3D bioprinting of mouse pre-osteoblasts and human MSCs using bioinks consisting of gelatin and decellularized bone particles

One of the key challenges in biofabrication applications is to obtain bioinks that provide a balance between printability, shape fidelity, cell viability, and tissue maturation. Decellularization methods allow the extraction of natural extracellular matrix, preserving tissue-specific matrix proteins. However, the critical challenge in bone decellularization is to preserve both organic (collagen, proteoglycans) and inorganic components (hydroxyapatite) to maintain the natural composition and functionality of bone. Besides, there is a need to investigate the effects of decellularized bone (DB) particles as a tissue-based additive in bioink formulation to develop functional bioinks. Here we evaluated the effect of incorporating DB particles of different sizes (<= 45 and <= 100 mu m) and concentrations (1%, 5%, 10% (wt %)) into bioink formulations containing gelatin (GEL) and pre-osteoblasts (MC3T3-E1) or human mesenchymal stem cells (hTERT-MSCs). In addition, we propose a minimalistic bioink formulation using GEL, DB particles and cells with an easy preparation process resulting in a high cell viability. The printability properties of the inks were evaluated. Additionally, rheological properties were determined with shear thinning and thixotropy tests. The bioprinted constructs were cultured for 28 days. The viability, proliferation, and osteogenic differentiation capacity of cells were evaluated using biochemical assays and fluorescence microscopy. The incorporation of DB particles enhanced cell proliferation and osteogenic differentiation capacity which might be due to the natural collagen and hydroxyapatite content of DB particles. Alkaline phosphatase activity is increased significantly by using DB particles, notably, without an osteogenic induction of the cells. Moreover, fluorescence images display pronounced cell-material interaction and cell attachment inside the constructs. With these promising results, the present minimalistic bioink formulation is envisioned as a potential candidate for bone tissue engineering as a clinically translatable material with straightforward preparation and high cell activity.