Bone tissue is an inorganic-organic nanocomposite, constituted of hydroxyapatite nanocrystals embedded within type I collagen fibrils. The bioink we offer, although does not get close to the real stiffness of the natural bone tissue, finely resembles its chemical composition. The advantage of such a soft material is to be able to incorporate cells and, during the bioprinting process, to locate them in precise position throughout the scaffold. In this way, any post perfusion step is made unnecessary. The good printability and self-sustainability of the ink makes it ideal to reproduce the characteristic porosity of this tissue.
The aim of this study was to provide an upgraded version of the current CELLINK BONE bioink by incorporating collagen and hydroxyapatite.
The bioink does not only allow to host a uniform distribution of cells, but it also protects them from shear stresses during the printing process. It can allow the incorporation of osteocytes and growth factors.
The ink presents a good printability down to 210 µm (27 G) nozzle diameter, see image beside. The filaments appear to be uniform and to closely maintain their shape. A new homogenization method employed disperses the nanostructured micron sizes hydroxyapatite and tricalcium phosphate particles thoroughly.
Dynamic oscillatory experiments were performed on the bioink, prior to cross-linking. They gave evidence of the shear-thinning behaviour the ink, with viscoelastic response to applied pressure: the viscosity decreases with increase in shear rate, according to a roughly linear relationship. This characteristic, therefore, makes it highly suitable for direct-write 3D bioprinting.
Oscillatory rheology, on the other hand, allowed the evaluation of the shear modulus, which reveals information about the rigidity of a material. The bioink samples were cross-linked in CaCl2 solution for five minutes prior testing. The shear modulus (the ratio of the shear stress to the corresponding deformation) was seen to be constant in the linear-elastic range, where the deformation is elastic and reversible.
The new upgraded formulation of the CELLINK BONE bioink offers a more biomimetic environment, by incorporating collagen and hydroxyapatite in addition to the traditional composition.
The environment in which cells are cultured offers more cues for osteogenic differentiation, combined with a great printability.
This promising ink gathers a set of useful features needed for development of bone tissue models. Coming soon to boost your bone research!