Medical devices implanted in the body or in contact with flowing blood faces two critical challenges that can threaten the life of the patient the device is meant to help - blood clotting and bacterial infection. Researchers from the Wyss Institute for Biologically Inspired Engineering at Harvard University have developed a new surface coating for medical devices using FDA-approved materials. The super-repellent coating can be adhered to existing, approved medical devices. In a two–step surface–coating process, the researchers chemically attached a monolayer of perfluorocarbon, which is similar to Teflon. Then they added a layer of liquid perfluorocarbon, which is widely used in medicine for applications such as eye surgery. The team calls the tethered perfluorocarbon plus the liquid layer a Tethered–Liquid Perfluorocarbon surface, or TLP for short. The coating successfully repelled blood from more than 20 medically relevant substrates the team tested - made of plastic to glass and metal - and also suppressed biofilm formation. The team also implanted medical–grade tubing and catheters coated with the material in large blood vessels in pigs, and it prevented blood from clotting for at least eight hours without the use of blood thinners such as heparin. Heparin is notorious for causing potentially lethal side–effects like excessive bleeding but is often a necessary evil in medical treatments where clotting is a risk.