An implant that shakes off bacteria: Michigan video shows surface with nano-wrinkles

Infections of implants such as catheters or joint replacements often start with biofilms – layers of bacteria that settle on surfaces and are hard to treat. A University of Michigan team has developed an active surface to counter them, called DARTS (dynamically actuated reconfigurable topographical surface). The study was published in the journal Advanced Functional Materials; Michigan Engineering presented it on 27 October with a short demonstration video.

To make the surface, a pre-stretched plastic film is coated and shrunk in an oven at 130 degrees Celsius. This creates wrinkles spaced less than 400 nanometres apart, which pierce bacteria according to the researchers; coarser wrinkles of around two micrometres did not stop bacterial growth. A metal coil inside a silicone block contracts when heated by an electric current, squeezing the surface and dislodging attached bacteria. It can also be triggered wirelessly with a near-infrared laser; the device kept its shape through 200 actuation cycles.

In mice, devices carrying the bacterium Staphylococcus aureus were implanted under the skin. After 20 activations immediately after surgery and further ones on days 1, 3 and 5, the researchers found markedly fewer bacteria after seven days and a better response of the surrounding tissue. “Rather than relying on passive coatings, our surface physically removes bacteria when needed,” says co-lead Jouha Min, assistant professor of chemical engineering. The technology has not yet been tested in humans.