Artificial "ionic skin" is of great interest for mimicking the functionality of human skin, such as subtle pressure sensing. However, the development of ionic skin is hindered by the strict requirements of device integration and the need for devices with satisfactory performance. Here, a dual-material printing strategy for ionic skin fabrication to eliminate signal drift and performance degradation during long-term use is proposed, while endowing the ionic skins with high sensitivity by 3D printing of ionic hydrogel electrodes with microstructures. The ionic skins are fabricated by alternative digital light processing 3D printing of two photocurable precursors: hydrogel and water-dilutable polyurethane acrylate (WPUA), in which the ionically conductive hydrogel layers serve as soft, transparent electrodes and the electrically insulated WPUA as flexible, transparent dielectric layers. This novel dualmaterial printing strategy enables strong chemical bonding between the hydrogel and the WPUA, endowing the device with designed characteristics. The resulting device has high sensitivity, minimal hysteresis, a response time in the millisecond range, and excellent repetition durability for pressure sensing. The results demonstrate the potential of the dual-material 3D printing strategy as a pathway to realize highly stable and high-performance ionic skin fabrication to monitor human physiological signals and humanmachine interactions.

In this study, 3D printing is coupled with interfacial polymerization to obtain electroactive hydrogels with complex and defined geometry. Conductive hydrogels are created through a two‐step procedure: first a digital light processing 3D printing system is used to fabricate poly(ethylene glycol)diacrylate 3D structure and then pyrrole is oxidized to polypyrrole (PPY), exploiting an interfacial polymerization mechanism through which PPY can be formed in the poly(ethylene glycol) matrix, thus creating a conductive phase.

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A novel adsorbent was prepared by NH4HCO3-modifying nanoalumina dioxide and was employed for the separation/preconcentration of ReVII ions from aqueous solution. It was found that ReVII ions could be adsorbed quantitatively (above 94%) on modified nano-Al2O3 in the pH range of 2.0–3.0, while only 8.3% of ReVII ions were adsorbed on unmodified nano-Al2O3. Effects of the pH, concentration of elution solution, and interfering ions on the recovery of ReVII were systematically investigated. Adsorption kinetics for ReVII was found to be very fast, and equilibrium was reached within 5 min following the pseudo-second-order model with observed rate constants (k 2) of 14.44 g·mg–1·min–1 at 298 K. The overall rate process appeared to be influenced by both external mass transfer and intraparticle diffusion. The sorption data could be well interpreted by the Langmuir model with a maximum adsorption capacity of 1.94 mg·g–1 of ReVII on modified nano-Al2O3. Moreover, the thermodynamic parameters showed the spontaneous and endothermic nature of the adsorption process. Finally, modified nano-Al2O3 as the sorbent was successfully applied to the separation of ReVII from the ore samples with satisfactory results.

Metamaterials with artificially designed architectures can achieve unique and even unprecedented physical properties, which show promising applications in actuators, amplifiers and micromechanical controls. An initiator-integrated 3D printing technology (i3DP) was applied in this study to create scalable, metal/polymer meta-mechanical materials, which can gradually achieve negative Poisson's ratio, high strength and ultralow density, as well as high compressive and super-elastic behavior. The i3DP was enabled by integrating an atomic-transfer radical polymerization (ATRP) initiator with UV-curable resin, followed by polyelectrolyte brushes (PMETAC) grafting via surface-initiated ATRP and thereafter electroless plating to form metal coatings. Compared with polymer structures, the compressive stress of metal-polymer structure can be doubled when deposited with a 190 nm copper layer. The hollow metallic materials possess a tunable Poisson's ratio, and the highest average recoverability, which can recover nearly completely to their original shape after over 30% compression. Overall, this i3DP approach provides meta-structures with substantial benefits from the hierarchical design and fabrication flexibility.