Thin And Flexible Thermotherapy Wrap Built With Nanowires

To ease the pain of sore wrists, knees, and other body parts, doctors often recommend applying heat. But heating pads and wraps can be bulky and rigid and don’t always distribute heat evenly. Seeking a better bandage for thermotherapy, a team led by Taeghwan Hyeon and Dae-Hyeong Kim of the Institute for Basic Science and Seoul National University, in South Korea, have created a soft, sleek, and stretchy device that heats evenly while conforming to the body’s contours (ACS Nano 2015, DOI: 10.1021/acsnano.5b02790). The device’s heating element is made from a composite of silver nanowires and a styrene-butadiene-styrene elastomer. Because silver nanowires are better at conducting heat than carbon nanotubes and are less expensive than gold, scientists have recognized them as potential heating elements. But the nanowires are made in aqueous solution, and because of the polar ligands that cling to the wires, they don’t easily blend with the organic elastomers that are needed for flexibility and even heating. Hyeon and Kim’s team solved this problem by developing a ligand-exchange process that makes the nanowires soluble in toluene. A small battery powers the nanowire-elastomer composite heater, making the device portable.