"The shape-memory effect of the composite systems could be induced by inductive heating in an alternating magnetic field," Sabine Benner of the Institute of Polymer Research told nanotechweb.org. "A desired temperature can be set by varying the proportion of nanoparticles in the polymer and the strength of the magnetic field."
Samples of the polymer that did not contain nanoparticles remained the same shape under a magnetic field. The scientists believe that the presence of nanoparticles enables heating of the polymer, which induces the shape change.
To make the composite, Benner and colleagues dispersed 20-30 nm diameter magnetite (iron oxide) nanoparticles in one of two thermoplastic polymers. They used either the polyetherurethane Tecoflex EG72D or the multiblock copolymer PDC, which was developed for medical applications and is biodegradable. Tecoflex has a transition temperature of 74°C while PDC's transition temperature is only just above body temperature (~37°C). To improve distribution of the nanoparticles in Tecoflex, the researchers used particles that were embedded in a silica matrix.
Applications for the material could include medical devices such as smart catheters or intelligent implants for treating ocular hypertension (high pressure of the fluid in the eye). The materials could also find a use in drug delivery, releasing chemicals when triggered to do so by a magnetic field. Surgeons could use smart instruments made with the material to make mechanical adjustments without contact.
"These catheters could be used to rinse, fill or drain organs or vessels without the need for extensive or painful surgery every time a modification to the therapy is required," said Andreas Lendlein of the Institute of Polymer Research.
The researchers reported their work in PNAS.