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•Changes in surface chemistry of a bulk metallic glass upon sliding were evaluated.•The composition of the surface oxide is not affected by tribological conditions.•The oxide ...thickness is affected by the stress level at contact the trailing edge.
Bulk metallic glasses (BMGs) are promising structural materials owing to their high elastic limit and yield strength-to-weight ratio. While BMGs also exhibit attractive tribological properties (e.g., high wear resistance), the scientific basis for this behavior is not yet established. In particular, tribologically-induced changes in surface chemistry upon sliding are still an open topic of research. Here, we evaluated by X-ray photoelectron spectroscopy (XPS) the evolution of the surface chemistry of Vitreloy 105 (a Zr-rich BMG) upon sliding under different contact conditions against a tungsten carbide countersurface. The spectroscopic results indicate that the relative fraction of the metallic elements in the near-surface region is not affected by the sliding speed when the applied contact pressure is lower than 1.37 GPa, while a decrease in metallic zirconium was observed at lower sliding speeds and higher applied contact pressure (i.e., 1.71 GPa). Based on the spectroscopic results, a model is proposed for the effect of mechanical stress on the extent of oxidation of the near-surface region of Zr-based BMGs. The results of this work provide novel insights into the surface phenomena occurring on BMGs upon sliding and add significantly to our understanding of the tribological response of this class of promising structural materials.
Access to multimaterial polymers with spatially localized properties and robust interfaces is anticipated to enable new capabilities in soft robotics, such as smooth actuation for advanced medical ...and manufacturing technologies. Here, orthogonal initiation is used to create interpenetrating polymer networks (IPNs) with spatial control over morphology and mechanical properties. Base catalyzes the formation of a stiff and strong polyurethane, while blue LEDs initiate the formation of a soft and elastic polyacrylate. IPN morphology is controlled by when the LED is turned “on”, with large phase separation occurring for short time delays (≈1–2 min) and a mixed morphology for longer time delays (>5 min), which is supported by dynamic mechanical analysis, small angle X‐ray scattering, and atomic force microscopy. Through tailoring morphology, tensile moduli and fracture toughness can be tuned across ≈1–2 orders of magnitude. Moreover, a simple spring model is used to explain the observed mechanical behavior. Photopatterning produces “multimorphic” materials, where morphology is spatially localized with fine precision (<100 µm), while maintaining a uniform chemical composition throughout to mitigate interfacial failure. As a final demonstration, the fabrication of hinges represents a possible use case for multimorphic materials in soft robotics.
Two disparate polymer networks are created simultaneously using non‐interacting chemical reactions and light as a stimulus. Upon turning the light on, the polymers want to phase‐separate like oil and water, but the process is hindered as they interlock. Thus, the degree and location of phase separation, and in‐turn mechanical properties, can be precisely controlled by the “flick of a switch”.
In this work, B4C, B4C + 5 at.% Al, B4C + B, and B4C + B + 5 at.% Al were arc melted, and the resultant solid products were characterized. Results from x‐ray diffraction and scanning electron ...microscopy showed that adding Al alone in B4C did not result in Al doping; adding Al and B in B4C led to Al doping. Al‐doping also changed the surface energy of boron carbide in the liquid state, thus altered the wettability. Transmission electron microscopy revealed that stacking faults are more likely to form in the Al‐doped sample, especially in the regions where the Al concentration is high.
While ionic liquids (ILs) have gained wide interest as potential alternative lubricants able to meet the requirements of next-generation tribological systems owing to their unique physico-chemical ...properties and promising lubricating behavior, our understanding of the mechanisms by which ILs reduce friction and/or wear is still elusive. Here, we combine macroscale tribological experiments with surface-analytical measurements to shed light on the lubrication mechanisms of a class of halogen-free ILs, namely tetraalkylammonium orthoborate ILs, at steel/steel sliding contacts. The tribological results indicate an improvement of the friction-reducing properties of these ILs as the length of the alkyl chains attached to ammonium cations increases. X-ray photoelectron spectroscopy analyses provide further evidence for the dependence of the lubrication mechanism of tetraalkylammonium orthoborate ILs on the IL structure. In the case of tetraalkylammonium orthoborate ILs with asymmetric ammonium cations containing a long alkyl chain, no sacrificial tribofilms were formed on steel surfaces, thus suggesting that the friction-reducing ability of these ILs originates from their propensity to undergo a pressure-induced morphological change at the sliding interface that leads to the generation of a lubricious, solid-like layered structure. Conversely, the higher friction response observed in tribological tests performed with tetraalkylammonium orthoborate ILs containing more symmetric ammonium cations and short alkyl chains is proposed to be due to the inability of this IL to create a transient interfacial layer owing to the reduced van der Waals interactions between the cationic alkyl chains. The resulting hard/hard contact between the sliding surfaces is proposed to lead to the cleavage of boron-oxygen bonds in the presence of water to form species that then adsorb onto the steel surface, including trivalent borate esters and oxalic acid from the decomposition of orthoborate anions, as well as tertiary amines from the degradation of alkylammonium cations induced by hydroxides released during the orthoborate decomposition reaction. The results of this work not only establish links between the molecular structure of a class of halogen-free ILs, their lubricating performance, and lubrication mechanism, but also provide evidence for the existence of multiple mechanisms underpinning the promising lubricating properties of ILs in general.
Graphical Abstract
We develop a new concept to impart new functions to biocatalysts by combining enzymes and metal–organic frameworks (MOFs). The proof-of-concept design is demonstrated by embedding catalase molecules ...into uniformly sized ZIF-90 crystals via a de novo approach. We have carried out electron microscopy, X-ray diffraction, nitrogen sorption, electrophoresis, thermogravimetric analysis, and confocal microscopy to confirm that the ∼10 nm catalase molecules are embedded in 2 μm single-crystalline ZIF-90 crystals with ∼5 wt % loading. Because catalase is immobilized and sheltered by the ZIF-90 crystals, the composites show activity in hydrogen peroxide degradation even in the presence of protease proteinase K.
Dopants and alloying elements are commonly introduced in amorphous carbon (a-C) materials to tailor their mechanical and tribological properties. While most published studies have focused on doping ...and alloying a-C coatings with metals or metalloids, doping a-C films with rare-earth elements has only recently been explored. Notably, our understanding of the shear-induced structural changes occurring in rare-earth-element-containing a-C films is still elusive, even in the absence of any liquid lubricants. Here, the friction response of Eu- and Gd-containing a-C films with low hydrogen content deposited by HiPIMS on silicon was evaluated in open air and at room temperature. The load-dependent friction measurements indicated that the introduction of Gd ((2.3 ± 0.1) at.%) and Eu ((2.4 ± 0.1) at.%) into the a-C matrix results in a significant reduction of the shear strength of the sliding interfaces ((41 ± 2) MPa for a-C, (16 ± 1) MPa for a-C:Gd2.3 at.%, and (11 ± 2) MPa for a-C:Eu2.4 at.%). NEXAFS spectromicroscopy experiments provided evidence that no stress-assisted sp3-to-sp2 rehybridization of carbon atoms was induced by the sliding process in the near-surface region of undoped a-C, while the amount of sp2-bonded carbon progressively increased in a-C:Gd2.3 at.% and a-C:Eu2.4 at.% upon increasing the applied normal load in tribological tests. The formation of an sp2-bonded carbon-rich surface layer in a-C:Gd2.3 at.% and a-C:Eu2.4 at.% films was not only proposed to be the origin for the reduced duration of the running-in period in tribological test, but was also postulated to induce shear localization within the sp2-carbon-rich layer and transfer film formation on the countersurface, thus decreasing the interfacial shear strength. These findings open the path for the use of Gd- and Eu-containing a-C even under critical conditions for nearly hydrogen-free a-C films (i.e., humid air).
With over 6 million tons produced annually, thermoplastic elastomers (TPEs) have become ubiquitous in modern society, due to their unique combination of elasticity, toughness, and reprocessability. ...Nevertheless, industrial TPEs display a tradeoff between softness and strength, along with low upper service temperatures, typically ≤100 °C. This limits their utility, such as in bio-interfacial applications where supersoft deformation is required in tandem with strength, in addition to applications that require thermal stability (e.g., encapsulation of electronics, seals/joints for aeronautics, protective clothing for firefighting, and biomedical devices that can be subjected to steam sterilization). Thus, combining softness, strength, and high thermal resistance into a single versatile TPE has remained an unmet opportunity. Through de novo design and synthesis of novel norbornene-based ABA triblock copolymers, this gap is filled. Ring-opening metathesis polymerization is employed to prepare TPEs with an unprecedented combination of properties, including skin-like moduli (<100 kPa), strength competitive with commercial TPEs (>5 MPa), and upper service temperatures akin to high-performance plastics (≈260 °C). Furthermore, the materials are elastic, tough, reprocessable, and shelf stable (≥2 months) without incorporation of plasticizer. Structure-property relationships identified herein inform development of next-generation TPEs that are both biologically soft yet thermomechanically durable.
Background and Purpose
Recent development in drug discovery have shown benzimidazole to be an important pharmacophore,. Benzimidazole derivatives exhibit broad‐spectrum pharmacological properties ...including anti‐microbial, anti‐diabetic and anti‐tumour activity. However, whether benzimidazole derivatives are effective in suppressing angiogenesis and its underlying mechanisms remain incompletely understood. In this study, we aim to characterize the anti‐angiogenic mechanisms of a novel 2‐aminobenzimidazole‐based compound, Jzu 17, in an effort to develop novel angiogenesis inhibitor.
Experimental Approach
Effects of Jzu 17 on endothelial cell proliferation, migration, invasion, and activation of signalling molecules induced by VEGF‐A, were analysed by immunoblotting, MTT, BrdU, migration, and invasion assays. We performed tube formation assay, aorta ring sprouting assay, matrigel plug assay, and a mouse model of metastasis to evaluate ex vivo and in vivo anti‐angiogenic effects of Jzu 17.
Key Results
Jzu 17 inhibited VEGF‐A‐induced cell proliferation, migration, invasion, and endothelial tube formation of HUVECs. Jzu 17 suppressed VEGF‐A‐induced microvessel sprouting ex vivo and attenuated VEGF‐A‐ or tumour cell‐induced neovascularization in vivo. Jzu 17 also reduced B16F10 melanoma lung metastasis. In addition, Jzu 17 inhibited the phosphorylation of VEGFR‐2 and its downstream signalling molecules in VEGF‐A‐stimulated HUVECs. Results from computer modelling further showed that Jzu 17 binds to VEGFR‐2 with high affinity.
Conclusions and Implications
Jzu 17 may inhibit endothelial remodelling and suppress angiogenesis through targeting VEGF‐A‐VEGFR‐2 signalling. These results also suggest Jzu 17 as a potential lead compound and warrant the clinical development of similar agents in the treatment of cancer and angiogenesis‐related diseases.
Abstract
Inaccessibility of stored memory in ensemble cells through the forgetting process causes animals to be unable to respond to natural recalling cues. While accumulating evidence has ...demonstrated that reactivating memory-stored cells can switch cells from an inaccessible state to an accessible form and lead to recall of previously learned information, the underlying cellular and molecular mechanisms remain elusive. The current study used
Drosophila
as a model to demonstrate that the memory of one-trial aversive olfactory conditioning, although inaccessible within a few hours after learning, is stored in KCαβ and retrievable after mild retraining. One-trial aversive conditioning triggers protein synthesis to form a long-lasting cellular memory trace, approximately 20 days, via creb in KCαβ, and a transient cellular memory trace, approximately one day, via orb in MBON-α3. PPL1-α3 negatively regulates forgotten one-trial conditioning memory retrieval. The current study demonstrated that KCαβ, PPL1-α3, and MBON-α3 collaboratively regulate the formation of forgotten one-cycle aversive conditioning memory formation and retrieval.
Silicon-containing diamond-like carbon (DLC) is a class of thin-film materials with excellent mechanical properties, high thermal stability, and good tribological performance over a wide range of ...environmental conditions. While non-alloyed/non-doped DLCs also exhibit good biocompatibility and bioinertness, our understanding of the effect of silicon in DLCs on biomolecules/DLC interactions is still elusive. Here, we evaluated the structural, mechanical, and tribological properties of Si-containing DLC coatings with silicon content fraction of 11% and 16%. Tribological tests, performed by sliding a stainless steel pin on the coatings in water, indicated a low friction response (steady-state coefficient of friction <0.11), while quartz crystal microbalance experiments indicated no adsorption of a model biomolecule, namely adenosine triphosphate (ATP), on Si-containing DLCs. Near-edge X-ray absorption fine structure spectromicroscopy analyses performed after tribological experiments provided evidence for an increase in the fraction of silanol surface terminal groups formed in the worn region upon sliding in water without any significant sp3-to-sp2 rehybridization of carbon atoms. The fraction of surface hydroxyl groups in the worn region increases with the silicon content in Si-containing DLC, which leads to a decrease in friction. This tribologically-induced change in surface termination did not lead to the adsorption of ATP upon incubation of tribotested samples in ATP solutions for several hours. These findings open the path for the use of Si-containing DLC in applications requiring good tribological properties in aqueous solution and an excellent resistance to biomolecule surface adsorption that is maintained even after tribologically-induced variations in surface termination.
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•Si-containing DLC coatings with Si fraction between 11% and 16% were grown.•Increasing Si in DLC decreases friction in water.•Sliding in water leads to an increase in silanol surface terminal groups.•No adsorption of ATP occurs on Si-DLCs independently of the surface termination.
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