Topology Outweighs Stiffness: Self-Reinforced Cell Mechanotransduction via Multiaxial Curvature Engineering of Ultrasoft Hydrogels.

Geometric curvature critically regulates cellular behavior in soft tissue microenvironments, yet its role in mechanotransduction is underexplored due to stiffness-centric paradigms and challenges in creating stable curvatures on ultrasoft materials. We developed a solvent-induced buckling strategy to engineer multiaxial curvatures on ultrasoft hydrogels (500-750 Pa), recapitulating the anisotropic topologies of natural tissues such as cerebral gyri and breast lobules. Human mesenchymal stem cells on these surfaces exhibit robust focal adhesion maturation, cytoskeletal reorganization, nuclear mechanosensing (e.g., elevated Lamin A/C), and enhanced osteogenesis─phenotypes typically seen on rigid substrates but markedly attenuated on flat ultrasoft controls. This curvature-dominated mechanosensing persists in 3D injectable microgels, decoupling topological cues from the substrate stiffness. Mechanistic studies and energy minimization modeling reveal that curvature segregates stress fiber functions: basal fibers align circumferentially in high-curvature regions to enhance Rho-mediated contractility and focal adhesions, while apical fibers orient radially in low-curvature zones to minimize the bending energy. These findings establish topology as a primary driver of cellular tension and fate, providing fundamental insights into designing biomaterials and biointerfaces for soft tissue repair and regenerative medicine.