Dual Delivery of EPO and BMP2 from a Novel Modular Poly-e-Caprolactone Construct to Increase the Bone Formation in Prefabricated Bone Flaps

Poly-e-caprolactone (PCL) is a biocompatible polymer that has mechanical properties suitable for bone tissue engineering; however, it must be integrated with biologics to stimulate bone formation. Bone morphogenetic protein-2 (BMP2) delivered from PCL produces bone when implanted subcutaneously, and erythropoietin (EPO) works synergistically with BMP2. In this study, EPO and BMP2 are adsorbed separately on two 3D-printed PCL scaffold modules that are assembled for codelivery on a single scaffold structure. This assembled modular PCL scaffold with dual BMP2 and EPO delivery was shown to increase bone growth in an ectopic location when compared with BMP2 delivery along a replicate scaffold structure. EPO (200 IU/mL) and BMP2 (65 mu g/mL) were adsorbed onto the outer and inner portions of a modular scaffold, respectively. Protein binding and release studies were first quantified. Subsequently, EPO+BMP2 and BMP2 scaffolds were implanted subcutaneously in mice for 4 and 8 weeks, and the regenerated bone was analyzed with microcomputed tomography and histology; 8.6 +/- 1.4 mu g BMP2 (22%) and 140 +/- 29 IU EPO (69.8%) bound to the scaffold and <1% BMP2 and 83% EPO was released in 7 days. Increased endothelial cell proliferation on EPO-adsorbed PCL discs indicated protein bioactivity. At 4 and 8 weeks, dual BMP2 and EPO delivery regenerated more bone (5.1 +/- 1.1 and 5.5 +/- 1.6 mm(3)) than BMP2 alone (3.8 +/- 1.1 and 4.3 +/- 1.7 mm(3)). BMP2 and EPO scaffolds had more ingrowth (1.4%+/- 0.6%) in the outer module when compared with BMP2 (0.8%+/- 0.3%) at 4 weeks. Dual delivery produced more dense cellular marrow, while BMP2 had more fatty marrow. Dual EPO and BMP2 delivery is a potential method to regenerate bone faster for prefabricated flaps.