Researchers at MIT have developed a stretchy, biodegradable tape that could replace surgical sutures and staples. The new sticky tape could also be made into drug-delivery patches for placement directly on organs including the heart. The tape, which has been tested in mice, slowly breaks down inside the body without causing any irritation.
The adhesive is inspired by geckos’ feet, which allow the reptiles to walk along the ceiling and up and down smooth walls. Gecko toes are sticky because they are covered with millions of flexible nanopillars, giving them a very large surface area. The MIT tape, which relies on both nanoscale pillars and a chemical glue, is the first such tape to show good adhesive strength and safety in animals. It’s being developed by Institute Professor Robert Langer and Jeffrey Karp, a bioengineer in the Harvard-MIT Division of Health Sciences, in collaboration with researchers at two Boston hospitals.
The tape is made of a biodegradable elastomer that can be laced with drugs. To make the adhesive, the liquid polymer is poured into microfabricated silicon molds pocked with 200-to-500-nanometer-wide indentations. The molded, hardened polymer is then spin-coated with a biocompatible dextran glue. When the tape is applied, capillary forces pull tissue into the spaces between the pillars, which also have some weak charge attractions; the dextran glue adheres to tissue proteins.
It’s a “really strong” adhesive, says Metin Sitti, associate professor of mechanical engineering at Carnegie Mellon University.
Making gecko tape that’s safe and effective for medical use has been challenging, says Sitti. Most gecko-inspired adhesives–like those designed to help robots scale walls–are engineered to work on smooth, hard surfaces. For these kinds of applications, it’s important that the tape be reusable. Medical tape like Karp’s needs to stick only once, but stick strongly. Getting high adhesive strength on tissues is hard to do, since they are “wet, soft, slippery, [and] rough,” says Sitti.
Langer and Karp also seem to have overcome another pitfall facing these gecko tapes. Some have appeared to have great strength when only a few nanopillars are tested, but are not as strong when tested on a larger scale. (See “No Spiderman Suit Anytime Soon.”) When tested on pork intestine and in mice, the MIT tape held up.
The advantage of such a tape over the sutures and staples traditionally used to close wounds is that it would be noninvasive and easy to place, says Karp. Sutures and staples puncture tissue and can cause damage that leads to necrosis. And sutures and staples must be very carefully placed along an incision. “You have to realign the tissue with each stitch,” says Karp. Tape could be placed in one motion, potentially shortening the time that patients are on the surgical table. The medical tape could also help doctors during laparoscopic surgeries, which are performed through a small scope. “It’s difficult to tie knots in small places,” says Karp. “You could have the tape unfold and apply it through the [laparoscopic] needle.”
Karp says that another application for the tape might be to reinforce sutures and staples used when a segment of the gastrointestinal tract is removed during gastric bypass surgery. “There are low complication rates, but leaks are catastrophic,” says Karp. The tape could release antibiotics as well as drugs that promote healing.
The MIT tape could also simply act as a drug patch, 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. After a heart attack, patients often have regions of damaged tissue that don’t get enough oxygen. This can lead to heart failure. Injecting a stem-cell-attracting factor into damaged areas of the heart encourages tissue regeneration, but piercing the heart in this way can be dangerous. Karp says that a patch of medical tape might deliver these factors just as effectively and put the patient at lower risk.
Both the mechanical properties of Karp’s tape and its rate of degradation can be tuned to suit different tissues. Karp says that his team’s next step is to work with doctors to identify medical applications that have the most to gain from the use of the tape, and then develop the tape to suit them.