Phase-like emergent order and bulk mechanical response in controllable living active solids

Living systems such as tissues consist of passive matrices and active units, and show emergent behaviors driven by the intrinsic non-equilibrium nature while maintaining the solid-like mechanical integrity. Viewing living systems as active solids provides a natural framework linking cellular activity to macroscopic mechanical response. However, experimental platforms for controlled and quantitative studies of active solid behaviors remain limited. Here, we develop a millimeter-scale experimental system where contractile cells are embedded in a collagen network, forming a living active solid. This platform enables systematic investigation of how active solids respond to internal cellular activity and external mechanical stretch. We identify distinct response regimes and phase-like behaviors as functions of activity and strain, which can be interpreted with a coupled active-elastic model. We show that the active solid generates bulk forces and induces out-of-plane deformations in a controllable manner. Together, our results establish an experimentally accessible platform for studying active solids and provide insights into tissue morphogenesis and soft robotic systems.