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Electronically conductive hydrogels integrated with dielectric elastomers show great promise in a wide range of applications, such as biomedical devices, soft robotics, and stretchable electronics. However, one big conundrum that impedes the functionality and performance of hydrogel-elastomer-based devices lies in the strict demands of device integration and the requirements for devices with satisfactory mechanical and electrical properties. Herein, the digital light processing three-dimensional (3D) printing method is used to fabricate 3D functional devices that bridge submillimeter-scale device resolution to centimeter-scale object size and simultaneously realize complex hybrid structures with strong adhesion interfaces and desired functionalities. The interconnected poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) network endows the PAAm hydrogel with high conductivity and superior electrical stability and poly(2-hydroxyethyl acrylate) functions as an insulating medium. The strong interfacial bonding between the hydrogel and elastomer is achieved by incomplete photopolymerization that ensures the stability of the hybrid structure. Lastly, applications of stretchable electronics illustrated as 3D-printed electroluminescent devices and 3D-printed capacitive sensors are conceptually demonstrated. This strategy will open up avenues to fabricate conductive hydrogel-elastomer hybrids in next-generation multifunctional stretchable electronics.

As one of the most promising drug delivery carriers, hydrogels have received considerable attention in recent years. Many previous efforts have focused on diffusion-controlled release, which allows hydrogels to load and release drugs in vitro and/or in vivo. However, it hardly applies to lipophilic drug delivery due to their poor compatibility with hydrogels. Herein, we propose a novel method for lipophilic drug release based on a dual pH-responsive hydrogel actuator. Specifically, the drug is encapsulated and can be released by a dual pH-controlled capsule switch. Inspired by the deformation mechanism of Drosera leaves, we fabricate the capsule switch with a double-layer structure that is made of two kinds of pH-responsive hydrogels. Two layers are covalently bonded together through silane coupling agents. They can bend collaboratively in a basic or acidic environment to achieve the "turn on" motion of the capsule switch. By incorporating an array of parallel elastomer stripes on one side of the hydrogel bilayer, various motions (e.g., bending, twisting, and rolling) of the hydrogel bilayer actuator were achieved. We conducted an in vitro lipophilic drug release test. The feasibility of this new drug release method is verified. We believe this dual pH-responsive actuator-controlled drug release method may shed light on the possibilities of various drug delivery systems.

Magnetic hydrogels have promising applications in flexible electronics, biomedical devices, and soft robotics. However, most existing magnetic hydrogels are fragile and suffer insufficient magnetic response. In this paper, we present a new approach to fabricate a strong, tough, and adhesive magnetic hydrogel with nontoxic polyacrylamide (PAAm) hydrogel as the matrix and the functional additive [3-(trimethoxysilyl)propyl methacrylate coated Fe 3 O 4 ] as the inclusions. This magnetic hydrogel not only offers a relatively high modulus and toughness compared to the pure hydrogel but also responds to the magnetic field rapidly because of high magnetic particle content (up to 60%, with respect to the total weight of the polymers and water). The hydrogel can be bonded to hydroxyl-rich hard and soft surfaces. Magnetic hydrogel with polydimethylsiloxane (PDMS) coating exhibits excellent underwater performance. The bonding between magnetic hydrogel and PDMS is very stable even under cyclic loading. An artificial muscle and its magnetomechanical coupling performance are demonstrated using this hydrogel. The adhesive tough magnetic hydrogel will open up extensive applications in many fields, such as controlled drug delivery systems, coating of soft devices, and microfluidics. The strategy is applicable to other functional soft materials.