3D printing lungs using blue light, hydrogel and 'yellow dye #5'

They say you are what you eat, but scientists at Rice University and the University of Washington may be taking that maxim a step further.

One of the principal challenges when it comes to 3D printing live organs has been, put succinctly, to keep them alive while doing so. This includes feeding the soft tissues with oxygen and nutrients, while also removing the cells’ waste products as they grow—something our bodies do naturally every day, of course, through a network of blood vessels.

But to create those interwoven networks from scratch in a laboratory, like the web of a human lung—an intricate architecture where blood and air interact and flow continuously, but never actually connect—has been a technical hurdle in the field for years.

To build the complex vascular channels around 3D-printed air sacs, with the smallest vessels only about 300 micrometers wide, the researchers built a system using a liquid hydrogel solution that solidifies when exposed to blue light. Projecting a fine image of the vessel onto the transparent hydrogel, layer by layer, allows the construction of complex and independent 3D structures across a soft scaffold.

That leads to a second hurdle: the light-absorbing chemicals used to control the process turned out to be highly toxic to living tissue.

“The researchers, including Bagrat Grigoryan, Jordan Miller, and Kelly Stevens, wondered whether they could swap out those noxious ingredients with synthetic and natural food dyes widely used in the food industry,” wrote Francis Collins, director of the National Institutes of Health, in a blog post featuring their work after it was published in the journal Science.

Those dyes include curcumin, the yellow-orange component in turmeric used to color butter, cheese and mustard—as well as yellow dye #5, also known as tartrazine, which is used in pretty much everything else, from Marshmallow Peeps to Mountain Dew to Kraft macaroni and cheese.

“Their studies showed that those fully biocompatible dyes worked as effective light absorbers, allowing the scientists to recreate the complex architectures of human vasculature,” Collins wrote. “Importantly, the living cells survived within the soft scaffold!”

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According to the university and its video, tests of the lung-like structure—in a scale model smaller than a penny—showed the vessels were strong enough to handle blood flow and the rhythmic breathing motions of inhaling and exhaling air, while red blood cells took up oxygen as they moved past.

The researchers plan to commercialize their bioprinting and bioink technologies through a Houston-based startup called Volumetric, while also making the data from their experiments freely accessible through open-source files.

“We envision bioprinting becoming a major component of medicine within the next two decades,” said Miller, an assistant professor of bioengineering at Rice. “Making the hydrogel design files available will allow others to explore our efforts here, even if they utilize some future 3D printing technology that doesn’t exist today.”