A simultaneous 3D printing process for the fabrication of bioceramic and cell-laden hydrogel core/shell scaffolds with potential application in bone tissue regeneration

A novel process was developed to fabricate core/shell-structured 3D scaffolds, made of calcium-deficient hydroxyapatite (CDHA) and alginate laden with pre-osteoblast MC3T3-E1 cells, through a combination of cement chemistry, dual paste-extruding deposition (PED), and cell printing. The cement reaction of calcium phosphates replaced the typical sintering process of the ceramic scaffold fabrication after the simultaneous printing of the ceramics and cell-laden hydrogel. The alginate crosslinking process was divided into two steps using different concentrations of CaCl2, during and after 3D printing, in order to obtain a stable 3D core/shell structure and high cell viability. The whole process was carried out under conditions (neutral pH and a temperature between room temperature and 37 degrees C) that were gentle to the cells, so the cells incorporated into the shell remained alive throughout the 3D scaffold for the entire culture period (35 days). The core/shell structured scaffold significantly enhanced the mechanical properties when compared with a hydrogel that uses a typical cell-printing process or with a ceramic scaffold, due to the co-operative effect of each material. The compressive strength of the CDHA/alginate scaffolds in the wet state was 3.2 MPa, whereas the compressive strength of alginate could not be determined in the wet state. The 3D structural morphology of CDHA/alginate scaffolds was well retained, even after a compression test, and showed less deformation because the CDHA ceramic-core was encapsulated within the elastic alginate. The process developed in this study suggests a new cell printing model that has excellent potential for application in the field of bone tissue regeneration.