The gecko has recently become an animal with nothing less than celebrity status, as both marketers and scientists can’t seem to get enough of these unusual creatures. Not only can they talk on TV, but the bristles of their feet are helping to create new glue-less adhesives. Researchers at MIT have been working on a gecko inspired adhesive that will work in wet environments, such as the human body.
Gecko-like dry adhesives have been around since about 2001 but there have been significant challenges to adapt this technology for medical applications given the strict design criteria required. For use in the body, they must be adapted to stick in a wet environment and be constructed from materials customized for medical applications. Such materials must be biocompatible, meaning they do not cause inflammation; biodegradable, meaning they dissolve over time without producing toxins; and elastic, so that they can conform to and stretch with the body’s tissues.
The MIT researchers met these requirements by building their medical adhesive with a “biorubber” invented by Karp, Langer and others. Using micropatterning technology–the same technology used to create computer chips–the researchers shaped the biorubber into different hill and valley profiles at nanoscale dimensions. After testing them on intestinal tissue taken from pigs, they selected the stickiest profile, one with pillars spaced just wide enough to grip and interlock with the underlying tissue.
Karp then added a very thin layer of a sugar-based glue, to create a strong bond even to a wet surface. The resulting bandage “is something we never expect to remove,” said Karp. Because of that difference, he continued, “we’re not mimicking the gecko”–which has sticky feet but can still lift them up to walk–“we are inspired by the gecko to create a patterned interface to enhance the surface area of contact and thus the overall strength of adhesion.”
When tested against the intestinal tissue samples from pigs, the nanopatterned adhesive bonds were twice as strong as unpatterned adhesives. In tests of the new adhesive in living rats, the glue-coated nanopatterned adhesive showed over a 100 percent increase in adhesive strength compared to the same material without the glue. Moreover, the rats showed only a mild inflammatory response to the adhesive, a minor reaction that does not need to be overcome for clinical use.
Among other advantages, the adhesive could be infused with drugs designed to release as the biorubber degrades. Further, the elasticity and degradation rate of the biorubber are tunable, as is the pillared landscape. This means that the new adhesives can be customized to have the right elasticity, resilience and grip for different medical applications.