The toes of gecko lizards adhere to a wide variety of surfaces, enabling geckos to climb smooth and vertical surfaces, as well as cross indoor ceilings. As this adhesion doesn’t utilize liquids or surface tension and it varies with humidity, it is thought to involve capillarity. MIT researchers in collaboration with researchers at two Boston hospitals relied on some of the principles that create geckos’ feet adhesiveness, while developing a waterproof adhesive bandage that may soon be used for patching up surgical wounds or internal injuries.
Led by the Harvard-MIT Division of Health Sciences and Technology (HST) faculty members, MIT Institute Professor Robert Langer and Jeffrey Karp, who is a bioengineer, the team utilized the micropatterning technology that is also used to create computer chips. By pouring a biodegradable polymer into microfabricated silicon molds with 200-to-500-nanometer-wide indentations, the researchers have created a “biorubber” tape with nanoscale hills and valleys on its surface, similar to the flexible nanopillars covering geckos’ sticky toes. “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.” said Karp.
The surface area of this “biorubber” was then coated with a very thin layer of biocompatible sugar-based glue enabling a strong bond even to wet surfaces such as to heart, bladder or lung tissue. When the tape is applied, capillary forces pull tissue into the spaces between the pillars, and the glue adheres to tissue proteins. This biodegradable bandage dissolves over time and does not have to be removed.
Adapting the previously known gecko-like dry adhesive technology for medical applications has been challenging, as a medical adhesive has to be able to stick once and strongly in a wet environment, and to be biocompatible (that does not cause inflammation), biodegradable (that dissolve over time without producing toxins) and elastic (in order to suit the bonded tissues and stretch with them).
The resulting “gecko tape” is the first such tape to show good adhesive strength and safety in animals. The tape’s nanopatterned adhesive bonds were twice as strong as unpatterned adhesives when tested against intestinal tissue samples from pigs, and adhesion of the tape’s glue-coated form was twice as strong as the same material without the glue when tested in living rats. Moreover, these rats showed only a minor inflammatory response to the adhesive that does not need to be overcome for clinical use.
The elasticity, degradation rate and pillared landscape of the biorubber are tunable hence the new adhesives can be customized for different medical applications. They can also be infused with drugs designed to be released as the biorubber degrades.
A tape-based medical adhesive may have many applications, as it is noninvasive and easy to place. Unlike sutures and staples traditionally used to close wounds, the new tape doesn’t puncture the tissue and could be placed in one motion. The medical tape can also be used during minimally invasive surgeries, which are performed through a very small incision; “It’s difficult to tie knots in small places. You could have the tape unfold and apply it through the [laparoscopic] needle.” says Karp.
Possible applications of the new surgical adhesive tape also include resealing of the intestine after the removal of a diseased segment or after a gastric bypass procedure, as well as patching a hole caused by an ulcer. Moreover, the tape could release drugs that promote healing, even in tissues that stretch and contract, like the heart. “It’s elastic, so it should withstand the mechanical forces of the heart,” says Karp. This ability of the bioadhesive patch may be utilized to deliver stem-cell-attracting factor that encourages tissue regeneration into damaged areas of the heart after a heart attack.
Another gecko-inspired synthetic adhesive tape has recently been developed in Berkeley University. Other related issues covered by TFOT include the discovery of a non-toxic, natural glue that has the strongest adhesion force of any known natural material, and the development of a painless microneedles skin patch that can replace conventional injections and enable drug delivery.
The press release regarding the gecko-inspired bioadhesive is available in this MIT news page.