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April 7, 2013

Gecko Stitches

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Unlocking the gecko's ability to walk on walls is leading researchers to find a way to replace surgical stitches with sticky tape. As this ScienCentral News video explains, the challenge is to make a surgical tape that works in the wet conditions inside your body.

Surgical Tape

In the operating room, surgical tape is used to help close a surgical site without the scarring from stitches or staples. It lessens scarring and can be easier for the surgeon to use. But inside the body, stitches and staples still rule. As anyone who has seen something taped together come apart in the rain knows, sticky stuff in wet conditions are often not so sticky, and during surgery there are lots of liquids that render surgical tape useless.

But a surgical tape inspired by the physics that allow geckos to seemingly defy gravity by walking on walls may soon change all that. Many researchers are exploring using gecko style adhesive tape but this newest effort is the first to show success in the wet conditions inside a body.

Jeff Karp of Boston's Brigham and Women's Hospital and Harvard Medical School along with Massachusetts Institute of Technology's Bob Langer and others writing in the Proceedings of the National Academy of Sciences, have demonstrated a tape that during initial tests can be used internally. Like internal stitches, the tape is designed to eventually break down inside the body after the body heals.

The feet of the lizard-like gecko are not sticky in the same way a tape or a glue is sticky. Researchers have learned that the gecko's tacky little secret lies in nano scale hairs on the bottom of its feet. Karp says, "They're able to use these nanofeatures to attach to a surface." The hairs give the gecko more surface area of contact on a molecular level than what other animals or people have. Karp explains, "All materials are able to interact with another through creating a little bit more of a positive charge or negative charge on one side of the molecule versus the other, and this can cause very small levels of attraction between different materials. And so if you can increase the surface area of contact, you can make these types of interactions significant." This interaction among stable molecules is known as the Van der Waals force.

However under the wet conditions of surgery, this force breaks down, so the researchers created similar hairs that mechanically interlock with the tissue. "We look at this (as) more of (a) gecko-inspired adhesive than a gecko-mimicking adhesive," says Karp.

Still, by itself this interaction still isn't enough. As Karp points out, "If the gecko's feet were too sticky the gecko wouldn't be able to move at all …(but) the surgeon would want to be able to place this adhesive and then not have it move. So, it needs to be very stable." So, Karp says the researchers added a "thin layer of a biodegradable glue to the surface…(that)…significantly enhances the interaction of our adhesive with the tissue surface."

The research team, which included experts on everything from materials to surgery to, of course, gecko feet, is also developing the biodegradable glue. Karp says the glue "gave us the advantage of chemical cross-links with the tissue in addition to the mechanical interlocking that we get from these adhesives."

Karp says they have tested this tape "against intestinal tissue in the laboratory," but are continuing to tweak both the gecko inspired nanoscale features of the tape and the glue to see if they can improve even more on the gecko's tacky little secret.

Among the other experts on the team were surgeons from Massachusetts General Hospital, Draper Laboratories for the nano scale work, and polymer chemists from Massachusetts Institute of Technology for the special glue.

This research was published online in the Proceedings of the National Academy of Sciences Online Early Edition for the week of February 18, 2008 and was funded by The National Institutes of Health, The National Science Foundation and a Charles Stark Draper Laboratory Fellowship.

       email to a friend by Jack Penland

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