Fundamental, mechanism and development of hydration lubrication: From bio-inspiration to artificial manufacturing.

Friction and lubrication are ubiquitous in all kinds of movements and play a vital role in the smooth operation of production machinery. Water is indispensable both in the lubrication systems of natural organisms and in hydration lubrication systems. There exists a high degree of similarity between these systems, which has driven the development of hydration lubrication from biomimetic to artificial manufacturing. In particular, significant advancements have been made in the understanding of the mechanisms of hydration lubrication over the past 30 years. This enhanced understanding has further stimulated the exploration of biomimetic inspiration from natural hydration lubrication systems, to develop novel artificial hydration lubrication systems that are cost-effective, easily transportable, and possess excellent capability. This review summarizes the recent experimental and theoretical advances in the understanding of hydration-lubrication processes. The entire paper is divided into three parts. Firstly, surface interactions relevant to hydration lubrication are discussed, encompassing topics such as hydrogen bonding, hydration layer, electric double layer force, hydration force, and Stribeck curve. The second part begins with an introduction to articular cartilage in biomaterial lubrication, discussing its compositional structure and lubrication mechanisms. Subsequently, three major categories of bio-inspired artificial manufacturing lubricating material systems are presented, including hydrogels, polymer brushes (e.g., neutral, positive, negative and zwitterionic brushes), hydration lubricant additives (e.g., nano-particles, polymers, ionic liquids), and their related lubrication mechanism is also described. Finally, the challenges and perspectives for hydration lubrication research and materials development are presented.

Atomic Oxygen-Induced Surface Erosion Behavior and Mechanical Degradation of Polyether Ether Ketone via Reactive Molecular Dynamics Simulations.

Atomic oxygen (AO) collision is one of the most serious threats to polymeric materials exposed to the space environment, yet understanding the structural changes and degradation of materials caused by AO impact remains a tremendous issue. Herein, we systematically evaluate the erosion collision and mechanical degradation of polyether ether ketone (PEEK) resin under hypervelocity AO impact using reactive molecular dynamics simulations. The interaction process and local evolution mechanism between high-speed AO and PEEK are investigated for the first time, suggesting that AO will either be scattered or adsorbed by PEEK, which is strongly correlated with the main degraded species evolution including O2, OH, CO, and CO2. Different AO fluxes and AO incidence angle simulations indicate that high-energy AO collision on the surface transfers kinetic energy to PEEK's thermal energy, thus inducing mass loss and surface penetration mechanisms. Vertically impacted AO causes less erosion on the PEEK matrix, rather than obliquely. Furthermore, PEEK chains modified with functional side groups are comprehensively investigated by 200 AO impact and high strain rate (1010 s-1) tensile simulations, demonstrating that the spatial configuration and stable benzene functionality of phenyl side groups can significantly improve the AO resistance and mechanical properties of PEEK at 300 and 800 K. This work revealed useful insights into the interaction mechanisms between AO and PEEK at the atomic scale and may provide a protocol for screening and designing new polymers of high AO tolerance.

Near-Infrared-I to III Absorption and Emission via Core Engineering of Open-Shelled Organic Mixed-Valence Systems.

A novel class of agents is developed based on the core engineering of open-shelled organic mixed-valence (MV) systems, which enable tunable absorption and emission across the near infrared (NIR)-I to III biowindow (700-1850 nm) by adjusting the number of central nitrogen oxidation sites and the length of the conjugated bridge. Organic mixed-valence (MV) systems are synthesized through a one-step partial chemical oxidation of starburst oligoarylamines, with varying nitrogen oxidation sites and conjugated bridge lengths, including tris(4-[diethylamino]phenyl)aminen+ (T4EPAn + ), N,N,N',N'-tetrakis(4-[diisobutylamino]phenyl)-1,4-phenylenediaminen+ (TPDAn + ), and N,N,N',N'-tetrakis(4-methoxyphenyl)benzidinen+ (TMPBn + ). The absorption wavelength of the MV systems redshifted clearly as the number of central nitrogen oxidation sites increased or the conjugated bridge length is prolonged. T4EPAn + with one central nitrogen oxidation site exhibits fluorescence emission in the range of 900-1400 nm, while TPDAn + with two central nitrogen oxidation sites demonstrate strong heat generation capabilities. Additionally, the absorption peak of TMPBn + with a biphenyl conjugated bridge reaches up to 1610 nm. Especially, these MV systems are highly stable for biological applications due to their high steric hindrance and hyperconjugation effect. These characteristics make MV systems promising candidates for constructing NIR-I/II/III emitters and photothermal agents, representing a significant advance toward developing the next generation of NIR-I to III agents.

Durability and corrosion behaviors of superhydrophobic amorphous coatings: a contrastive investigation.

Superhydrophobic surfaces can be derived from roughening hydrophobic materials. However, the superhydrophobic surfaces with various micro/nano morphologies present variations of chemical and mechanical durability, which limits their practical applications. Very little actually is known about comparing durability and corrosion resistance of concave and convex superhydrophobic surface structures systematically. In this paper, two kinds of superhydrophobic AlNiTi amorphous coatings with concave and convex surfaces were obtained by chemical etching and hydrothermal methods, respectively. Benefiting from nanoscale sheet structure, the convex superhydrophobic coating displays higher water-repellence (contact angle = 157.6°), better self-cleaning performance and corrosion resistance. The corrosion current density of the convex superhydrophobic surface is approximately one order of magnitude smaller than the concave superhydrophobic surface. Besides, the long-term chemical stability and mechanical durability of both superhydrophobic surfaces were also investigated. The formation and damage mechanisms of these two kinds of superhydrophobic surfaces were proposed. It is hoped that these investigations could provide clear guidance for the real-world applications of superhydrophobic amorphous coatings.

Formation and Properties of Superhydrophobic Al Coatings on Steel.

Thermal sprayed aluminum coatings are widely scalable to corrosion protection of the offshore steel structure. However, the corrosion rate of the Al coating increases considerably due to the severe marine environment. It has remained a challenge to improve the corrosion resistance and protective ability of Al coatings. The superhydrophobic surface provides a potential way to improve the corrosion resistance of metal materials. Hence, the development of superhydrophobic Al coatings with superior corrosion resistance is of great interest. In this work, the feasibility of the preparation of superhydrophobic Al coatings on a steel substrate was explored. First, Al coatings were prepared onto the steel substrate by the arc-spraying process, followed by ultrasonic etching with 0.1 M NaOH solution, and afterward passivated using 1% fluorosilanes. The effects of the etching time on morphology, contact angle, and corrosion resistance of the Al coatings were evaluated. The schematic model of the fluorosilane passivation process on the Al coating surface was provided. The micro/nanoscale surface structure of the low-surface-energy fluorosilanes promotes the wetting angle of 153.4° and a rolling angle to 6.6°, denoting the superhydrophobic properties. The superhydrophobic Al coating surface displays excellent self-cleaning performance due to its weak adhesion to water droplets. The corrosion current density of the superhydrophobic Al coating (1.36 × 10-8 A cm-2) is 2 orders of magnitude lower than that of the as-sprayed Al coating (1.18 × 10-6 A cm-2). Similarly, the charge-transfer resistance is found to be 12 times larger for the superhydrophobic Al coating and the corresponding corrosion inhibition efficiency reaches 98.9%. The superhydrophobic Al coating displays superior corrosion resistance and promising applications in a marine corrosion environment.

A superhydrophobic coating harvesting mechanical robustness, passive anti-icing and active de-icing performances.

HYPOTHESIS: Ice accretion is a challenging issue for various residential activities and industrial facilities. However, most of the current anti/de-icing coatings fail to maintain their properties when subject to frequent mechanical wear, and their limited functionality (either anti-icing or de-icing individually) cannot meet the requirement of all-weather utilization. EXPERIMENTS: Herein, a multifunctional superhydrophobic coating is prepared by compositing ferroferric oxide nanoparticles (Fe3O4 NPs) with fluorinated epoxy resin via an inverse infiltration process. The surface composition, morphology and wettability are systematically characterized using Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), laser scanning microscopy and contact angle tensiometer. The anti-icing and de-icing performances are evaluated by investigating the freezing delay and photothermal effect, respectively. FINDINGS: This coating shows outstanding water repellency (water contact angle up to 161.0°, sliding angle down to 1.4°) and can maintain superhydrophobicity within 400 cycles of tape peeling, 260 cycles of sandpaper abrasion or 25 cycles of sand impact. Besides, because the hydrophobic nano/micro hierarchical structures tremendously retard the heat transfer, the freezing process of water droplet on this coating can be apparently delayed by up to 35 min as compared to the uncoated substrate. Moreover, owing to the photothermal effect of the Fe3O4 NPs, the coating's surface temperature can be rapidly increased above 0 °C under infrared irradiation, which facilitates the ice melting on cold surfaces. Our work offers a versatile approach to address the icing problems in diverse weather conditions, which exhibits great prospects in various engineering applications.

S100A16-induced adipogenesis is associated with up-regulation of 11 ß-hydroxysteroid dehydrogenase type 1 (11ß-HSD1).

The steadily increasing epidemic of obesity continues at alarming rates, is an important public health problem, and expression changes of S100A16 and 11 ß-hydroxysteroid dehydrogenase type 1(11ß-HSD1) is attributable to the adipocyte differentiation. In our previous study, we found that 11ß-HSD1 protein expression increased in S100A16-overexpressed 3T3-L1 cell model. In order to further investigate the relationship between S100A16 and 11ß-HSD1, and the molecular mechanisms of S100A16-induced adipogenesis, we constructed S100A16 transgenic and knockout mouse, and S100A16-overexpressed 3T3-L1 preadipocyte cell. Using S100A16 transgenic (S100A16Tg/+) mice fed with normal fat diet (NFD) and high fat diet (HFD) diet model, we evaluated the effect of S100A16 on adipogenesis, expression of 11ß-HSD1, and RNA sequencing and quantification of gene expression. Using the 3T3-L1 cell model, we examined the effect of S100A16 and 11ß-HSD1 on pre-adipocyte differentiation, and cell signaling events of 11ß-HSD1 overexpression induced by S100A16. We found that when compared with C57BL/6 mice, overexpression of S100A16 under the condition of HFD increased lipid content in WAT and fat infiltration in hepatocytes, 11ß-HSD1 protein expression increased along with S100A16. Elevated S100A16 and 11ß-HSD1 expression promoted adipogenesis in 3T3-L1 cells. Overexpression of S100A16 inhibited the degradation of 11ß-HSD1. We conclude that S100A16-induced adipogenesis is associated with up-regulation of 11ß-HSD1.

Different-Shaped Ultrafine MoNbTaW HEA Powders Prepared via Mechanical Alloying.

Different-shaped ultrafine MoNbTaW high-entropy alloy powders were firstly prepared by a convenient mechanical alloying method. The phase composition and microstructure of the powders were characterized. The powders are ultrafine with nano-sized grains and a good homogeneous microstructure. All the powders have a single body-centered cubic solid solution phase and form the high-entropy alloy during mechanical alloying. These powders with different shapes are quite attractive for developing high-performance MoNbTaW high-entropy alloy bulk and coatings combined with a following sintering, spraying, or additive manufacturing technique.