1, Seoul National University, Seoul, , Korea (the Republic of)
Intrinsically stretchable conductors form a vital component of advanced bioelectronics. And novel nanocomposites based on conductive nanomaterials have been used in diverse areas including wearable and implantable bioelectronics. Among many nanomaterials for the composites, silver (Ag) nanowires are popular because they are highly conductive and the ultralong nanowires form highly percolated conductive networks in the elastomeric media. However, achieving highly conductive and soft composites is challenging because current methods produce materials that are either highly conductive or soft but never both. Furthermore, because bioelectronics is necessarily exposed to biofluids, preventing Ag nanowire oxidation and Ag ion leaching are significant challenges. And we have achieved a highly conductive, biocompatible, and soft nanocomposite by using silver-gold (Ag-Au) core-sheath nanowires and polystyrene-butadiene-styrene (SBS) elastomer. We synthesized ultralong Ag nanowires encapsulated with a smooth and uniform Au sheath and then mixed them with the polymer. Phase separation of Ag-Au NWs and SBS occurs, which forms microstructures in the composite, reduces Young’s modulus, and increase softness and conductivity of the composite, allowing it to be stretched up to ~266% whilst maintaining a conductivity of 41,850 S/cm. By increasing the content of Ag-Au nanowires, the nanocomposite can achieve conductivity up to ~72,600 S/cm. Using the heat rolling-press, stretchability of the nanocomposite can be further increased up to 840%. We used the Ag-Au nanocomposite to develop a wearable device for recording electrophysiological signals through the human skin and delivering electrical and thermal stimulations that respond to sensor signals. We also designed and fabricated a customized multi-channel soft cardiac mesh for the swine heart. The mesh monitors cardiac activation signals from ventricles and stimulates at any sites in the ventricles without being hindered by anatomical obstacles.