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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 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.

In this paper, the self-consistent solution of Schrödinger-Poisson equations was realized to estimate the radiative recombination coefficient and the lifetime of a single blue light InGaN/GaN quantum well (QW). The results revealed that the recombination rate was not in proportion to the total injected carriers, and thus the Bnp item was not an accurate method to analyze the recombination process. Carrier screening and band filling effects were also investigated, and an extended Shockley-Read-Hall coefficient A(kt) with a statistical weight factor due to the carrier distributions in real and phase space of the QW was proposed to estimate the total nonradative current loss including carrier nonradiative recombination, leakage and spillover to explain the efficiency droop behaviors. Without consideration of the Auger recombination, the blue shift of the electroluminescence spectrum, light output power and efficiency droop curves as a function of injected current were all investigated and compared with the experimental data of a high brightness blue light InGaN/GaN multiple QWs light emitting diode to confirm the reliability of our theoretical hypothesis.

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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Three dual-wavelength InGaN/GaN multiple quantum well (MQW) light emitting diodes (LEDs) with increasing indium content are grown by metal-organic chemical vapor deposition, which contain six periods of low-In-content MQWs and two periods of high-In-content MQWs. For the low-In-content MQWs of three studied samples, their internal quantum efficiency (IQE) shows a rising trend as the emission wavelength increases from 406 nm to 430 nm due to the suppression of carriers escape from the wells to the barriers. However, for the high-In-content MQWs, the sample IQE falls rapidly with a further increase of emission wavelength from 496 nm to 575 nm. Theoretical calculation reveals that the electron-hole wave function overlap in the high-In-content MQWs is reduced because of an increase in the internal polarization field as indium content is increased. In addition, time-resolved photoluminescence decay curves show that the carriers generated in the low-In-content MQWs can be effectively transferred to the high-In-content part through the reabsorption process. However, the transfer time gradually becomes longer as emission wavelength increases, which means a reduction of carrier transfer rate between the different indium content MQWs. Furthermore, nonradiative recombination is enhanced in the high-In-content MQWs with longer emission wavelength due to the decline of crystal quality. Therefore, the fast drop of IQE for high-In-content MQWs can be attributed to the increase of the internal polarization field, the decrease of carrier transfer efficiency, and the enhanced nonradiative recombination. This research has a certain guiding value for an understanding of the recombination mechanism in the InGaN/GaN MQWs and for achieving high quality multiple-wavelength LEDs with better performance.