HOW good would you be at tying knots through a tiny opening? It’s a challenge that many surgeons are having to face, as keyhole surgery becomes more and more widespread.
One of the toughest surgical techniques in keyhole surgery is tying stitches, or sutures, to close incisions. They have to be tied with the right amount of tension, explains Robert Langer, a chemical and biomedical engineer at the Massachusetts Institute of Technology. If the knot is too loose, the tissues won’t heal properly, and if it’s too tight it can destroy the surrounding tissue.
But now materials scientists have come up with a biodegradable suture that can be tied loosely, but will tighten up automatically when warmed up by body heat. It will then break down, like conventional dissolving stitches, after the wound has healed.
Advertisement
The sutures were developed by Langer and Andreas Lendlein of German company mnemoScience. They created their smart plastic by using a biodegradable polymer that contains two sets of chemical bonds which are stable at different temperatures. One set breaks down only at a high temperature (90 °C) and this property is used to give the plastic its permanent shape during manufacture. The second set are stable at room temperature but break down at body temperature.
To make their suture, the researchers used polymer fibres wound into permanent, tight coils. They then heated them to 50 °C and stretched them to twice their length, which loosened the coils. They then cooled the fibres to room temperature and used them to make loose sutures to close up incisions in the bellies of dead rats.
When an incision was kept at room temperature, it remained open. But when it was allowed to warm up to a living rat’s body temperature, the room-temperature-stable bonds broke down and the threads contracted back to their original length, closing the wound. Measurements of the force on the wound suggested it was applying just the right amount of pressure, Langer and Lendlein will report in a forthcoming issue of Science.
“I’ve had this idea to make these polymers for a long time,” says Langer. “Now I feel we’ve taken a huge step forward.” But sutures or other devices made from the plastic will need to undergo years of testing in animals before finding their way into operating theatres, he says.
The new self-adjusting sutures are only the first demonstration of how shape-memory thermoplastics could make the lives of surgeons easier. “Using the same material we’ll also be able scrunch up devices like stents [tiny props used to keep arteries open] so that they are really tiny and then have them snap back into shape inside the patient like a rubber band,” says Langer.