Scientists at the University of Florida developed a way to print soft, delicate, detailed structures from a 3D printer, an advance that is already helping neurosurgeons and cancer researchers.

Typical 3D printers use melted plastic to draw a solid structure. In their paper, published Friday in the journal Science Advances, the researchers described one challenge as a race against instabilities — the tendency of the thing to change shape after it is printed because of surface tension, gravity, particle diffusion. If it’s too soft, it sags, it droops, it collapses.

The secret? Hand sanitizer.

The researchers used a substance almost identical to common hand sanitizer, minus the alcohol and perfume, to solve the problem.

By using a granular gel which goes from fluid quickly to solid, they were able to make far more complex structures than were previously possible, essentially because the gel supports the thing being made while it’s being made.

Researchers now can inject different materials — they can use all sorts of things, from silicone polymers to living cells — out of a nozzle to draw structures.

“Whatever it is that comes out of the nozzle is trapped in space wherever we place it,” explained Tommy Angelini, assistant professor in the department of mechanical and aerospace engineering at the University of Florida, who led the research funded by a National Science Foundation grant. “So 3D printing is no longer a game of making a solid material that has to support itself; it’s now a game of trapping stuff in space and leaving it wherever you want to put it.”

If you look at a bottle of hand sanitizer, he said, it almost always has bubbles in it. That’s because it’s solid inside the bottle. “The bubbles want to rise, but they’re trapped.” A pump, or the action of rubbing your hands together can force it to liquify, he said. So if the scientists draw an octopus, say, the gel gives way as a liquid would, but holds it in place the way a solid would.

It’s like a bag of sugar, he said. If it’s sitting there on a table it’s solid; all the forces are balanced. “Stick your finger down there, drag it through, those grains can flow. It temporarily fluidizes it. Take your finger out, it becomes a solid again.”

They can stop writing in one place, write a structure somewhere else, then go back to the first one. That’s how they made an overhand knot that couldn’t be made with existing 3D printing methods unless a support structure were built simultaneously to hold it all together.

“The stability provided by the granular gel medium allows for un-connected parts of the knot to be created independently and joined later,” they wrote in the paper.

University of Florida researchers demonstrate the 3D printing process of soft matter. (University of Florida)

While the paper has been under review, for a year or so prior to publication, a team of scientists from fields as varied as medicine to chemistry to material science to mechanical engineering came together to work on applications for this new type of printing. It could be used for flexible electronics, for example.

It is already being used in two new ways. They’re 3D-printing human organs. That means neurosurgeons taking on a rare, complex, delicate surgery can print out a simulation of the patient’s brain and practice beforehand.

“For high-risk, very challenging surgeries that have a high rate of failure, the surgeon can assure the patient, ‘I’ve printed your brain five times, practiced it, mastered it, we think you’re in good hands,'” Angelini said.

“We think that will completely change the standard of care for surgery.”

They’re building a medical fabrication area for University of Florida Health surgeons to print replicas of tissues and organs.

“We’re building a machine for our cancer-research collaborators to 3D-print vast arrays of microscopic tumors that can then be studied in a huge diversity of ways,” Angelini said. “If you put them in a petri dish most of the time they lose all of their malignant properties.”

Now they can suspend the cancer cells in gel instead.

When they explain the technology, the researchers often hand people a jellyfish they made. “It’s almost like a jellyfish cloud,” he said, “with a shell that’s whisper-thin. When you hold it in your hand it jiggles, it feels incredibly delicate. It’s so finely detailed, but it maintains its structure,” even through airport security, stuffed in a backpack as he did recently for a conference in Germany.

It holds its structure — yet if they want to go back and change something later, they can, he said. “It opens a completely new dimension in 3D printing.”

University of Florida researchers demonstrate the 3D printing process of soft matter. (University of Florida)