The research investigates how local cell–ECM interactions regulate the global mechanics of collagen networks in a biomimetic tissue model composed of type I fibrillar collagen with embedded cancer cells (volume fractions: 0.4%–20%). Experiments compare the behavior of human dermal fibroblasts and MDA-MB-231 breast cancer cells, which are known to actively remodel collagen networks. Collagen polymerization and network mechanics were characterized using bulk shear rheology. A custom-built rheo-confocal microscope was used to visualize real-time local remodeling of collagen during polymerization. All raw data, processed results, and MATLAB/python scripts for data analysis and figure generation are included.