In 2023, McKayla Torbett-Dougherty could spend an entire day leaning over an oil bath, coaxing individual drops of water down tiny ramps and hoping they would settle against each other correctly.
“This technique is called the droplet interface bilayer (DIB),” explained Dougherty, a PhD student in the Department of Biomedical Engineering (BME). “Each droplet has a lipid monolayer (single-layer coating), so when you bring them together, the interface between them forms a bilayer (double layer) synonymous with all cell membranes.”
Dougherty conducts research in the lab of James Conklin Fellow Andy Sarles, a joint professor in BME and the Department of Mechanical and Aerospace Engineering. Sarles’ group works to understand fundamental features of living systems and create biologically inspired (bio-inspired) soft materials that bridge biology and technology.
“One of our goals is to construct three-dimensional materials that maintain (bilayer) membrane-separated compartments like the cells and tissues in our bodies,” Sarles said. “The challenge for this study was, how do you take a DIB that mimics a cell membrane and scale it up to be a material?”
Thanks to a National Science Foundation (NSF)-sponsored partnership with the University of Texas at Austin (UT-Austin) and Pennsylvania State University, Dougherty and Sarles now have an answer.
This July, Dougherty was the second author on a publication in Nature Materials describing a new method that makes billions of bilayer-bound droplets within minutes. They even stick together on their own—no tiny ramps required.
The resulting material, JIBE (Jammed Interconnected Bilayer Emulsion), is 3D-printable, very stable in water-based solutions, and highly customizable, forecasting potential applications in healthcare, chemical processing, and even computation.
“There were a lot of challenges in this project,” Sarles said. “But by working as a team, we were able to demonstrate a simple, quick, scalable technique to make very modular, bio-inspired materials.”
Breakthroughs Built on Collaboration
As an undergraduate working in Sarles’ lab, Dougherty was working to create DIBs using lipids, the same molecules that make up cell membranes. Every lipid is amphiphilic, meaning that it has a hydrophilic (water-attracting) head and hydrophobic (water-resistant) tails. When Dougherty 3D printed individual droplets of water into an oil-and-lipid bath, the hydrophilic heads rushed towards them, coating each drop in a lipid monolayer.
When she started her PhD, Dougherty transitioned to making DIBs out of other amphiphilic molecules. Scientists can join hydrophilic and hydrophobic polymer molecules into larger lipid-like assemblies called block copolymers. While that makes them more customizable than natural lipids, it didn’t change the fact that Dougherty’s specialized 3D printer could only dispense a water droplet every few seconds. On a good day, ten hours of work yielded only a small network of about 1000 DIBs.
In 2021, Sarles and several of his colleagues outside Tennessee were awarded an NSF grant to develop better ways to investigate lipid and block copolymer bilayers. That November, UT-Austin PhD student Aida Fica came to Sarles’ lab for three weeks to learn how to assemble and characterize lipid DIBs alongside an undergraduate Dougherty.
When Dougherty started her PhD program in 2022 and began making DIBs with block copolymers, she used the same copolymers studied and synthesized by Fica’s mentor, UT-Austin Professor Manish Kumar.
“Collaboration is very helpful in research—we can’t come up with every idea on our own,” Dougherty said. “There’s definitely things we can all learn from each other.”
In 2023, Dougherty and Fica were continuing the cross-institutional exchange by discussing a recent breakthrough at UT-Austin. Fica and Manish had discovered that they could turn a milliliter-sized mixture of water, oil, and lipids into billions of bilayer-bound droplets: the first JIBEs.
Fica and Manish’s method can produce up to 50 mL of JIBEs in just ten minutes, and the material can be printed using a standard laboratory 3D bioprinter, making sample creation and tissue construction thousands of times faster than individual droplet-dispensing approaches. They can also be 3D printed directly into water-based solutions, a revolutionary step in bilayer research.
However, because lipid membranes degrade quickly, the printed samples did not hold their shape well. The team was concerned that the internal bilayers, too, might be unreliable.
“We were discussing my work with polymer DIBs,” Dougherty recalled, “and then we had the idea of, ‘Maybe we can try using these copolymers in the JIBEs.’”
The team discovered that polymer-based JIBEs have the same speed advantage as the lipid versions, with much greater stability—they maintain both their printed shapes and internal droplet compartments for months. The ability to use block copolymers also significantly expands the material’s possible uses.
“Block copolymers can be functionalized in many ways that aren’t possible with lipids,” Sarles said, “which would enable adding additional functionality to every monolayer or bilayer in the system.”
A Plug-and-Play Biomimetic Material
In their Nature Materials paper, Fica, Dougherty, and their colleagues demonstrated that creating lipid and polymer-based JIBEs with different membrane proteins can give them a variety of functional properties—from selectively transporting sodium, calcium, or other ions to adaptively processing and storing information like neurons in the brain.
“The versatility and multifunctionality of this tissue is what’s really intriguing to me,” Dougherty said. “We showed just three examples in the paper, (but there are) so many possibilities for its use.”
Since JIBEs are soft, malleable, and stable in water-based environments, they could be used to create more comfortable medical devices. Layered JIBEs made from different block copolymers could have applications in water filtration or chemical sorting. The team is currently investigating how different JIBEs could be printed in patterns to create multifunctional materials or even soft ionic circuits.
There are also plenty of complex fundamental phenomena Sarles’ team can investigate now that they have achieved a compartmentalized, tissue-like material.
“There’s still a lot of hard questions to try to address with this technique, like, ‘How do you program specific functionalities into different compartments of the JIBE? How do you arrange them effectively and get them to function together as a collective unit?’” Sarles said. “But having such a simple approach to make a scalable, soft material that mimics some of the fundamental properties of biological tissues, I think, is pretty exciting.”
Contact
Izzie Gall ([email protected])