A Stretchable, Strain-Limiting and Mechanically Stable Bio-Inspired Microfiber for Wearable Electronics

Since fiber-based approaches have high stretchability, the devices fabricated on them with limited stretchability cannot fully withstand large stretching, particularly when the wearer participates in vigorous activity. Stretchable systems can replicate the “j-shaped stress-strain or strain-limiting” mechanical behavior of biological tissues under deformations and provide mechanical compliance and comfort to wearers. A network of soft elastin fibers and stiff collagen fibers causes the biological tissues to be stretchable at low strains, and exhibit strain-limiting behavior when deformed at large strains. We developed a combined microfiber and nanofiber (NFs)-based approach to mimic this mechanical behavior of tissues, which involved wrapping soft polyurethane (PU) microfiber with stiff and inflexible poly(vinyldenefluoride) (PVDF) NFs and coating them in polydimethylsiloxane (PDMS). By tailoring the loading ratios of the PVDF NFs it is possible to tame the elastic moduli of the bio-inspired microfibers to match well with those of biological tissues. As shown by confocal imaging during stretching, PU microfibers maintain stretchability and stiff PVDF NFs play a role in strain-limiting characteristics. The stretchable poly(3,4-ethylenedioxythiophene) polystyrene sulfonate/ Polyurethane dispersion (PEDOT: PSS/PUD) coating on the bio-inspired microfiber showed a negligible difference in current-time (I-T) response after static stretching (~ up to 30%- human skin stretchability range) which indicated the efficient absorption of stress by the bio-inspired microfiber. An electrical response of a stretchable temperature sensor was measured by directly attaching it to the fist and stitching it into the bandage to demonstrate microfiber's ability to measure skin temperature and accommodate body movements. A light-emitting diode (LED) ON/OFF test was performed to demonstrate that bio-inspired microfibers could be used as electrodes in the future. Wearable electronics based on mechanically stable and stretchable bio-inspired microfibers have the potential to be the frontier due to their high adaptability for non-planar bodies and ease of sewing in fabrics.