Hydroxyapatite Formation on Bioactive Materials

Human body fluid and SBF contain calcium and phosphate ions that are already supersaturated with respect to hydroxyapatite [20]. However, these fluids do not spontaneously deposit hydroxyapatite under normal conditions. This is because the activation energy barrier for hydroxyapatite nudeation is very high. Therefore, the ability of substrates to induce heterogeneous nudeation of hydroxyapatite and the degree of supersaturation of SBF with respect to hydroxyapatite are important factors for hydroxyapatite formation on materials in the body fluid and SBF. 

Ohtsuki et al. [22] assumed the hydroxyapatite formation mechanism to be as follows. The formation of the hydroxyapatite layer is triggered by release of Ca2+ ions 

30 days, o hydroxyapatite formation, no hydroxyapatite formation, severe dissolution. 

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