Robocasting of self-setting bioceramics: from paste formulation to 3D part characteristics

This study aims to investigate the feasibility of generating three-dimensional scaffold structures by robocasting 3D printing for bone tissue engineering and anatomical model applications. Robocasting is an additive manufacturing process that generates parts directly from CAD draws in a layer-wise manner, enabling the construction of complex 3D structures with controlled chemistry and specific interconnected porosity. Our strategy was based on the reactivity of the involved components in mineral bone cement or plaster self-setting pastes, but the simultaneity of manufacturing process and chemical setting reactions required a careful adaptation of paste formulations to secure enough time to fabricate a 3D scaffold under homogeneous extruding conditions at room temperature. The two self-setting pastes reactions studied in the present work were the transformation of calcium sulphate hemi-hydrate into gypsum and a mixture of brushite and vaterite into apatite. Additives such as carboxymethyl cellulose (CMC) or polyvinyl alcohol (PVA) were introduced in limited amounts (2-3% for CMC and 9-13% for PVA) in the self-setting paste formulations to favour extrusion while achieving self-standing brands. To complete the 3D scaffold setting reaction, a post-drying protocol was developed. 3D parts of various sizes and architectures were produced. Their crystalline phase and chemical composition characterisations allowed establishing the progress of the chemical setting reaction for all the pastes. A rheological study allowed defining a common trend for all the extruded pastes. Compression tests presented great mechanical properties of plaster 3D samples, particularly improved by the presence of PVA, while water absorption study presented suitable values for all the compositions, according to their different applications.