been applied more closely to the human body. Owing to the soft and curved nature of human skin, the systems need to be flexible, robust, and transparent to ensure operational reliabilities and to provide comforts. [3,4] However, it has been challenging to ensure these desirable properties due to the complicated structures of conventional touch-sensing systems, which contain a network of individual electrodes and stacked multilayers. [4,5,8,10,12] More importantly, sensing systems inevitably rely on external power sources, which potentially sacrifice flexibility, add weight, and decrease the lifetime of the sensing systems. [4,5,8,[12][13][14] To address the issues originated from the use of external power sources, systems that rely on energy-harvesting technologies have been highlighted as an alternative to conventional touch-sensing systems. [3,[15][16][17] Recently, triboelectric nanogenerators (TENGs), which convert mechanical touch to electrical energy, have been developed to provide a platform for touch-sensing capability that does not rely on additional power sources. [16][17][18][19][20] The self-powered touch-sensing capability of TENGs can be realized with a couple of materials, i.e., a dielectric layer attached to a conducting layer, based on the combined effects of contact electrification and electrostatic induction. [3,17,18,21] To ensure that triboelectric touch sensors are skin-mountable, researchers have worked to make the components stretchable and transparent. Soft materials such as poly(dimethylsiloxane) (PDMS) and ionically conductive gels are suitable for use in skin-mountable triboelectric touch sensors thanks to their high transparency, stretchability, resilience, and easily tunable mechanical properties. [17,[22][23][24][25] Nonetheless, the development of triboelectric touch position sensors with reliable stretchability and transparency remains challenging due to the complicated structures of the sensors, which contain multiple stacked layers and arrays of individual electrodes. [16,17,19,21,26,27] Unfortunately, the stacking process deteriorates the outstanding mechanical/optical properties of the soft materials in TENGs since the sensors require an additional conducting layer of a material such as metal, ceramic, carbon materials, etc. [16,[28][29][30] The inclusion of transparent and stretchable materials like gels also results in easy delamination and blurring at the bonding interfaces. [17,19,31] Relying on a complex array of individual electrodes and corresponding wires Recent growing pursuit of skin-mountable devices has been impeded by the complicated structures of most sensing systems, containing electrode grids, stacked multilayers, and even external power sources. Here, a type of touch sensing, termed "triboresistive touch sensing", is introduced for gridless touch recognition based on monolayered ionic power generators. A homogeneous monolayer, i.e., ionic poly(dimethylsiloxane) (PDMS), generates electricity based on the electric field generated by touch. Voltages generated at ...

Structure changes mediated by anisotropic volume changes of stimuli‐responsive hydrogels are useful for many research fields, yet relatively simple structured objects are mostly used due to limitation in fabrication methods. To fabricate complex 3 dimensional (3D) structures that undergo structure changes in response to external stimuli, jammed microgel‐based inks containing precursors of stimuli‐responsive hydrogels are developed for extrusion‐based 3D printing. Specifically, the jammed microgel‐based inks are prepared by absorbing precursors of poly(acrylic acid) or poly(N‐isopropylacrylamide) in poly(acrylamide) (PAAm) microgels, and jamming them. The inks exhibit shear‐thinning and self‐healing properties that allow extrusion of the inks through a nozzle and rapid stabilization after printing. Stimuli‐mediated volume changes are observed for the extruded structures when they are post‐crosslinked by UV light to form interpenetrating networks of PAAm microgels and stimuli‐responsive hydrogels. Using this method, a dumbbell‐shaped object that can transform to a biconvex shape, and a gripper that can grasp and lift an object in response to stimuli are 3D‐printed. The jammed microgel‐based 3D printing strategy is a versatile method useful for variety of applications as diverse types of monomers absorbable in the microgels can be used to fabricate complex 3D objects transformable by external stimuli.

In article number 2108586, Jeong-Yun Sun and co-workers report a novel type of touch sensing, termed triboresistive touch sensing, which is developed for self-powered gridless touch recognition. An ionic poly(dimethylsiloxane) exhibiting high transmittance (96.5%), stretchability (539.1%), resilience (99.0%), and ionic conductivity (0.25 mS m −1 ) is designed to generate power based on the electric field generated by touch. The generated voltages ensure recognition of the touch positions without electrode grid layers and external power sources.