Scientists have built a 3-D printer that creates material resembling human tissues. The novel substance, a deceptively simple network of water droplets coated in lipids, could one day be used to deliver drugs to the body — or perhaps even to replace damaged tissue in living organs.
The creation, described in the journal Science, consists of lipid bilayers separating droplets of water — rather like cell membranes, whose double layers allow the body’s cells to mesh with their watery environments while still protecting their contents.
“The great thing about these droplets is that they use pretty much exclusively biological materials,” said study co-author and University of Oxford researcher Gabriel Villar, making them ideal for medical uses.
Lipid bilayers are formed by two rows of molecules that each have a hydrophobic, water-repelling side and a hydrophilic, water-loving side. They’re crucial to the existence of cells: In cell membranes, the hydrophobic tails of each layer face inward, creating the inner layer of the cell membrane, and the water-loving heads point outward.
Scientists had been creating lipid layers by inserting droplets into lipid-filled oil, causing the lipids to collect around the water droplets’ surface, and then pushing them together. The lipid ends would attract to one another and pull the monolayers together, creating a lipid bilayer.
But doing this by hand was a laborious process. So Villar built a 3-D printer that would use a micropipette to squeeze out droplets in exact orders, speeding up the process. They created networks of up to 35,000 droplets. And in the process, they began to look at the material they were creating differently.
“What we didn’t really expect was that once we could print these droplets out and eject them en masse and assemble them into different geometries, the collection of droplets behaved not just as a loose aggregate of objects but really as a cohesive material, and that kind of changed our thinking throughout the work,” Villar said.
The lipid bilayers surround droplets 50 microns across — about five times bigger than living cells — but they’re biocompatible, and scientists think that if protein channels can be inserted into the layers, they can act as nerve pathways through the system.
Villar also showed that the material could be triggered into contracting like a muscle — folding up into unprintable, flower-like shapes. They were even able to send electrical signals after building a conductive pathway through some of the tissue — like a rudimentary nerve.
Any potential medical uses were far out on the horizon, Villar said — but the faux-tissue could be used to graft onto organs to replace damaged parts, employed as scaffolding on which to grow more cells, or could be inserted into the body to release medication at given times, in certain spots, with specific triggers.