Hydrogels consist of a cross-linked porous polymer network and water molecules occupying the interspace between the polymer chains. Therefore, hydrogels are soft and moisturized, with mechanical structures and physical properties similar to those of human tissue. Such hydrogels have a potential to turn the microscale gap between wearable devices and human skin into a tissue-like space. Here, we present material and device strategies to form a tissue-like, quasi-solid interface between wearable bioelectronics and human skin. The key material is an ultrathin type of functionalized hydrogel that shows unusual features of high mass-permeability and low impedance. The functionalized hydrogel acted as a liquid electrolyte on the skin and formed an extremely conformal and low-impedance interface for wearable electrochemical biosensors and electrical stimulators. Furthermore, its porous structure and ultrathin thickness facilitated the efficient transport of target molecules through the interface. Therefore, this functionalized hydrogel can maximize the performance of various wearable bioelectronics.

Wearable electronic devices are used to perform various electronic functions on the human skin, and their mechanical softness while maintaining high performances is critical. Therefore, there is a need to develop novel materials with outstanding softness and high electrical and ionic conductivity for wearable electronics. Here, we present an intrinsically stretchable and conductive nanocomposite based on alginate hydrogels and silver nanowires (AgNWs). The developed nanocomposite was applied to highly conductive soft electrodes that can be used in various wearable electronic devices. The nanocomposite electrode was prepared by cross-linking alginate molecules in the presence of AgNWs, exhibiting higher electrical, ionic conductivity, higher stretchability, and lower modulus than conventional conducting rubbers. By forming a bilayer structure with the nanocomposite and the ultrasoft hydrogel layer, the mechanical properties of the nanocomposite device could be matched to that of the human skin. We used the nanocomposite electrode for fabricating key device components of wearable electronics, such as a wearable antenna and a skin-mountable supercapacitor. Such demonstrations successfully proved the effectiveness of the proposed nanocomposite as a soft conducting material for wearable electronics.

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.

The integration of patterning technologies and functional hydrogel nanocomposites enables their advanced device applications such as sensors, actuators, energy devices, and tissue engineering scaffolds.