While 3D printed human tissue has been printed before, researchers have been limited to producing relatively thin layers. Efforts to create layers thicker than around a third of a dime have encountered problems due to the cells on the interior starving of oxygen and nutrients, while also having no way to dispose of waste, ultimately causing them to suffocate and die.

To combat this problem, the Wyss Institute researchers used three specially developed "bio-inks," that is, inks borrowing certain biological properties from real living tissue. The first used extracellular matrix, which joins the cells together to form tissue, while the second ink used a combination of the extracellular matrix and living cells.