Wearable and implantable devices require conductive, stretchable and biocompatible materials. However, obtaining composites that simultaneously fulfil these requirements is challenging due to a trade-off between conductivity and stretchability. Here, we report on Ag-Au nanocomposites composed of ultralong gold-coated silver nanowires in an elastomeric block-copolymer matrix. Owing to the high aspect ratio and percolation network of the Ag-Au nanowires, the nanocomposites exhibit an optimized conductivity of 41,850 S cm (maximum of 72,600 S cm). Phase separation in the Ag-Au nanocomposite during the solvent-drying process generates a microstructure that yields an optimized stretchability of 266% (maximum of 840%). The thick gold sheath deposited on the silver nanowire surface prevents oxidation and silver ion leaching, making the composite biocompatible and highly conductive. Using the nanocomposite, we successfully fabricate wearable and implantable soft bioelectronic devices that can be conformally integrated with human skin and swine heart for continuous electrophysiological recording, and electrical and thermal stimulation.
Skin electronics require stretchable conductors that satisfy metallike conductivity, high stretchability, ultrathin thickness, and facile patternability, but achieving these characteristics simultaneously is challenging. We present a float assembly method to fabricate a nanomembrane that meets all these requirements. The method enables a compact assembly of nanomaterials at the water–oil interface and their partial embedment in an ultrathin elastomer membrane, which can distribute the applied strain in the elastomer membrane and thus lead to a high elasticity even with the high loading of the nanomaterials. Furthermore, the structure allows cold welding and bilayer stacking, resulting in high conductivity. These properties are preserved even after high-resolution patterning by using photolithography. A multifunctional epidermal sensor array can be fabricated with the patterned nanomembranes.
Stretchable conductive nanocomposites fabricated by integrating metallic nanomaterials with elastomers have become a vital component of human‐friendly electronics, such as wearable and implantable devices, due to their unconventional electrical and mechanical characteristics. Understanding the detailed material design and fabrication strategies to improve the conductivity and stretchability of the nanocomposites is therefore important. This Review discusses the recent technological advances toward high performance stretchable metallic nanocomposites. First, the effect of the filler material design on the conductivity is briefly discussed, followed by various nanocomposite fabrication techniques to achieve high conductivity. Methods for maintaining the initial conductivity over a long period of time are also summarized. Then, strategies on controlled percolation of nanomaterials are highlighted, followed by a discussion regarding the effects of the morphology of the nanocomposite and postfabricated 3D structures on achieving high stretchability. Finally, representative examples of applications of such nanocomposites in biointegrated electronics are provided. A brief outlook concludes this Review.
Cardiac resynchronization therapy (CRT) presents effective means to modulate cardiac conduction and related functions in heart failure patients. However, the conventional CRT delivers electric current at only two points on the heart, therefore, it is unable to provide comprehensive electrical support to the heart. Additionally, the CRT‐device structure faces several issues, such as those associated with the endocardial screw tip, which may cause myocardial degeneration, and the metal lead wire, which may lead to intravascular thrombosis and lead infection. Moreover, the conventional CRT has limitations in mechanically improving the cardiac contractility, which often cannot prevent further ventricular dilation. Here, a fabrication of an elastoconductive epicardial mesh using a stretchable low‐impedance nanocomposite comprising Ag–Au core–shell nanowires and platinum black (Pt black) in elastomer to provide a potential solution to the above‐mentioned clinical issues is reported. The proposed nanocomposite structure exhibits high stretchability, conductivity, and biocompatibility in combination with low impedance. These features facilitate the realization of high signal‐to‐noise ratios in electrocardiogram recordings, and high‐quality electrical stimulations. The proposed epicardial mesh is implanted on the surface of an animal heart with minimum traumatic stress, and is consequently able to conduct high‐quality cardiac recording and electrical stimulation in rodents.
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