Osteoconductive Property of a Mechanical Mixture of Octacalcium Phosphate and Amorphous Calcium Phosphate

Abstract

The present study was designed to investigate the extent of osteoconductive property of a mechanical mixture of octacalcium phosphate (OCP) and amorphous calcium phosphate (ACP). OCP was mixed with ACP in granules that had a diameter of 300 and 500 μm, respectively, and at 25, 50, or 75 wt %. The physicochemical characteristics and the osteoconductive properties of the mixtures were compared with OCP alone or ACP alone through implantation into rat critical-sized calvaria defects for up to 12 weeks and simulated body fluid (SBF) immersion for 2 weeks. The mixtures of OCP and ACP, in particular the OCP 25 wt % and ACP 75 wt % (O25A75), had higher radiopacity compared to ACP and OCP alone. O25A75 induced greater enhancement of bone regeneration than ACP alone at 8 weeks and that than OCP alone at 12 weeks. X-ray diffraction and Fourier transform infrared (FTIR) analyses of the retrieved mixtures showed that ACP, OCP, and O25A75 tended to convert to hydroxyapatite (HA) after the implantation, while the structure of OCP remains without complete conversion after SBF immersion. Analyses by FTIR curve fitting of the solids and the degree of supersaturation of the SBF supported the observation that the existence of ACP enhances the kinetics of the conversion. Scanning electron microscopy found that the surface of O25A75 had distinct characteristics with OCP and ACP after SBF immersion. The results suggest that the extent of the osteoconduction of OCP could be controlled by the copresence of ACP most probably through the prevailing dissolution-precipitation of the surface of ACP crystals to form HA.

Effect of calcium phosphate phases affecting the crosstalk between osteoblasts and osteoclasts in vitro

“…The FTIR spectrum of each powder was obtain by FTIR spectroscopy (FT/IR‐4600; JASCO Corporation, Tokyo, Japan) with the sample diluted in KBr over a range of 1400–400 cm −1 with 4 cm −1 resolution. FTIR curve fitting analysis was performed following the method described in our previous study . The intensities of apatitic OH − and nonapatitic HPO 4 2− in FTIR spectra were estimated through curve‐fitting using Spectra Manager Version 2.15.05 (Curve fitting Version 2.06).…”

“…FTIR curve fitting analysis was performed following the method described in our previous study. 41 The intensities of apatitic OH − and nonapatitic HPO 4 2− in FTIR spectra were estimated through curve-fitting using Spectra Manager Version 2.15.05 (Curve fitting Version 2.06). An IR band ratio between 450 and 700 cm −1 was used according to a method reported by Rey et al 50,51…”

“…There is consensus that OCP stacks apatite layers alternatively with hydrated layers 10 and that hydrolysis proceeds spontaneously and irreversibly once it is initiated under supersaturated conditions. 5,40,41 It is a reasonable hypothesis that calcium and phosphate ion reordering within the hydrated layers of an OCP structure through ion exchange with an external solution or re-precipitation of new HA and/or OCP crystals onto the original OCP is associated with controlling the degree of supersaturation around the crystals exposed to adjacent cells. 42 However, there is no information to date on how such apatite formation within the structure or near the surface of OCP affects cellular activity around the crystals.…”

Amorphous calcium phosphate (ACP) in tissue repair process

“…Furthermore, the ACP conversion process can serve as a vehicle for delivering calcium and phosphate ions which are necessary for mineralization (Popp et al, ). The literature has demonstrated that the use of ACP has been limited to grafts for bone regeneration in vivo due to its prevailing dissolution‐precipitation (Kobayashi et al, ).…”

On the pathway of mineral deposition in larval zebrafish caudal fin bone

“…The crystalline phase of OCP differs from the apatite crystalline phase, by a water layer that is located between two layers of apatite [18]. The ACP → OCP → carbonated hydroxyapatite transformation reaction is known to occur in vitro at neutral pH conditions, as well as at physiological pH [19][20][21][22].…”