Hydration mechanism of partially amorphized β-tricalcium phosphate.

Calcium phosphate cements (CPCs) are applied as bone cements due to their excellent biocompatibility. In the present study, the quantitative phase content development during hydration of partially amorphized β-tricalcium phosphate (β-TCP) within the first 24h was investigated by in-situ X-ray diffraction (XRD) combined with the G-factor method, an external standard method. The quantity of amorphous phase (ATCP) in the powders was determined by the G-factor method. The hydration model established for partially amorphized β-TCP indicates that ATCP reacted first, followed by the hydration of a small fraction of crystalline β-TCP starting after some h. Consequently, hydration resulted in biphasic samples composed of calcium deficient hydroxyapatite (CDHA) and crystalline β-TCP. The ratio wt%(CDHA)/wt%(β-TCP) after 24h hydration was adjustable by the initial ATCP content. The crystallinity of CDHA was nearly independent of the ATCP content. Since the biological degradability of CDHA and β-TCP differ, the degradation performance of the set cements is expected to be adjustable by varying the ATCP content. The present study provided a basic understanding of the hydration mechanism of partially amorphized β-TCP, which is the prerequisite for the development of applicable CPC formulations.

STATEMENT OF SIGNIFICANCE: Calcium phosphate cements (CPCs) are medically applied for bone repair due to their excellent biocompatibility. β-Tricalcium phosphate (β-TCP), which is hardly reactive in water in its crystalline state, was previously shown to be activatable by partial amorphization. This provides potential for the development of new CPCs setting to biphasic samples composed of β-TCP and calcium deficient hydroxyapatite (CDHA). The degradation performance of these cements is expected to be adjustable by varying the ratio of CDHA to β-TCP. In the present study, the so far unknown setting mechanism of partially amorphized β-TCP was investigated in detail. The results contribute to the basic understanding of the hydration of partially amorphized β-TCP, which is important for the targeted development of new cement formulations.