Fatigue-resistant Hydrogels

Hydrogels have been extensively studied for applications in various fields, such as tissue engineering and soft robotics, as determined by their mechanical properties. The mechanical design of hydrogels typically focuses on the modulus, toughness, and deformability. These characteristics play important roles and make great achievements for hydrogel use. In recent years, a growing body of research has concentrated on the fatigue property of hydrogels, which determines their resistance to crack propagation in the networks during cyclic mechanical loads for applications. However, knowledge of hydrogel fatigue behavior remains notably deficient. Here, we present a brief overview of the fatigue behavior of hydrogels, encompassing the general experimental methods to measure the fatigue property and fundamental theoretical calculation models. Then, we highlight multiple strategies to enhance the fatigue resistance of hydrogels. Finally, we present our perspectives on fatigue-resistant hydrogels, outstanding challenges and potential directions for future research.

Advancing homogeneous networking principles for the development of fatigue-resistant,low-swelling and sprayable hydrogels for sealing wet,dynamic and concealed wounds in vivo

Effective sealing of wet,dynamic and concealed wounds remains a formidable challenge in clinical practice.Sprayable hydrogel sealants are promising due to their ability to cover a wide area rapidly,but they face limitations in dynamic and moist environments.To address this issue,we have employed the principle of a homogeneous network to design a sprayable hydrogel sealant with enhanced fatigue resistance and reduced swelling.This network is formed by combining the spherical structure of lysozyme(LZM)with the orthotetrahedral structure of 4-arm-polyethylene glycol(4-arm-PEG).We have achieved exceptional sprayability by controlling the pH of the precursor solution.The homogeneous network,constructed through uniform cross-linking of amino groups in protein and 4-arm-PEG-NHS,provides the hydrogel with outstanding fatigue resistance,low swelling and sustained adhesion.In vitro testing demonstrated that it could endure 2000 cycles of underwater shearing,while in vivo experiments showed adhesion maintenance exceeding 24 h.Furthermore,the hydrogel excelled in sealing leaks and promoting ulcer healing in models including porcine cardiac hemorrhage,lung air leakage and rat oral ulcers,surpassing commonly used clinical materials.Therefore,our research presents an advanced biomaterial strategy with the potential to advance the clinical management of wet,dynamic and concealed wounds.

Boosting energy storage performance of low-temperature sputtered CaBi_(2)Nb_(2)O_(9) thin film capacitors via rapid thermal annealing

CaBi_(2)Nb_(2)O_(9) thin film capacitors were fabricated on SrRuO_(3)-buffered Pt(111)/Ti/Si(100)substrates by adopting a two-step fabrication process.This process combines a low-temperature sputtering deposition with a rapid thermal annealing(RTA)to inhibit the grain growth,for the purposes of delaying the polarization saturation and reducing the ferroelectric hysteresis.By using this method,CaBi_(2)Nb_(2)O_(9) thin films with uniformly distributed nanograins were obtained,which display a large recyclable energy density Wrec≈69 J/cm^(3) and a high energy efficiencyη≈82.4%.A superior fatigue-resistance(negligible energy performance degradation after 10^(9) charge-discharge cycles)and a good thermal stability(from-170 to 150℃)have also been achieved.This two-step method can be used to prepare other bismuth layer-structured ferroelectric film capacitors with enhanced energy storage performances.

Fluidized Electrocatalysis

Particle-based electrocatalysts need to be glued on an electrode,where fast and slow steps of the reaction are spatially and temporally convoluted near the particles.Since the particles are under continuous electrochemical stress,decay in their catalytic performance(a.k.a.,fatigue)often occurs due to degradation of the active materials,detachment of particles and deteriorating kinetics.Here we report that these problems are well addressed by fluidizing the particles.The catalysts,instead of being fixed on an electrode,are now fluidized in the electrolyte.Reaction occurs when individual particles collide with the electrode,which collectively delivers a continuous,scalable and stable electrochemical current.Since the catalysts now work in rotation,they experience much faster kinetics and avoid the buildup of excessive electrochemical stress,leading to orders of magnitude higher particle-average efficiency and greatly enhanced fatigue resistance.Proof-ofconcepts are demonstrated using Pt/C catalysts for three well-known reactions,including oxygen evolution,hydrogen evolution and methanol oxidation reactions,all of which suffer severe performance decay using Pt/C under different mechanisms.Fluidized electrocatalysis breaks the spatial and temporal continuum of electrocatalytic reactions,and makes them drastically more fatigue resistant.It is material-and reaction-agnostic,and should be a general approach to enhance electrocatalytic reactions.