Additive manufacturing of ceramic alumina/calcium phosphate structures by DLP 3D printing

Producing micro and macroporous 3D structures that mimic the bone architecture of a specific anatomic region, namely the rounded trabeculae in trabecular bone, is a considerable challenge, to which additive manufacturing can make a fundamental contribution. The main objective of the work was to explore the Digital Light Processing (DLP) technique in obtaining customized parts, from a ceramic suspension composed of two different materials, specifically alumina and hydroxyapatite (HA), with a trabecular bone architecture, using Computer Assisted Design (CAD) modelling techniques and additive manufacturing. Hydroxyapatite (HA) was added to the alumina matrix to improve the biocompatibility and bioactivity of the composites after sintering. After optimizing all printing parameters and the suspensions rheological properties, samples in alumina and alumina-hydroxyapatite with the desired architecture were obtained. The influence of the incorporation of hydroxyapatite in the alumina formulations was also analyzed, with increasing hydroxyapatite contents: 5, 10, and 15 wt%. The rheological behaviour of the suspensions was studied in a plate-to-plate system. The physical-chemical and mechanical characterization of produced samples were carried out by X-ray diffraction, Scanning electron microscopy, and compressive tests. The suspensions prepared with two different materials showed adequate viscosity to achieve a good spread and homogeneous layers in the 3D printing process. In the produced samples, the occurrence of a hibonite phase (CaAl12O19), resulting from the reaction between alumina and hydroxyapatite during the sintering step, increased the compressive strength of the samples. The high temperature needed for sintering alumina led to the conversation of HA into TCP. The achieved mechanical strength results from the porosity level and the thickness of the struts of the printed architecture. DLP showed to be a precision printing technology of low cost that can be used to fabricate parts in the industry from a suspension composed of a mixture of alumina and HA powders, which is very useful in the bone repair field and not previously reported.