1) Materials required for hydrogel synthesis.
For bio-ink preparation, hydrogels, mixtures of materials that have high water content, are used. Hydrogels are comprised of a large variety of materials, including collagen, alginate, gelatin etc. – depending on the purpose of their use. Moreover, in many cases, different additives are being mixed with them, to mimic the content of the natural tissues (for example: hydroxyapatite added in case of bone bioprinting). Also, growth factors, such as endothelial growth factor (EGF) or fibroblast growth factor (FGF), can be incorporated in the hydrogels that, upon addition of cells, control and stimulate their specific functions as they do in vivo. In order to acquire the proper stiffness and viscoelastic properties, many of the hydrogels require cross-linking: in which, cross-linking agents must also be added.
2) Materials required for cell culture.
The use of cells in bioprinting poses additional requirement of materials necessary for cell isolation and cell culture. The list includes (but is not limited to): nutritional media (such as DMEM or RPMI) to provide nutrition to the cells; buffers (such as PBS) that are used in different steps such as sub-culturing procedure; enzymes (such as trypsin or collagenase) – they are often used to detach the cells from the substrates; antibiotics and antimycotics to protect the cell cultures from infectious agents.
Many bioprinting approaches, besides bio-inks, use other materials known as bio-papers. These materials may not be present in the end-result, but are used during the bioprinting process, to support the proper construction and 3D architecture of the tissue sample being created. The bio-paper can be present in a form of slurry (in case of the so-called FRESH bioprinting) that helps the filaments of the newly printed tissue to obtain and maintain specific spatial layouts. In other cases, the bio-papers are put inside the extruders in the same way as bio-inks, and printed simultaneously, so that the bio-ink and bio-paper form united complex 3D-structure, followed by the removal of the supporting bio-paper and leaving only the bio-ink-based scaffold structure.