Controlled Sequential Delivery of PDGF-BB and BMP-2 for Vascularized Bone Regeneration

摘要

Bone regeneration consists of a series of complex biological events, that in vivo, requires the highly coordinated presentation of biochemical cues to regulate these stages of healing. Taking inspiration from the natural healing process, a wide variety of growth factors are currently being released from tissue engineered scaffolds to aid in healing non-union fractures and bone defects. Currently, several scaffolding design techniques exist for releasing multiple growth factors with unique release profiles, which include polymer encapsulation, layer-by-layer fabrication, and core-shell construction, as well as growth factor delivery through other biological agents, such as plasmids and platelet-rich plasma. Several studies have suggested that the efficacy of multiple growth factor presentation may be influenced by several factors, including the sequence of presentation, and the dosage at various stages. Accordingly, building evidence suggests that in vivo growth factor presentation consists of highly coordinated temporal appearance, intricate crosstalk, and multi-pathway signaling. Therefore, determining effective growth factor release schedules for incorporation in bone scaffolding requires an assay platform that, in some ways, begins to account for these complexities. For the purposes of our studies, we have developed a three-dimensional assay system, capable of supporting multiple cell types, that providing control over growth factor delivery presentation schedules.udTo begin to understand the effects of multiple growth factor presentation on the stages of bone repair, we have used this assay system to assess cellular responses to a variety of growth factor delivery schedules with variations in sequence, length of delivery, and overlap in delivery. By varying these parameters, we have identified a schedule of PDGF and BMP-2 presentation capable of promoting angiogenic tubule formation in co-cultures of hMSCs and HUVECs. Based on this information, we have engineered a biomaterial-based system to controllably release this sequential schedule of PDGF and BMP-2 autonomously. This preprogrammed controlled release system was then incorporated with a three-dimensional, porous calcium phosphate scaffold, and resulting material properties and cellular responses were characterized. The following experiments and results aim to take inspiration from the in vivo bone healing milieu, and to use specific cellular responses to guide the fabrication of a truly biomimetic scaffolding system.