Abstract
The microstructure of biomaterials influences the cellular and biological responses in the bone. Octacalcium phosphate (OCP) exhibits higher biodegradability and osteoconductivity than hydroxyapatite (HA) during the conversion process from OCP to HA. However, the effect of the microstructure of OCP crystals on long tubular bones has not been clarified. In this study, two types of OCPs with different microstructures, fine-OCP (F-OCP) and coarse-OCP (C-OCP), were implanted in rat tibia for 4 weeks. F-OCP promoted cortical bone regeneration compared with C-OCP. The osteoclasts appearance was significantly higher in the C-OCP group than in the control group (defect only) at 1-week post-implantation. To investigate whether the solubility equilibrium depends on the different particle sizes of OCPs, Nano-OCP, which consisted of nanometer-sized OCPs, was prepared. The degree of supersaturation (DS) tended to decrease modestly in the order of C-OCP, F-OCP, and Nano-OCP with respect to HA and OCP in Tris-HCl buffer. F-OCP showed a higher phosphate ion concentration and lower calcium ion concentration after immersion in the buffer than C-OCP. The crystal structures of both OCPs tended to be converted to HA by rat abdominal implantation. These results suggest that differences in the microstructure of OCPs may affect osteoclastogenesis and result in osteoconductivity of this material in long tubular bone by altering dissolution behavior.
Highlights
Osteoconductive inorganic bone substitute materials include calcium phosphate (CaP)ceramic, such as sintered hydroxyapatite (HA), beta-tricalcium phosphate (β-TCP), biphasic calcium phosphate (BCP), octacalcium phosphate (OCP), calcium cement, glass-ceramic and bioglass
These results suggest that F-OCP shows better cortical bone regeneration than C-OCP in rat tibia defects
Bone formation rate in the total area was the highest in F-OCP at 1-week post-implantation. These results suggest that F-OCP exhibits higher bone formation ability than C-OCP in rat. These results suggest that F-OCP exhibits higher bone formation ability than C-OCP in rat tibia defects
Summary
Osteoconductive inorganic bone substitute materials include calcium phosphate (CaP)ceramic, such as sintered hydroxyapatite (HA), beta-tricalcium phosphate (β-TCP), biphasic calcium phosphate (BCP), octacalcium phosphate (OCP), calcium cement, glass-ceramic and bioglass. Osteoconductive inorganic bone substitute materials include calcium phosphate (CaP). The material characteristics of bone substitutes, such as chemical solubility [1], granule size [2], and crystal morphology [3], affect cellular function, material resorption, and osteoconductivity. An increase in the surface area and microstructure of BCP can concentrate more proteins and affect cell adhesion, proliferation, and differentiation [4,5]. The surface microstructure of β-TCP has been reported to affect osteogenic differentiation of mesenchymal stem cells and ectopic bone formation [6]. The microstructure of bioglass (30 mol% CaO-70 mol% SiO2 porous bioactive glass) promotes MC3T3 cell adhesion as the β-sheet/α-helix ratio of adsorbed BSA protein increases [8]
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