Magnetic appeal of shape-change polymer

German polymer scientists have developed polymers that change shape in response to a magnetic field.

Shape-memory polymers like these can revert back to their original shape after being bent, like metal alloys. Traditionally, they have to be heated to get them to return to their original shape. But for some proposed applications of shape-memory polymers, such as medical implants, direct heating would not be possible. Researchers have been exploring other ways of triggering shape change.

Last year, researchers led by Andreas Lendlein from the Institute of Polymer Research in Teltow, Germany, developed a shape-memory polymer that responded to light. Lendlein’s team has now created a polymer that responds to magnetic fields by incorporating magnetic iron(III)oxide nanoparticles into a shape-memory polyetherurethane compound known as TFX.

The researchers discovered that exposing this polymer to an alternating magnetic field caused the magnetic nanoparticles to heat up, which in turn heated the TFX to a high enough temperature to trigger shape change. They tested the effect by twisting a flat strip of the polymer into a corkscrew shape and then exposing it to a magnetic field. It naturally reverted back to a flat strip within around 20 seconds (see image above).

The researchers have shown they can obtain a similar shape change effect when the iron oxide nanoparticles are incorporated in a biodegradable multi-block copolymer known as PDC. This could be adapted for medical applications, they say.

’It’s an interesting paper demonstrating a sound application of a novel approach,’ said Allan Amass, head of the speciality materials research group at Aston University, UK. Amass highlighted the broad dispersal of iron oxide nanoparticles in the TFX as the most significant development in the study.

Jon Evans