Organohydrogels with High-Speed Lubrication by Confining Polymer Chain Mobility by an Interpenetrated Heteronetwork.

Hydrogels with pure hydrophilic network have received much attention due to their excellent low frictional behavior. However, the lubrication performance of hydrogels is not satisfied under high-speed condition due to the energy dissipation caused by adsorbed polymer chains as well as the failure of lubricating mechanisms accompanied by the transition of lubrication regime. In this work, interpenetrating double-network organohydrogels were constructed by combining hydrophilic and oleophilic polymer networks to modify the physiochemical properties of surface polymer chains, especially the chain mobility. The oleophilic polymer network spatially restricting the mobility of the swollen hydrophilic network in water, resulted in a low coefficient of friction (ca. 0.01) compared with conventional hydrogels at high speed (0.1 m s-1 ). Meanwhile, the organohydrogels had superior wear resistance, with almost no wear observed on the sliding track after 5 k cycles of rubbing at high speed. The design concept of organohydrogels can be extended to a variety of low-wear, highly-lubricating materials.

Microchannel and Nanofiber Array Morphology Enhanced Rapid Superspreading on Animals' Corneas.

The dynamic spreading phenomenon of liquids is vital for both understanding wetting mechanisms and visual reaction time-related applications. However, how to control and accelerate the spreading process is still an enormous challenge. Here, a unique microchannel and nanofiber array morphology enhanced rapid superspreading (RSS) effect on animals' corneas with a superspreading time (ST) of 830 ms is found, and the respective roles of the nanofiber array and the microchannel in the RSS effect are explicitly demonstrated. Specifically, the superspreading is induced by in-/out-of-plane nanocapillary forces among the nanofiber array; the microchannel is responsible for tremendously speeding up the superspreading process. Inspired by the RSS strategy, not only is an RSS surface fabricated with an ST of only 450 ms, which is, respectively, more than 26 and 1.8 times faster than conventional superamphiphilic surfaces and animal's corneas and can be applied as RSS surfaces on video monitors to record clear videos, but also it is demonstrated that the RSS effect has tremendous potential as advanced ophthalmic material surfaces to enhance its biocompatibility for clear vision.

Fabrication of Elastic Macroporous Polymers with Enhanced Oil Absorbability and Antiwaxing Performance.

Porous polymers are of great interest in potential energy storage and environmental remediation applications. However, traditional fabrication methods are either time-consuming or energy-consuming and deteriorate the mechanical strength of polymer materials. In this study, polymerization-induced phase separation was used to realize the template-free fabrication of superflexible macroporous polymers. Since the solvent is also used as a porogen, this method can be widely used to synthesize several porous polymers by carefully choosing the solvent and monomer. Compared to nonstructured polymers, the prepared macroporous polymers exhibited enhanced mechanical strength, superflexibility, multicompressibility, and bending properties. Along with hydrophobicity/oleophilicity and macroporous structures, the as-prepared porous polymers demonstrated controllable oil absorbability and release; furthermore, after infusing with lubrication liquid, these materials can be used as antiwaxing materials. The elastic porous polymers prepared using this simple and universal method show great potential for various applications, including controlled drug release, antiwaxing, and lubrication.

Author Correction: Layered nanocomposites by shear-flow-induced alignment of nanosheets.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Reversibly Thermosecreting Organogels with Switchable Lubrication and Anti-Icing Performance.

Synthetic gels with switchable interfacial properties have great potential in smart devices and controllable transport. Herein, we design an organogel by incorporating a binary liquid mixture with an upper critical solution temperature (UCST) into a polymer network, resulting in reversible modulation of lubrication and adhesion properties. As the temperature changes, the lubricating mechanism changes reversibly from boundary lubrication to hydrodynamic lubrication due to phase separation within the binary solution permeating the gel (friction coefficient 0.4-0.03). Droplets appear on the gel surface at low temperature and disappear with temperature higher than the critical phase separation temperature (Tps ) of the organogel. The organogel possesses a relatively low ice adhesive strength (less than 1 kPa). This material has potential applications in anti-icing and smart devices, and we believe that this design strategy can be expanded to other systems such as aqueous solutions and hydrogels.

Layered nanocomposites by shear-flow-induced alignment of nanosheets.

Biological materials, such as bones, teeth and mollusc shells, are well known for their excellent strength, modulus and toughness1-3. Such properties are attributed to the elaborate layered microstructure of inorganic reinforcing nanofillers, especially two-dimensional nanosheets or nanoplatelets, within a ductile organic matrix4-6. Inspired by these biological structures, several assembly strategies-including layer-by-layer4,7,8, casting9,10, vacuum filtration11-13 and use of magnetic fields14,15-have been used to develop layered nanocomposites. However, how to produce ultrastrong layered nanocomposites in a universal, viable and scalable manner remains an open issue. Here we present a strategy to produce nanocomposites with highly ordered layered structures using shear-flow-induced alignment of two-dimensional nanosheets at an immiscible hydrogel/oil interface. For example, nanocomposites based on nanosheets of graphene oxide and clay exhibit a tensile strength of up to 1,215 ± 80 megapascals and a Young's modulus of 198.8 ± 6.5 gigapascals, which are 9.0 and 2.8 times higher, respectively, than those of natural nacre (mother of pearl). When nanosheets of clay are used, the toughness of the resulting nanocomposite can reach 36.7 ± 3.0 megajoules per cubic metre, which is 20.4 times higher than that of natural nacre; meanwhile, the tensile strength is 1,195 ± 60 megapascals. Quantitative analysis indicates that the well aligned nanosheets form a critical interphase, and this results in the observed mechanical properties. We consider that our strategy, which could be readily extended to align a variety of two-dimensional nanofillers, could be applied to a wide range of structural composites and lead to the development of high-performance composites.

Imparting Functionality to the Hydrogel by Magnetic-Field-Induced Nano-assembly and Macro-response.

Hydrogels are composed of 3D hydrophilic networks with an abundance of water; they are analogous to biological soft tissues. Their unique physico-chemical properties endow hydrogels with great potential in many fields, including tissue engineering and flexible sensing. However, inadequate functionality, such as lack of rapid responsiveness, severely limits practical applications in many areas. Therefore, imparting functionality to the hydrogel is a hot research topic. The magnetic field, as an important physical field, provides a new strategy with a variety of advantages. Magnetic-field-induced ordered nano-assembly brought anisotropic properties and novel performance. Furthermore, the magnetic responsiveness of hydrogels with magnetic nanoparticles can lead to the generation of functionality under magnetic fields. Thus, we aim to systematically describe the significant effect of magnetic fields on the functionality of the hydrogel. In this review, magnetic-field-induced assembly of nanomaterials with different dimensions and resulting functional performance are introduced. The functionalities of hydrogels based on magnetic-field-induced macroscopic responses are also summarized. We believe this review will motivate more exploration of the application of magnetic fields to develop functional hydrogel materials.

Diffusion-Freezing-Induced Microphase Separation for Constructing Large-Area Multiscale Structures on Hydrogel Surfaces.

Hydrogels with multiscale structured surface have attracted significant attention for their valuable applications in diverse areas. However, current strategies for the design and fabrication of structured hydrogel surfaces, which suffer from complicated manufacturing processes and specific material modeling, are not efficient to produce structured hydrogel surfaces in large area, and therefore restrict their practical applications. To address this problem, a general and reliable method is reported, which relies on the interplay between polymer chain diffusion and the subsequent freezing-induced gelation and microphase separation processes. The basic idea is systematically analyzed and further exploited to manufacture gel surfaces with gradient structures and patterns through the introduction of temperature gradient and shape control of the contact area. Moreover, the formed micro/nanostructured surfaces are exemplified to work as capillary systems and thus can uplift the liquid spontaneously indicating the potential application for anti-dehydration. It is believed that the proposed facile and large-area fabrication method can inspire the design of materials with various functionalized surfaces.

Dual-Programmable Shape-Morphing and Self-Healing Organohydrogels Through Orthogonal Supramolecular Heteronetworks.

Programmable materials that can change their inherent shapes or properties are highly desirable due to their promising applications. However, among various programmable shape-morphing materials, the single control route allows temporary states to recover the unchangeable former state, thus lacking the sophisticated programmability for their shape-encoding behaviors and mechanics. Herein, dual-programmable shape-morphing organohydrogels featuring supramolecular heteronetworks are developed. In the system, the metallo-supramolecular hydrogel framework and micro-organogels featuring semicrystalline comb-type networks independently respond to different stimuli, thereby providing orthogonal dual-switching mechanics and ultrahigh mechanical strength. The supramolecular heteronetworks also possess excellent self-healing properties. More notably, such orthogonal supramolecular heteronetworks demonstrate hierarchical shape morphing performance that far exceeds conventional shape-morphing materials. Utilizing this dual programming strategy of the orthogonal supramolecular heteronetworks, the material's permanent shape can be manipulated in a step-wise shape morphing process, thereby realizing sophisticated shape changes with a high degree of freedom. The organohydrogels can act as a biomimetic smart device for the on-demand control of unidirectional liquid transport. Based on these characteristics, it is anticipated that the supramolecular organohydrogels may serve as adaptive programmable materials for a variety of applications.

General Strategy to Fabricate Highly Filled Microcomposite Hydrogels with High Mechanical Strength and Stiffness.

Conventional synthetic hydrogels are intrinsically soft and brittle, which severely limits the scope of their applications. A variety of approaches have been proposed to improve the mechanical strength of hydrogels. However, a facile and ubiquitous strategy to prepare hydrogels with high mechanical strength and stiffness is still a challenge. Here, we report a general strategy to prepare highly filled microcomposite hydrogels with high mechanical performance using an ultrasonic assisted strategy. The microparticles were dispersed in the polymer network evenly, resulting in homogeneous and closely packed structures. The as-prepared hydrogels with extraordinary mechanical performance can endure compressive stress up to 20 MPa (at 75% strain) and exhibit high stiffness (elastic modulus is around 18 MPa). By using our comprehensive strategy, different hydrogels can enhance their mechanical strength and stiffness by doping various microparticles, leading to a much wider variety of applications.

Bioinspired Nanocomposite Hydrogels with Highly Ordered Structures.

In the human body, many soft tissues with hierarchically ordered composite structures, such as cartilage, skeletal muscle, the corneas, and blood vessels, exhibit highly anisotropic mechanical strength and functionality to adapt to complex environments. In artificial soft materials, hydrogels are analogous to these biological soft tissues due to their "soft and wet" properties, their biocompatibility, and their elastic performance. However, conventional hydrogel materials with unordered homogeneous structures inevitably lack high mechanical properties and anisotropic functional performances; thus, their further application is limited. Inspired by biological soft tissues with well-ordered structures, researchers have increasingly investigated highly ordered nanocomposite hydrogels as functional biological engineering soft materials with unique mechanical, optical, and biological properties. These hydrogels incorporate long-range ordered nanocomposite structures within hydrogel network matrixes. Here, the critical design criteria and the state-of-the-art fabrication strategies of nanocomposite hydrogels with highly ordered structures are systemically reviewed. Then, recent progress in applications in the fields of soft actuators, tissue engineering, and sensors is highlighted. The future development and prospective application of highly ordered nanocomposite hydrogels are also discussed.

Biphasic Synergistic Gel Materials with Switchable Mechanics and Self-Healing Capacity.

A fabrication strategy for biphasic gels is reported, which incorporates high-internal-phase emulsions. Closely packed micro-inclusions within the elastic hydrogel matrix greatly improve the mechanical properties of the materials. The materials exhibit excellent switchable mechanics and shape-memory performance because of the switchable micro- inclusions that are incorporated into the hydrogel matrix. The produced materials demonstrated a self-healing capacity that originates from the noncovalent effect of the biphasic heteronetwork. The aforementioned characteristics suggest that the biphasic gels may serve as ideal composite gel materials with validity in a variety of applications, such as soft actuators, flexible devices, and biological materials.

Oscillatory Reaction Induced Periodic C-Quadruplex DNA Gating of Artificial Ion Channels.

Many biological ion channels controlled by biochemical reactions have autonomous and periodic gating functions, which play important roles in continuous mass transport and signal transmission in living systems. Inspired by these functional biological ion channel systems, here we report an artificial self-oscillating nanochannel system that can autonomously and periodically control its gating process under constant conditions. The system is constructed by integrating a chemical oscillator, consisting of BrO3-, Fe(CN)64-, H+, and SO32-, into a synthetic proton-sensitive nanochannel modified with C-quadruplex (C4) DNA motors. The chemical oscillator, containing H+-producing and H+-consuming reactions, can cyclically drive conformational changes of the C4-DNA motors on the channel wall between random coil and folded i-motif structures, thus leading to autonomous gating of the nanochannel between open and closed states. The autonomous gating processes are confirmed by periodic high-low ionic current oscillations of the channel monitored under constant reaction conditions. The utilization of a chemical oscillator integrated with DNA molecules represents a method to directly convert chemical energy of oscillating reactions to kinetic energy of conformational changes of the artificial nanochannels and even to achieve diverse autonomous gating functions in artificial nanofluidic devices.

Supramolecular Self-Assembly Induced Adjustable Multiple Gating States of Nanofluidic Diodes.

Artificial nanochannels, inheriting smart gating functions of biological ion channels, promote the development of artificial functional nanofluidic devices for high-performance biosensing and electricity generation. However, gating states of the artificial nanochannels have been mainly realized through chemical modification of the channels with responsive molecules, and their gating states cannot be further regulated once the nanochannel is modified. In this work, we employed a new supramolecular layer-by-layer (LbL) self-assembly method to achieve reversible and adjustable multiple gating features in nanofluidic diodes. Initially, a self-assembly precursor was modified into a single conical nanochannel, then host molecule-cucurbit[8]uril (CB[8]) and guest molecule, a naphthalene derivative, were self-assembled onto the precursor through an LbL method driven by host-enhanced π-π interaction, forming supramolecular monolayer or multilayers on the inner surface of the channel. These self-assemblies with different layer numbers possessed remarkable charge effects and steric effects, exhibiting a capability to regulate the surface charge density and polarity, the effective diameter, and the geometric asymmetry of the single nanochannel, realizing reversible gating of the single nanochannel among multiple rectification and ion-conduction states. As an example of self-assembly of supramolecular networks in nanoconfinements, this work provides a new approach for enhancing functionalities of artificial nanochannels by LbL supramolecular self-assemblies. Meanwhile, since the host molecule, CB[8], used in this work can interact with different kinds of biomolecules and stimuli-responsive chemical species, this work can be further extended to build a novel stable multiple-state research platform for a variety of uses such as sensing and controllable release.

Tuning polymeric amphiphilicity via Se-N interactions: towards one-step double emulsion for highly selective enzyme mimics.

A selenium-containing small molecule is exploited to controllably tune the polymer amphiphilicity, leading to fabrication of appropriate polymer surfactants through which one-step double emulsions can be obtained in a facile, scalable, surfactant-free approach. After solvent evaporation, these resulting porous microparticles are shown to be the exceptional artificial GPx enzyme mimics.

A multi-structural and multi-functional integrated fog collection system in cactus.

Multiple biological structures have demonstrated fog collection abilities, such as beetle backs with bumps and spider silks with periodic spindle-knots and joints. Many Cactaceae species live in arid environments and are extremely drought-tolerant. Here we report that one of the survival systems of the cactus Opuntia microdasys lies in its efficient fog collection system. This unique system is composed of well-distributed clusters of conical spines and trichomes on the cactus stem; each spine contains three integrated parts that have different roles in the fog collection process according to their surface structural features. The gradient of the Laplace pressure, the gradient of the surface-free energy and multi-function integration endow the cactus with an efficient fog collection system. Investigations of the structure-function relationship in this system may help us to design novel materials and devices to collect water from fog with high efficiencies.

Supramolecular polymerization at low monomer concentrations: enhancing intermolecular interactions and suppressing cyclization by rational molecular design.

We present the construction of long-chain water-soluble supramolecular polymers at low monomer concentrations. Naphthalene-based host-enhanced π-π interactions, which possess high binding constants, were used as the driving force of supramolecular polymerization. A monomer, DNDAB, with a rigid, bulky 1,4-diazabicyclo[2.2.2]octane-1,4-diium linker was designed. The design of the monomer structure strongly influenced the efficiency of the supramolecular polymerization. The rigid, bulky linker in DNDAB effectively eliminates cyclization, promoting the formation of long-chain supramolecular polymers at low monomer concentrations. In contrast, a reference monomer containing a flexible linker (DNPDN) only forms oligomers owing to cyclization.