Light-driven biological actuators to probe the rheology of 3D microtissues
The mechanical properties of biological tissues are key to the regulation of their physical integrity and function. Although the application of external loading or biochemical treatments allows to estimate these properties globally, it remains problematic to assess how such external stimuli compare with internal, cell-generated contractions. Here we engineered 3D microtissues composed of optogenetically-modified fibroblasts encapsulated within collagen. Using light to control the activity of RhoA, a major regulator of cellular contractility, we induced local mechanical perturbation within 3D fibrous microtissues, while tracking in real time microtissue stress and strain. We thus investigated the dynamic regulation of light-induced, local contractions and their spatio-temporal propagation in microtissues. By comparing the evolution of stresses and strains upon stimulation, we demonstrated the potential of our technique for quantifying tissue elasticity and strain propagation, before examining the possibility of using light to create and map local anisotropies in mechanically heterogeneous microtissues. Altogether, our results open an avenue to guide the formation of 3D tissues while non-destructively charting their rheology of 3D tissues in real time, using their own constituting cells as internal actuators.