Spheroidization of β-TCP by Suspension Induction-Plasma Spraying for Better Injectability

Calcium phosphate bone cements are well known orthopedic filling bone materials. The goal of this study is to provide a solution for the limited injectability of Calcium-phosphate (CaP) bone cements used in vertebroplasty [1,2,3]. More specifically, the issue under investigation is the phase separation of the CaP suspension into liquid and solid components when pressure is applied to extrude the suspension through a cannula which in turn affect the V% can be extruded, the force required to extrude the paste and also, the homogeneity of the extruded paste. β-Tricalcium phosphate powder (β-TCP Fluka No.21218, Buchs, Switzerland) was used to investigate the injectability of calcium phosphate pastes. Induction plasma technique was used to spheroidize calcium phosphate powders, thus facilitating the injection process. Both treated and untreated powders were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Specific surface area and particle size distribution (PSD). The injectability test was applied for both powders using a hydraulic press to inject the paste through the syringe and the cannula. The force required to inject the paste and the extruded V% were measured.  The liquid to power ratio (L/P) of the extruded paste was measured and compared with the initial (L/P) to examine the extruded paste homogeneity. The SEM shows that plasma-treated powders have a spherical shape with a wide particle size distribution. The mean particle diameter d (0.5) for untreated and treated powders are 3.4 µm and 0.56 µm respectively. The treated powder shows better injectability. No more than 80% of non-treated paste can be extruded, on the other hand; more than 95% of treated powder paste can be easily extruded without any significant increase in the force applied. The plasma treated powders have a spherical shape which in turn affects the paste viscosity due to a decrease of the particles interactions.