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.

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Mechanical flexibility and electrical reliability establish the fundamental criteria for wearable and implantable electronic devices. In order to receive intrinsically stretchable resistive switching memories, both the electrode and storage media should be flexible yet retain stable electrical properties. Experimental results and finite element analysis reveal that the formation of 3D liquid metal galinstan (GaInSn) calabash bunch conductive network in poly(dimethyl siloxane) (PDMS) matrix allows GaInSn@PDMS composite as soft electrode with the stable conductivity of >1.3 × 103 S cm−1 at the stretching strains of >80% and a fracture strain extreme of 108.14%, while the third‐generation metal–organic framework MIL‐53 thin film with a facial rhombohedral topology enables large mechanical deformation up to a theoretical level of 17.7%. Combining the use of liquid metal–based electrode and MIL‐53 switching layer, for the first time, intrinsically stretchable RRAM device Ag/MIL‐53/GaInSn@PDMS is demonstrated that can exhibit reliable resistive switching characteristics at the strain level of 10%. The formation of fluidic gallium conductive filaments, together with the structural flexibility of the GaInSn@PDMS soft electrode and MIL‐53 insulating layer, accounts for the uniform resistive switching under stretching deformation scenario.

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 Fe3O4] 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.

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hydrogel devices. For example, the conductivity of hydrogels can be enhanced by adding ions or carbon nanomaterials. [20] Adding photochromic, thermochromic, or photonic materials endows hydrogel the ability to change color under certain external stimulations. [21][22][23][24] Using this method, we prepare a novel thermochromic hydrogel by embedding thermochromic capsule powders (TCPs) into the hydrogel (Figure 1, see details in the Experimental Section).TCPs change color in response to temperature. The particles are usually spheres with 3-5 μm in diameters as shown in images of the scanning electron microscope (SEM) (Figure 1a,b). The exterior of the particle is a 0.2-0.5 μm thick transparent shell that neither dissolves nor melts when environment temperature changes. The components of the TCPs are shown in Table S1 in the Supporting Information. The shell protects the components from being eroded by the external environment during the reversible reaction of coloration, so the thermochromic property is quite stable. [25] Besides the shell layer, the thermochromic components consist of two ingredients: a color agent (CA), and a solvent. The critical temperature for color changing is determined by the phase change temperature of the solvent: when the ambient temperature is lower than the critical temperature, the solvent is solid, and the CA displays color 1. As Figure 1c shows, when the temperature rises above the critical temperature, the electron transfer occurs between them resulting in the change of the molecular structure of the CA and the color displayed of the system. [26] Under a certain temperature, the coloration and discoloration reactions reach an equilibrium state, which determines the saturation of the color. Furthermore, the critical temperature can be changed by controlling the melting point of the solvent component. [27] The color of the prepared hydrogel can switch between two modes at a specific temperature with a prompt response. As TCPs can disperse well in water, the addition of a small amount of powders (5 mg mL −1 ) is enough to dye the hydrogel. This color-changing hydrogel has good mechanical properties and retains its ability of color changing even after cyclic loading. To explore the mechanical properties of the thermochromic hydrogel, one may use quasi-static stretching tests to measure the initial modulus of the hydrogel, and cyclic stretching tests to analyze the functional performance of the hydrogel. We characterize the color-changing ability by absorbance spectra at different temperatures through a spectrophotometer. In addition, we demonstrate that this thermochromic hydrogel Recently, hydrogels with coloration have attracted researchers from various fields, such as camouflage, anti-counterfeiting, and soft display. However, existing thermochromic hydrogels are limited by their weak color display performance and insufficient sensitivity. Here proposed is a new kind of thermochromic hydrogel which possesses bright colors, fast response time, and reliable results across a long lif...

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