Why A Cotton Candy Machine May Hold The Future Of Artificial Organs

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From Post-It Notes to Viagra, some of the world's most ingenious developments came from using something in a way it wasn't meant to be used. A cotton-candy machine, for instance, has no place in a tissue engineering lab. For researchers at Vanderbilt University, however, it was just the device they needed to solve a problem that has plagued their field for years.

A cotton candy machine spins hydrogel fibers.

The Challenge They Faced

Scientists have gotten pretty good at growing cells in the lab. But growing a two-dimensional living structure (say, a layer of cells in a petri dish) is very different than growing a three-dimensional organ. Engineers have used a variety of water-based gels called hydrogels to create a kind of scaffolding that can support cells within a three-dimensional structure, but that poses its own problem. The cells need to get oxygen and nutrients while disposing of waste, and although those can travel through the hydrogel, they can only move so far. That means that the cells must be very close to the source of the nutrients — we're talking within a hair's width. A better way to get nutrients to cells is to do it the way your own body does it: with capillaries.

Capillaries, as you might have guessed, aren't easy to build. So far, scientists have tried doing them in two ways. With a "bottom-up" method, they leave the cells to grow their own capillaries. That works, but it can take weeks, making it impossible to stack cells too high without starving the ones in the center while they wait for nutrients. In a "top-down" approach, engineers create their own capillaries, but so far the smallest ones they've been able to make have been 100 microns thick—about 10 times the size of the capillaries in your body.

This three-dimensional slab of gelatin contains a microvascular network.

Sweet Success

Vanderbilt University assistant professor of mechanical engineering Leon Bellan first got his stroke of genius in graduate school. He was doing research on the nanofiber-building process of electrospinning when he attended a lecture about the need to create artificial vascular systems for engineered tissue. It all began to fall into place: electrospinning made fibers kind of like capillaries, but they're too small to be useful. People sometimes compared electrospun fibers to silly string or cotton candy. "So I decided to give the cotton candy machine a try," Bellan told Vanderbilt University News. "I went to Target and bought a cotton candy machine for about $40. It turned out that it formed threads that were about one tenth the diameter of a human hair – roughly the same size as capillaries – so they could be used to make channel structures in other materials."

The final product Bellan and his colleagues reported on in Advanced Healthcare Materials didn't quite rely on a $40 machine from Target—but it wasn't far off. They used it to spin threads of poly (N-isopropylacrylamide), or PNIPAM — a cell-friendly polymer that is only soluble in water at room temperature or below — which they coat in a gelatin that's been mixed with human cells. That gelatin goes in a warm incubator, which keeps the threads solid while the gelatin sets. Once it's allowed to cool at room temperature, the threads dissolve and leave behind a network of very tiny tunnels. Those are your artificial capillaries. After that, all scientists need to do is start pumping nutrients into their new organ, and the cells can survive. The study found that after a week, 90 percent of the human cells in their sample were still thriving. Here's to one more step toward artificial organ transplants!

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