Highly Porous Carbonate Apatite Scaffolds Fabricated via Freeze-Drying for Accelerated Bone Replacement

Bone scaffolds should ideally possess good osteoconductivity and biodegradability, form abundant bone at an early stage, maintain the regenerated bone tissue, and be completely replaced by newly formed bone. Therefore, highly porous scaffolds composed of resorbable bioactive ceramics are promising candidates for bone repair. However, the methods for fabricating such scaffolds remain underdeveloped, and the in vivo efficacies of the generated structures have not been sufficiently evaluated. Therefore, the aims of this study were to develop a novel method for fabricating a highly porous carbonate apatite (CA) scaffold via a freeze-drying technique and to evaluate its structural, chemical, mechanical, and in vivo performance using a rabbit model of femoral condyle defect. The CA scaffold structure consisted of three-dimensionally interconnected pores, exhibiting high porosity (91.7%). Despite its high porosity, the scaffold did not collapse during implantation into the bone defect and was easy to handle. When implanted into critically sized bone defects, the CA scaffolds formed three times more new bone than that formed by clinically used CA granules after 4 weeks, with the bone area percentages in the CA scaffold, CA granule, and sham groups being 51.7% ± 8.1%, 14.0% ± 4.9%, and 1.2% ± 0.4%, respectively. After 12 weeks, the CA scaffolds maintained approximately three times the bone area of that formed by the CA granules and were almost completely replaced by newly formed bone. These findings indicate that the highly interconnected porous CA scaffold can achieve rapid bone regeneration and dynamically adjust its structure to accommodate newly formed bone, making it a promising candidate for bone regeneration applications.