Right now, wearable fitness trackers and bionic devices like electronic skin look cool, but they’re a bit clunky. One reason is that rigid wires tend to lose their conductivity after being bent, limiting the range of flexibility for wearables. Now, researchers report the creation of an ultrathin, fabric circuit that keeps high conductivity even while bending and stretching as much as yoga pants. The fiber’s core mimics spandex, consisting of an elastic synthetic thread—polyurethane—twinned by two cotton yarns. These stretchy strings were then dipped in silver nanoparticles to instill conductivity and then liquid silicone to encase everything. This silver nanoyarn could stretch as much as spandex—500% of its original length—and retain a high conductivity (688 siemens per centimeter), the team reports online this month in ACS Nano. That’s 34 times the conductivity and five times the flexibility seen with prior attempts at nanowires made from graphene. The fibers kept high conductivity after being bent 1000 times or wrapped around fingers. The team used their yarn to link light-emitting diodes within foldable plastic (shown above), meaning the fibers might serve as flexible wiring in new-age curved TVs, stretchable digital screens, or electronic clothing. The team tested the biocompatibility of these nanowires by surgically embedding them in the skin of mice for 8 weeks. No inflammation surfaced, suggesting that this silver yarn could be used to wire bionic implants in the future.

(Linked video credit: Cheng et al., ACS Nano. 2015)