Self-organized buckling patterns underlie transition from macroscopic extension to contraction in active nonlinear elastic networks.*

Many fundamental cellular processes require exquisitely orchestrated large-scale reorganization of structural filaments. One mechanism of reorganization is via internal forces generated by motor proteins. The transmission of these forces is mediated by a highly non-linear network of fiber-like filaments. To understand the role of buckling and failure in such networks, we examine a model nonlinear elastic network subjected to an internal force dipole. Such networks exhibit non-monotonic elastic deformation in response to the applied force. We observe a transition from linear and non-linear extensility to global contractile behavior. We demonstrate this emergence of contractile behavior is associated with a large-scale transformation of the underlying lattice structure. These results recapitulate observations of active microtubule/actin gels which transition from extensile flows to global contraction [J. Berezney et. al., arXiv 2110.00166]. This work underscores the importance of cytoskeletal networks and metamaterials whose failure modes and nonlinear mechanics can be engineered to generate complex and adaptive large-scale phenomena.