Low Temperature Fabrication of Brushite by PowderBased Three Dimensional Printing Coupled with Phase Transformation Process

Abstract

Hydroxyapatite (HA) is widely used as bone graft, but showed limited resorption in the body which could affect its bone integration. In addition to HA, dicalcium phosphate dihydrate or brushite had greater resorption rate and was reported to be biocompatible and osteoconductive. Fabrication of brushite was experimentally carried out by using a combination of a powder-based three dimensional printing (3DP) technique and a phase transformation by a dissolution-precipitation process. The 3D printed calcium sulfate based sample was soaked in 1M disodium hydrogen phosphate solution at various conditions by varying pH (6 and 7), temperature (25˚C, 37˚C and 80˚C) and time (24, 48 and 72 hours). X-ray diffraction showed that brushite could be obtained by using pH 7 and 37 ˚C at all soaking durations and the crystal shape was observed to be plate-like. Samples were damaged at 80˚C for both pH values. For other conditions, brushite was found as a major phase in the converted samples, but the samples still contained calcium sulfate dihydrate and monetite as minor phases. However, the amount of brushite phase increased with increasing conversion times. Resorbability of the 3D printed brushite was evaluated by measuring a weight loss and calcium and phosphorus ion releasing in simulated body fluid at pH 7.4 and 37˚C for up to 28 days. Weight loss of the sample was high initially for up to 7 days and leveled off afterward. The total weight loss was approximately 43% at 28 days. 3D printed brushite was also found to transform to other calcium phosphate phases during resorption process. Hydroxyapatite was detected at the surface region while a mixture of hydroxyapatite and octacalcium phosphate was found in the core area. This phase transformation could be associated with the release of calcium and phosphate ions from specimens during resorption and re-precipitation into different phases under desired conditions for each phase.