These glass slides were dipped in blood to demonstrate the effectiveness of the tethered–liquid perfluorocarbon or TLP coating. While blood sticks to the untreated slide on the left, the slide treated with TLP on the right emerges entirely clear. (Wyss Institute, Harvard University)
13 October 2014. Engineers and medical researchers at Harvard University developed a material to coat tubes in medical devices that repels blood, preventing clots from forming and reducing the need for blood-thinning drugs. The new material from Harvard’s Wyss Institute for Biologically Inspired Engineering and collaborators at affiliated labs and hospitals is described in an article published yesterday in the journal Nature Biotechnology (paid subscription required).
Blood clots and infections are concerns for people needing dialysis or catheter-based treatments, which can cause serious complications for people already with significant medical burdens. Preventing blood clots when using these devices often requires taking anticoagulants or blood-thinners, which can have adverse side-effects, such as excessive bleeding.
The Wyss team adapted a technology developed by Joanna Aizenberg, one its researchers and a senior author of the article, called Slippery Liquid-Infused Porous Surfaces or Slips, that creates a surface highly repellent to foreign matter. Slips is inspired in part by carnivorous pitcher plants that trap insects in a slippery inner chamber from which they cannot climb out. “Traditional Slips uses porous, textured surface substrates to immobilize the liquid layer,” says Aizenberg in a university statement, “whereas medical surfaces are mostly flat and smooth. So we further adapted our approach by capitalizing on the natural roughness of chemically modified surfaces of medical devices.”
The researchers had another requirement for adapting Slips to medical devices, namely to use materials already approved by the U.S. Food and Drug Administration, to speed adoption by industry. Their solution binds two types of perfluorocarbons: a layer of perfluorocarbon similar to Teflon, with a liquid perfluorocarbon now used clinically to help infants with breathing difficulties. Perfluorocarbons are twice as dense as water and can dissolve gases like oxygen and carbon dioxide.
The team calls this new material tethered–liquid perfluorocarbon or TLP, which they tested in the lab on 20 different surfaces. The results show the super-slippery TLPs prevent the attachment of fibrins and platelets that cause blood clots, as well as the formation of biofilms, colonies of bacteria associated with medically-related infections.
In one of the tests, researchers tried to grow Pseudomonas aeruginosa bacteria in medical tubing coated with TLP for 6 weeks, and found less than 1 in a billion bacteria were able to adhere to the tube surface. An estimated 51,000 healthcare-associated P. aeruginosa infections occur in the U.S. each year, according to the CDC, with 13 percent of those infections involving antibiotic resistant bacteria.
In addition, the team implanted pigs with medical tubing similar to those in medical devices, and coated with TLP. The tests with pigs showed the coated tubing maintains high blood flow rates without the need for anticoagulant drugs.
The following video tells more about TLPs, including a test with a live gecko.
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