The effect of crystallinity on strength development of alpha-TCP bone substitutes

Alpha phase tricalcium phosphates (alpha-TCP) were produced using a solid-state reaction method and milled for various periods of time. The resulting four materials were alpha-TCPs, ranging in crystalline content. Powders were exposed to X-ray diffraction for material identification as well as for use in crystallinity and purity calculations. Powder particle size was investigated using laser diffraction. Materials were mixed with 2.5% Na(2)HPO(4) solution to initiate the hydration of alpha-TCP to calcium-deficient hydroxyapatite (CDHA). Isothermal calorimetry was performed to observe thermal response of the powders over a period of time. During the reaction process, at various time points up to 216 h, the material was compression tested to observe strength development. Materials proved to be predominantly alpha phase, while amorphous content determined by XRD varied. Reactivity, as measured by isothermal calorimetry, varied with crystallinity of the alpha-TCP powder. Speed of strength development did not change except for the most finely ground powder. In addition, crystal size of the CDHA was changed only in the product formed from the most highly ground material. It is proposed that increasing reactivity of alpha-TCP cements does not result in a corresponding increase in rate of strength development until there is sufficient supersaturation to produce significant crystal nucleation.