Programmable extracellular matrix heterogeneity directs least-resistance migration in three dimensions

Cell migration through 3D extracellular matrices (ECMs) is central to development, immune response, and cancer metastasis, yet how cells navigate mechanically heterogeneous environments remains poorly understood. Here, we introduce a light-guided in situ ECM photopatterning method that enables micron-scale, programmable modulation of matrix mechanics within 3D collagen networks. Using this platform, we engineer well-defined mechanical barriers around tumor spheroids. Both bulk rheology and micromechanical measurements show photocrosslinking increases local stiffness by up to 5-fold, creating sharp mechanical gradients. Strikingly, even small localized barriers strongly suppress cell dissemination over extended spatial ranges, far exceeding their geometric footprint. Systematic variation of barrier geometry reveals that invasion is not governed by direct steric obstruction but by long-range mechanical modulation of the ECM, which reshapes least-resistance migration paths and is tightly coupled to transitions in migratory phenotype. These results establish a quantitative framework for how microscale mechanical heterogeneity directs collective invasion and suggest that cancer cells integrate nonlocal mechanical cues to modulate their phenotype transitions when navigating complex environments.