Described in Tissue Engineering Part A, the technique involves creating bioinks made from animal collagen. Endothelial cells which line the inside of blood vessels, and human pericyte cells that wrap around the endothelial cells, are also added. Once printed into skin grafts, the cells were found to start communicating with each other and developing vasculature structures within a few weeks.
"As engineers working to recreate biology, we've always appreciated and been aware of the fact that biology is far more complex than the simple systems we make in the lab," said research lead Pankaj Karande, an associate professor of chemical and biological engineering at Rensselaer.
"We were pleasantly surprised to find that, once we start approaching that complexity, biology takes over and starts getting closer and closer to what exists in nature."
While 3D printed skin has previously been created, until now it has lacked the complex blood vessel systems that are vital for skin grafts to integrate with the body. As such, the lifespan of these bio-printed grafts has been limited.
"Right now, whatever is available as a clinical product is more like a fancy Band-Aid," said Karande. "It provides some accelerated wound healing, but eventually it just falls off; it never really integrates with the host cells."
The Rensselaer team worked with researchers at the Yale School of Medicine, who grafted the 3D printed skin on to a mouse. It was found that vessels from the graft could communicate with the mouse’s native vasculature.
"That's extremely important, because we know there is actually a transfer of blood and nutrients to the graft which is keeping the graft alive," Karande explained.
For the technology to be usable at a clinical level, researchers will need to be able to edit the donor cells using something like the CRISPR gene-editing tool, so that the vessels can integrate and be accepted by the patient's body. This is some way off, but if successfully adopted in the future, could enable custom grafts to be developed for burn victims or diabetics with pressure ulcers.
"For those patients, these would be perfect, because ulcers usually appear at distinct locations on the body and can be addressed with smaller pieces of skin," said Karande. "Wound healing typically takes longer in diabetic patients, and this could also help to accelerate that process."