Abstract: Dipyridamole Releasing 3D Printed Bioactive Ceramic Scaffolds with Osseoconductive Geometries Promote Craniofacial Bone Regeneration

Abstract

INTRODUCTION: The standard of care for critical-sized bony defects is autologous bone tissue transfer. However, its limitations (e.g., morbidity, secondary procedures, cost) have driven progress in alternatives such as tissue engineering-based treatments. We explored the bone regenerative capacity of customized, 3D printed bioactive ceramic (3DBC) scaffolds with dipyridamole (DIPY), an adenosine A2A receptor (A2AR) indirect agonist known to enhance bone formation, at the ramus of the rabbit mandible. METHODS: Critical-sized bony defects (10mm height, 10mm length, full thickness) were created at the inferior aspect of the right mandibular rami of rabbits, adjacent to the angular process (n=15). Each defect was replaced by a custom-to-defect, 3DBC printed porous scaffold composed of β-tricalcium phosphate. Scaffolds were either uncoated (control), collagen-coated (COLL), or collagen coated and immersed in 100μM dipyridamole (DIPY). At t=8 weeks, animals were euthanized and the rami retrieved. Bone growth was assessed exclusively within scaffold pores, and evaluated by microCT/advanced reconstruction computer software. MicroCT quantification was calculated in segments as a function of distance from proximal to distal scaffold insertion. Bone morphology was assessed by histology. One-way ANOVA analysis was performed to compare group means, and 95% confidence intervals (CI) were included. RESULTS: Qualitative analysis did not show an inflammatory response. On 3D analysis, the control and COLL groups (12.3 ± 8.3% and 6.9 ± 8.3% bone occupancy of free space, respectively) had less bone growth, while the most bone growth was in the DIPY group (26.9 ± 10.7%), a statistically significant difference (p<0.03 DIPY vs. control and p<0.01 DIPY vs. COLL). Evaluation of scaffold presence resulted in a significantly higher presence of material for the COLL group relative to the DIPY group (p<0.015), whereas the control group presented intermediate values (non-significant relative to both COLL and DIPY). A general linear mixed model was performed for bone growth as a function of distance from the most proximal (deepest) aspect scaffold insertion site to the most superficial (distal at the mandibular border) aspect, for which DIPY-treated scaffolds demonstrated the most bone growth at the thinnest region of ramus bone at the proximal defect. Highly cellular and vascularized intramembranous-like bone healing was observed in all groups. CONCLUSION: COL-DIPY significantly increased the 3DBC scaffold’s ability to regenerate bone. Irrespective of treatment group, all scaffolds demonstrated bone regeneration with predominant focal growth at bone-scaffold interfaces.