Droplet evaporation on super liquid-repellent surfaces: A controllable approach for supraparticle fabrication.

Supraparticles are agglomerates of nano- and/or microparticles with sizes ranging from tens to hundreds of microns, making them more accessible for handling and recovery than the building blocks. Supraparticles not only inherit the properties and functions of primary particles but also exhibit characteristics such as high porosity, large specific surface area, and improved functionalities, which can be attributed to the synergism, coupling, and co-localization among the constituents. Therefore, supraparticles hold promising applications in catalysis, drug delivery, sensing, etc. Among the various synthesizing strategies, evaporating droplets on a liquid-repellent surface is proposed as an effective approach to fabricate supraparticles with unique structural features and functions. The boundary conditions of such droplet-confinement methods significantly drive the formation of supraparticles by reducing or avoiding the use of solvents or processing liquids, which further accelerates the development and utilization of supraparticles. This paper presents an overview of recent developments in the fabrication of supraparticles by evaporating droplets on liquid-repellent surfaces. The review focuses on the evaporation processes on lubricant and superhydrophobic surfaces, structural regulation, and applications of supraparticles. Finally, an outlook on the future directions of evaporation on liquid-repellent surfaces mediated supraparticle fabrication is presented.

Fabrication of Vanadium Oxide-encapsulated Hybrid Carbon Nanospheres for Enhanced Tribological Performance.

A new sulfur-containing carbon nanospheres encapsulated with vanadium oxide (V@SCN) is synthesized through a one-pot oxidation polymerization and then carbonization method. The prepared V@SCNs exhibit good dispersibility as a lubricant additive, which is owing to the inherited lipophilic organic functional groups in the sulfur-containing carbon shell derived from the carbonization of polythiophene. The agglomeration and precipitation of metals in the base oil are also avoided through the encapsulation of lipophilic carbon shells. The stress and thermal simulation results show that the vanadium oxide core bestows upon the carbon nanospheres enhanced load resistance and superior thermal conductivity, which contributes to their excellent tribological properties. Introducing 0.04M-V@SCN to the base oil leads to favorable tribological characteristics, such as a fourfold rise in extreme pressure capacity from 250 to 1050N, a reduction in friction coefficient from 0.2 to ≈0.1, and a substantial decrease in wear by 90.2%. The lubrication mechanism of V@SCNs as lubricant additive involves the formation of a robust protective film on the friction pair, which is formed via complex physical and chemical reactions with the friction pair during friction.

Significantly less wear of UHMWPE rubbing against pyrocarbon than against CoCr.

The history of joint replacement can be framed as a battle to reduce wear. Pyrocarbon has been shown to be a low wear material, but can low wear against an ultra high molecular weight polyethylene (UHMWPE) counterface be achieved? To investigate this research question, a 50-station, clinically validated wear screening machine was used. Half the stations tested UHMWPE pins against pyrocarbon discs, and half the stations tested UHMWPE pins against cobalt chromium (CoCr) discs. The test rig ran at 1Hz, the nominal contact stress was 2.07 MPa, and testing ran to 5 million cycles. A biomimetic lubricant was used, it was replaced every 500,000 cycles. At the end of testing, the UHMWPE pins rubbing against pyrocarbon discs had a statistically significant reduced wear, compared with the UHMWPE pins rubbing against CoCr discs (p ≤ 0.01). Analysis of the discs at the end of testing showed greater adherence of phospholipids on the pyrocarbon discs than the CoCr discs. In turn, it was also seen that far less UHMWPE was attached to the pyrocarbon discs than to the CoCr discs. Based on this evidence, it is suggested that pyrocarbon surfaces are associated with reduced adhesive wear of UHMWPE compared with CoCr surfaces. In addition, at the end of testing, the CoCr discs were found to be significantly rougher than the pyrocarbon discs. Therefore, pyrocarbon maintained a smoother surface than CoCr, likely meaning that abrasive wear of UHMWPE was reduced compared with CoCr.

Hyaluronic Acid in Nanopharmaceuticals: An Overview.

Hyaluronic acid (HA) is a naturally occurring, long, unbranched polysaccharide that plays a critical role in maintaining skin structure and hydration. Its unique properties make it a valuable component in the field of nanopharmaceuticals. The combination of HA into nanopharmaceuticals enhances its ability to interact with various therapeutic agents, improving the delivery and efficacy of drugs. HA-based nanoparticles, including solid lipid nanoparticles, and polymeric nanogels, offer controlled release, enhanced stability, and targeted delivery of therapeutic agents. These innovations significantly improve therapeutic outcomes and reduce side effects, making HA an essential tool in modern medicine. In general, HA-modified liposomes enhance drug encapsulation and targeting, while HA-modified solid lipid nanoparticles (SLNs) provide a solid lipid core for drug encapsulation, offering controlled release and stability. This article provides an overview of the potential applications and recent advancements of HA in nanopharmaceuticals, emphasizing its significant impact on the evolving field of targeted drug delivery and advanced therapeutic strategies. By delving into the unique properties of HA and its compatibility with various therapeutic agents, this review underscores the promising potential of HA in revolutionizing nanopharmaceuticals.

Ultraslippery Surface for Efficient Fog Harvesting and Anti-Icing/Fouling.

The conventional Slippery Liquid Infused Porous Surface (SLIPS) encounters challenges such as silicone oil leakage and complex manufacturing of rough substrate structures. Thus, it is crucial to develop a lubricant that is highly adaptable and less prone to loss for surface structures; a temperature-controlled method of infusing oleogel into a superhydrophobic surface (SHS) is presented in this paper. This approach draws inspiration from the characteristics of Nepenthes pitcher plant structures, albeit without the need for intricate pore-making or nanowire structures. It is demonstrated that this resulting surface has exceptional fog harvesting capability, with a fog harvesting efficiency of 0.3222 g cm-2 min-1, which is twice as high as that of the laser aluminum (Al) sheet (0.1553 g cm-2 min-1). Moreover, the surface exhibits remarkable anti-icing properties, significantly prolonging the icing time by 21-fold compared to the pure Al sheet while maintaining a minimal ice adhesion force of only 0.16 N. Additionally, the surface showcases excellent antifouling performance, because contaminated droplets readily slide off without leaving residue. The environmentally friendly and straightforward preparation process ensures that it is suitable for large-scale industrial applications.

Comparison of Eco-Friendly Ionic Liquids and Commercial Bio-Derived Lubricant Additives in Terms of Tribological Performance and Aquatic Toxicity.

Approximately half of the lubricants sold globally find their way into the environment. The need for Environmentally Acceptable Lubricants (EALs) is gaining increased recognition. A lubricant is composed of a base oil and multiple functional additives. The literature has been focused on EAL base oils, with much less attention given to eco-friendly additives. This study presents the tribological performance and aquatic toxicity of four short-chain phosphonium-phosphate and ammonium-phosphate ionic liquids (ILs) as candidate anti-wear and friction-reducing additives for EALs. The results are benchmarked against those of four commercial bio-derived additives. The four ILs, at a mere 0.5 wt% concentration in a synthetic ester, demonstrated a 30-40% friction reduction and >99% wear reduction, superior to the commercial baselines. More impressively, all four ILs showed significantly lower toxicity than the bio-derived products. In an EPA-standard chronic aquatic toxicity test, the sensitive model organism, Ceriodaphnia dubia, had 90-100% survival when exposed to the ILs but 0% survival in exposure to the bio-derived products at the same concentration. This study offers scientific insights for the future development of eco-friendly ILs as lubricant additives.

On-demand bactericidal and self-adaptive antifouling hydrogels for self-healing and lubricant coatings of catheters.

Catheter-related infections are one of the most common nosocomial infections with increasing morbidity and mortality, and robust antibacterial or antifouling catheter coatings remain great challenges for long-term implantation. Herein, multifunctional hydrogel coatings were developed to provide persistent and self-adaptive antifouling and antibacterial effects with self-healing and lubricant capabilities. Polyvinyl alcohol (PVA) with ß-cyclodextrin (ß-CD) grafts (PVA-Cd) and 4-arm polyethylene glycol (PEG) with adamantane and quaternary ammonium compound (QAC) terminals (QA-PEG-Ad) were crosslinked through host-guest recognitions between adamantane and ß-CD moieties to acquire PVEQ coatings. In response to bacterial infections, QACs exhibit reversible transformation between zwitterions (pH 7.4) and cationic lactones (pH 5.5) to generate on-demand bactericidal effect. Highly hydrophilic PEG/PVA backbones and zwitterionic QACs build a lubricate surface and decrease the friction coefficient 10 times compared with that of bare catheters. The antifouling hydrated layer significantly inhibits blood protein adsorption and platelet activation and reveals negligible hemolysis and cytotoxicity. The dynamic host-guest crosslinking achieves full self-healing of cracks in PVEQ hydrogels, and the mechanical profiles were recovered to over 90 % after rejuvenating the broken hydrogels, exhibiting a long-term stability after mechanical stretching, twisting, knotting and compression. After subcutaneous implantation and local bacterial infection, the retrieved PVEQ-coated catheters display no tissue adhesion and 3 log folds lower bacterial number than that of bare catheters. PVEQ coatings effectively prevent the repeated bacterial infections and there are few inflammatory reactions in the surrounding tissue, while substantial lymphoid infiltration and inflammatory cell aggregation occur in muscle tissues around the bare catheter. Thus, this study demonstrates a catheter coating strategy by on-demand bactericidal, self-adaptive antifouling, self-healing and lubricant hydrogels to address medical devices-related infections. STATEMENT OF SIGNIFICANCE: It is estimated over two billion peripheral intravenous catheters are annually used in hospitals around the world, and catheter-associated infection has become a great clinical challenge with rapidly rising morbidity and mortality. Surface coating is considered a promising approach, but substantial challenges remain in the development of coatings that simultaneously satisfy both anti-fouling and antibacterial attributes. Even more, few attempts have been made to design mechanically robust coatings and reversible antibacterial or antifouling capabilities, which are critical for long-term medical implants. To address these challenges, we propose a concise strategy to develop hydrogel coatings from commercially available poly(ethylene glycol) and polyvinyl alcohol. In addition to self-healing and lubricant capabilities, the reversible conversion between zwitterionic and cationic lactones of quaternary ammonium compounds enables on-demand bactericidal and self-adaptive antifouling effects.

Evaluating the Impact of Rotary Instrument Lubricants on Dental Implant Osseointegration: An Experimental Rabbit Tibia Study.

Purpose: The osseointegration in dental implants is greatly affected by various surface properties, such as chemistry, texture, and overall cleanliness. This study aimed to investigate the impact of mineral oil lubricants used in rotary instruments on osseointegration within rabbit tibiae, with a specific focus on potential contamination from dental handpices. Materials and Methods: Twelve New Zealand rabbits were included in this study, each receiving two implants in each tibia, resulting in a total of 48 implants across the study. Groups were organized based on the time until euthanasia and the degree of implant contamination. Three contamination levels were defined: the first group received implants without any lubricant in the handpiece (control group); the second group received implants with handpices managed as recommended; the third group had implants placed using fixtures pre-soaked in lubricant. These groups were further subdivided based on euthanization periods of two and four weeks. We measured and analyzed both the removal torque and the bone-implant contact. Results: We observed a non-significant inverse correlation between the severity of fixture contamination and removal torque. However, there was a significant reduction in bone-implant contact associated with higher contamination levels, particularly after four weeks. Conclusions: Even brief exposure to lubricants from handpieces can jeopardize the osseointegration of implants in bone. Therefore, it is imperative to implement thorough procedures for lubricant removal post-application and to employ precise cleaning and suction during implant drilling and placement to minimize residual oil on the implant surface.

Simulation-based research on enhancing lubricity: investigating wettability and textured surfaces in alkane lubricants under boundary lubrication conditions.

Changing the wettability and surface texturing have a significant impact on lubrication. In this study, the researchers used the molecular dynamics method to investigate how adjusting the interaction between alkanes and the wall affects oil film morphology and frictional properties under boundary lubrication. The findings revealed that the bearing capacity was influenced by both the morphology of the oil film and the strength of solid-liquid adsorption. In cases where the walls had weak wettability, the alkanes formed clusters to effectively separate the walls, while in cases where the walls had strong wettability, the oil film spread and formed a strong adsorption film. The super oleophilic textured surface could enhance the oil film adsorption capacity and replenish the oil film to the friction area in time, and the super oleophobic smooth surface could further reduce the friction coefficient. Therefore, a composite surface consisting of a super oleophilic textured surface and a super oleophobic smooth surface can be designed to enhance the bearing capacity of the oil film and reduce friction.

The effect of carbomer versus noncarbomer lubricant on the adequacy of cervical cytology specimens.

INTRODUCTION: Cervical cytology remains a critical screening tool for cervical cancer. While various factors can influence cytology quality, the effect of lubricant type used during specimen collection has been previously studied with inconclusive results. This study aimed to evaluate the impact of surgical lubricant on cervical cytology results and elucidate risk factors associated with unsatisfactory results. We hypothesized that switching from a carbomer-containing lubricant to a noncarbomer, water-soluble lubricant would improve specimen adequacy in cervical cytology. MATERIALS AND METHODS: A retrospective chart review was performed examining patient cytologic results from January to December 2017 at a single academic institution. After historical rates of unsatisfactory cytology were higher than acceptable standards, the practice changed lubricant formulation from a carbomer containing lubricant to a noncarbomer, water soluble lubricant. Demographic data and treatment characteristics were collected for eligible patients. Matched analysis was performed to examine factors associated with an unsatisfactory cytology result. RESULTS: After the change in lubricant, there was a significant decline in the rates of unsatisfactory cytology from 9.6% to 5.7%, P = 0.01. This decline was also observed when patients were matched based on menopausal status, personal history of gynecologic malignancy, pregnancy status, and cytology specimen type (10.0% to 4.8%, P = 0.001). CONCLUSIONS: Change in lubricant from a carbomer containing to noncarbomer, water soluble product was associated with a statistically significant decline in the rates of unsatisfactory cytology. Although prior data have had mixed results as to the etiology of unsatisfactory cytology, we feel that this directly contributed to the high rates observed at our institution.

Impact of CuO nanoparticles on the viscosity and vibration damping characteristics of shock absorber oil.

This study investigates the potential of copper oxide (CuO) nanoparticles as additives to enhance the viscosity and vibration-damping characteristics of shock absorber oil. Shock absorbers play a critical role in vehicle safety and handling by mitigating vibrations from road irregularities. However, their effectiveness deteriorates over time. To address this, CuO nanoparticles were explored for their ability to improve lubricant performance. Nano-lubricants were prepared by dispersing CuO nanoparticles at varying concentrations of 0.25 wt%, 0.5 wt%, 1 wt%, and 1.5 wt% in a base oil using ultrasonication. The novelty of this research lies in the innovative use of CuO nanoparticles to significantly enhance the viscosity and vibration-damping properties of shock absorber oil. The viscosity of these nano-lubricants increased significantly, with the 1 wt% CuO nano-lubricant achieving a 20% increase at 25 °C compared to the base oil, indicating improved load-carrying capacity and potential friction reduction. Vibration damping performance was evaluated using a dedicated shock absorber test rig. The nano-lubricants exhibited reduced overall vibration acceleration compared to plain oil, with a 15% improvement in damping effectiveness at the optimal CuO concentration. However, the transmissibility ratio, a key damping metric, did not show significant variation, suggesting that traditional shock absorber designs might require modifications to fully leverage the benefits of CuO nanoparticles. These findings demonstrate the potential of CuO nanoparticles to enhance the viscosity and damping characteristics of shock absorber oil, leading to improved performance at lower temperatures.

Molecular Interaction Mechanisms Between Lubricant-Infused Slippery Surfaces and Mussel-Inspired Polydopamine Adhesive and DOPA Moiety.

Lubricant-infused slippery surfaces have recently emerged as promising antifouling coatings, showing potential against proteins, cells, and marine mussels. However, a comprehensive understanding of the molecular binding behaviors and interaction strength of foulants to these surfaces is lacking. In this work, mussel-inspired chemistry based on catechol-containing chemicals including 3,4-dihydroxyphenylalanine (DOPA) and polydopamine (PDA) is employed to investigate the antifouling performance and repellence mechanisms of fluorinated-based slippery surface, and the correlated interaction mechanisms are probed using atomic force microscopy (AFM). Intermolecular force measurements and deposition experiments between PDA and the surface reveal the ability of lubricant film to inhibit the contact of PDA particles with the substrate. Moreover, the binding mechanisms and bond dissociation energy between a single DOPA moiety and the lubricant-infused slippery surface are quantitatively investigated employing single-molecule force spectroscopy based on AFM (SM-AFM), which reveal that the infused lubricant layer can remarkably influence the dissociation forces and weaken the binding strength between DOPA and underneath per-fluorinated monolayer surface. This work provides new nanomechanical insights into the fundamental antifouling mechanisms of the lubricant-infused slippery surfaces against mussel-derived adhesive chemicals, with important implications for the design of lubricant-infused materials and other novel antifouling platforms for various bioengineering and engineering applications.

Investigating the Effects of Lubricant Infusion Methods on Polymer SLIPS.

Slippery lubricant infused porous surfaces (SLIPSs) are promising bioinspired surfaces with self-healing and droplet wetting properties, among many others, that are desirable due to their range of applications. Recently, there have been many developments in the SLIPS field regarding the creation of textured surfaces and lubricant selection. However, there is a lack of knowledge regarding the method of lubricant infusion. In this study, we aim to fill this void by investigating different infusion methods that impose external forces on the lubricant. We developed our SLIPS by hot embossing nanostructures onto polypropylene by using molds that were laser micromachined. These textured surfaces were then infused with silicone oil using three different infusion methods: ultrasonication, vacuum, and hydrostatic pressure. We analyzed the wettability and slipperiness of the SLIPS by evaluating the critical tilt angle and comparing the sliding velocities of water droplets on each sample at a tilt angle of 20°. Additionally, the durability of the SLIPS was tested by dropping 50 successive water drops onto the samples and evaluating the droplet-surface interactions throughout. The sonicated infusion method yielded SLIPS that performed the best with a contact angle hysteresis of 13°, a critical tilt angle of 18.3°, a sliding velocity of 1.66 mm/s, and the least accumulation of droplets over time with use. These values are greatly improved when compared to the control sample where lubricant was simply dripped on, which resulted in a contact angle hysteresis of 20°, a critical tilt angle of 26.3°, and a sliding velocity of 0.23 mm/s. The sonicated and drip infusion methods were also compared with different materials (stainless steel) and different textures (microstructures). It was found that the improvement in slipperiness using the sonicated infusion method is prominent for nanoscale textures on both stainless steel and polypropylene. In this study, we discuss the challenges with oil depletion in SLIPS (cloaking and wetting ridges) and with the selection of contact angle measurement methods. While further investigation as to why certain applied forces during infusion yield better SLIPS is warranted, these forces greatly affect the outcome. This work suggests that researchers should consider using sonication or other methods of lubricant infusion that apply external forces as infusion techniques to yield better SLIPS on the nanoscale.

Dynamic Directional Ultrasonically In Situ-Generated N,S-Codoped Carbon Dots in Poly(ethylene glycol) for Improved Tribological Performance.

The dispersion stability of nanomaterials in lubricants significantly influences tribological performance, yet their addition as lubricant additives often presents challenges in secondary dispersion. Here, we present a straightforward method for in situ preparation of N,S-codoped CDs (N,S-CDs)-based lubricants using heterocyclic aromatic hydrocarbons containing N/S elements in poly(ethylene glycol) (PEG) base oil by a directional ultrasound strategy. Two types of N,S-CDs were successfully prepared via the directional ultrasound treatment of PEG with benzothiazole (BTA) and benzothiadiazole (BTH) separately. The resultant N,S-CDs have a uniform distribution of N and S elements and maintain good colloidal dispersion stability in PEG even after 9 months of storage. The N,S-CDs can enter the surface gap of the friction pairs and then induce a tribochemical reaction. Benefiting from the synergistic effect of N and S activating elements, a robust and stable protective film consisting of iron sulfides, iron oxides, carbon nitrides, and amorphous carbonaceous compounds is formed, thus endowing N,S-CDs-based lubricants with improved antiwear and friction-reducing performance. Compared with pure PEG, the coefficient of friction (COF) of the N,S-CDs(BTH)-based lubricant decreased to 0.108 from 0.292, accompanied by a 91.2% reduction in wear volume, and the maximum load carrying capacity increased to 450 from 150 N.

Successful management of dry eye disease with a new eye drop formulation combining hyaluronic acid, trehalose, and N-acetyl-aspartyl-glutamic acid (NAAGA).

PURPOSE: To assess the clinical efficacy and safety of T2769, a new preservative-free eye drop combining hyaluronic acid (HA), trehalose and N-acetyl-aspartyl-glutamic acid (NAAGA), in dry eye patients. PATIENTS AND METHODS: This was a multicenter, non-comparative, open-label study. After a run-in period with NaCl 0.9% solution, 62 patients with moderate-to-severe dry eye disease (DED) were included and treated with T2769, 3 to 6 times/day for 42 days. The primary efficacy endpoint was the change in global ocular symptomatology assessed on a visual analog scale between Day 1 (D1) and D42. Other efficacy endpoints included ocular surface disease index (OSDI), soothing sensation, individual dry eye symptoms, conjunctival hyperemia, global ocular staining, tear break-up time, Schirmer test, and global efficacy assessed by the investigator. Safety was assessed throughout the study. RESULTS: A marked reduction in ocular symptomatology was observed from D1 to D42 with a mean change of -55.9±23.1mm (P<0.001). This was accompanied by a mean change in OSDI score from baseline of -44.6±15.9 (P<0.001) and a substantial soothing sensation in 82.3% of patients. Clinically significant improvements were observed for all ocular symptoms (mainly burning/irritation, stinging/pain, feeling of ocular dryness, foreign body sensation, itching/pruritus). Conjunctival hyperemia significantly decreased in 96.8% of patients (56.5% displayed no conjunctival hyperemia at D42 versus 0% at baseline). All signs and symptoms improved by D14 and further improved at D42. Investigators assessed the ocular efficacy of T2769 as very satisfactory or satisfactory for 91.9% of patients at D42. T2769 was well tolerated, with no ocular adverse events and only a few ocular symptoms upon instillation. CONCLUSION: Management of moderate-to-severe DED patients with the new formulation T2769, combining NAAGA to HA and trehalose, led to rapid and significant improvements in dry eye signs and symptoms with good tolerability.

Cyclotriphosphazene: A Versatile Building Block for Diverse Functional Materials.

Cyclotriphosphazene (CP) is a cyclic inorganic compound with the chemical formula N3P3. This unique molecule consists of a six-membered ring composed of alternating nitrogen and phosphorus atoms, each bonded to two chlorine atoms. CP exhibits remarkable versatility and significance in the realm of materials chemistry due to its easy functionalization via facile nucleophilic substitution reactions in mild conditions as well as intriguing properties of resultant final CP-based molecules or polymers. CP has been served as an important building block for numerous functional materials. This review provides a general and broad overview of the synthesis of CP-based small molecules through nucleophilic substitution of hexachlorocyclotriphosphazene (HCCP), and their applications, including flame retardants, liquid crystals (LC), chemosensors, electronics, biomedical materials, and lubricants, have been summarized and discussed. It would be expected that this review would offer a timely summary of various CP-based materials and hence give an insight into further exploration of CP-based molecules in the future.

Lubricant-Coated Organ-on-a-Chip for Enhanced Precision in Preclinical Drug Testing.

In drug discovery, human organ-on-a-chip (organ chip) technology has emerged as an essential tool for preclinical testing, offering a realistic representation of human physiology, real-time monitoring, and disease modeling. Polydimethylsiloxane (PDMS) is commonly used in organ chip fabrication owing to its biocompatibility, flexibility, transparency, and ability to replicate features down to the nanoscale. However, the porous nature of PDMS leads to unintended absorption of small molecules, critically affecting the drug response analysis. Addressing this challenge, the precision drug testing organ chip (PreD chip) is introduced, an innovative platform engineered to minimize small molecule absorption while facilitating cell culture. This chip features a PDMS microchannel wall coated with a perfluoropolyether-based lubricant, providing slipperiness and antifouling properties. It also incorporates an ECM-coated semi-porous membrane that supports robust multicellular cultures. The PreD chip demonstrates its outstanding antifouling properties and resistance to various biological fluids, small molecule drugs, and plasma proteins. In simulating the human gut barrier, the PreD chip demonstrates highly enhanced sensitivity in tests for dexamethasone toxicity and is highly effective in assessing drug transport across the human blood-brain barrier. These findings emphasize the potential of the PreD chip in advancing organ chip-based drug testing methodologies.

Micro- and Nanoengineered Metal Additively Manufactured Surfaces for Enhanced Anti-Frosting Applications.

The greater geometrical design freedom offered by additive manufacturing (AM) as compared to the conventional manufacturing method has attracted increasing interest in AM to develop innovative and complex designs for enhanced performance. However, the difference in material composition and surface properties from conventional alloys has made surface micro-/nanostructuring of AM metals challenging. Frost accretion is a safety hazard in numerous engineering applications. To expand the application of AM, this study experimentally investigates the antifrosting performance of superhydrophobic and slippery lubricant-infused porous surfaces (SLIPSs) generated on AM alloy, AlSi10Mg. By strategically utilizing the subgrain structure in the metallography of the AM alloy, the functionalized superhydrophobic AM surface featuring hierarchical structures was shown to greatly reduce frost formation as compared to functionalized single-tier structured surfaces, hierarchical structures formed on conventional aluminum alloy surfaces, and SLIPSs. Optical observation of frost propagation demonstrated that the mechanism of frost delay is governed by the inhibition of spontaneous droplet freezing through exceptional Cassie state stability during condensation frosting. The Cassie stability results from the unique AM structure morphology, which creates a higher structural energy barrier to prevent condensate from infiltrating the cavities. This phenomenon also enables the formation of a high surface-to-droplet thermal resistance, which eliminates spontaneous droplet freezing down to a -15 °C surface temperature. Our work demonstrates a scalable structuring method for AM metals, which can result in delayed frost formation, and it also provides guidelines for the development of engineered surfaces requiring the antifrosting function for several industries.

Covalent organic frameworks in tribology - A perspective.

Two-dimensional covalent organic frameworks (2D COFs) are an emerging class of crystalline porous materials formed through covalent bonds between organic building blocks. COFs uniquely combine a large surface area, an excellent stability, numerous abundant active sites, and tunable functionalities, thus making them highly attractive for numerous applications. Especially, their abundant active sites and weak interlayer interaction make these materials promising candidates for tribological research. Recently, notable attention has been paid to COFs as lubricant additives due to their excellent tribological performance. Our review aims at critically summarizing the state-of-art developments of 2D COFs in tribology. We discuss their structural and functional design principles, as well as synthetic strategies with a special focus on tribology. The generation of COF thin films is also assessed in detail, which can alleviate their most challenging drawbacks for this application. Subsequently, we analyze the existing state-of-the-art regarding the usage of COFs as lubricant additives, self-lubrication composite coatings, and solid lubricants at the nanoscale. Finally, critical challenges and future trends of 2D COFs in tribology are outlined to initiate and boost new research activities in this exciting field.

Express Method for Assessing Performance of Lubricant Compositions Containing Nano-Additives Used for Wheel-Rail Pairs.

An express method for assessing the effectiveness of lubricating compositions with nano-additives of various chemical compositions is proposed, and a joint analysis of experimental data on the changes in the value of wear and the level of damage to the surface layers of metallic friction pairs was performed. The variation in the current relative hardness of the sample's surface, the variation in the current relative material damage level, the current value of wear, and the current level of the coefficient of friction were chosen as the key parameters to conduct a performance assessment. The level of material damage in the contact zone was determined using the parameters of the statistical law of hardness value scattering. Based on an analysis of data in the literature, it was observed that the structural changes occurring in metallic materials during long-term, cyclic, static, and frictional loading are correlated with changes in the statistical characteristics of the hardness scattering results. An experimental substantiation of the proposed method was carried out for steel-sliding friction pairs using lubricating compositions based on Greaseline Lithium BIO Rail 000 oil manufactured by AIMOL with nano-additives of copper, magnesium and aluminum alloys, graphite, and two grades of medium-carbon steel. According to the system of indicators presented in this research, the greatest efficiency (in terms of increasing the wear resistance of friction steel pairs) was achieved with lubricating compositions including nano-powder additives made of steel, which have lower hardness. For the friction experiments, where the determining factor was abrasive wear, such lubricants ensured minimal damage and wear to the friction surface, while the value of the friction coefficient was maintained at a level that is optimal for wheel-rail friction pairs.