Wetting-Enabled Three-Dimensional Interfacial Polymerization (WET-DIP) for Bioinspired Anti-Dehydration Hydrogels.

Anti-dehydration hydrogels have attracted considerable attention due to their promising applications in stretchable sensors, flexible electronics, and soft robots. However, anti-dehydration hydrogels prepared by conventional strategies inevitably depend on additional chemicals or suffer from cumbersome preparation processes. Here, inspired by the succulent Fenestraria aurantiaca a one-step wetting-enabled three-dimensional interfacial polymerization (WET-DIP) strategy for constructing organogel-sealed anti-dehydration hydrogels is developed. By virtue of the preferential wetting on the hydrophobic-oleophilic substrate surfaces, the organogel precursor solution can spread on the three-dimensional (3D) surface and encapsulate the hydrogel precursor solution, forming anti-dehydration hydrogel with 3D shape after in situ interfacial polymerization. The WET-DIP strategy is simple and ingenious, and accessible to discretionary 3D-shaped anti-dehydration hydrogels with a controllable thickness of the organogel outer layer. Strain sensors based on this anti-dehydration hydrogel also exhibit long-term stability in signal monitoring. This WET-DIP strategy shows great potentialities for constructing hydrogel-based devices with long-term stability.

Self-Pumping Janus Hydrogel with Aligned Channels for Accelerating Diabetic Wound Healing.

Excessive exudate secreted from diabetic wounds often results in skin overhydration, severe infections, and secondary damage upon dressing changes. However, conventional wound dressings are difficult to synchronously realize the non-maceration of wound sites and rapid exudate transport due to their random porous structure. Herein, a self-pumping Janus hydrogel with aligned channels (JHA) composed of hydrophilic poly (ethylene glycol) diacrylate (PEGDA) hydrogel layer and hydrophobic polyurethane (PU)/graphene oxide (GO)/polytetrafluoroethylene (PTFE) layer is designed to rapidly export exudate and accelerate diabetic wound healing. In the design, the ice-templating process endows the hydrophilic hydrogel layer with superior liquid transport ability and mechanical strength due to the formation of aligned channel structure. The hydrophobic layer with controlled thickness functions as an effective barrier to prevent exudate from wetting the skin surface. Experiments in diabetic rat model show that JHA can significantly promote re-epithelialization and collagen deposition, shorten the inflammation phase, and accelerate wound healing. This unique JHA dressing may have great potential for real-life usage in clinical patients.

Prediction of the Lotus Effect on Solid Surfaces by Machine Learning.

Superhydrophobic surfaces with the "lotus effect" have wide applications in daily life and industry, such as self-cleaning, anti-freezing, and anti-corrosion. However, it is difficult to reliably predict whether a designed superhydrophobic surface has the "lotus effect" by traditional theoretical models due to complex surface topographies. Here, a reliable machine learning (ML) model to accurately predict the "lotus effect" of solid surfaces by designing a set of descriptors about nano-scale roughness and micro-scale topographies in addition to the surface hydrophobic modification is demonstrated. Geometrical and mathematical descriptors combined with gray level cooccurrence matrices (GLCM) offer a feasible solution to the puzzle of accurate descriptions of complex topographies. Furthermore, the "black box" is opened by feature importance and Shapley-additive-explanations (SHAP) analysis to extract waterdrop adhesion trends on superhydrophobic surfaces. The accurate prediction on as-fabricated superhydrophobic surfaces strongly affirms the extensionality of the ML model. This approach can be easily generalized to screen solid surfaces with other properties.

Thermo-Responsive Jamming of Nanoparticle Dense Suspensions towards Macroscopic Liquid-Solid Switchable Materials.

Nanoparticle aggregation for constructing functional materials has shown enormous advantages in various applications. Most efforts focused on ordered nanoparticle aggregation for specific functions but were often limited to irreversible aggregation processes due to the thermodynamic equilibrium. Herein, we report a reversible disordered aggregation of SiO2 -PNIPAAm nanoparticles (SPNPs) through thermo-responsive jamming, obtaining smart liquid-solid switchable materials. The smart materials can display a switch between liquid-like state and solid-like state responding to a temperature change. This unique macroscopic behavior originates from the reversible disordered aggregation modulated by temperature-dependent hydrophobic interactions among the SPNPs. Notably, the materials at the solid-like state show anti-impact properties and can withstand the impact of a steel sphere with a speed of 328 cm s-1 . We envision that this finding offers inspiration to design smart liquid-solid switchable materials for impact protection.

High-Strength Plus Reversible Supramolecular Adhesives Achieved by Regulating Intermolecular PtII ⋠⋠⋠PtII Interactions.

Surface adhesion has a great contradiction in high strength and good reversibility given their mutually exclusive requirements of fixed crosslinked networks and dynamic chain motion. Herein, we demonstrate a supramolecular organoplatinum(II) adhesive system regulated by intermolecular PtII ⋅⋅⋅PtII interactions that can simultaneously achieve high-strength and excellent reversible adhesion to various substrates. Upon alternating temperature, the assembly of suitably substituted organoplatinum(II) molecules can switch between well-ordered and disordered states via tuning PtII ⋅⋅⋅PtII interactions, resulting in stable reversible adhesion even after 100 cycles with a robust strength of ≈1.25 MPa and a large on-off ratio of ≈25. Along with the switch of PtII ⋅⋅⋅PtII contacts, the surface adhesion of organoplatinum(II) adhesives can be monitored by their changes in electrical signals. This study will open up new inspirations for developing high-performance reversible adhesives.

A Viscous-Biofluid Self-Pumping Organohydrogel Dressing to Accelerate Diabetic Wound Healing.

Viscous biofluids on wounds challenge conventional "water-absorbing" wound dressings in efficient drainage due to their poor fluidity, generally causing prolonged inflammation, anti-angiogenesis, and delayed wound closure. Herein, it is reported that a self-pumping organohydrogel dressing (SPD) with aligned hydrated hydrogel channels, prepared by a three-dimensional-templated wetting-enabled-transfer (3D-WET) polymerization process, can efficiently drain viscous fluids and accelerate diabetic wound healing. The asymmetric wettability of the hydrophobic-hydrophilic layers and aligned hydrated hydrogel channels enable unidirectional and efficient drainage of viscous fluids away from the wounds, preventing their overhydration and inflammatory stimulation. The organogel layer can adhere onto the skin around the wounds but can be easily detached from the wet wound area, avoiding secondary trauma to the newly formed tissues. Taking a diabetic rat model as an example, the SPD can significantly downregulate the inflammation response by ≈70.8%, enhance the dermal remodeling by ≈14.3%, and shorten wound closure time by about 1/3 compared with the commercial dressing (3M, Tegaderm hydrocolloid thin dressing). This study sheds light on the development of the next generation of functional dressings for chronic wounds involving viscous biofluids.

From Nanoscopic to Macroscopic Materials by Stimuli-Responsive Nanoparticle Aggregation.

Stimuli-responsive nanoparticle (NP) aggregation plays an increasingly important role in regulating NP assembly into microscopic superstructures, macroscopic 2D, and 3D functional materials. Diverse external stimuli are widely used to adjust the aggregation of responsive NPs, such as light, temperature, pH, electric, and magnetic fields. Many unique structures based on responsive NPs are constructed including disordered aggregates, ordered superlattices, structural droplets, colloidosomes, and bulk solids. In this review, the strategies for NP aggregation by external stimuli, and their recent progress ranging from nanoscale aggregates, microscale superstructures to macroscale bulk materials along the length scales as well as their applications are summarized. The future opportunities and challenges for designing functional materials through NP aggregation at different length scales are also discussed.

Leaf-Inspired Patterned Organohydrogel Surface for Ultrawide Time-Range Open Biosensing.

Droplet arrays show great significance in biosensing and biodetection because of low sample consumption and easy operation. However, inevitable water evaporation in open environment severely limits their applications in time-consuming reactions. Herein, inspired by the unique water retention features of leaves, it is demonstrated that an open droplet array on patterned organohydrogel surface with water evaporating replenishment (POWER) for ultrawide time-range biosensing, which integrated hydrophilic hydrogel domains and hydrophobic organogel background. The hydrogel domains on the surface can supply water to the pinned droplets through capillary channels formed in the nether organohydrogel bulk. The organogel background can inhibit water evaporation like the wax coating of leaves. Such a unique bioinspired design enables ultrawide time-range biosensing in open environment from a few minutes to more than five hours involving a variety of analytes such as ions, small molecules, and macromolecules. The POWER provides a feasible and open biosensing platform for ultrawide time-range reactions.

Interfacial Instability-Induced (3I) Adhesives through "Mediator" Solvent Diffusion for Robust Underoil Adhesion.

Underoil adhesives are intensively needed in case of oil spill caused by pipeline rupture, but remain a challenge owing to the obstruction of oil layer or their swelling in oil. Herein, a general solvent diffusion principle is demonstrated by introducing dual-soluble "mediator" solvents to develop a new type of interfacial instability-induced (3I) adhesives, achieving effective underoil adhesion on various substrates and blocking the oil leakage within seconds. Microscopic characterization reveals a fast and dynamic solvent exchange process that destroys the oil layer by liquid-liquid interfacial diffusion between the "mediator" solvent and oil, enabling 3I adhesives to contact the solid surfaces directly. The principle of interfacial instability-induced liquid replacement is quite different from typical immiscible liquid replacement and is not restricted by the surface tension of solvents, surface energy, and roughness of solid surfaces, successfully directing the construction of a series of effective 3I adhesives with commercially available feedstocks. This study provides a unique clue for the design of next-generation adhesives in complex environments.

WET-Induced Layered Organohydrogel as Bioinspired "Sticky-Slippy Skin" for Robust Underwater Oil-Repellency.

Underwater superoleophobic surfaces featuring anti-oil-fouling properties are of great significance in widespread fields. However, their complicated engineering process and weak interfacial adhesion strength with underlying substrates severely hamper these ideal surfaces toward practical applications. Here, a moss-inspired sticky-slippy skin composed of layered organohydrogel is reported through a one-step wetting-enabled-transfer (WET) strategy, which unprecedentedly integrates robust inherent adhesion with durable anti-oil-fouling properties. The sticky organogel layer can be simply attached to various substrates, from metals and plastics to glass, independent of any surface pretreatment. The slippy hydrogel layer enables stable underwater superoleophobicity and ultralow oil adhesion for diverse kinds of oils. The sticky-slippy skin features outstanding comprehensive properties including easy-pasting, anti-swelling/anti-bending, compatibility with commercial adhesives, acid/alkali resistance, environmental friendliness, and substrate universality. The design strategy with integrated functions provides a clue to accelerate the development of bioinspired multifunctional interfacial materials toward real-world applications.

Space-Confinment-Enhanced Fluorescence Detection of DNA on Hydrogel Particles Array.

Fluorescent biosensors have been widely applied in DNA detection because of their reliability and reproducibility. However, low kinetics in DNA hybridization often brings out long test terms, thus restricting their practical use. Here, we demonstrate unexpected fast DNA fluorescence detection on the confined surface of hydrogel particles. When the pore size and surface charge of hydrogel particles are tailored, DNA molecules can be confined in the outer water layer of hydrogel particles. We fabricated a fluorescence-on DNA sensor based on the hydrogel particle array by utilizing the fluorescence quenching property of graphene oxide and its different adsorption behaviors toward single-strand DNA or double-strand DNA. Benefiting from the confinement effect of hydrogel particle surface and the enrichment effect of water evaporation, the DNA-recognition time was descreased significantly from 3000 s to less than 10 s under the target concentration of 400 nM. Moreover, rapid detection can be achieved at concentrations between 50 and 400 nM. The study provides another insight to fabricate fast biosensors and shows great potential in DNA diagnostics, gene analysis, and liquid biopsy.

A Wetting-Enabled-Transfer (WET) Strategy for Precise Surface Patterning of Organohydrogels.

The ability to manipulate water and oil phases in a designable manner is of great significance in widespread fields from art paintings to materials science. However, achieving precise and stable surface patterns for two immiscible phases of water and oil remains a challenge. Herein, a general wetting-enabled-transfer (WET) strategy is reported to construct discretionary shape-defined surface patterns of organohydrogels along with their monolithic formation either from flat to curved surfaces or from the microscale to the macroscale. Locally differentiated wettability induces hydrophilic monomers and hydrophobic monomers from an emulsion system onto the wettability-matching regions of the prepatterned substrates, subsequently forming corresponding hydrogel and organogel patterns on the organohydrogel surface after in situ photopolymerization. The precision of the surface patterns can be controlled by optimizing the gel monomers, emulsion droplet size, and surface chemical composition of the prepatterned substrates. This finding may provide a feasible strategy for precisely patterning functional materials from two-immiscible-phase systems.

A Spider-Silk-Inspired Wet Adhesive with Supercold Tolerance.

Conventional adhesives often encounter interfacial failure in humid conditions due to small droplets of water condensed on surface, but spider silks can capture prey in such environment. Here a robust spider-silk-inspired wet adhesive (SA) composed of core-sheath nanostructured fibers with hygroscopic adhesive nanosheath (poly(vinylpyrrolidone)) and supporting nanocore (polyurethane) is reported. The wet adhesion of the SA is achieved by a unique dissolving-wetting-adhering process of core-sheath nanostructured fibers, revealed by in situ observations at macro- and microscales. Further, the SA maintains reliable adhesion on wet and cold substrates from 4 to -196 °C and even tolerates splashing, violent shaking, and weight loading in liquid nitrogen (-196 °C), showing promising applicability in cryogenic environments. This study will provide an innovative route to design functional wet adhesives.

Bioinspired Janus Textile with Conical Micropores for Human Body Moisture and Thermal Management.

Excessive sweat secreted from the skin often causes undesired adhesion from wetted textiles and cold sensations. Traditional hydrophilic textiles such as cotton can absorb sweat but retain it. A hydrophobic/superhydrophilic Janus polyester/nitrocellulose textile embedded with a conical micropore array with a hydrophilic inner surface that can achieve directional liquid transport (with an ultrahigh directional water transport capability of 1246%) and maintain human body temperature (2-3 °C higher than with cotton textiles) is demonstrated. When the hydrophobic polyester layer with large opening of hydrophilic conical micropores contacts the liquid, the Janus polyester/nitrocellulose textile can pump it to the superhydrophilic nitrocellulose layer through the hydrophilic conical micropores driven by capillary force. The Janus polyester/nitrocellulose textile can weaken undesired wet adhesion and heat loss due to the removal of liquid. The water wicking and air permeability of the Janus polyester/nitrocellulose textile is comparable to those of traditional cloths. This study is valuable for designing of functional textiles with directional water transport properties for personal drying and warming applications.

Skin Adhesives with Controlled Adhesion by Polymer Chain Mobility.

Wearable devices have attracted a lot of attention because of their importance in the biomedical and electronic fields. However, as one of the important fixing materials, skin adhesives with controlled adhesion are often ignored. Although remarkable progress has been achieved in revealing the natural adhesion mechanism and biomimetic materials to complex solid surfaces, it remains a great challenge to explore nonirritant, controlled skin adhesives without surface structure. Herein, we present skin-adhesive patches of polydimethylsiloxanes (SAPs) with controlled adhesion by simply modulating polymer chain mobility at the molecular level. The controlled adhesion of SAPs strongly depends on the proportion of polymer chains with different mobility exposed to the solid surface, including free chains, dangling chains, and cross-linking chains. As a proof of concept, we demonstrate that the SAP can act as a skin-friendly fix to monitor the human pulse by integrating with the poly(vinylidene fluoride-trifluorethylene)/reduced graphene oxide (P(VDF-TrFE)@rGO) nanofiber sensor. This study provides a clue to design durable and skin-friendly adhesives with controlled adhesion for wearable devices.