Wearable transistor can heal its own wounds

The ideal wearable electronic device would, in many ways, resemble human skin. It would be stretchable, durable, and able to heal itself when damaged. But semiconductors, key ingredients in electronic devices, are typically hard and brittle. Now a team led by Stanford University’s Zhenan Bao has tinkered with the organic polymer diketopyrrolopyrrole (DPP) to create a semiconductor that’s flexible and self-healing. On its own, DPP is semiconducting but stiff—it tends to fold into tight, rigid crystals. To make the polymer stretchy, Bao and her coworkers inserted molecules of pyridine dicarboxamide along its molecular backbone. The pyridine dicarboxamide disrupts the crystalline ordering and causes segments of the polymer to remain floppy and amorphous. (In the illustration, floppy segments are shown in gray, crystalline portions in blue.) The floppy segments are linked by hydrogen bonds (red), which both strengthen the material and give it the ability to self-heal: They’ll snap if the polymer is stretched too tight but then spontaneously reform when it’s treated with solvent and heat. As a proof of concept, Bao and her colleagues used their semiconducting polymer to build thin-film field-effect transistors, which they mounted on rubber patches and stuck to the hands, arms, and elbows of human test subjects. Hundreds of hand twists, arm folds, and elbow flexes later, the transistors still functioned. Granted, turning the proof-of-concept transistors into commercial devices will take work. For instance, the researchers will need to figure out how to reduce the operating voltage—currently on the order of 10 V—to levels more practical for use in autonomous wearable devices. (J. Y. Oh et al., Nature 539, 411, 2016, doi:10.1038/nature20102 .)