January 3rd, 2022
Before the end of the year, researchers from the University of Toronto reportedly developed a new coating that allows certain liquids to move across surfaces without experiencing fluid loss. Created in the Durable Repellent Engineered Advanced Materials (DREAM) Laboratory and led by Professor Kevin Golovin (MIE), the coating can aid in new advances in a range of fields, including medical testing.
A paper on the study has since been published in Advanced Functional Materials.
According to the university, with current microfluidics—known as a field where small quantities of liquids are transported within tiny channels, often less than a millimetre wide—devices are limited in that they can only effectively handle liquids with high surface tension or cohesion, such as water.
These high surface tension liquids tend to stick to themselves rather than getting caught on the sides of the channel it is being transported through, unlike low surface tension liquids, such as alcohols and other solvents. Instead of moving independently, like raindrops on window glass, the low surface tension liquids stick to the sides of a given channel. They have only been reported to travel about 10 millimetres before the droplet disintegrates.
Because the capillary action doesn’t apply to these materials, the transport requires an external force, such as magnetism or heat, to move the droplets. However, looking at other ways the materials could be moved, researchers looked to aspects in nature when working to develop a coating solution. “Nature has already developed strategies to transport liquids across surfaces to survive,” said Mohammad Soltani (MIE Ph.D. candidate), a researcher in the DREAM Laboratory and lead author of the paper. “We were inspired by the structural model of natural materials such as cactus leaves or spider silk.
“Our new technology can directionally transport not only water droplets but also low surface tension liquids that easily spread on most surfaces.” To develop the material, with microfluidics in mind, the team used two newly developed polymer coatings, both composed of liquid-like polymer brushes. However, one of which was more liquid-repellent than the other. In strategically combining these polymers, the more repellent coating acts as a background, surrounding the less repellent coating and creating tiny channels along the surface. This channel allows the liquids to move in a desired pattern or direction without losing any of the liquid during transport or requiring additional energy input.
“Polymer brush coatings reduce the fluid friction and allow the droplets to be transported passively,” said Soltani, “Less friction means more energy is available to transport the liquid. We then create a driving force by designing the channels with specific patterns.” In looking at the numbers specifically, the team reported that the new coating could be transported over distances of over 150 millimetres without losing any of the liquid, about 15 times longer than currently possible.
These findings mean that in the future, liquids could be transported over a more extended range or moved in conjunction with other liquids along a precise pathway and even merge and split droplets—all without losing any volume or experiencing cross-contamination. Ideally, the coating could diagnose multiple conditions in minutes using only a drop or two of blood. In addition, the solution will allow for advancements in lab-on-a-chip devices. Still, the coating also has the potential for other applications, such as miniaturizing standard analytical tests often performed in chemical laboratories.
The new technology will also help limit waste in research labs. With no residue left behind on the surface of the device and therefore no risk of cross-contamination, researchers can use the same devices over and over again.
“We’re looking at using this technology for microfluidics bioassays, as this is an area where every drop of liquid is precious,” said Golovin. “Our findings also have great potential to advance point-of-care diagnostics, such as liver or kidney disease, where biological marker screening is often performed in non-aqueous media.”
