Opposing mechanical anchorage drives collective cell-matrix interaction

Collective cell behaviors emerge from mechanical interactions with the extracellular matrix (ECM), yet the physical principles governing long-range cell-cell communication remain elusive. Existing models assume that neighboring cells couple by strain-stiffening the ECM between them, amplifying contractility through positive feedback. Here we show that pairwise interactions are insufficient. Instead, stable mechanical communication requires opposing mechanical anchors that allow a cell to strain-stiffen the matrix on both sides. Combining ECM strain mapping, direct cell-force measurements, and live-cell imaging, we find that isolated cell pairs generate only weak, stochastic matrix strains without persistent interactions. In contrast, cells supported by opposing neighbors, or rigid beads acting as mechanical anchors, generate large bilateral matrix strains, increase effective matrix stiffness, align collagen fibers, and form stable multicellular networks. To explain these observations, we develop a predictive mechanosensitive theory introducing effective matrix stiffness and a critical contractile force governing the transition from stochastic to persistent interaction. The theory predicts, and experiments confirm, that opposing mechanical anchorage enables cells to exceed the critical force, trigger collective matrix remodeling, and compact the matrix through collagen-fiber buckling. Together, these findings provide a unifying framework for understanding collective force generation in development, wound repair, fibrosis, and tumor progression.