Restoration of critical-size defects in the rabbit mandible using porous nanohydroxyapatite-polyamide scaffolds

Composite nanohydroxyapatite/polyamide (n-HA/PA) biomaterials have been indicated for bone defect reconstruction, where PA is added to enhance the toughness of n-HA. However, a comprehensive understanding of the biological performance of this implant material remains to be determined. In this study, the biological activity of n-HA/PA biomaterials was characterized in vitro by assessing the growth of bone marrow stromal cells (BMSCs), and in an in vivo rabbit model. To evaluate the n-HA/PA performance under different osteogenic conditions in vivo, implants were inserted to critical-size bone defects in the angle and body of the rabbit mandible. To determine the necessity of ectogenic BMSC-n-HA/PA hybrids at different implantation sites, both raw n-HA/PA materials and BMSC-seeded n-HA/PA hybrids were implanted. Bone formation was detected by radiology and histological studies. The results showed that n-HA/PA composites had great bioactivity, demonstrating significant BMSC proliferation, active alkaline phosphatase secretion, and stimulating the expression of osteogenic proteins (bone morphogenetic protein 2 [BMP2], osteoprotegerin [OPG], osteopontin [OPN], collagen type I [Col I], and osteocalcin [OCN]), in comparison to the control (polyethylene). At marrow-rich implantation sites (mandibular body), the amount of new bone formation was significant, but was not enhanced by the presence of BMSCs in the BMSC-n-HA/PA hybrids. However, the BMSC-n-HA/PA hybrids were essential for promoting bone formation in marrow-poor sites (mandibular angle). In conclusion, n-HA/PA biomaterials, which offer the advantage of enhanced mechanical performance over n-HA, exhibit significant bioactivity, including the capacity for bone regeneration at marrow-poor sites when implanted in combination with BMSCs.