Lubrication Properties Research Articles

A sustainable glycolipid hydrotrope‐solubilizer for cleansers and detergents

AbstractAlkyl polyglycosides (APGs), based on renewable glucose and fatty alcohols, are recognized for their performance and biodegradability. Hydrotropic/solubilizing effect properties have already been identified on short‐chain variants such as hexyl and ethylhexyl, but these ingredients were not fully bio‐based. This study investigated the hydrotropic/solubilizing properties of eco‐designed 100% bio‐based heptyl glucoside, under various conditions, compared to industrial and personal care benchmarks and other short chain APGs. Foaming power was firstly evaluated at different temperatures with two static methods. Hydrotropic performance was assessed with a commonly used surfactant in the presence of high electrolyte, acid and alkali concentrations. Further trials were done using ethoxylated rapeseed oil as an oil lubricant model in electrolyte‐charged aqueous solution. The solubilizing effect of hydrophobic additives such as fragrances, essential oils and vitamin E was quantified. Finally, effects on formulation preservation were screened with two natural personal care preservatives. Heptyl glucoside was found to be an effective and versatile hydrotrope for industrial applications, with additional intrinsic lubrication properties. It was also revealed as an efficient solubilizer for personal care products with the additional benefit of reducing the preservative dosage required in natural formulations. Its unusual non‐foaming nature, while not disrupting the foaming capacity of surfactants, makes it suitable for all types of cleansers. The calculated carbon footprint has a low value, making heptyl glucoside a valuable ingredient combining both performance and low environmental impact.

Fast-polymerized lubricant and antibacterial hydrogel coatings for medical catheters

Medical catheters are highly susceptible to friction and infection when intervening or implanting in the body, and to thrombosis when in contact with blood. Coating medical catheters with lubricant and antibacterial hydrogel is an effective strategy but struggle to achieve. Here, hydrogel coating on the catheter surface with lubrication and antibacterial properties was constructed by the rapid polymerization of acrylamide (AAM) and sulfobetaine methacrylate (SBMA) in the presence of quaternary ammonium chitosan (QCS) based on the redox-based cross-linking method. First, the medical catheter surface was decorated with a polyethyleneimine (PEI) adhesive layer. The pre-gel solution was then applied to the catheter surface, followed by immersion in an aqueous FeSO4·7H2O solution, where a large amount of SO4-• was generated by a redox reaction between ammonium persulfate (APS) and Fe2+, which rapidly triggered the monomer to cross-link to form the coating. Polyelectrolyte PEI as the adhesive layer could bind the coating to the substrate through hydrogen bonding interactions and confer antimicrobial properties to the coating with the assistance of QCS (antibacterial rate of 95.88 % against E. coli and 97.11 % against B. subtilis). The hydrogel coatings exhibited outstanding lubricity with a low coefficient of friction (COF ≈ 0.053) and excellent antifouling properties (resists non-specific protein adsorption, inhibits platelet adhesion and prevents thrombosis (The clotting time was extended from 25.6 s to 74.7 s)) based on the integration of SBMA. This work shed new light on the design of hydrogel coatings to achieve modification of the substrate surface.

Epoxidation of mixture of waste cooking oil and soybean oil with different compositions

Epoxidation of soybean oil (SO) blended with waste cooking oil (WCO) of different mass ratio (90:10, 80:20, 70:30, 60:40 and 50:50) was carried out at reaction temperature of 65 °C and reaction time of 7 h. Physicochemical properties of the reagent and product such as viscosity at 40 °C and 100 °C, viscosity index, iodine index as well as FT-IR spectral analysis are studied to investigate the effect of the mixing ratio of SO and WCO on C=C conversion and physical properties of epoxidized product. The experiment results showed that conversion of C=C in the feed oil of different blending ratio through epoxidation at 65 °C and 7 h could reach high value (almost 98 %) with corresponding Iodine Value of all products of nearly 2. The viscosity of epoxidized oil at both 40 °C and 100 °C increased remarkably compared to the values of soybean oil while viscosity index decreased. However, the VI of epoxidized products are in the range of requirement for lubricating oil. Among all samples studied, the mixture of SO and WCO of 90:10 (mass ratio) had the best lubricating properties, with the highest viscosity at both 40 °C and 100 °C (138.22 and 18.50 cSt) and viscosity index (151).

Dry Mouth Dilemma: A Comprehensive Review of Xerostomia in Complete Denture Wearers.

Xerostomia, commonly known as dry mouth, presents a significant challenge for individuals wearing complete dentures, affecting their oral health and quality of life. This review explores the relationship between saliva and complete dentures, highlighting the varied management strategies for xerostomia. Saliva plays a critical role in denture retention, lubrication, and oral environment buffering. Complete denture wearers often experience reduced salivary flow, aggravating symptoms of xerostomia.Various management approaches are discussed, including general measures such as hydration and salivary stimulation techniques which aim to boost saliva production naturally. The use of salivary substitutes provides artificial lubrication and moisture to alleviate dry mouth discomfort. Oral lubricating devices, such as sprays, gels, and lozenges, offer relief by mimicking saliva's lubricating properties, thereby improving denture stability and comfort.This review addresses the etiology of xerostomia in complete denture wearers and explores preventive measures to reduce its impact. A comprehensive approach has been discussed for the management of xerostomia which will help to improve the oral health and well-being of complete denture wearers experiencing dry mouth.

Comparative Study on the Lubrication Mechanism and Performance of Two Representative Ionic and Nonionic Self-Adhesive Polymer Coatings.

Surface modification of lubricating coatings on biomedical devices is a pivotal strategy to improve the overall performance and clinical efficacy, significantly reducing friction between devices and human tissues and mitigating tissue damage during intervention and long-term implantation. Recently, various hydrophilic polymeric materials have been used for achieving surface functionalization, endowing the biomedical device with excellent superlubrication performance. N-Vinylpyrrolidone (NVP) and 2-methacryloyloxyethyl phosphorylcholine (MPC) are two typical representatives of nonionic and zwitterionic materials. However, there is still a research gap in a comparative study of the lubrication mechanisms and properties between them. In this study, a bioinspired and dopamine-assisted codeposition technique was used to fabricate biomimetic hydrophilic coatings, including P(DMA-NVP) and P(DMA-MPC), on polyurethane. To achieve a thorough comparative analysis of the self-adhesive coating performance, 3 M ratios of the copolymers were synthesized and comprehensive material evaluations were conducted. Additionally, surface morphology, hydrophilicity, and lubrication at both the microscale and macroscale were performed. It was found that both hydrophilic coatings exhibited good stability. The P(DMA-MPC) coating, due to the ability to attract and bind a large number of water molecules, demonstrated superior lubrication effects compared to the P(DMA-NVP) coating. The study provides an in-depth understanding of the lubrication behavior of the self-adhesive coatings to enhance the functionality and application in biomedical engineering.

Enhancing wear resistance and mechanical property of epoxy coating via “roller wheel” liquid metal‐MXene

AbstractThis work presents a design of a unique “roller wheel” structure combining rigid MXene and flexible liquid metal (LM), aiming to construct an epoxy composite coating with simultaneous advanced mechanical strength and lubrication properties. The antiwear property of the epoxy composites is improved by 72.8% when the LM is 0.5 wt% and MXene is 0.03 wt%. The incorporation of LM‐MXene improved the mechanical properties of the epoxy composite coating, resulting in an approximately 136.6% increase in elastic modulus. The unique “roller wheel” structure provides additional mechanical support and leads to lower adhesion between the MXene layers and LM. As a result, LM reduces the stripping and sliding of the interface between MXene layers during the friction process, further enhancing the lubrication performance of the epoxy composite coating.

The Effects of the Lubricant Properties and Surface Finish Characteristics on the Tribology of High-Speed Gears for EV Transmissions

Electric vehicle (EV) transmissions operate at high speeds. High-speed operation puts higher demands on bearings, seals, and gears. Bearings in EV transmissions are prone to electrically induced bearing damage and may exhibit signs of pitting and fluting. Surface-initiated rolling contact fatigue is another common problem gaining increased attention lately. Most EV transmissions require a coupling between an oil-lubricated gearbox to an electrical motor that runs with minimal lubrication at very high rpm. The high mechanical and thermal stresses the seals are exposed to under starved lubrication conditions have a detrimental impact on their service life. Hence, proper lubrication is critical. In general, EV transmission fluids call for a somewhat different spectrum of properties compared to conventional ATFs. Gear tribology simulations open new ways to the design and optimization of lubrication for EV transmissions. Additionally, such simulations can also provide valuable insights into the effects of different oil properties on cooling and lubrication efficiencies, thereby helping in matching the lubricant and hardware characteristics for optimal performance. In the present communication, we demonstrate the effects of different lubricants and surface finishing technologies on the tribology of high-speed gears using tribological tests and advanced thermal elastohydrodynamic (TEHD) simulations. The important roles of lubricity additives and surface finish optimization are highlighted in conjunction with a move towards ultralow viscosity EV transmission fluids.

Titanium nitride induced wide temperature range self-lubricating silicon nitride ceramics with low wear and stable low friction coefficient

Silicon nitride (Si3N4) with excellent mechanical properties and chemical stability, has been widely used in many fields. However, wear failure is often the cause of the short life of Si3N4 devices at high temperatures, thereby the wear resistance of Si3N4 ceramics still needs to be further improved. In this work, titanium nitride is used as a reinforcing phase to prepare wear-resistance Si3N4 ceramics in a wide temperature range by spark plasma sintering. The effect of TiN particles on densification process, phase transformation, mechanical properties, and tribological properties in wide temperature range from 25 to 800 °C were tested and analyzed. At room temperature, TiN particles hindered the propagation of microcracks, and the wear rate was reduced by an order of magnitude, reaching 3.69×10−6 mm3·N−1·m−1. At 800 °C, the completed TiO2 oxide film exhibited self-repairing and lubricating properties, which further reduced the wear rate to 9.35×10−7 mm3·N−1·m−1. Additionally, the friction coefficient of Si3N4 ceramics with 30 vol% TiN decreased considerably and remained stable in the wide temperature range of 25 ∼ 800 °C, with a range of 0.69 ∼ 0.85.

Excellent hydration lubrication based on Zwitterionic Poly (N-vinylpyrrolidone-co-methacrylic acid) for hair combing improvement

In the present work, Poly (N-vinylpyrrolidone-co-methacrylic acid) (P(NVP-co-MAA)) was synthesized with free radical polymerization, and the hydration lubrication of the zwitterionic copolymer were investigated. P(NVP-co-MAA) as a lubricant to improve hair combing was also explored. The contact angle measurement showed that P(NVP-co-MAA) could adsorb onto both PDMS and hair surfaces. Adsorption equilibrium was achieved at the polymeric concentration of 0.2% and 0.3% on the surfaces of PDMS and hair, leading to a decrease in the contact angles by 5° and 11°, respectively. The hydration lubricity of P(NVP-co-MAA) was tested, and the results demonstrated that P(NVP-co-MAA) exhibited excellent lubricity properties in both boundary lubrication and mixed lubrication. It provided stable lubricity for up to 2 h with continuous friction. Scanning electron microscope (SEM) and atomic force microscope (AFM) showed that the copolymer adsorbed on hair surfaces, mainly concentrated around the cuticles. It implied that the adsorption of the copolymer on hair surfaces relied on electrostatic interactions as well as hydrophobic interactions. The polymeric solution could lower the friction coefficient of wet hair compared to polyquaternium-10 (JR-400), a commonly used hair conditioner. When the concentration of copolymer was greater than 0.2%, the friction coefficient of wet hair was 0.129. At this concentration, copolymer molecules formed a hydration layer on the hair surface, which reduced the friction coefficient by 34.1%.

Evaluation of Temperature-Dependent Boundary Lubrication Behavior of Stearic Acid Using a Force-Controlled Tribometer.

A quick evaluation of the effectiveness of additives is important in lubricant formulation. In this study, we employed a friction-force measurement approach using a newly designed lateral force-controlled tribometer. This tribometer evaluates the lubricant properties under boundary lubrication. In this lateral force-controlled tribometer, the absence of a stiffness-altering sensor enables the modeling of the actual contact conditions without altering the contact stiffness. Indirect friction force measurement ensures precise measurements of friction properties while avoiding common measurement errors encountered in conventional tribometers, such as sensor misalignment and changes in the stiffness of the machine due to the sensor. The tribometer designed and built consists of a pendulum that measures the rate of dissipation of the oscillation amplitude as a function of time. The unique characteristics of the machine are the possibility of changing the energy input into the tribosystem without altering the tribo-contact conditions and the capability to do experiments at higher temperatures. To evaluate the capabilities of this tribometer, the impact of temperature on the frictional properties of a base oil and a blend of base oil and stearic acid (SA) (a prominent Organic Friction Modifier) is investigated. The test result shows that frictional energy dissipation decreases when stearic acid is present in the lubricant. And, as the temperature of the oil increases, the energy dissipation increases for pure base oil but reduces for the blend. The observed frictional trends are attributed to the decrease in the viscosity of the base oil with an increase in the temperature. The decrease in friction for the SA blend is attributed to tribofilm formation. Fourier transform infrared (FTIR) and X-ray Photoelectron Spectroscopy (XPS) analyses confirm the presence of the SA tribofilm on the surface. XPS indicates an increase in tribofilm quantity with rising temperatures. The kinetics of film formation and thickness increase with temperature, consequently reducing the friction in the SA blend.

Tribological property of dendritic fibrous nano silica composite particle as lubricant additive

In this study, a novel Dendritic Fibrous Nano Silica (DFNS) solid-liquid composite lubricant additive (DFNS@ILs) was prepared by the simple of bi-continuous microemulsion polymerization and vacuum impregnation adsorption ionic liquids (ILs) method. The microstructure and chemical composition were characterized by transmission electron microscopy (TEM), scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The oil lubrication properties of the DFNS@ILs were investigated and the results showed that the DFNS@ILs additive had the most excellent tribological properties when compared to the pure PAO6 oil, commercially available ZDDP and nano-silica. Moreover, DFNS@ILs have long-term stability as lubricant additives. Based on the analysis of the wear surfaces, it is concluded that the excellent performance of DFNS@ILs additive are owing to the synergistic lubrication effect of DFNS and ILs as well as the formation of transfer film, which makes it a promising lubricant material.

Formulation and evaluation of bio-grease from the blend of chemically modified rice bran oil and Calophyllum inophyllum oil

Vegetable oils are a highly promising alternative to produce various lubricants, owing to their biodegradability and eco-friendliness. In comparison to mineral oil, these oils possess a higher flash point and viscosity index, along with superior lubricating properties. Additionally, most of the vegetable oils are easily accessible in local markets in India. However, their industrial application is limited by poor thermal and oxidative stability, which can be addressed through chemical modification, the addition of appropriate additives, or by blending these oils. Greases, characterized by their semi-solid consistency, are widely used lubricants. Most of the grease production is based on mineral oils as base oil and lithium soap as a thickener. These materials are not only non-biodegradable but also scarce and have health implications. Consequently, biodegradable grease represents an eco-friendly and healthy alternative. Grease made using vegetable oils with the required properties has the potential to bring about revolutionary changes. The present work focuses on the feasibility of using chemically modified blended rice bran oil (RBO) and Calophyllum inophyllum oil (CIO) as a bio-lubricant. The oils undergo a two-step modification process, involving a transesterification reaction followed by epoxidation. Significant improvements have been observed in the chemical properties (acid, peroxide, and iodine values) of transesterified epoxidized rice bran oil Calophyllum inophyllum oil mixture–50:50 (ETRCIO) when compared with Unmodified Rice bran oil Calophyllum inophyllum oil mixture–50:50 (RCIO). The acid value, peroxide value, and iodine value improved by 91.66%, 87.08%, and 15.78% respectively. The rheological, tribological, and chemical properties of the blended samples have been evaluated and compared to pure oils using American Society for Testing and Materials (ASTM) and Indian Standards (IS). Additionally, ETRCIO was used to develop a bio-grease, and its tribological properties were extensively analyzed. The mean coefficient of friction (COF) and wear scar diameter (WSD) of the ETRCIO grease sample improved by 10.20% and 29.32% respectively when compared with that of commercially available grease. These findings indicate that the ETRCIO bio-grease exhibits superior tribological properties in comparison to commercially available grease.

Utilization and Evaluation of Rice Bran and Rice Bran Wax as a Tablet Lubricant.

The rice bran and rice bran wax of the KJ CMU107 rice strain were investigated as potential tablet lubricants in a directly compressed tablet formulation. Stabilized full-fatted rice bran (sFFRB), stabilized defatted rice bran (sDFRB), and rice bran wax (RBW) extracted and purified from crude rice bran oil (cRBO) were tested. Two commercial lubricants, including magnesium stearate (MGS) and hydrogenated cottonseed oil (HVO), were employed as the standards in the formulated mixtures, which contained spray-dried rice starch (SDRS) as a diluent. The tableting was carried out for each formulation, and the obtained tablets were physically and mechanically evaluated. Among the parameters investigated were the general appearance, ejection force, weight variation, hardness, friability, and disintegration time. The powder flow was also determined for each formulation. The results showed that the tablet ejection forces for all the lubricated formulations (58-259 N) were significantly lower than that of the non-lubricated control formulation (349 N). The use of sFFRB as a lubricant at 0.5-2.0% w/w could lower the ejection force up to 78%, but the hardness reduced so drastically that the formulations failed the friability test due to the chipping of the tablets' edges. Moreover, sDFRB performed significantly better as the use at 0.5-1.0% w/w in the formulation helped to lower the ejection forces by up to 80% while maintaining the changes in the tablet hardness within 10%. RBW functioned effectively as a tablet lubricant at a concentration of 0.5% w/w, yielding tablets with good strength comparable to standard HVO lubricant while helping to reduce the ejection force by 82%. In formulations with good lubrication, i.e., friability < 1%, the powder flow was improved, and the tablet disintegration times were within the same range as the control and HVO formulations. In conclusion, sDFRB displayed a lubricant property at concentrations between 0.5 and 1.0% w/w, with slightly negative effects on the tablet hardness. RBW from KJ CMU107 rice was an effective tablet lubricant at 0.5% w/w, with no effect on tablet hardness. Both materials can be further developed for use as commercial lubricants in direct compression.

Tailoring microstructures of oleogel-based HIPEs to modulate oral processing properties: Rheology, tribology and mastication effects

High internal phase emulsions (HIPEs, 80 wt%) with different structures were developed by using different oleogelators (beeswax and ethyl cellulose) and emulsifiers (whey protein isolate and OSA starch) via a facile shearing approach. The effects of the oleogelators and emulsifiers on the stability and oral processing properties were investigated. The addition of oleogelator resulted in smaller particle sizes and higher accelerated centrifugal stability. Microstructural observations indicated the droplets were tightly packed to form oil-in-water HIPEs. Rheology tests showed that the addition of the oleogelators resulted in strain-thinning behavior and weak strain overshoot for OSA and WPI stabilized HIPEs, respectively. Tribology tests suggested that emulsifiers dominated the lubrication properties of the mixing regime, whereas oleogelators were crucial to the lubricating effects of the hydrodynamic regime. Instrumental mastication assays revealed that the WPI-HIPEs required stronger chewing force, and the addition of oleogelator weakened the normal force. After being masticated by the bionic chewing robot, droplet coalescence and phase separation occurred in the HIPEs, which was attenuated by the addition of oleogelators. These findings will assist in designing the structures of desirable textural attributes and support the creation of functional foods.

High temperature lubrication performance of chlorophenyl silicone oil

Most studies of liquid lubricants were carried out at temperatures below 200 °C. However, the service temperature of lubricants for aerospace and aeroengine has reached above 300 °C. In order to investigate the friction mechanism and provide data for high temperature lubrication, the friction and wear properties of chlorophenyl silicone oil (CPSO)-lubricated M50 steel and Si3N4 friction pairs were investigated herein. Ball-on-disk experimental results show that the lubrication performance of CPSO varies significantly with temperature. Below 150 °C, coefficient of friction (COF) remains at 0.13–0.15 after the short running-in stage (600 s), while the COF in the running-in stage is 0.2–0.3. At 200 °C and above, the running-in time is much longer (1,200 s), and the initial instantaneous maximum COF can reach 0.5. Under this condition, the COF gradually decreases and finally stabilizes at around 0.16–0.17 afterwards. This phenomenon is mainly due to the different thickness of boundary adsorption film. More importantly, the wear rate of M50 steel increases significantly with the temperature, while the wear rate barely changes at temperatures above 200 °C. The anti-wear mechanism is explained as tribochemical reactions are more likely to occur between CPSO and steel surface with the increased temperature, generating the FeCl2 protective film on the metal surface. Accordingly, FeCl2 tribochemical film improves the lubrication and anti-wear capacity of the system. At high temperatures (200–350 °C), FeCl2 film becomes thicker, and the contact region pressure becomes lower due to the larger wear scar size, so the wear rate growth of M50 steel is much smaller compared with that of low temperatures (22–150 °C). The main findings in this study demonstrate that CPSO lubricant has good anti-wear and lubrication capacity, which is capable of working under temperatures up to 350 °C.

Design and construction of a single orifice oscillatory flow reactor for the continuous production of biodiesel from sunflower oil

Biodiesel, a renewable energy replacing fossil fuels, exhibits eco-friendly traits with beneficial lubrication properties. This research aims to design and construct a single-orifice oscillatory flow reactor to reduce the reaction time, improve the mixing process, and increase efficiency. The response surface method was used for the analysis of independent parameters like molar ratio (1:6–1:12), temperature (30–50 °C), reactor length (1–3 m), and catalyst concentration (0.75%-1.25%) on yield as the dependent variable. Elevated temperature up to 50 °C enhances conversion from 61.91% to 69.51%, peaking at 65.43% by 60 °C, adjusting the molar ratio to 1:9 boosts biodiesel conversion from 58.70% to 69.51%, dropping by 4% at 1:12 ratio. Catalyst concentration at 1% heightens conversion from 48.82% to 69.51%, but at 1.25%, it falls to 57.26%. Increasing reactor length to 2 m yields a 20% boost, while at 3 m, conversion drops by 4%. Optimal conditions, at 40 °C, 1:9 ratio, 1% catalyst, and 3 m reactor, resulted in a 91.98% conversion percentage. Experimental verification at the suggested point yields an 89% conversion, aligning acceptably with the model’s prediction. Biodiesel meets EN 14214 standards, positioning it as a viable diesel fuel alternative.

A Review on the Impact of Bio-Additives on Tribological Behavior of Diesel Fuels

Automobile engines require lubrication to lessen the impact of friction due to the high levels of wear and frictional heat generated by the sliding parts. Wear and friction will cause engine parts to endure for less time, be less reliable, and require more maintenance. Diesel fuel can potentially be replaced with biodiesel among other fuels. Diesel engines have a serious problem with equipment that is lubricated by the fuel itself. This study’s goal is to assess the influence of bio-additives on the diesel fuel tribological behavior and energy balance during the car’s idle running, acceleration, constant speed, and braking. Lubricity issues with reformulated diesel and lubricity test procedures are explained. The relationship between tribology and bio-additives is also briefly illustrated. According to the literature, adding bio-additives to fuel boosts its lubricity. Biodiesel has long been considered an additive with excellent lubricant properties. Even in small amounts, adding biodiesel to diesel fuel can increase its lubricity without the need for conventional lubricity additives. This is especially true for diesel fuel with ultralow sulfur. Diesel fuel characteristics determine the precise blending percentage needed to provide the proper lubricity of maximum 520 μm testing wear scars with a high-frequency reciprocating rig (HFRR), although 2% biodiesel nearly invariably imparts adequate lubricity to biodiesel blends. Tall oil fatty acid (TOFA) was one of the bio-additives investigated by HFRR. When the additive concentration was raised from 0 to 500 g/g, the wear scar diameter (WSD) of nonadditive diesel fuel was lowered by 60.3%, from 630 to 250 μm, and the coefficient of friction (COF) was lowered by 95.7%, from 0.47 to 0.02.

Position of Carbonyl Group Affects Tribological Performance of Ester Friction Modifiers.

The tribological properties of lubricants can be effectively improved by the introduction of amphiphilic molecules, whose performance is largely affected by their polar head groups. In this work, the tribological performance in steel-steel contacts of two isomers, glycerol monostearate (GMS) and stearyl glycerate (SG), a glyceride and a glycerate, were investigated as organic friction modifiers (OFM) in hexadecane. SG exhibits a much lower friction coefficient and wear than GMS despite their similar structures. The same applies when comparing the performance of oleyl glycerate (OG) and its isomer, glycerol monooleate (GMO). Surface chemical analysis shows that SG forms a polar, carbon-based, tribofilm of around tens of nanometers thick, while GMS does not. This tribofilm shows low friction and robustness under nanotribology test, which may contribute to its superior performance at the macro-scale. The reason for this tribofilm formation can be due to the stronger adsorption of SG on the steel surface than that of GMS. The tribofilm formation can be stress-activated since lower friction and higher tribofilm coverage can be obtained under high load. This work offers insights into the lubrication mechanism of a novel OFM and provides strategies for OFM design.

Polyvinylpyrrolidone hydrogel coating for ureteral stent: Safety and performance evaluation.

Ureteral stents are commonly used in urology. However, complications such as encrustation and infection on the surface of the stent, and injury to the ureteral mucosa can occur after implantation, causing discomfort for patients. We intend to confirm the biosafety of polyvinylpyrrolidone (PVP) hydrophilic coating and its lubrication properties for surface modification of ureteral stents to reduce friction and improve patient comfort. Based on our previous studies, we have developed a PVP hydrophilic coating for surface modification of ureteral stents. We firstly investigated the cytotoxicity, intradermal irritation, delayed type hypersensitivity, and acute systemic reactions of stent coating extracts. We further characterized the break strength, retention strength, and dynamic friction of the stent. The cell survival rate of all experimental groups was greater than 70%. No hypersensitivity reaction, systemic toxicity reaction, or obvious intradermal reaction were observed. The above results indicate that the test results of the modified stent meet the requirements of ISO 10993-5: 2009 (Cytotoxicity); ISO 10993-10:2021 (Sensitization and Irritation); ISO 10993-11:2017 (Acute Systemic Toxicity). After soaking in artificial urine for an extended period, there was no obvious change in its super-slip performance. Our results confirm the safety and lubrication characteristics of PVP hydrophilic coating for ureteral stent surface modification. The performance of this coating has the potential to reduce complications after stent implantation, thereby improving patient comfort, reducing medical burden, and has a good clinical application prospect.

The Investigation of Broad-Spectrum Sealing Drilling Fluid Based on Horsfield Close-Packing Theory

Summary In shale gas drilling operations, oil-based drilling fluids have proved to be effective in addressing the issue of shale reservoir hydration expansion, serving as the primary working fluid for complex subsurface shale formations. However, the presence of shale laminations and the development of microfractures with varying widths require drilling fluids with excellent sealing capabilities. In this study, a comprehensive investigation was conducted to develop a drilling fluid system with broad-spectrum high-sealing performance. The porosity of bridging particles was determined by using the Archimedean drainage method. The bridging particle size and quantity at each level were meticulously designed through leveraging the Horsfield close-packing theory. The incorporation of deformable nanoscale polymer sealing materials further enhanced the sealing performance of the drilling fluid system. Additionally, hydrophobic nanoscale silica particles were introduced as coemulsifier to prepare Pickering emulsions, thereby improving emulsion stability and enhancing particle-size distribution for improved sealing. Through formulation optimization, a drilling fluid system with broad-spectrum, high-sealing performance capabilities was developed. The study revealed a reduction in porosity of closely packed bridging particles from 35.36% to 11.38%. The drilling fluid system exhibited a remarkable sealing efficiency of 99.2% for microfractures in the 1–10 μm range and 95.8% for microfractures in the 30–50 μm range. Furthermore, it demonstrated excellent sedimentation stability, with a sedimentation factor of less than 0.52 after 48 hours of static sedimentation at 150°C. The drilling fluid system also exhibited favorable rheological, lubrication, and inhibition properties, thus meeting the demands of field applications.