Development of novel organic/inorganic osteomimetic inks for 3D bioprinted in vitro bone models

3D bioprinting is a promising strategy to develop predictive 3D in vitro bone models, surpassing the limitations of 2D and in vivo animal models. The 3D bioprinted models can achieve a high level of complexity, effectively mimicking the native bone niche composition. Furthermore, they allow to tailor the 3D structure geometry and enable precise control over pore size and orientation patterns. In this study, gelatin methacryloyl (GelMA) was selected to develop cell-laden 3D structures by 3D printing extrusion-based technology. Different GelMA concentrations (5, 7.5, 10 % w/v) were tested in terms of rheological behavior to select the most suitable for the 3D printing process. Then, the printing process parameters (i.e., pressure, extrusion speed) were optimized to obtain reproducible and accurate 3D printed structures. The optimal concentration (GelMA 7.5 %) was then enriched by stoichiometric hydroxyapatite nanocrystals (nHA, 0.1, 0.2, 0.5, and 1 % w/v), to mimic the inorganic component of bone, and evaluated in terms of 3D printing process and stability properties over 14 days, with enhanced stability in GelMA/nHA hydrogels. Osteosarcoma Saos-2 cells were considered for in vitro biological characterization, and no cytotoxic effect was obtained for GelMA and GelMA/nHA hydrogels. Saos-2 cells embedded in printed GelMA and GelMA/nHA bioinks proliferated over the 14 days of the in vitro culture. The developed formulations can be proposed as osteomimetic bioinks for 3D in vitro bone models, suitable for investigating bone disease mechanisms or for drug screening purposes.