Fabrication of Monetite by a Controlled Phase Transformation of Three Dimensionally Printed Calcium Sulfate Construct

Abstract

M onetite is one of the calcium phosphates that has been used for bone regeneration and repair. Comparing to the widely used hydroxyapatite, monetite displayed greater resorption at physiological pH and could induce osteoclast resorption. Fabrication of a shape-customizable monetite construct by using a powder-based three dimensional printing (3DP) technique in combination with a phase transformation at low temperature was studied. Phase transformation of 3D printed calcium sulfate-based sample was carried out in 1M disodium hydrogen phosphate solution at pH5. Various processing parameters were then varied including temperatures (37 oC, 65 oC and 100 oC), sample weight to solution volume ratios (1:20, 1:30, 1:40 and 1:50) and soaking periods (24 h, 48 h, 72 h, 96 h and 120 h). It was found that a temperature of 100 oC, a sample weight to volume ratio of 1:50 and a time greater than 48 h were needed to fully transform the as-printed sample to monophasic monetite without causing the destruction of the structure or the incomplete transformation. Consistently, the microstructure of samples changed from rod-like crystals of calcium sulfate to petal-like crystals of monetite during the transformation process. Density, compressive modulus and strength decreased with soaking times during the course of transformation, but they did not further change with times after complete transformation. In vitro resorbability showed that 3D printed resorbed without conversion to other phase and its weight loss and ions release were greater than those of 3D printed hydroxyapatite indicating its greater resorption potential.