Teflon Heart

A nagging problem with artificial hearts and other medical implants is that blood proteins stick to them, gumming them up and sometimes leading to dangerous blood clots. Now scientists have devised a new coating that repels these proteins by mimicking the cells that line blood vessels. The coating, described in the current Nature, could be modified to imitate other cell types and perhaps be useful for other devices as well.

Until now, researchers have focused on developing coatings with synthetic polymers that, to proteins, are like teflon-coated pans to pancakes. Typically, however, it is difficult to make such coatings uniform and dense enough to repel all blood proteins. A team led by biomedical engineers Roger Marchant and Nolan Holland of Case Western Reserve University in Cleveland, Ohio, wanted to find a better solution.

The researchers modeled their coating on a feature of all cell membranes, the glycocalyx. This layer of sugar molecules, which varies by cell type, dictates how the cell interacts with others. The researchers homed in on the glycocalyx of cells that line blood vessel walls; this glycocalyx has an outer layer of sugar molecules that repels blood proteins. By layering sugar molecules onto a flexible polymer backbone, the researchers created a structure that, in test-tube experiments, was as repellent as a glycocalyx to blood proteins. To the other side of the backbone they attached a layer of hydrophobic molecules that stick to the water-repellent surfaces of implants.

"It's a very well done study," says Barbara Boyan, a biologist at the University of Texas Health Science Center in San Antonio, but she points out a potential drawback: Bacteria love sugar-based materials. The researchers, however, believe that their coating will also repel bacteria and plan to test it soon in animals. Down the road, says Marchant, "This model could be applied to a wide range of applications." The sugar chains, he says, could be modified to mimic different cell types and even stick to proteins or cells.