Cross-link collective: Entangled robotic matter with cohesive motion

Robotic applications increasingly demand systems that are resilient, adaptable, and scalable. One promising route is through collectives of simple modules, where complex group-level behavior emerges from local interactions. By omitting fixed topologies and tight coordination, this approach sacrifices predictability and conventional tools for behaviors inherently optimized through stochastic mechanical interactions. A key challenge is maintaining cohesion and functionality without fixed connections and explicit coordination. We introduce the cross-link collective, a physically entangled robotic system inspired by cross-linking in active gels. Through shape morphing and transient entanglement, individually immobile modules produce sustained collective motion. The mechanically intelligent robot matter favors chains and phase relationships that reduce joint torques and reconfigures in response to perturbations. We show that distributed control can be added to this substrate to further enhance cohesion. Leveraging weak, reversible connections, the cross-link collective is adaptable, scalable, and fault tolerant, offering insights to applications from soft matter and robotics.