Human skin is a unique functional material that perfectly covers body parts having various complicated shapes, spontaneously heals mechanical damage, and senses a touch. E-skin devices have been actively researched, focusing on the sensing functionality of skin. However, most e-skin devices still have limitations in their shapes, and it is a challenging issue of interest to realize multiple functionalities in one device as human skin does. Here, new artificial skin devices are demonstrated in application-oriented three-dimensional (3D) shapes, which can sense exact touch location and heal mechanical damage spontaneously. Beyond the conventional film-type e-skin devices, the artificial skin devices are fabricated in optimal three-dimensional structures, via systematic material design and characterization of ion-conductive self-healing hydrogel system and its extrusion-based 3D printing. The ring-shaped and fingertip-shaped artificial skin devices are successfully fabricated to fit perfectly on finger models, and shows large electronic signal contrast, ∼5.4 times increase in current, upon a human finger contact. Furthermore, like human skin, the device provides the exact positional information of an arbitrary touch location on a three-dimensional artificial skin device without complicated device fabrication or data processing.

Ceramic suspension is a basic ingredient for various ceramic processing, and designing a ceramic suspension system is important to secure material processability in various applications. Especially when engineering ceramics, a highly loaded ceramic suspension is essential to fabricate dense ceramic bodies for proper mechanical properties. However, as solid loading increases, the viscosity of ceramic suspension keeps increasing and shows a shear-thickening behavior under a shear condition, which makes suspension formulation a challenging issue of interest. Herein, a strategy to design highly loaded ceramic suspension with optimal organic materials system is given based on the systematic correlation between solubility parameter of organic materials system and rheological processability of highly loaded ceramic suspensions. Especially with silicon nitride suspension that generally suffers from inferior rheological processability, a trend between solubility parameter of organic dispersing media and rheological behavior of suspensions is defined as a material selection guideline. Based on this selection strategy, a photocurable monomer is selected as an optimal dispersing media and directly applied to prepare highly loaded silicon nitride suspension (%51 vol%) showing low viscosity and a shear-thinning behavior. The designed ceramic suspension is successfully applied to a photocuring-based additive manufacturing process, the digital light processing, for fabrication of various 3D silicon nitride shapes.

Hydrogels are attractive, active materials for various e‐skin devices based on their unique functionalities such as flexibility and biocompatibility. Still, e‐skin devices are generally limited to simple structures, and the realization of optimal‐shaped 3D e‐skin devices for target applications is an intriguing issue of interest. Furthermore, hydrogels intrinsically suffer from drying and freezing issues in operational capability for practical applications. Herein, 3D artificial skin devices are demonstrated with highly improved device stability. The devices are fabricated in a target‐oriented 3D structure by extrusion‐based 3D printing, spontaneously heal mechanical damage, and enable stable device operation over time and under freezing conditions. Based on the material design to improve drying and freezing resistance, an organohydrogel, prepared by solvent displacement of hydrogel with ethylene glycol for 3 h, exhibits excellent drying resistance over 1000 h and improved freezing resistance by showing no phase transition down to −60 °C while maintaining its self‐healing functionality. Based on the improved drying and freezing resistance, artificial skin devices in target‐oriented optimal 3D structures are presented, which enable accurate positioning of touchpoints even on a complicated 3D structure stably over time and excellent operation at temperatures below 0 °C without losing their flexibility.