Enhancing material and biological properties of calcium phosphate bone substitute

Abstract: Calcium phosphate materials (CaPs) have proven biocompatible and useful in clinical situations. One CaP showing promise in the clinic is alpha phase tricalcium phosphate ([alpha]-TCP). [alpha]-TCP in powder form can be hydrated and undergoes a reaction resulting in calcium deficient hydroxyapatite (CDHA). The similarity of CDHA and human bone makes [alpha]-TCP a very viable material for application in bone defect. Studies were carried out investigating methods to enhance material and biological properties of calcium phosphate bone substitutes. Hydration reaction, reaction completion, and strength characteristics were studied, as well as effects of particle size on the reactivity of such compounds. Reactivity with relation to material crystallite size was further studied. X-ray amorphous fraction of powders and crystallite size was then investigated with relation to the speed of strength development. Addition of silicon to the [alpha]-TCP matrix was also examined. A silicon doped [alpha]-TCP was achieved which yielded promising results of increased osteoblastic activity both in vitro and in vivo. It was seen with proper milling procedure that it was possible to prepare an [alpha]-TCP powder by solid state reaction that was potentially similar to one prepared using precipitation technique and that during hydration most of the strength developed during later stages of reaction. Surface area of the [alpha]-TCP has a significant impact on the reactivity however according to calculations, is not an accurate measure of degree of reaction. During high energy milling crystallite size is altered which has significant relation to thermal events during hydration as well as speed of reaction. The time needed to achieve maximum strength of hydrated [alpha]-TCP compounds appeared to relate to final CDHA crystal size and implied existence of a threshold of super-saturation needed to form CDHA at an accelerated rate. The [alpha]-TCP lattice was able to incorporate silicon and the in vitro and in vivo reactivity of the silica doped [alpha]-TCP was significantly increased upon testing in a bone harvest chamber rabbit model. CaPs as materials in the clinic are note only versatile, with the possibility of injectability, but can be adjusted in many ways to fit the desired application.