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

Abstract

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 125 I 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.

Calcium Phosphate Cement with BMP-2-loaded Gelatin Microspheres Enhances Bone Healing in Osteoporosis: A Pilot Study

“…There were, however, no differences among the three groups at the end of implantation. We speculate prolonged retention of rhBMP-2 in a carrier might result in the loss of its osteoinductive capacity [8]. The release of more growth factors during the early period is apparently important for a carrier, and this is also important for healing of osteoporotic bone defects because osteoporosis most influences the early period of defect healing [21].…”

“…rhBMP-2 is widely used to enhance osteoinduction of bone substitutes [8,11,17,25,28,29]. In several studies rhBMP-2/carrier formulations were associated with bridging of critical-sized bone defects [11,28,29], but rhBMP-2/CPC was the only combination to restore torsional mechanical properties equivalent to those of normal bone [29].…”

Bone tissue engineering: A review in bone biomimetics and drug delivery strategies

“…For example, one group recently demonstrated that growth factor-loaded PLGA microspheres imbedded within a poly(propylene fumarate) (PPF) matrix displayed prolonged release of active growth factor in vivo for a period of 12 weeks. 278 This resulted in a substantially better bone formation compared with controls. Other groups have investigated similar approached by entrapping growth factors within PLGA scaffolds which have been mineralized through soaking in a simulated body fluid.…”

Potential of Hydrogels Based on Poly(Ethylene Glycol) and Sebacic Acid as Orthopedic Tissue Engineering Scaffolds

“…28 Briefly, 20 mL of alkaline working buffer solution, 80 mL of the lysate solution, and 100 mL of substrate solution (5 mM p-nitrophenyl phosphate) were added to a 96-well plate. The plate was incubated at 378C for 1 h, and the reaction was stopped by adding 100 mL of 0.3 N NaOH solution to each well.…”

“…These cells are known to respond well to BMP-2 by sensitive changes in alkaline phosphatase production, 28,30 one of the early bone markers, whereas MSCs in the presence of osteogenic molecules may not produce significant amount of ALP when compared with the control (tissue culture plates). 8 The cells were plated at a density of 20,000 cells=cm 2 on 24-well tissue culture plates (Corning, Cambridge, MA).…”