In vitro Physico-chemical Dissolution Processes

Dicalcium phosphate dihydrate [CaHP04.2H20] Dicalcium phosphate anhydrate [CaHPOJ Octacalcium phosphate [CagHj (P04)g.5H20] Tricaldum phosphate [Caj (P04)2] Hydroxyapatite [Cam ( 04)6 (0 )2] Tetracalcium phosphate [Ca4 (P04)20] 

Dissolution of a solid material continues until an equilibrium condition is reached, followed by a saturated condition where a solid and a liquid remain in equilibrium. Solubility is defined as the maximum concentration of solute in the solution under the equilibrium condition. This concept of solubility is very convenient to know how much the material has actually dissolved. However, it is not convenient for showing general solubility of the material since its value depends on the pH of the solution. 

Therefore, a thermodynamic equilibrium constant known as the solubility product constant Kjp is used for slightly soluble salts. This solubility product constant is useful for understanding the dissolution characteristics, because its value does not change in either acid or basic solutions under the same conditions of temperature, pressure and ionic strength. 

There are many reports on solubility product constants of calcium phosphate compounds obtained by the above equation, and these values are shown in Table 8.1. 

Dicalcium phosphate dihydrate DCPD CaHP04. 2H2O 6.59 1,2 

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This chapter overviews the literature regarding the biodegradation processes of bioactive calcium phosphate ceramics from the viewpoint of in vitro physico-chemical dissolution processes and in vivolin vitro biological degradation processes. 

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