, making measurements in situ challenging. Here, Fengzhu Xiong, Olivier Pourquié, L. Mahadevan and colleagues describe tissue force microscopy (TiFM), a new system to measure forces in live chick embryos with minimal invasiveness. The system consists of a cantilever (adapted from atomic force microscopy) attached to a chip, which is connected to an electric piezo and capacitators to detect chip location. This chip-piezo setup is then mounted on a microscope to image the cantilever location as it inserts into a tissue. The deflection of the cantilever is measured by comparing the cantilever tip position (through imaging) with the chip position (detected by capacitors), allowing the user to calculate the force exerted on the cantilever. As proof of principle, the authors show that TiFM can capture tissue dynamics during body axis elongation. Additionally, they demonstrate the use of TiFM to perform controlled mechanical perturbations in live embryos. Overall, this technique adds to the expanding set of tools to investigate complex tissue mechanics during development.
