Stromal cell identity affects ECM mechanics both locally and globally and regulates vascular morphogenesis in 3D

ECM stiffness is a potential instructive cue during capillary morphogenesis. Bulk measurements have often been used to investigate matrix stiffness as a cellular cue. However, local peri-cellular stiffness can be heterogeneous and vary greatly from measured bulk properties spatially and temporally. Here, we utilize bulk rheology and optical tweezers active microrheology (AMR) to investigate the dynamic mechanical crosstalk between cells and the surrounding matrix during capillary morphogenesis across length scales with various supporting stromal cells (SCs). We found that local pericellular stiffness around growing capillaries was highly heterogeneous and SC-dependent. Additionally, the density of formed capillaries across 14 days in culture was also SC-dependent and was accompanied by ECM stiffening both locally and at the bulk level with local stiffness anisotropy emerging in the direction of capillary growth.