Craniofacial surgeries and autologous bone grafts are often required to address congenital birth defects and traumatic injuries to the face and jaw. Local delivery of osteogenic protein growth factors, particularly bone morphogenetic protein-2 (BMP2), has been shown to promote healing in these injuries. Bone defect treatment with pro-angiogenic therapies such as vascular endothelial growth factor (VEGF) also improves healing through improved tissue vascularization; compellingly, emerging evidence indicates that sequential delivery of pro- angiogenic and pro-osteogenic therapies promotes even more pronounced bone development than sole administration of either drug. Despite years of effort developing biomaterial systems as localized growth factor delivery depots for bone regeneration, many of these technologies still fail to completely regenerate orthopedic tissue primarily due to poor drug pharmacokinetics and premature therapeutic release. It is hypothesized that directly matching drug delivery kinetics with the rate of tissue growth will significantly improve bone regeneration in craniofacial defects. Cell-produced signals, particularly reactive oxygen species (ROS), can be leveraged to produce selective, “healing-responsive” drug release from activatable biomaterial systems. This proposed work seeks to develop injectable drug carriers that will mediate sequential, localized release of VEGF and BMP2 upon triggering by cell-generated oxidation during bone regeneration. These responsive delivery vehicles will be created using ROS-degradable microparticles coated with ROS-degradable layer-by- layer (LbL) films, thereby combining the strengths of two controlled release technologies (injectable antioxidant particles, responsive surface coatings) into a single drug delivery platform. The project’s first aim will optimize these coated microparticles for dual-stage protein release and potent bioactivity upon oxidative triggering, while the second aim will evaluate VEGF/BMP2-loaded LbL microparticles for in vivo drug release kinetics and bone regeneration in critically-sized rat skull defects. We anticipate that the ROS-responsive, dually-loaded particles will promote more robust bone repair than single-drug formulations or conventional, non-responsive microparticle analogues. In short, the proposal brings together a highly-qualified research team to achieve the overall project goal of developing and validating a clinically-translatable approach for controlled, on-demand delivery of regenerative growth factors to foster robust craniofacial bone regeneration.