Hydrolysis of Tetracalcium Phosphate Under a Near Constant-Composition Condition: Effects of pH and Particle Size
Laurence C. Chow, Milenko Markovic, B A. Frukhtbyen, Shozo Takagi
Tetracalcium phosphate (TTCP) is a component of a number of calcium phosphate cements used clinically for bone defect repairs. The properties of the cement such as setting time, strength, phase composition, and solubility are highly dependent on cement setting reactions. This study investigated hydrolysis reactions of TTCP under solution compositions chosen to mimic the compositions of the cement liquid during setting to gain understanding on factor that may have major effects on the cement setting. The study utilized a pseudo constant-composition technique that allowed both the rate and stoichiometry of the reaction to be determined while the reaction proceeded under a specific, constantly held solution pH. The hydrolysis experiments were conducted using either a fine (mean particle size 5.1 mm) or coarse (median particle size 13.1 mm) TTCP powder at pH 7, 8 and 10. Calcium (Ca) deficient low crystalline hydroxyapatite was the product in all experiments.Both the solution pH and TTCP particle size produced significant effects on all aspects of the hydrolysis reaction. At a given pH, the fine TTCP produced a hydroxyapatite product with a greater Ca-deficiency than did the coarse TTCP. For a given particle size, the Ca deficiency generally decreased with in creasing pH. Hydrolysis reaction rate generally decreased with increasing pH or TTCP particle size. At pH 7 and 8, the solution was undersaturated with respect to TTCP hydrolysis and supersaturated with respect to HA, suggesting that the reaction rate was limited by TTCP dissolution. In contrast, at pH 10, the solution was approximately saturated with respect to TTCP and highly supersaturated with respect to HA, suggesting that HA formation was the rate determining step of the reaction. The findings provided useful insights into the setting reaction mechanism of TTP-containing calcium phosphate cements.
, Markovic, M.
, Frukhtbyen, B.
and Takagi, S.
Hydrolysis of Tetracalcium Phosphate Under a Near Constant-Composition Condition: Effects of pH and Particle Size, Biomaterials
(Accessed November 30, 2023)