Blood clotting is essential to surviving any wound but it can work against us when modern medicine needs to operate inside the body. In cases where a piece of equipment must be inserted to extract fluids or deliver medicine, blood clots can foul up the intricate parts of this technology. The disruption could turn out to be catastrophic, defeating the original purpose of the therapy.
Benjamin Hatton got a crash course in such a problem when he was approached by a colleague working with the Defense Advanced Research Projects Agency (DARPA) in the United States. Agency researchers were looking at ways of preventing wounded soldiers from dying of infection in the battlefield by passing their blood through a filter to remove bacteria. “The challenge is that you would normally need to use an anticoagulant to prevent the blood from clotting in the small channels of this device,” says Hatton. Unfortunately, the use of such “blood thinners” could pose an even greater threat to an individual’s survival.
The medical technicians working with DARPA were therefore seeking to keep blood from clogging the invasive equipment. Hatton, now a professor at the University of Toronto’s Department of Materials Science and Engineering, had been working with researchers at Harvard University on how to coat a surface to prevent this kind of accumulation. More specifically, they had been looking at how to stop a liquid from wetting a surface, a challenge they tackled by introducing another liquid that would compete against the first one. “If you have already wet that surface with liquid that has a much stronger binding, then the liquid trying to make contact will never get a foothold,” he says. Nature’s own model for this approach is the notorious pitcher plant, which coats its interior lining in a similar way to create a slippery slope trapping insects that fall in.
When Hatton began to consider how to coat the surface of a medical instrument, he identified perfluorocarbons as a suitable candidate. These chemicals are inert, immiscible with water and unlikely to mix with anything found in the human body. Once placed on a surface, they turned out to be every bit as slippery as the pitcher plant’s lining. “We call it an omniphobic surface,” he says. “We haven’t found anything that can adhere to it.”
As a proof of principle, the researchers tested this design using a gecko, which is famous for the gripping ability of its fine-haired foot pads. Even at a relatively gentle 30-degree incline, the lizard was unable to attach itself to the surface. When the perfluorocarbon coating was finally tested on DARPA’s blood-cleansing apparatus, it reduced the amount of blood coagulation by a factor of five, eliminating the need for a blood thinner.
These findings have since been published in Nature, even as Hatton continues to look for other sticky situations to resolve. He is currently working with Ontario Power Generation on a similar lining for the cooling water intake lines into nuclear reactors. The utility currently uses bleach to prevent zebra mussels from clogging those lines, but that chemical will eventually wind up being flushed into the environment when this cooling water is returned to one of the Great Lakes. If these water lines can be turned into an omniphobic surface, however, the mussels would not be able to stick to it and the cooling water could circulate without any kind of chemical change.
Similarly, Hatton is working with a colleague at the Hospital for Sick Children in Toronto on a new type of wound dressing that will not stick to a patient’s skin. This feature is especially important for the recovering skin of burn victims, which needs to be protected from infection without being damaged by that protection.