A new 3D-printing technique can create tissues as soft as a human’s squishy brain or spongy lungs — something that has not been possible before. “Additive manufacturing,” or 3D printing, promises to allow doctors to produce tailored organs for patients using the patients’ own cells, which could help bring down the severe shortage of organs available for people who need transplants. However, the technology still has significant limitations. To create these organs, bioengineers need to 3D print scaffolds that mimic the structure of the organs, which are then populated with the cells. So far, only relatively stiff materials can be 3D-printed. But some organs in the body, such as the brain and the lungs, have an extremely soft structure.
“We have used a very soft material, which is a composite hydrogel, and printed the softer tissues similar to the brain and possibly lung as well,” Tan told Live Science. But the problem with 3D printing very soft materials is that the underlying layers tend to collapse as additional layers are added on top of them during the 3D-printing process, Tan said. Indeed, the process of 3D printing involves creating an object layer by layer, which means that the lower layers need to be able to support the weight of the growing structure.
To get around this problem, the researchers cooled things down — literally. “We are using a cryogenic printing process, which means that the previous layer is frozen,” Tan said. “Freezing makes the layer very solid and stable so that the next layer can be printed on top of that and the 3D object doesn’t collapse under its own weight.” After the printing is complete, the engineers can slowly thaw the object, and it keeps its shape, she said.
To 3D print the scaffold, the researchers used a novel composite hydrogel that consists of two components: a water-soluble synthetic polymer polyvinyl alcohol, and a jelly-like substance called Phytagel. Then, they coated the resulting structure with collagen and populated it with human cells. For the purposes of the experiment, however, the researchers used skin cells instead of brain cells on scaffold designed to mimic the human brain.
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