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Hydrogels are made tough to resist crack propagation. However, for seamless integration into devices and machines, it necessitates robustness against cyclic loads. Central to this objective is enhancing fatigue resistance, an indispensable attribute facilitating the optimal performance of hydrogels within a multitude of biological contexts, spanning various plant and animal tissues, as well as diverse biomedical and engineering areas. In this review, recent research concerning the fatigue behavior of hydrogels, presenting a comprehensive consolidation of the inherent mechanisms that underpin diverse strategies aimed at fortifying fatigue resistance, is summarized. A critical facet in the architectural blueprint of fatigue‐resistant hydrogels is emphasized, involving the imposition of spatial constraints upon the main chains at the crack tips, thereby effectuating a protracted delay in their fracture initiation during prolonged cyclic loading. The integration of multiscale mechanisms encompassing networks, interactions, media, and structures stands as a pivotal factor in the design of fatigue‐resistant hydrogels. It is hoped that the review will considerably propel the pragmatic deployment of fatigue‐resistant hydrogels across a diverse array of applications, thus catalyzing advancements in multiple fields. [ABSTRACT FROM AUTHOR]

Fatigue is the most common failure mode for engineering materials in various industrial applications. Generally, designing new products and components based on typical deterministic fatigue design approaches is slow and expensive. Although numerous investigations have been carried on this topic over decades, there still lacks a robust and efficient method to design a super‐fatigue‐resistant and testless structure. In this investigation, a novel data‐driven approach based on the deep learning algorithm is applied on designing a fatigue‐resistant notched structure under different loading via numerical simulations and deep learning. The notches with various shapes are designed by employing the same material. Then finite element (FE) simulations are performed to obtain the mechanical behaviors of notched structures under different loading conditions. The deep learning algorithm is applied to predict mechanical behaviors of unknown notched structures based on input training set of simple notched geometries and relative lower computational cost. It is demonstrated that deep learning on the fatigue‐resistant structure is a promising approach of fatigue design. This work offers an alternative design strategy of fatigue‐resistant structure and cost‐effective solution to accelerate the design of engineering components under different loading conditions. Highlights: A data‐driven‐based design method for novel notched structure is proposed.The modified strain energy density is investigated in the nonconstant notches.The designed notched structures are studied under three loading conditions.The designed notch shows high fatigue‐resistant than commonly used notches. [ABSTRACT FROM AUTHOR]

Flexible strain sensor as a measurement tool plays a significant role in agricultural development by long-term stable monitoring of the dynamic progress of plant growth. However, existing strain sensors still suffer from severe drawbacks, such as large hysteresis, insufficient fatigue resistance, and inferior stability, limiting their broad applications in the long-term monitoring of plant growth. Herein, we fabricate a novel conductive hydrogel strain sensor which is achieved through uniformly dispersing the conductive activated charcoal (AC) in high-viscosity polyvinyl alcohol (PVA) solution forming a continuous conductive network and simple preparation by freezing-thawing. The as-prepared strain sensor demonstrates low hysteresis (<1.5%), fatigue resistance (fatigue threshold of 40.87 J m−2), and long-term sensing stability upon mechanical cycling. We further exhibit the integration and application of PVA-AC strain sensor to monitor the growth of plants for 14 days. This work may offer an effective strategy for monitoring plant growth with conductive hydrogel strain sensor, facilitating the advancement of agriculture. [ABSTRACT FROM AUTHOR]

Environmentally friendly BiFeO 3 -based capacitors have attracted great attention in energy storage applications. Herein, a large W rec of 2.91 J/cm3 and a high η of 85% were obtained under the electric field of 220 kV/cm in (1-x)(0.67BiFeO 3 -0. 3 3BaTiO 3)-xSr 0.7 Sm 0.2 TiO 3 (BF-BT-xSST) ceramics at x = 0.30. The addition of SST facilitates to enhance the relaxor behavior and suppress the early polarization saturation of ceramics. The breakdown strength of BF-BT-xSST ceramics is enhanced due to the significantly decreased grain size and the increased band gap. More importantly, the BF-BT-0.30SST ceramic exhibits an excellent fatigue endurance (< 1.1%, after 105 fatigue cycles), which is superior to most of previous works. In addition, BF-BT-0.30SST ceramic also shows high thermal and frequency stability, and fast discharge rate (t 0.9 < 0.16 μs). We propose that the SST or a combination of SST and Sr 0.7 Bi 0.2 TiO 3 is a better additive for the BF-based energy storage materials. [ABSTRACT FROM AUTHOR]

Polyacrylamide (PAM) hydrogels are widely used in wide-ranging applications in biology, medicine, pharmaceuticals and environmental sectors. However, achieving the requisite mechanical properties, fatigue resistance, self-recovery, biocompatibility, and biodegradability remains a challenge. Herein, we present a facile method to construct a nanocomposite hydrogel by integrating short linear glucan (SLG), obtained by debranching waxy corn starch, into a PAM network through self-assembly. The resulting composite hydrogel with 10 % SLG content exhibited satisfactory stretchability (withstanding over 1200 % strain), along with maximum compressive and shear strengths of about 490 kPa and 39 kPa at 90 % deformation, respectively. The hydrogel demonstrated remarkable resilience and could endure repeated compression and stretching. Notably, the nanocomposite hydrogel with 10 % SLG content exhibited full stress recovery at 90 % compression deformation after 20 s, without requiring specific environmental conditions, achieving an energy dissipation recovery rate of 98 %. Meanwhile, these hydrogels exhibited strong adhesion to various soft and hard substrates, including skin, glasses and metals. Furthermore, they maintain solid integrity at both 37 °C and 50 °C after swelling equilibrium, unlike traditional PAM hydrogels, which exhibited softening under similar conditions. We hope that this PAM-SLG hydrogel will open up new avenues for the development of multifunctional electronic devices, offering enhanced performance and versatility. [Display omitted] [ABSTRACT FROM AUTHOR]

Flexible strain sensor as a measurement tool plays a significant role in agricultural development by long-term stable monitoring of the dynamic progress of plant growth. However, existing strain sensors still suffer from severe drawbacks, such as large hysteresis, insufficient fatigue resistance, and inferior stability, limiting their broad applications in the long-term monitoring of plant growth. Herein, we fabricate a novel conductive hydrogel strain sensor which is achieved through uniformly dispersing the conductive activated charcoal (AC) in high-viscosity polyvinyl alcohol (PVA) solution forming a continuous conductive network and simple preparation by freezing-thawing. The as-prepared strain sensor demonstrates low hysteresis (−2), and long-term sensing stability upon mechanical cycling. We further exhibit the integration and application of PVA-AC strain sensor to monitor the growth of plants for 14 days. This work may offer an effective strategy for monitoring plant growth with conductive hydrogel strain sensor, facilitating the advancement of agriculture.

Because of their distinct electrochemical and mechanical properties, conducting polymer hydrogels have been widely exploited as soft, wet, and conducting coatings for conventional metallic electrodes, providing mechanically compliant interfaces and mitigating foreign body responses. However, the long-term viability of these hydrogel coatings is hindered by concerns regarding fatigue crack propagation and/or delamination caused by repetitive volumetric expansion/shrinkage during long-term electrical interfacing. This study reports a general yet reliable approach to achieving a fatigue-resistant conducting polymer hydrogel coating on conventional metallic bioelectrodes by engineering nanocrystalline domains at the interface between the hydrogel and metallic substrates. It demonstrates the efficacy of this robust, biocompatible, and fatigue-resistant conducting hydrogel coating in cardiac pacing, showcasing its ability to effectively reduce the pacing threshold voltage and enhance the long-term reliability of electric stimulation. This study findings highlight the potential of its approach as a promising design and fabrication strategy for the next generation of seamless bioelectronic interfaces., (© 2023 Wiley-VCH GmbH.)

Cryogels with extreme mechanical properties such as ultrahigh compressibility, fatigue resistance, and rapid recovery are attractive in biomedical, environmental remediation, and energy storage applications, which, however, are difficult to achieve in man-made materials. Here, inspired by the multiscale macro-/microfiber network structure of spider web, we construct an ultraelastic chitosan cryogel with interconnected hybrid micro-/nanofibers (CMNF cryogels) via freeze-induced physicochemical cross-linking. Chitosan chains are directionally assembled into high-aspect-ratio microfibers and nanofibers under shear-flow induction, which are further assembled into an interconnected three-dimensional (3D) network structure with staggered microfibers and nanofibers. In this multiscale network, nanofibers connecting the microfibers improve the stability, while microfibers improve the elasticity of the CMNF cryogels through long-range interaction. The synergy of the two-scale fibers endows the CMNF cryogel with extraordinary mechanical properties in comparison to those assembled with single-scale fibers, including its ultrahigh ultimate strain (97% strain with 50 cycles), excellent fatigue resistance (3200 compressing-releasing cycles at 60% compression strain), and rapid water-triggered shape recovery (recovering in ∼1 s). Moreover, the fibrous CMNF cryogel shows excellent functionalization capability via the rapid assembly of nanoscale building blocks for flexible electronics and environmental remediation. Our work thereby demonstrates the potential of this bioinspired strategy for designing gel materials with extreme mechanical properties.

Flexible strain sensor as a measurement tool plays a significant role in agricultural development by long-term stable monitoring of the dynamic progress of plant growth. However, existing strain sensors still suffer from severe drawbacks, such as large hysteresis, insufficient fatigue resistance, and inferior stability, limiting their broad applications in the long-term monitoring of plant growth. Herein, we fabricate a novel conductive hydrogel strain sensor which is achieved through uniformly dispersing the conductive activated charcoal (AC) in high-viscosity polyvinyl alcohol (PVA) solution forming a continuous conductive network and simple preparation by freezing-thawing. The as-prepared strain sensor demonstrates low hysteresis (<1.5%), fatigue resistance (fatigue threshold of 40.87 J m−2), and long-term sensing stability upon mechanical cycling. We further exhibit the integration and application of PVA-AC strain sensor to monitor the growth of plants for 14 days. This work may offer an effective strategy for monitoring plant growth with conductive hydrogel strain sensor, facilitating the advancement of agriculture.

At the neuromuscular junction (NMJ), motor neurons and myocytes maintain a bidirectional communication that guarantees adequate functionality. Thus, motor neurons' firing pattern, which is influenced by retrograde muscle-derived neurotrophic factors, modulates myocyte contractibility. Myocytes can be fast-twitch fibers and become easily fatigued or slow-twitch fibers and resistant to fatigue. Extraocular muscles (EOM) show mixed properties that guarantee fast contraction speed and resistance to fatigue and the degeneration caused by Amyotrophic lateral sclerosis (ALS) disease. The TrkB signaling is an activity-dependent pathway implicated in the NMJ well-functioning. Therefore, it could mediate the differences between fast and slow myocytes' resistance to fatigue. The present study elucidates a specific protein expression profile concerning the TrkB signaling that correlates with higher resistance to fatigue and better neuroprotective capacity through time. The results unveil that Extra-ocular muscles (EOM) express lower levels of NT-4 that extend TrkB signaling, differential PKC expression, and a higher abundance of phosphorylated synaptic proteins that correlate with continuous neurotransmission requirements. Furthermore, common molecular features between EOM and slow soleus muscles including higher neurotrophic consumption and classic and novel PKC isoforms balance correlate with better preservation of these two muscles in ALS. Altogether, higher resistance of Soleus and EOM to fatigue and ALS seems to be associated with specific protein levels concerning the TrkB neurotrophic signaling., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Just-Borràs, Cilleros-Mañé, Polishchuk, Balanyà-Segura, Tomàs, Garcia, Tomàs and Lanuza.)

[Display omitted] • A facile strategy was reported to fabricate multifunctional PVA-based material. • The strength and toughness of material increased by 210% and 860%, respectively. • The material sets an impressive new record of folding-failure (900 000 times). • The material shows excellent self-healing, UV-blocking, and fluorescent properties. In the quest of materials that can tolerate extreme environments (i.e. , aerospace, polar regions of earth), facile design of self-healing, high fatigue-resistant and multifunctional nanocomposite materials with excellent ultralow temperature toughness, especially by utilizing inexpensive and sustainable bioresources is still currently challengeable. In current study, we deliver a general method by mixing PVA/BN and hydrogen bond cross-linked polymers to fabricate a nanocomposite material with ultralow temperature toughness, which shows excellent toughness (107.3 MJ·m−3) at − 196 °C and maintains high mechanical strength in highly humid environments. This material is a spider silk-inspired, poly(vinyl alcohol) (PVA)-based, autonomous room temperature self-healable nanocomposite by complexation of boron nitride (BN), quantum dots (QDs) and soy protein isolate grafted lignin (SPI-lignin). The fabricated material, namely PVA-BN-QDs-SPI-lignin, simultaneously exhibits outstanding tensile strength (53.3 MPa), toughness (182.8 MJ·m−3), fatigue-resistance as well as antiultraviolet and fluorescent properties and sets an impressive new record of folding-failure (900 000 times) and toughness, which are 10.6 to 45.7 times higher than other graphene-based nanocomposites. It can be impressively self-healed within only 2 min. Of particular interest is its facile, green, mild and inexpensive preparation method that can be easily scaled up. It is believed that this work, beginning with abundant biodegradable resources, opens the door to develop biobased multifunctional materials in practical applications, which may satisfy the demands of applications in ultralow environments such as in Antarctica, Moon, and Mars. [ABSTRACT FROM AUTHOR]