For the first time, scientists have printed structures that mimic the texture, consistency and certain properties of biological tissue.
The manmade "tissues" are nothing more than water droplets encased in oil, stacked atop one another, but the scientists were able to construct stable structures that held their form for weeks, structures that conducted electricity and even structures that folded similarly to how muscle cells do.
"These structures ―you can see them as basic tissues," said Alex Graham, a doctoral student at the University of Oxford in the United Kingdom, and one of the authors of the new paper describing the materials. "It's such a simple structure...but you can foresee in the future you could start to functionalize it in a way that could be useful."
The researchers used a type of 3D printer to eject an aqueous solution (water containing some salts) into a bead of oil, which was suspended in more of the aqueous solution. By carefully arranging the droplets, the researchers were able to get them to stick together. In other words, Graham said, "You're just dropping spheres onto other sticky spheres."
After the "print" was completed, the researchers skimmed off the extra oil, leaving a sturdy, jelly-like structure that somewhat resembled brain and fat tissues.
Graham and the other Oxford researchers used their technique to print a number of structures, ranging from the very tiny ―a cube approximately 1 millimeter on each side and consisting of about 16,000 drops ―to a rectangular object about an inch long. That latter structure contained 35,000 droplets. "It was a long print ― over a day," Graham said.
In addition to proving that 3D printing can be used to make gloopy structures out of oil and water, the team explored some future practical uses. By printing a structure that had one side made of saltier drops than the other side, the team was able to create a folding "cage."
Here's how it works. The droplets are printed at the same size, but with different salt concentrations inside the droplets on each layer. The saltier layer absorbs water to become less salty, while the less-salty layer gives off water to become more salty. As the water-salt balance equalizes, the saltier layer swells and the other layer shrinks, causing the structure to fold.
"Maybe there's a way to use it as a drug-delivery mechanism in the future," Graham mused. Doctors could – in theory – fold the tissue-like structure around a drug. The structure could be made to dissolve or unfold upon a second chemical signal.
The team also mimicked a nerve by printing a trail of electrically-conducting droplets surrounded by insulating droplets.
"It's cool [that] you can have this electrical property in something made of water," Graham said.
The research was detailed in this week’s issue of the journal Science.