Shape Shifting Tools

Langer and his research team have been working for many years to develop a new generation of materials that can be used for specific functions, rather than simply using readily available materials to design new biomedical technologies.

"For most of the 20th century what people did was they took materials off the shelf that were used in household objects and made them into medical devices," he explains. "A good example of that is: ladies girdle material is what's used in artificial hearts today because there's a good flex life. And while that approach has enabled progress to be made, it also creates problems, so what I wanted to do was go over a number of areas where we might make new advances where they apply to medicine, sometimes tailor-making specific materials for medical devices."

So, he developed new materials with shape-memory properties — plastics made up of molecules that change shape when triggered by certain conditions.

At room temperature the plastic is in the form of a string. With heat, when placed in warm water or inside the body, it converts to a coil. image: Robert Langer, MIT

At room temperature, the plastic could have one shape, such as a string or a sheet, but with an increase in temperature, when it is placed in hot water or within the warmth of the body, it changes its shape to a tube or a coil.

Langer hopes his plastic will one day allow surgeons to slip tiny tools into the body and then convert them to larger instruments to perform an operation. And when the operation is over, the plastics can be returned to their original form and be easily removed.

The researchers have also made plastics that change shape just by shining ultraviolet light on them.

"We built in light-sensitive bonds into the plastic, so instead of the temperature causing the switch, the light causes the switch. Because it affects the light-sensitive bonds in the plastic, it goes from shape one to shape two," Langer explains.

He says his clever plastics could also be used to feed into a blocked artery and when in place, curl up into a stent — used to keep the artery open and the blood flowing.

But they will need to develop shape-shifting plastics in much more elaborate shapes before they will be of use to surgeons. In the meantime, Langer and his team have already created a plastic thread for medical stitches that tighten their own knots, and they have had some positive results testing the safety of his plastics in animals.