The substances used by the bioprinters as “ink” are referred to as Bio-inks.
Generally speaking, the bio-inks are a mixture of living cells and biomaterials. Usually, the living cells are grown in a cell culture incubator separately, while the special biomaterial formulations (called hydrogels) are mixed with the cells afterwards, often just prior to the bioprinting process, and serve as a scaffold (i.e., support material that plays the role of an extracellular matrix present in the natural tissues). Thus, the mixtures of cells and the hydrogels form the bio-inks, to which bioactive molecules, such as growth factors, can also be added. These molecules play various roles, most importantly including the support and guidance of the cell functions into desired pathways. The hydrogels, due to their high water content and the structure of the comprising molecules, are rather jelly-like substances. They can be easily placed into a syringe-based extruder and be extruded from its nozzle. 

Afterwards, they undergo a process known as cross-linking (aka gelation), during which they acquire the stiffness and viscoelastic properties characteristic of the natural tissues. The gelation process is facilitated by the influence of the so-called cross-linking agents. Subsequently, the bio-ink is deposited in a layer-by-layer fashion, and, due to the cross-linking that concurrently takes place, forms the desired 3D structures that represent living tissue constructs. There are also relatively novel approaches that avoid the cross-linking step. Many of them rely on the properties of self-organization of its components, such as proteins.Bio-inks are the crucial elements of the bioprinting process. The fabrication of the bio-inks, the proper choice of their components, their storage and handling play a critical role for the successful performance of the bioprinting technology. Thus, in order to perform high-quality bioprinting, one must carefully choose the bio-ink types based on the purpose of their planned experiment or manipulation, and also make sure that the specifically chosen bio-ink is compatible with the technical characteristics of the bioprinter. Foldink has developed different formulations of bio-inks, that can be customised according to different specific purposes. We offer bio-inks containing primary, immortalized and/or stem cell lines, mixed with biomaterials such as collagen, alginate, gelatin and many others. We also offer the cross-linking agents, whenever applicable. Our bio-inks are specifically designed to be maximally adapted to the use in Foldink bioprinter, however, can be used in other bioprinters as well (if their use is in accordance with the manufacturers’ guidelines).