Engineering 3D Printed Bioceramic Scaffolds to Reconstruct Critical-Sized Calvaria Defects in a Skeletally Immature Pig Model

Abstract

Background: Three-dimensional printed bioceramic scaffolds composed of 100% β-tricalcium phosphate augmented with dipyridamole (3DPBC-DIPY) can regenerate bone across critically sized defects in skeletally mature and immature animal models. Before human application, safe and effective bone formation should be demonstrated in a large translational animal model. This study evaluated the ability of 3DPBC-DIPY scaffolds to restore critically sized calvarial defects in a skeletally immature, growing minipig. Methods: Unilateral calvarial defects (~1.4 cm) were created in 6-week-old Göttingen minipigs (n = 12). Four defects were filled with a 1000 μm 3DPBC-DIPY scaffold with a cap (a solid barrier on the ectocortical side of the scaffold to prevent soft-tissue infiltration), four defects were filled with a 1000 μm 3DPBC-DIPY scaffold without a cap, and four defects served as negative controls (no scaffold). Animals were euthanized 12 weeks postoperatively. Calvariae were subjected to micro–computed tomography, 3D reconstruction with volumetric analysis, qualitative histologic analysis, and nanoindentation. Results: Scaffold-induced bone growth was statistically greater than in negative controls (P ≤ 0.001), and the scaffolds with caps produced significantly more bone generation compared with the scaffolds without caps (P ≤ 0.001). Histologic analysis revealed woven and lamellar bone with haversian canals throughout the regenerated bone. Cranial sutures were observed to be patent, and there was no evidence of ectopic bone formation or excess inflammatory response. Reduced elastic modulus and hardness of scaffold-regenerated bone were found to be statistically equivalent to native bone (P = 0.148 for reduced elastic modulus of scaffolds with and without caps and P = 0.228 and P = 0.902 for hardness of scaffolds with and without caps, respectively). Conclusion: 3DPBC-DIPY scaffolds have the capacity to regenerate bone across critically sized calvarial defects in a skeletally immature translational pig model. Clinical Relevance Statement: This study assessed the bone generative capacity of 3D-printed bioceramic scaffolds composed of 100% β-tricalcium phosphate and augmented with dipyridamole placed within critical-sized calvarial defects in a growing porcine model.