The coating could also find uses in biomedical applications to make microfluidic chips. Typically, microfluidic devices contain enclosed micrometer-wide channels etched into silicon, glass, or plastic plates. Then pressure or electric fields drive tiny volumes of fluids, typically nanoliters, along these channels for diagnostic tests and genetics research. For instance, to test for the presence of a certain protein in blood you could take blood in one channel and direct it to another channel containing a chemical reagent that identifies the protein.
Compared with conventional microfluidics, a microfluidic chip based on the new surface would have the advantage of easier mixing, Rubner says. Right now, the chips need pumps and valves that move the liquid around to induce mixing. “In our case you can mix the liquids by just controlling the amount of liquid you put on the surface,” he says. With a pipette, you could add precise amounts of fluid into two hydrophilic grooves placed close to each other. As you add more fluid, the droplets bulge out at the edge of the grooves because of the surrounding hydrophobic area. Eventually, the bulging surfaces touch and mix. Being able to confine liquids to a small region could provide densely packed reaction sites with more control over the reaction, he says, since adjacent drops won’t mix unless they are forced to.
While the exact uses of this new material are still uncertain, it opens up many possibilities, says Kenneth Wynne, a chemical engineering professor at Virginia Commonwealth University. “Patterning ultra-hydrophilic patches on a ultra-hydrophobic surface in this way is new and useful,” he says.