Fabrics are widely used in hospitals and many other settings for bedding, clothing, and face masks; however, microbial pathogens can survive on surfaces for a long time, leading to microbial transmission. Coatings of metallic particles on fabrics have been widely used to eradicate pathogens. However, current metal particle coating technologies encounter numerous issues such as nonuniformity, processing complexity, and poor adhesion. To overcome these issues, an easy‐to‐control and straightforward method is reported to coat a wide range of fabrics by using gallium liquid metal (LM) particles to facilitate the deposition of liquid metal copper alloy (LMCu) particles. Gallium particles coated on the fabric provide nucleation sites for forming LMCu particles at room temperature via galvanic replacement of Cu2+ ions. The LM helps promote strong adhesion of the particles to the fabric. The presence of the LMCu particles can eradicate over 99% of pathogens (including bacteria, fungi, and viruses) within 5 min, which is significantly more effective than control samples coated with only Cu. The coating remains effective over multiple usages and against contaminated droplets and aerosols, such as those encountered in facemasks. This facile coating method is promising for generating robust antibacterial, antifungal, and antiviral fabrics and surfaces.

We suggest gelatin hydrogel as an electrolyte and demonstrate organic electrochemical transistors (OECTs) based on a sheet of gelatin. We also modulate electrical characteristics of the OECT with respect to pH condition of the gelatin hydrogel from acid to base and analyze its characteristics based on the electrochemical theory. Moreover, we extend the gelatin-based OECT to electrochemical logic circuits, for example, NOT, NOR, and NAND gates.

This review focuses on surface modifications of liquid metal (LM). Gallium (Ga) and Ga-based LMs show the promising ability to maintain metallic properties under large mechanical strains when encapsulated inside an elastomer matrix. [1-7] This property is useful in a variety of applications, including wearable/deformable devices, sensors, and soft actuators-the focus of this special issue. There are several motives for creating soft and stretchable devices. For example, devices that are soft and flexible can make conformal contact to human skin for continuous and long-term monitoring. [8-11] Likewise, devices assembled on or within soft robots can maintain function during actuation (bending or stretching) while sensing dynamic motion. Conventional conductors in electronic systems are typically rigid (e.g., copper) and thus poorly suited for soft and stretchable devices. To address this issue, efforts have been taken to create stretchable and deformable conductors using thin metal films with special geometries [12-14] (e.g., pop-up and serpentine electrodes) on a deformable substrate or polymer composites filled with conductive nanomaterials in a stretchable matrix. [15,16] These approaches effectively render rigid materials stretchable through clever engineering of their geometry. However, due to the inherently nonstretchable nature of solid metal films or solid conductive particles, these components/inclusions would add to the overall rigidity of the composite and limit their deformability. LMs are interesting as stretchable conductors because they have metallic conductivity and deformability defined primarily by the encasing material (e.g., elastomer).

Demands for precise health information tracking techniques are increasing, especially for daily dietry requirements to prevent obesity, diabetes, etc. Many commercially available sensors that detect dynamic motions of the body lack accuracy, while novel strain sensors at the research level mostly lack the capability to analyze measurements in real life conditions. Here, a stretchable, patch‐type calorie expenditure measurement system is demonstrated that integrates an ultrasensitive crack‐based strain sensor and Bluetooth‐enabled wireless communication circuit to offer both accurate measurements and practical diagnosis of motion. The crack‐based strain gauge transformed into a pop‐up‐shaped structure provides reliable measurements and broad range of strain (≈100%). Combined with the stretchable analysis circuit, the skin attachable tool translates variation of the knee flexion angle into calorie expenditure amount, using relative resistance change (R/R0) data from the flexible sensor. As signals from the knee joint angular movement translates velocity and walking/running behavior, the total amount of calorie expenditure is accurately analyzed. Finally, theoretical, experimental, and simulation analysis of signal stability, dynamic noises, and calorie expenditure calculation obtained from the device during exercise are demonstrated. For further applications, the devices are expected to be used in broader range of dynamic motion of the body for diagnosis of abnormalities and for rehabilitation.