Self-Sutures: New material knots up on its own

Researchers have used a new biodegradable material to make surgical sutures that knot and tighten themselves as they warm to body temperature.

The new material could help surgeons working in tight spaces within the body, says Robert Langer of the Massachusetts Institute of Technology in Cambridge. Surgeons might loosely stitch a suture and then let the polymer tighten itself. Eventually, doctors may insert through a tiny incision a compressed implant made of the new material that will expand into a predetermined shape, such as a short tube, or stent, that holds open a blood vessel.

Known as a shape memory polymer, the material assumes a temporary structure at room temperature. Its makers, however, can program it to hold a different, permanent shape after it warms up. Langer and Andreas Lendlein of the company mnemoScience GmbH and the Rheinisch-Westfälische University of Technology in Aachen, Germany, describe the new material in an upcoming issue of Science.

The researchers incorporated two temperature-dependent components into the new material. One, called oligo(e-caprolactone)diol, maintains the polymer’s temporary form at room temperature and higher. The other component, called oligo(r-dioxanone)diol, determines the material’s shape at body temperature and higher. When the material is first made, the researchers form it into the final shape at high temperature, over 90C, and then cool it and construct the temporary shape. In one case, the team made a thread that knots itself as it warms.

Shape memory materials, which include metal alloys, have been around for years. Last year, Langer and Lendlein reported the first polymer version that would biodegrade in the body.

The new polymer is tougher than the previous one, an improvement that Langer says should make it better suited for use in biomedical implants. To show this, Langer and Lendlein fashioned the material into threads and used them to stitch four incisions on two rats. When the threads warmed, they tightened. Toxicity studies done so far have not revealed any problems, the scientists report.

The new polymer is programmed more easily than metal shape memory materials, says Lendlein. Moreover, the temporary polymer can be four times the size of its permanent shape, while the alloys can change only 8 percent.

The self-tying fiber “is a nice demonstration of what you can do . . . with a piece of plastic,” says W. Mark Saltzman of Cornell University.