First of all, there already are commercially-available 3D-bioprinted skin grafts, made from living cells. These are typically intended just to be temporary wound coverings, however, as they lack the vasculature that would allow life-giving blood to flow from the patient's body and into them. As a result, such grafts eventually die, sloughing off the patient's own skin.

Looking to overcome this limitation, a team at New York's Rensselaer Polytechnic Institute initially started by mixing two types of living human cells to produce so-called "bio-inks." These were printed into a skin-like structure, although it still lacked a vascular system.

More recently, in collaboration with colleagues at Yale University, they added certain "key elements" to those bio-inks. These elements included human endothelial cells – which line the inside of blood vessels – and human pericyte cells, which wrap around the endothelial cells. These were combined with ingredients that are typically found in bioprinted skin grafts, such as animal collagen and other structural cells.

Within the space of a few weeks, blood vessels began growing in skin that had been printed from the new bio-inks. When these pieces of the skin were grafted over open wounds on mice, the animals' blood vessels began communicating with those in the bioprinted skin, causing the grafts to become perfused with blood after four weeks.