Tissue engineering and 3D printing were hot topics at least thirty years ago but it is only in recent years that these two areas have started to mature fully so that their promise for producing artificial body parts made from biomaterials might ultimately be possible. Researchers in the USA have now cleared what they referred to as a major hurdle in 3D printing replacement organs. [Grigoryan, B. et al., Science (2019); DOI: 10.1126/science.aav9750]

The team has found a way to print an object from hydrogel that in many ways is closer to intricate structure to one of the lungs' air sac, an alveolus, than anything constructed previously. The network of material replicates the structure of organs for transport of blood, diffusion of gases, and other vital body fluids. In the same research paper, the team also reports the implantation of such 3D printed artificial organ structures containing liver cells into live mice.

Bioengineers Jordan Miller of Rice University and Kelly Stevens of the University of Washington led a team from across the USA. "One of the biggest road blocks to generating functional tissue replacements has been our inability to print the complex vasculature that can supply nutrients to densely populated tissues," explains Miller. "Further, our organs actually contain independent vascular networks - like the airways and blood vessels of the lung or the bile ducts and blood vessels in the liver." Such interpenetrating networks are physically and biochemically entangled, Miller adds, and the architecture itself is so intimately related to tissue function that it cannot be distentangled in any meaningful way. "Ours is the first bioprinting technology that addresses the challenge of multivascularization in a direct and comprehensive way," he says.

The need for this new technology is driven by the growing transplant queues wherein patients with imminent organ failure await precious donor organs from other people. It also might address an ethical issue that faces many would be transplant recipients who choose not to have tissue from another human being for whatever reason. Miller suggests that it might still be a decade or two before bioprinting becomes a major part of routine medicine. He adds that it will perhaps be the liver that is the first target for development of an artificial organ. "The liver's complexity means there is currently no machine or therapy that can replace all its functions when it fails," he says. "Bioprinted human organs might someday supply that therapy."