Cancer therapy is often limited by poor selectivity and severe side effects, highlighting the need for localized and controllable platforms. In this study, we engineered a three-dimensional hydrogel system as a light-responsive biomaterial for photodynamic therapy. A biocompatible, photo-crosslinkable polymer network served as the structural matrix to support reproducible fabrication and cell compatibility. Inorganic nanoscale additives were introduced to tune mechanical performance, while a light-activated sensitizing molecule was embedded to generate reactive oxygen species under irradiation. Adipose tissue–derived stem cells were included as a biological component responsive to oxidative microenvironments. Physicochemical properties were assessed by mechanical testing, rheological analysis, swelling measurements, and microstructural/elemental observation to identify cell-suitable formulations for light-mediated therapy, with minimal invasiveness.