A soft, fatigue-free, and self-healable ionic elastomer via the synergy of skin-like assembly and Bouligand structure.

Soft ionic elastomers that are self-healable, fatigue-free, and environment-tolerant are ideal structural and sensing materials for artificial prosthetics, soft electronics, and robotics to survive unpredictable service conditions. However, most synthetic strategies failed to unite rapid healing, fatigue resistance, and environmental robustness, limited by their singular compositional/structural designs. Here, we present a soft, tough, fatigue-resistant, and self-healable ionic elastomer (STFSI elastomer), which fuses skin-like binary assembly and Bouligand helicoidal structure into a composite of thermoplastic polyurethane (TPU) fibers and a supramolecular ionic biopolymer. The interlocked binary assembly enables skin-like softness, high stretchability, and strain-adaptive stiffening through a matrix-to-scaffold stress transfer. The Bouligand structure contributes to superhigh fracture toughness (101.6 kJ m-2) and fatigue resistance (4937 J m-2) via mechanical toughening by interlayer slipping and twisted crack propagation path. Besides, the STFSI elastomer is self-healable through a "bridging" method and environment-tolerant (-20 ˚C ~ 60 ˚C, strong acid/alkali, saltwater). To demonstrate the versatile structural and sensing applications, we showcase a safety cushion with efficient damping and suppressed rebounding, and a robotic sensor with excellent fatigue crack tolerance and instant sensation recovery upon cutting-off damage. Our presented synthetic strategy is generalizable to other fiber-reinforced tough polymers for applications involving demanding mechanical/environmental conditions.

Objective assessment of fatigue among aviation personnel using a bio-mathematical model: An experimental study.

Background: There are many subjective and objective tools to detect, assess, and quantify fatigue. This study is a novice attempt to assess the occupational fatigue among the aviation personnel employing a computerized work-rest schedule tool integrated with actigraphy. Methods: Thirty-eight aviation personnel were assessed for their sleep by using an actigraphy device. A work-rest scheduling software program called Fatigue Avoidance Scheduling Tool (FAST) was used to obtain fatigue parameters like Fatigue Risk Time (FRT), Fatigue Free Time (FFT), and Fatigue Free Occupational Time (FFOT). Results: The percentages of crew having a night sleep of the duration of more than 6 hours were 50% (Mon), 44.7% (Tue), 44.7% (Wed), and 47.3% (Thu) for weekdays and 65.8% (Fri), 57.9% (Sat), and 57.9% (Sun) for the weekend. There was a gradual increase in FRT, FFT, and FFOT from Day 1 to Day 5 of the week, and the differences were statistically significant. Conclusion: Increase in the FRT with a reciprocal drop of FFT and FFOT was observed with the progress of the week. Total Sleep Time (TST) of less than 8 hours could be the reason for a gradual increase in sleep debt, leading to fatigue depicted as increase in fatigue risk parameter FRT and gradual decrease in fatigue preventing parameters like FFT and FFOT. It was further confirmed by regression analysis in which TST was found to be a statistically significant predictor for all fatigue parameters. Regression equation for FFOT as 498.53 + (0.39 x TST) - (58.8 x Day of the week) can be used.

Exploring a Fatigue-Free Layered Hybrid Perovskite Ferroelectric for Photovoltaic Non-Volatile Memories.

Through a functional unit-transmutation strategy, a fatigue-free layered hybrid perovskite ferroelectric (C6 H5 CH2 NH3 )2 CsPb2 Br7 (BCPB) has been developed, which demonstrates stable spontaneous polarization (Ps ) of 6.5 µC cm-2 and high Curie temperature up to 425 K. Meanwhile, BCPB shows splendid bulk photovoltaic effect (BPVE) properties with noticeable zero-bias photocurrent density (5 µA cm-2 ), and high on/off switching ratio of current (over 3×105 ); these merits even overmatch the most known ferroelectric semiconductor BiFeO3 . The unique structure with self-regulated net electrical charged layers gives rise to the fatigue-free feature of Ps and BPVE (no significant fatigue after 108 polarity switching cycles), promoting the potential applications of BCPB in photovoltaic non-volatile memories. This work offers an efficient approach for exploring fatigue-free semiconducting ferroelectrics as well as excavates their further applications in next-generation electronic devices.

Fatigue-free, superstretchable, transparent, and biocompatible metal electrodes.

Next-generation flexible electronics require highly stretchable and transparent electrodes. Few electronic conductors are both transparent and stretchable, and even fewer can be cyclically stretched to a large strain without causing fatigue. Fatigue, which is often an issue of strained materials causing failure at low strain levels of cyclic loading, is detrimental to materials under repeated loads in practical applications. Here we show that optimizing topology and/or tuning adhesion of metal nanomeshes can significantly improve stretchability and eliminate strain fatigue. The ligaments in an Au nanomesh on a slippery substrate can locally shift to relax stress upon stretching and return to the original configuration when stress is removed. The Au nanomesh keeps a low sheet resistance and high transparency, comparable to those of strain-free indium tin oxide films, when the nanomesh is stretched to a strain of 300%, or shows no fatigue after 50,000 stretches to a strain up to 150%. Moreover, the Au nanomesh is biocompatible and penetrable to biomacromolecules in fluid. The superstretchable transparent conductors are highly desirable for stretchable photoelectronics, electronic skins, and implantable electronics.

A Novel Approach to Determining the Alactic Time Span in Connection with Assessment of the Maximal Rate of Lactate Accumulation in Elite Track Cyclists.

PURPOSE: Following short-term all-out exercise, the maximal rate of glycolysis is frequently assessed on the basis of the maximal rate of lactate accumulation in the blood. Since the end of the interval without significant accumulation (talac) is 1 of 2 denominators in the calculation employed, accurate determination of this parameter is crucial. Although the very existence and definition of talac, as well as the validity of its determination as time-to-peak power (tPpeak), remain controversial, this parameter plays a key role in anaerobic diagnostics. Here, we describe a novel approach to determination of talac and compare it to the current standard. METHODS: Twelve elite track cyclists performed 3 maximal sprints (3, 8, and 12 s) and a high-rate, low-resistance pedaling test on an ergometer with monitoring of crank force and pedaling rate. Before and after each sprint, capillary blood samples were taken for determination of lactate accumulation. Fatigue-free force-velocity and power-velocity profiles were generated. talac was determined as tPpeak and as the time point of the first systematic deviation from the force-velocity profile (tFf). RESULTS: Accumulation of lactate after the 3-second sprint was significant (0.58 [0.19] mmol L-1; P < .001, d = 1.982). tFf was <3 seconds and tPpeak was ≥3 seconds during all sprints (P < .001, d = - 2.111). Peak power output was lower than maximal power output (P < .001, d = -0.937). Blood lactate accumulation increased linearly with increasing duration of exercise (R2 ≥ .99) and intercepted the x-axis at ∼tFf. CONCLUSION: Definition of talac as tPpeak can lead to incorrect conclusions. We propose determination of talac based on tFf, the end of the fatigue-free state that may reflect the beginning of blood lactate accumulation.

Fatigue-Free Force-Velocity and Power-Velocity Profiles for Elite Track Sprint Cyclists: The Influence of Duration, Gear Ratio and Pedalling Rates.

Background: Maximal force-velocity (F/v) profiles for track cyclists are commonly derived from ergometer sprints using an isovelocity or isoinertial approach. Previously, an attempt was made to derive maximal F/v profiles from a single maximal 65-m sprint on the cycling track. Hypothesising that this approach may not accurately reflect the fatigue-free F/v profile, we propose an alternative procedure and compare it to the previous method. Moreover, we test for the impact of gear ratio on diagnostic results. Methods: Twelve elite track cyclists completed a high-cadence low-resistance pedalling test on a freestanding roller (motoric test) and two series of three maximal 65-m sprints on a cycling track with different gear ratios. F/v profiles were calculated based on the measured crank force and cadence either during the first 6−7 revolutions (≤6 s) on the track (model I) or were derived from the first 3−4 revolutions (≤3 s) on the track combined with 1 or 2 fatigue-free cycles at cadences above 160 rpm from the motoric test (model II). Results: Although both models exhibit high-to-excellent linearity between force and velocity, the extrapolated isometric force was higher (1507.51 ± 257.60 N and 1384.35 ± 276.84 N; p < 0.002; d = 2.555) and the slope steeper (−6.78 ± 1.17 and −5.24 ± 1.11; p < 0.003, d = −2.401) with model I. An ICC of 1.00 indicates excellent model consistency when comparing the F/v profiles (model II) derived from the different geared sprints. Conclusions: Assuring fatigue-free measurements and including high-cadence data points in the calculations provide valid maximal F/v and P/v profiles from a single acceleration-sprint independent of gear ratio.

Nanocrystalline Engineering Induced High Energy Storage Performances of Fatigue-Free Ba2Bi3.9Pr0.1Ti5O18 Ferroelectric Thin Films.

Electrostatic capacitors, though presenting faster rate capability and higher power density, are hindered in applications because of their low energy density. Accordingly, many efforts in electrostatic capacitors, for electronics and electrical power systems, have mainly concentrated on the development of dielectric materials with high-energy density (Ud) and charge-discharge efficiency (η) as well as good stability performances of thermal and fatigue endurance. Herein, we demonstrate that an excellent Ud (∼90 J/cm3) and high η (∼84.2%), as well as outstanding fatigue cycles (1 × 108 st), frequency stability (20-2000 Hz), and a wide temperature range (RT ∼ 160 °C), can be attained in Ba2Bi3.9Pr0.1Ti5O18 (BBPT) ferroelectric thin films via nanocrystalline engineering. It is revealed that nanocrystalline engineering of the BBPT ferroelectric thin films could be controlled via the heat-treatment temperature, which could effectively regulate the breakdown strength and polarization. The enhanced breakdown strength and polarization of the nanocrystalline engineering is further verified through the theoretical phase-field simulations along with experimental results. These results indicate that this is a feasible and scalable route to develop dielectric thin film materials with a high energy storage capability.

Flexible, Temperature-Resistant, and Fatigue-Free Ferroelectric Memory Based on Bi(Fe0.93Mn0.05Ti0.02)O3 Thin Film.

A recent hot-spot topic for flexible and wearable devices involves high-performance nonvolatile ferroelectric memories operating under compressive or tensile mechanical deformations. This work presents the direct fabrication of a flexible (Mn,Ti)-codoped multiferroic BiFeO3 film capacitor with Pt bottom and Au top electrodes on mica substrate. The fabricated polycrystalline Bi(Fe0.93Mn0.05Ti0.02)O3 film on mica exhibits superior ferroelectric switching behavior with robust saturated polarization ( Ps ∼ 93 µC/cm2) and remanent polarization ( Pr ∼ 66 µC/cm2) and excellent frequency stability (1-50 kHz) and temperature resistance (25-200 °C), as well as reliable long-lifetime operation. More saliently, it can be safely bent to a small radius of curvature, as low as 2 mm, or go through repeated compressive/tensile mechanical flexing for 103 bending times at 4 mm radius without any obvious deterioration in polarization, retention time at 105 s, or fatigue resistance after 109 switching cycles. These findings demonstrate a novel route to designing flexible BiFeO3-based ferroelectric memories for information storage and data processing, with promising applications in next-generation smart electronics.

Transparent, Flexible, Fatigue-Free, Optical-Read, and Nonvolatile Ferroelectric Memories.

Perovskite oxide films are widely used in various commercial industries. However, they are usually prepared at high temperature and in oxygen ambience, detrimental to most transparent and flexible substrates and bottom conductive electrodes such as indium tin oxide (ITO). It remains challenging to integrate perovskite oxides into transparent and flexible electronics. Here, the 1.2 wt % Ag-doped ITO (Ag-ITO) grown on a mica substrate is employed as the bottom electrode, which can withstand high temperature and repeated bending, and then we achieve the transparent, flexible, fatigue-free, and optical-read ferroelectric nonvolatile memories based on the mica/Ag-ITO/Bi3.25La0.75Ti3O12/ITO structures. The as-prepared memories show ∼80% transmittance for visible lights and fatigue-free performance after more than 108 writing/erasing cycles. These performances are stable after repeated bending down to 3 mm in a curvature radius. More importantly, the "1/0" state of the memory can be read out by the photovoltaic current rather than destructive polarization switching, an emergent functionality for many applications. This work substantially promotes the applications of perovskite oxide films in transparent and flexible electronics, including wearable devices.

Flexible, Fatigue-Free, and Large-Scale Bi3.25La0.75Ti3O12 Ferroelectric Memories.

Flexible, fatigue-free, large-scale, and nonvolatile memory is an emerging technological goal in a variety of fields, including electronic skins, wearable devices, and other flexible electronics. Perovskite oxide films deposited on rigid substrates (e.g., Si and SrTiO3) at 500-700 °C and >1.0 Pa oxygen ambience have been widely used in electronic industries. However, their applications in flexible electronics are challenging, if not impossible. Here, the Bi3.25La0.75Ti3O12 ferroelectric films with SrRuO3 or Pt electrodes were prepared on the two-dimensional mica substrates, and then the flexible Pt/SrRuO3/Bi3.25La0.75Ti3O12/Pt memories have been achieved through reducing the mica to ∼10 µm thickness. These memories show the saturated polarization of Ps ∼ 20 µC/cm2, and either the <1% bending strain or a normal light illumination hardly overcomes the potential barrier among different polarizations which originate from the noncentral symmetry of the atomic structure. As a result, they can undergo 109 write/erase cycles and/or 10000 times bending with 1.4 mm in radius without any fatigue or damage. Furthermore, they can withstand the operation at 20-200 °C or under light illumination. In short, these flexible oxide memories provide comprehensive performance for industrial applications.