Premixed Calcium Phosphate Cement for Extrusion-based 3D Printing: Planetary Centrifugal Mixer and Homogeneity Evaluation

Self-setting calcium phosphate cement (CPC), used in orthopedic surgery for bone replacement, usually consists of the powder mixture and setting liquid (aqueous) or carrier liquid (non-aqueous). After mixing two-phase compounds, the injectable viscous solution was formed and able to mold into the desired shape of the bone. The heterogeneous mixture, however, affects the dissolution-precipitation reaction ending in the unwanted chemical products, the deformed shape of solidified materials, and the undesired mechanical properties. In addition, the debris of heterogeneity increased the clogged needle probability when extruding with the cartridge of the 3D printer. In order to overcome these sort of problems and refine the homogeneity of CPC, the blade-free planetary mixer was used. Herein, the planetary centrifugal mixer was developed to increase the homogeneity of the CPC mixtures in batch production. The preliminary study of characteristics of the mixer, the revolution speed, centrifugal acceleration (1-66G), and their relations, was reported. The homogeneity of a CPC mixture was tested into two parts: the mixings of the powder-powder compound, and the powder-liquid paste. ImageJ, Fiji bundles, was used to evaluate the homogeneity of the mixture. The centrifugal acceleration of 16G and 66G homogeneously mixed a 1.2g of CaCO₃/Orange Red 735 and a 1.5g of αTCP/Glycerine respectively within 3 minutes. This study intentionally contributed to the fields of bio-printing and biofabrication, especially artificial bone, by improving the mixing process of the bone cement formula and demonstrating the idea for industrializing the bone cement into the commercial product.