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[MIS12-08] Inhibition of phase transition of calcium phosphate by carbonate ion
Keywords:calcium phosphate
Introduction
Multiple pathways exist while the phase transition from amorphous calcium phosphate (ACP) to most stable hydroxyapatite (HAP) depending on the environment. 1) Saito et al. have found new pathway that ACP transforms into calcium hydrogen phosphate dihydrate (DCPD) on a silica glass in the presence of calcite in simulated body fluid (SBF). 2) They estimated that the carbonate ion dissolved from calcite inhibit the phase transition into HAp, but its mechanism has been unclear yet. In this study, we observed the crystallization process of calcium phosphate ex-situ and in-situ on silica glass in the presence of calcite in SBF in order to clarify the effects of calcium and carbonate ions on the formation of DCPD.
Experimental
In ex-situ observation, we soaked silica glass and calcite into SBF at 36.5 ℃ for 22 and 48 hours and observed the glass surface by polarizing microscope after the sample was dried by Nitrogen gas. In in-situ observation, we sealed calcite and simulated body fluid in a cell made of silica grass and observed the glass surface by polarizing microscope while keeping the temperature at 36.5 ℃
Results
The calcium phosphate particles were formed on the silica glass after soaking for 48 hours (Fig. 1). Polarized particles and non-polarized particles (indicated by red circles in Fig.1) were observed at the gap of calcite and silica glass. Polarization of the particles show that they are crystalized, because crystals with optical anisotropy have polarity. We found that the number of calcium phosphate particles and the proportion of the polarized particles increased farther from calcite. The concentration of carbonate ion would be higher in the vicinity of calcite. Therefore, this result strongly suggests the correlation between carbonate ion and DCPD formation. Moreover, many non-polarized particles were observed in the gap between calcite and the glass. Convection hardly occurs in the gap, so that the concentration of carbonate ion become higher. These results indicate that the higher concentration of carbonate ion, the longer the time to phase transition to DCPD.
References
1) C. Ohtsuki et al., J. Non-cryst. Solids 143 (1992) 84.
2) H. Saito et al., J. Cryst. Growth 553 (2021) 125937.
Multiple pathways exist while the phase transition from amorphous calcium phosphate (ACP) to most stable hydroxyapatite (HAP) depending on the environment. 1) Saito et al. have found new pathway that ACP transforms into calcium hydrogen phosphate dihydrate (DCPD) on a silica glass in the presence of calcite in simulated body fluid (SBF). 2) They estimated that the carbonate ion dissolved from calcite inhibit the phase transition into HAp, but its mechanism has been unclear yet. In this study, we observed the crystallization process of calcium phosphate ex-situ and in-situ on silica glass in the presence of calcite in SBF in order to clarify the effects of calcium and carbonate ions on the formation of DCPD.
Experimental
In ex-situ observation, we soaked silica glass and calcite into SBF at 36.5 ℃ for 22 and 48 hours and observed the glass surface by polarizing microscope after the sample was dried by Nitrogen gas. In in-situ observation, we sealed calcite and simulated body fluid in a cell made of silica grass and observed the glass surface by polarizing microscope while keeping the temperature at 36.5 ℃
Results
The calcium phosphate particles were formed on the silica glass after soaking for 48 hours (Fig. 1). Polarized particles and non-polarized particles (indicated by red circles in Fig.1) were observed at the gap of calcite and silica glass. Polarization of the particles show that they are crystalized, because crystals with optical anisotropy have polarity. We found that the number of calcium phosphate particles and the proportion of the polarized particles increased farther from calcite. The concentration of carbonate ion would be higher in the vicinity of calcite. Therefore, this result strongly suggests the correlation between carbonate ion and DCPD formation. Moreover, many non-polarized particles were observed in the gap between calcite and the glass. Convection hardly occurs in the gap, so that the concentration of carbonate ion become higher. These results indicate that the higher concentration of carbonate ion, the longer the time to phase transition to DCPD.
References
1) C. Ohtsuki et al., J. Non-cryst. Solids 143 (1992) 84.
2) H. Saito et al., J. Cryst. Growth 553 (2021) 125937.