Jeff Karp considers the surgical bandage he helped develop an inside-the-body Band-Aid. "But I like the duct tape analogy," the Harvard-MIT Division of Health Sciences and Technology (HST) faculty member says. An ulcerous hole in the intestine? Patch it up. A bowel resection as a result of Crohn's disease? Wrap the sutured halves to prevent leaking. "There are a lot of glues, including the cyanoacrylates, which are basically medical-grade Krazy Glue, but many of these have poor mechanical properties and elicit strong inflammatory responses. There really was no tape-based adhesive for tissue."
Karp and biotech pioneer Robert Langer, an HST colleague, decided to change that. They knew that a tissue tape should meet a list of criteria: It should be biocompatible to avoid attack by the body's immune system, biodegradable in order to dissolve in place over time, soft and elastic so as to conform to different tissue surfaces, and sticky even on moist surfaces. Working with a multidisciplined team of researchers—polymer and organic chemists, polymer engineers, polymer physicists, nanofabrication experts and surgeons—they created a "biorubber" polymer that satisfies them all.
What's most exciting is the sticky surface. Inspired by the foot of a gecko, it's covered in the same kind of hills and valleys that greatly increase the foot's surface area, letting the lizard defy gravity by sticking to walls and ceilings. Stanford researchers have developed a wall-walking robot that mimics the gecko, and a University of Akron team created a gecko-like reusable dry tape. Now, the concept is moving inside the body—with a key difference. "Unlike the gecko, which needs to be able to walk, we didn't need strong adhesion and de-adhesion," Karp says. They decided to coat their surface layer of nanopillows with a thin layer of biodegradable sugar-based glue to enhance the stickiness.
Using a fabrication process called micropatterning—the same technique used to make microchips—the team can make its sticky biorubber at room temperature. They create molds within silicon wafers and pour in liquid polymer—a process known as soft lithography. After capillary forces pull the polymer into nano-sized holes in the wafer, the polymer is photocured in two minutes by exposure to UV light. The sheet that comes out is soft, stretchable by 200 percent in all directions and sticks to moist surfaces with a bond twice as strong as non-patterned surfaces. In rat tests, their biorubber only caused mild inflammation, a perfectly acceptable result considering that all foreign bodies cause some inflammation.
Karp and Langer will now focus on customizing their biorubber bandages for different applications on specific organs and tissues. In addition to taking the place of sutures and sealing leaky organs, a surgical adhesive tape could also be infused with drugs to time-release as the material biodegrades. For example, says Karp, "we're thinking of developing a heart patch that would deliver drugs normally injected directly into the heart." The elasticity would allow the patch to respond to the rhythmic beating of the heart.
Drug-enhanced tape adhesives might take a while to bring to the operating room. Karp is hopeful, however, that in 2 to 5 years, his team can be in clinical trials with a sticky suture-alternative, with thanks due to the gecko. —Logan Ward