Initial residual stress is omnipresent in biological tissues and soft matter, and can affect growth-induced pattern selection significantly. Here we demonstrate this effect experimentally by letting soft tubes grow in the presence or absence of initial residual stress and by observing different growth pattern evolutions. These experiments motivate us to model the mechanisms at play when a growing bilayer tubular organ spontaneously displays buckling patterns on its inner surface. We demonstrate that not only differential growth, geometry and elasticity, but also initial residual stress distribution, exert a notable influence on these pattern phenomena. Prescribing an initial residual stress distribution offers an alternative or a more effective way to implement pattern selection for growable bio-tissues or soft matter. The results also show promise for the design of 4D bio-mimic printing protocols or for controlling hydrogel actuators.
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.
Abstract Soft ionic conductors, such as hydrogels and ionogels, have enabled stretchable and transparent ionotronics, but they suffer from key limitations inherent to the liquid components, which may leak and evaporate. Here, novel liquid‐free ionic conductive elastomers (ICE) that are copolymer networks hosting lithium cations and associated anions via lithium bonds and hydrogen bonds are demonstrated, such that they are intrinsically immune from leakage and evaporation. The ICEs show extraordinary mechanical versatility including excellent stretchability, high strength and toughness, self‐healing, quick self‐recovery, and 3D‐printability. More intriguingly, the ICEs can defeat the conflict of strength versus toughness—a compromise well recognized in mechanics and material science—and simultaneously overcome the conflict between ionic conductivity and mechanical properties, which is common for ionogels. Several liquid‐free ionotronics based on the ICE are further developed, including resistive force sensors, multifunctional ionic skins, and triboelectric nanogenerators (TENGs), which are not subject to limitations of previous gel‐based devices, such as leakage, evaporation, and weak hydrogel–elastomer interfaces. Also, the 3D printability of the ICEs is demonstrated by printing a series of structures with fine features. The findings offer promise for a variety of ionotronics requiring environmental stability and durability.
Abstract Stretchable ionic conductors such as hydrogels and ionic‐liquid‐based gels (aka ionogels) have garnered great attention as they enable the development of soft ionotronics. Notably, soft ionotronic devices inevitably operate in humid environments or under mechanical loads. However, many previously reported hydrogels and ionogels, however, are unstable in environments with varying humidity levels owing to hydrophilicity, and their liquid components (i.e., ionic liquid, water) may leak easily from polymer matrices under mechanical loads, causing deterioration of device performance. This work presents novel hydrophobic ionogels with strong ionic liquid retention capability. The ionogels are ambiently and mechanically stable, capable of not absorbing moisture in environments with high relative humidity and almost not losing liquid components during long periods of mechanical loading. Moreover, the ionogels exhibit desirable conductivity (10 −4 –10 −5 S cm −1 ), large rupturing strain (>2000%), moderate fractocohesive length (0.51 – 1.03 mm), and wide working temperature range (−60 to 200 °C). An ionic skin is further designed by integrating the concept of sensory artificial skins and triboelectric nanogenerators, which can convert multiple stimuli into various types of signals, including resistance, capacitance, short‐circuit current, and open‐circuit voltage. This work may open new avenues for the development of soft ionotronics with stable performance.
This study investigates nonisothermal co-drying kinetics of two typical biomasses (cornstalk and red pine) with lignite in the presence of a nitrogen atmosphere using a thermal gravimetric analysis technique. The drying rate can be increased by either decreasing the blending ratio of biomass or increasing the heating rate. The activation energies of cornstalk/lignite blends and red pine/lignite blends in the two falling rate periods are less than that of their parent samples. In the first falling rate period, the dominant mechanisms of drying for lignite are described by the Avrami–Erofeev equation (n = 1.5), while the mechanisms for the cornstalk, red pine, and mixture samples are fitted to the Mample equation (n = 1.0). In the second falling rate period, the mechanisms are described by the Avrami–Erofeev equation (n = 1.5 or n = 2.0). The general kinetic compensation effect correlations are obtained for all samples within heating rates of 10–30°C/min. Significant synergistic interactions between the Chinese lignite and cornstalk or red pine are detected during co-drying.
Abstract Many emerging technologies such as wearable batteries and electronics require stretchable functional structures made from intrinsically less deformable materials. The stretch capability of most demonstrated stretchable structures often relies on either initially out‐of‐plane configurations or the out‐of‐plane deflection of planar patterns. Such nonplanar features may dramatically increase the surface roughness, cause poor adhesion and adverse effects on subsequent multilayer processing, thereby posing a great challenge for flexible devices that require smooth surfaces (e.g., transparent electrodes in which flat‐surface‐enabled high optical transmittance is preferred). Inspired by the lamellar layouts of collagenous tissues, this work demonstrates a planar bilayer lattice structure, which can elongate substantially via only in‐plane motion and thus maintain a smooth surfaces. The constructed bilayer lattice exhibits a large stretchability up to 360%, far beyond the inherent deformability of the brittle constituent material and comparable to that of state‐of‐the‐art stretchable structures for flexible electronics. A stretchable conductor employing the bilayer lattice designs can remain electrically conductive at a strain of 300%, demonstrating the functionality and potential applications of the bilayer lattice structure. This design opens a new avenue for the development of stretchable structures that demand smooth surfaces.
Soft display has been intensively studied in recent years in the wake of rapid development of a variety of soft materials. The currently existing solutions for translating the traditional hard display into the more convenient soft display mainly include light-emitting diodes, liquid crystals, quantum dots, and phosphors. The desired soft display should take the advantages of facile fabrication processes and cheap raw materials. Besides, the device should be colorful, nontoxic, and not only flexible but also stretchable. However, the foregoing devices may not own all of the desired features. Here, a new type of soft display, which consists of dielectric elastomer and photonic crystals that cover all of the features mentioned above and can achieve the color change dynamically and in situ, is reported. In addition to the above features, the angle-dependent characteristic and the excellent mechanical reliability make it a great candidate for the next generation of soft display. Finally, the vast applications of the present concept in a variety of fields are also prospected.
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