Introduction: Hydroxyapatite (HAp) and tricalcium phosphate (TCP) are used as a filler for bone graft. Calcium-phosphate cement (CPC) pastes have such as biocompatibility and osteoconductivility, in addition to injectability which is freely moldable and adaptable to complex bone defects. However, CPC remains in a host body for a long term and does not replace with newly-formed bone. In previous study, we have developed CPC hybridized with gelatin particle [1]. This hybridized CPC paste was injectable by a syringe and exhibited anti-washout property, and this hybridized CPC specimens showed high bioresorbablity and osteoconductivity at 8 weeks after implantation. The aim of this study is to examine bioresorption and bone formation of the above mentioned CPC using pig tibia model after implantation for 24 weeks.
Materials and Methods: Hybridized CPC pastes were prepared according to our previous report [1]. The pig weighting about 110 kg was used in this study. Cylindrical defects (4.0 mm in diameter) were drilled in the right tibia of the pig, and the prepared CPC pastes were injected into these defects through a syringe. At 24 weeks after implantation, the pig was sacrificed, and the right tibia was removed and cut to carry out using X-ray micro-computed tomography (X-ray µCT). For biological evaluations, samples were stained with Villanueva bone stain. The rates of bioresorption and bone formation were calculated by imaging software.
Results and Discussion: The X-ray µCT images revealed that there was not any fragmentation in both hybridized CPC with gelatin particles of 10 mass% and non-hybridized CPC without gelatin ones specimens after 24 weeks implantation. No inflammatory cells and fibrous tissues were observed in the interface and both of the CPC specimens were directly in contact with the surrounding cortical bone. Thus, all CPC specimens had good biocompatibility. Bioresorption rates of non- and hybridized CPC specimens were at 18.4% and 68.8%, respectively. It was obvious that resorption rate of hybridized CPC specimens was higher than that of non-hybridized CPC specimens. This reason was thought that formed pores degraded gelatin particles had promoted hybridized CPC bioresorption by cell invasion, and enhanced bioresorption. Each rate of bone formation in the non- and hybridized CPC specimens was at 41.4% and 43.3, respectively. More over 70% of newly-formed bone was calcified bone. This result suggests that the addition of gelatin particles to CPC does not effect to the formation newly-formed bone. In addition, the balance of CPC specimens’ bioresorption and bone formation is suitable.
Conclusion: The resorption rate of the hybridized CPC specimens was about three times higher than that of non-hybridized CPCs specimens. The rate of bone formation in the hybridized CPC specimens was almost the same as that of non-hybridized. The present CPC hybridized with gelatin particles is a promising application as artificial bone with high bioresorbability and good osteoconductivity.
References:
[1] K. Kiminami et al., “Development of Bioresorbable Calcium-phosphate Cements Hybridized with Gelatin Particles and Their in vivo Evaluation. Key Eng. Mat., 631, 397-401 (2014).