Every day an average of 18 people die waiting for an organ transplant in the United States. Donated organs are tough to come by, which is why many scientists have spent the last two decades trying to create new livers, kidneys, hearts or lungs from scratch. One potential way to craft such delicate structures is 3-D printing with biologically compatible materials, or bioprinting—which has now reportedly produced functional models of lung and liver tissues, with a little help from an unconventional ingredient: food dye.
Would-be organ printers previously have been stymied by the complexity of certain organs. Our lungs and livers, for example, contain physically and biochemically entangled networks of blood vessels and airways (in the lung) or bile ducts (in the liver). Being able to recreate this vasculature—and make the fluid dynamics work so blood and other fluids flow properly—has been an ongoing challenge.
Now, a team of researchers from the University of Washington and Rice University say they have produced functional tissue models using a 3-D printing technique called projection stereolithography. This method exposes thin layers of liquid resin to blue light, which solidifies them into intricate arrangements of hydrogels—gels made up of tangled strings of polymer molecules. These form a structural “scaffolding,” into which researchers can implant live cells that enable it do the work of a lung or liver. In the new study the implanted cells survived, and the resulting models of organ tissue demonstrated some functions of the real thing.
But there was a challenge. This type of printing process relies on photoreactor chemicals (ones that respond to light), so that certain preprogrammed areas of the liquid will solidify while other areas remain soft and can later be washed away. Unfortunately, many of these chemicals are carcinogenic. For a 3-D printer to create the fine vasculature an organ requires for nutrient delivery and waste removal, it needs the precision offered by stereolithography; but for transplants it would need safe, water-soluble photoreactors.
So, the researchers had to find a replacement for the proven but toxic chemicals. When Miller and his team guessed food dye might do the trick—they knew it would absorb the right light wavelengths to make the 3-D printing process work, and is relatively biocompatible—they were too impatient to wait for a supplier to ship the ingredient. So, Miller says, “I went to the supermarket, and I bought a kit of food coloring dye that people use to make confectionery.”