Retention of in vitro and in vivo BMP-2 bioactivity in sustained delivery vehicles for bone tissue engineering

摘要

In this study, we investigated the in vitro and in vivo biologic activity of bone morphogenetic protein 2 (BMP-2) released from four sustained delivery vehicles for bone regeneration. BMP-2 was incorporated in 1) a gelatin hydrogel, 2) poly(lactic-co-glycolic acid) (PLGA) microspheres embedded in a gelatin hydrogel, 3) microspheres embedded in a poly(propylene fumarate) (PPF) scaffold and 4) microspheres embedded in a PPF scaffold surrounded by a gelatin hydrogel. A fraction of the incorporated BMP-2 was radiolabeled with ¹²⁵I to determine its in vitro and in vivo release profiles. The release and bioactivity of BMP-2 were tested weekly over a period of 12 weeks in preosteoblast W20-17 cell line culture and in a rat subcutaneous implantation model. Outcome parameters for in vitro and in vivo bioactivity of the released BMP-2 were alkaline phosphatase (AP) induction and bone formation, respectively. The four implant types showed different in vitro release profiles over the 12-week period, which changed significantly upon implantation. The AP induction by BMP-2 released from gelatin implants showed a loss in bioactivity after 6 weeks in culture, while the BMP-2 released from the other implants continued to show bioactivity over the full 12-week period. Micro-CT and histological analysis of the delivery vehicles after 6 weeks of implantation showed significantly more bone in the microsphere/PPF scaffold composites (implant 3, p < 0.02). After 12 weeks, the amount of newly formed bone in the microsphere/PPF scaffolds remained significantly higher than in the gelatin and microsphere/gelatin hydrogels (p < 0.001), however there was no statistical difference compared to the microsphere/PPF/gelatin composite. Overall, the results from this study show that BMP-2 could be incorporated into various bone tissue engineering composites for sustained release over a prolonged period of time with retention of bioactivity.