Fabrication of Microstructured Calcium Phosphate Ceramics Scaffolds by Material Extrusion-Based 3D Printing Approach.

Natural materials such as bone and enamel have intricate microstructures with inorganic minerals oriented to perform multiple mechanical and biological functions. Current additive manufacturing methods for biominerals from the calcium phosphate (CaP) family enable fabrication of custom-shaped bioactive scaffolds with controlled pore structures for patient-specific bone repair. Yet, these scaffolds do not feature intricate microstructures similar to those found in natural materials. In this work, we used direct material extrusion to 3D print water-based inks containing CaP microplatelets, and obtained microstructured scaffolds with various designs. To be shear-thinning and printable, the ink incorporated a concentration of 21 - 24 vol% CaP microplatelets of high aspect ratio. Good shape retention, print fidelity and overhanging layers were achieved by simultaneous printing and drying. Combined with the 3D design, versatile CaP microstructured objects can be built, from porous scaffolds to bulk parts. Extruded filaments featured a core-shell microstructure with graded microplatelet orientations, which was not affected by the printing parameters and the print design. A simple model is proposed to predict the core-shell microstructure according to the ink rheology. Given the remaining open porosity after calcination, microstructured scaffolds could be infiltrated with an organic phase in future to yield CaP biocomposites for hard tissue engineering.