Interfacial friction dictates long-range force propagation in tissues

Tissues are characterized by layers of functional units such as cells and extracellular matrix (ECM). Nevertheless, how dynamics at interlayer interfaces help transmit cellular forces in tissues remains overlooked. Here, we investigate a multi-layer system where a layer of epithelial cells is seeded upon an elastic substrate in contact with a hard surface. Our experiments show that, upon a cell extrusion event in the cellular layer, long-range wave propagation emerges in the substrate only when the two substrate layers were weakly attached to each other. We then derive a theoretical model which quantitatively reproduces the wave dynamics and explains how frictional sliding between substrate layers helps propagate cellular forces at a variety of scales, depending on the stiffness, thickness, and slipperiness of the substrate. These results highlight the importance of interfacial friction between layers in transmitting mechanical cues in tissues in vivo.