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3-D Printing

Liquid Scaffolds From A 3-D Printer

Materials Science: Patterned droplet structures might one day help grow artificial tissue

by Lauren K. Wolf
April 4, 2013 | APPEARED IN VOLUME 91, ISSUE 14

DROP BY DROP
Credit: University of Oxford/C&EN/YouTube
3-D printers don’t build only solid objects anymore. They also build liquid objects, thanks to a research team at the University of Oxford. In this video, watch as microscopic water-filled, lipid-coated droplets pop from a printer’s nozzles and stick to one another to form patterned structures. The researchers envision the clusters’ use in future tissue engineering. They also demonstrate the construction of a flowerlike droplet network that curls into a sphere because of osmosis. This self-folding behavior, the research team contends, might be put to use in drug delivery systems someday.

Scientists trying to engineer tissue typically start with biodegradable solid or gel scaffolds and then seed living cells onto them. But having greater control over cell spreading and tissue growth would be a big plus for researchers.

A scaffold made of liquid compartments could provide that versatility. A method for fabricating such frameworks has been reported by a team led by Hagan Bayley of Oxford University (Science, DOI: 10.1126/science.1229495).

To create liquid scaffolds, the researchers custom-built a three-dimensional printer—a device that usually constructs solid objects layer by layer—to squirt tiny liquid droplets from its nozzles. When the machine prints lipid-coated water droplets onto a platform submerged in an oil bath, the 50-µm-diameter droplets adhere to one another. Oil-water repulsion partly drives the interaction.

[+]Enlarge
A customized 3-D printer can create patterned materials (bottom) by sticking together different types of lipid-coated, dye-filled water droplets.
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A customized 3-D printer can create patterned materials (bottom) by sticking together different types of lipid-coated, dye-filled water droplets.

“Instead of fusing to form a larger droplet, the tiny droplets ‘kiss’ and form a very thin bilayer interface” because of their lipid coatings, says former Oxford graduate student and the report’s lead author Gabriel Villar.

The researchers have been able to produce 3-D patterned networks of tens of thousands of connected caviar-like droplets. And they’ve printed more than one kind of droplet with their multinozzle printer. For instance, the team mimicked the behavior of a nerve fiber by incorporating an arc of electrically conductive droplets into a network of insulating droplets. The electrically active droplets had a pore-forming membrane protein in their outer shells.

Villar says he envisions several ways in which the printed scaffolds could help in future tissue engineering. One possibility is to load cells into the droplets during printing to create living tissue. That way, he says, the cells aren’t as free to migrate as they are on solid scaffolds, and “you might be able to achieve more control over the resulting tissue.”

This study “extends 3-D printing to a new class of materials,” says Christopher S. Chen, a bioengineer at the University of Pennsylvania. Because Bayley’s team has yet to demonstrate it, Chen is uncertain of the networks’ use in tissue engineering.

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