Search Results (3,949)

Wear remains a dominant cause of performance loss and premature failure in mechanical components, motivating the development of environmentally benign surface-engineering solutions. Among thermal spray systems, high-velocity oxy-fuel (HVOF)-sprayed WC-Co coatings are widely applied under severe wear conditions. The development of nanophase coatings offers the potential for enhanced mechanical performance. However, retaining the nanostructure and limiting decarburization during deposition remain key challenges. In this study, nanophase WC-12Co feedstocks with two particle size ranges, together with Al-modified nanophase powders, were used to deposit coatings under optimized HVOF spraying conditions (spray distance 200 mm, reduced O₂/fuel ratio, and high particle velocity) and were benchmarked against a conventional WC-12Co (12 wt.% Co) coating. The coatings were characterized in terms of microstructure and phase constitution (OM, SEM/EDS, XRD) as well as thickness, porosity (0.5–3.6%), adhesion strength (up to 65 MPa), and microhardness (~1040–1210 HV). Tribological behavior was assessed by ASTM G99 pin-on-disk testing and counterbody wear was quantified via geometric volume loss estimations. The use of larger nanophase particles enabled effective nanostructure retention with limited decarburization, whereas reducing particle size intensified decarburization, promoting increased W₂C formation, and markedly reduced coating cohesion, despite lower porosity and higher hardness. Aluminum additions enhanced coating microhardness and suppressed Co₃W₃C formation, indicating improved phase stability with minimal additional decarburization. Although coating wear remained negligible for all systems, Al-containing coatings exhibited increased friction (up to 35%) and significantly higher counterbody wear (up to sevenfold) compared to the Al-free nanophase coating, which was found to correlate with coating microhardness. Overall, the results demonstrate that optimizing nanophase WC-Co coatings requires balancing competing mechanisms between microstructural stability, cohesive integrity, and tribological response, highlighting the critical role of feedstock design in tailoring coating performance. Full article

Cellulose ether, like hypromellose (HM), is an extremely versatile material that is widely used in pharmaceutical products as film coatings. To modify the surface properties of HM films, additives are routinely included during the film formulation process, which are typically hydrophobic lubricants or hydrophilic plasticizers. Plasticizers increase the flexibility and reduce the brittleness of the film. The first goal of this study is to demonstrate that plasticization of HM films by low-molecular-weight (400 g∙mol⁻¹) polyethylene glycol (PEG) allows tuning adhesion and friction properties of HM films, both at nano- and macroscales. Surface morphology, surface energy, nano/macro adhesion, and nano/macro friction coefficient were studied by atomic force microscopy (AFM) in adhesion or friction modes at the nanoscale, wettability, and probe-tack adhesion, as well as pin-on-disk friction experiments at the macroscale. The results show that the addition of PEG decreases the Young’s modulus and the Tg of HM-plasticized films while increasing their strain at break and surface energy. The macroadhesion force increases from 9 to 90 mN by the addition of 40% w/w of PEG, whereas the macrofriction coefficient is reduced by 50%. The hypothesis of insertion of plasticizer molecules in HM chains’ nano-domains is evidenced and explains these results. The second goal of this study is to investigate nanoscale versus macroscale correlation of adhesion and friction properties and the role of adhesion in friction experiments. The results show, first, that the evolution of the adhesion energy at the macroscale as a function of adhesion energy at the nanoscale is linear. On the contrary, a high friction coefficient at the nanoscale corresponds to a low friction coefficient at the macroscale and vice versa, showing a first linear decrease for PEG contents ranging from 0 to 30% (w/w) and the second linear decrease, less pronounced, is observed for PEG contents ranging from 30 to 40% (w/w). The hypothesis of a difference in contact pressure applied on the probe at both scales, as well as HM-PEG surface phase separation at a high PEG content (>30% w/w), is proposed to explain this difference. The variations in friction coefficients are linear according to the PEG plasticizer content and suggest its lubricant role in HM-Plasticized films. Finally, the interplay between adhesion and friction, in friction experiments, is evidenced and appears dominant at the nanoscale. Full article

Background: Additive manufacturing provides a rapid and flexible alternative to conventional micromolding for producing microneedle systems. This study evaluates the potential of a cost-effective LCD 3D printer for fabricating microneedle arrays (MNAs) and investigates how the geometry of MNAs and the formulation of hydrogel influence the performance of lidocaine-coated arrays. Methods: Conical and pyramidal MNAs, along with a reservoir plate, were designed and manufactured. Lidocaine-loaded and placebo hydrogels with two different polymer concentrations were prepared for dip-coating using both single and multilayer applications. Mechanical resistance and insertion efficiency were evaluated under controlled compression. The physicochemical behavior of the hydrogels were characterized, including pH, spreadability, adhesiveness, and rheological behavior. The uniformity of the coating was analyzed using 3D confocal microscopy. Drug loading was quantified by HPLC, drug release was studied using Franz diffusion cells, and skin penetration was confirmed by 3D confocal imaging and Raman mapping. Results: Conical microneedles exhibited high mechanical integrity, showing only a 2% reduction in height compared to 4% for pyramidal MNAs. Stronger drug signals were achieved in deeper skin layers with the conical geometry, indicating enhanced penetration, while pyramidal MNAs provided slightly higher lidocaine loading due to their larger lateral surface. Hydrogels with higher polymer content produced more stable, uniform coatings, particularly when applied in three layers. Rapid drug release was observed, with over 70% of the drug delivered within minutes. Conclusions: LCD 3D printing offers a cost-effective approach for fabricating MNAs with suitable structural stability and sharpness. The optimized hydrogel formulation ensured uniform coverage, as well as maximal and consistence penetration, making this platform a promising candidate for the dermal delivery of other potent drugs. Full article

The poor tribological and mechanical performance of Al alloys hinders their use in practical applications where low COF and high durability are required. This study examined and evaluated a novel laser-sintered Ni-Cr coating to improve the load-carrying capacity and tribological performance of an Al alloy (Al 6061) substrate. The authors demonstrate that laser sintering cycle count is a decisive process variable governing coating dispersion, microstructural consolidation, and tribological performance in Ni-Cr coatings fabricated via Selective Laser Sintering (SLS). Increasing the laser cycle count progressively refined the surface morphology, improved coating dispersion, and strengthened interparticle bonding. As a result, the average durability after three cycles was seven times that after one laser cycle, accompanied by markedly improved COF. To further improve durability and load-carrying capacity, Ti₃SiC₂ was introduced into the Ni-Cr coating. The coating containing 10 wt% Ti₃SiC₂ exhibited a 20-fold increase in durability, extending the time to failure to approximately 70,000 s (700 m) while maintaining a low coefficient of friction (~0.48) compared with the coating containing no Ti₃SiC₂. The greater durability of the Ni-Cr-10wt%Ti₃SiC₂ coating in this novel study was attributed to improved adhesion to the substrate, better particle distribution during sintering, and greater load-carrying capacity. While further process changes do not yield feasible samples, this study showed that surface properties can be improved within the available small-process regime. Overall, laser sintering of a Ni-Cr-10wt%Ti₃SiC₂ coating shows promise as a means to improve the tribological and mechanical performance of Al 6061. This study should aid researchers and other stakeholders in fabricating well-adhering, durable, and tribotactic composite coatings on Al6061 and similar material systems. Full article

Magnesium alloys are promising materials for orthopedic applications due to their biodegradability and mechanical properties compatible with bone. However, their rapid degradation in physiological environments limits clinical use. In this study, WE43B magnesium alloy was coated with a PEO layer followed by a P(L/G/TMC) polymer applied via ultrasonic spraying. The influence of polymer layer number (10, 20, 30) on coating properties was systematically investigated. Scanning electron microscopy (SEM) analysis revealed an approximately fourfold reduction in porosity after polymer deposition, with progressive pore filling at higher layer numbers, while Fourier transform infrared spectroscopy (FT-IR) mapping indicated uniform polymer coverage. Compared to PEO alone, polymer-modified samples exhibited an approximately 7-fold increase in water contact angle, a ~50% reduction in surface roughness, and improved adhesion. Degradation-related analyses, including ion release, post-immersion SEM, and scanning acoustic microscopy (SAM), indicated that increasing polymer thickness effectively limited degradation processes. Ion release decreased by ~40–50% for the 30-layer coating compared to PEO, with the most pronounced reduction observed between the uncoated PEO and polymer-modified samples. These results demonstrate that the number of polymer layers plays a key role in controlling the barrier properties and stability of hybrid PEO/polymer coatings under simulated physiological conditions. Full article

Graphene solution was spin coated onto an aluminum substrate to investigate its tribological behavior compared to bare 6082–T6 aluminum alloy. The coefficient of friction (COF) was measured for varying loads (1–5 N) and sliding speeds (0.05–0.25 m/s) using a pin-on-disk tribometer in a ball-on-flat configuration. Results indicated that, under all tested conditions, the graphene coating reduced the COF by more than 70–80% compared to uncoated aluminum. Specifically, at 0.25 m/s and 1 N, the COF decreased from approximately 0.63 for uncoated aluminum to about 0.13 for the coated sample. The samples were analyzed using optical microscopy, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS), providing insights into morphology and composition. Furthermore, the coated samples exhibited a stable friction regime, with COF values consistently in the range of 0.10–0.15, while uncoated samples showed higher and more fluctuating values between 0.40 and 0.60. The graphene coating reached steady-state conditions within the first 50 m of sliding, in contrast to the pronounced running-in behavior of uncoated aluminum. SEM and EDS analyses confirmed the formation of a graphene transfer layer on the counterface, which maintained low friction even after partial coating removal. Additionally, the average coating thickness was approximately 15 μm, and the coating significantly reduced adhesive wear and material transfer, demonstrating its effectiveness as a sacrificial, self-lubricating tribological layer. Full article

Cr–N coatings are promising for severe-service applications owing to their high corrosion and wear resistance, yet their performance is governed by phase constitution and multilayer architecture. In this study, a monolithic Cr coating and three Cr-based multilayer coatings, Cr/Cr(N), Cr/Cr₂N, and Cr/CrN, were synthesized by a hybrid DCMS/HiPIMS process and systematically compared with respect to structure, mechanical properties, and oxidation behavior at 900 °C. XRD and TEM showed that Cr/Cr(N) was primarily characterized by a bcc Cr-type structure, while the N-containing layers exhibited slightly expanded lattice spacings relative to pure Cr; no Cr₂N precipitates were detected within the resolution of the analyses. Among the multilayers, Cr/Cr(N) provided the most favorable combination of hardness, adhesion, and indentation damage tolerance, reaching 885 HV and a critical scratch load of 80 N while maintaining damage tolerance comparable to monolithic Cr. By contrast, Cr/Cr₂N and Cr/CrN displayed more pronounced brittle damage and lower interfacial reliability. Upon oxidation at 900 °C, Cr and Cr/Cr(N) formed relatively compact Cr₂O₃ scales, whereas Cr/Cr₂N, and particularly Cr/CrN, experienced stronger oxidation-induced phase decomposition, blistering, and local delamination. These findings identify Cr(N) solid-solution sublayers as an effective alternative to brittle ceramic nitride layers. Full article

Preparing a highly wear-resistant AlTiN coating on a powder metallurgy (PM) M42 high-speed steel substrate is a key strategy to enhance tool performance and meet the demands of efficient machining. This study adopted a process route comprising substrate preparation, heat treatment regulation, and arc-PVD deposition of AlTiN coatings to systematically investigate the influence of sintering temperature (1130, 1160, and 1190 °C) and austenitizing time (1150 °C for 0, 15, 60, and 120 min) on the microstructure and mechanical properties of the substrate, as well as on the tribological performance of the AlTiN coatings. The results indicate that elevating the sintering temperature promotes densification of the matrix, with Vickers hardness increasing from 366 HV to 462 HV and bending strength (σ) increasing from 1064 MPa to 1310 MPa. The predominant carbide phases identified are MC, M₂C, and M₆C. During austenitizing, microstructural changes consistent with a progressive transformation from M₂C to MC and M₆C carbides were indicated by SEM and XRD analyses. Precipitation strengthening was most evident after 60 min, with hardness reaching 868 HV. In contrast, bending strength (σ) exhibited a progressive decline with increasing austenitizing time, decreasing from 1310 MPa to 1015 MPa after 120 min, illustrating a clear trade-off between hardness and toughness. The wear behavior of the coating is governed synergistically by substrate hardness, bending strength (σ), coating–substrate interfacial adhesion strength (L_C), and carbide phase transformation. Elevated substrate hardness enhances anti-wear performance; bending strength influences crack propagation and spallation tendency; and L_C determines the efficiency of interfacial load transfer. The carbide phase evolution appears to modulate the coating’s wear behavior by regulating both the microstructure and mechanical properties of the substrate. Among the six sample conditions evaluated, the A3 sample (sintered at 1190 °C and austenitized for 120 min) exhibited the lowest wear rate (2.38 × 10⁻⁶ mm³·N⁻¹·m⁻¹), demonstrating superior wear resistance. These findings provide a reference for process optimization and rational design of M42/AlTiN composite coating systems. Full article

Titanium and its alloys are used in dental and orthopedic implants. However, long-term stability remains a clinical challenge. To overcome this limitation, surface modification has been investigated to improve surface properties. Our previous study demonstrated that the immobilization of secretory leukocyte protease inhibitor (SLPI) on the titanium surface promotes osteoblast adhesion, proliferation, and differentiation in vitro. The current study demonstrated the first in vivo evaluation of SLPI as a bioactive coating for medical implants. Grade 5 titanium screws were coated with 10 µg/mL of recombinant human SLPI (rhSLPI) for 24 h via simple physical adsorption, and the results were preliminarily validated via FE-SEM and ELISA. These SLPI-coated titanium screws (TiSs) were then placed in the tibia of Sprague–Dawley rats for 4 and 8 weeks. The hematological and biochemical parameters (BUN, Creatinine, AST, and Troponin I) demonstrated no acute systemic alterations within the 8-week period across all groups. Moreover, micro-computed tomography (micro-CT) and histological analysis revealed significantly higher bone volume fraction (%BV/TV) at 4 weeks compared to uncoated controls (20.64% ± 2.452% vs. 11.73% ± 0.524%). Finally, the biomechanical stability of implants, assessed using the removal torque test, showed that TiSs showed higher strength compared to Ti at both 4 and 8 weeks. In conclusion, this study represents a novel approach to transitioning rhSLPI-coated titanium evaluation from in vitro models to an in vivo rat model. rhSLPI surface functionalization enhances early-stage osseointegration and improves implant mechanical stability without acute hematological and biochemical alterations. These proof-of-concept findings suggest the potential of SLPI as a bioactive coating strategy. Full article

Background/Objectives: Commercially available drug-eluting stents still suffer from poor blood compatibility, polymer coating delamination, polymer cracking and lack of stability during and after stent implantation that led to adverse events such as stent thrombosis and in-stent restenosis. This article highlights the advantages of using silicon nanofilament (SiNf) as an interface between stent surface and drug-in-polymer coating or bloodstream. Methods: Thin layer of SiNf was successfully formed on the surface of Co-Cr substrate via one-step simple method. For stent applications, sirolimus-in-poly(D,L-lactide) (PDLLA/SRL) matrix was coated on control and SiNf-modified Co-Cr substrates and the stability, cracking, and long-term degradation was compared. Blood compatibility studies were also compared between control and SiNf-modified Co-Cr substrates. Results: The morphology of the filaments showed nanosized structures with nano-gaps between the filaments which support mechanical interlocking of PDLLA/SRL coating and enhanced the coating stability with no coating delamination whereas, the control substrate presented 97% of coating delamination. The PDLLA/SRL coating on stent platform demonstrates smooth and uniform morphology without webbing between stent struts. After stent ballooning, the control stent presented cracking and peeling of the polymer coating from the surface whereas, the SiNf-modified stent did not show any signs of these unfavorable defects. Moreover, SiNf-modified surface showed reduced fibrinogen adsorption and lower number of platelet adhesion with round shape morphology. Conclusions: Overall, this suggests that modifying the metallic substrates with SiNf could act as a universal coating for reinforcing the polymer coating stability, prevent coating defects that accompany stent ballooning, and improve the blood compatibility of the material surfaces that could have various applications to medical implants and devices. Full article

Post-harvest economic losses in the strawberry industry are predominantly driven by disease caused by food-contaminating fungi and the loss of physicochemical quality. The gel-like matrix of the edible coating (EC) serves as a carrier for delivering lactic acid bacteria (LAB). This structured network, characterized by its excellent adhesion and film-forming stability, maintains fruit integrity and delivers antifungal properties to control pathogens. This study tested an exopolysaccharide coating with L. plantarum A6 to assess its impact on strawberry shelf life and quality stored at 4 °C and 30 °C for eight days. Through the analysis of physicochemical properties, it was possible to observe that weight loss increased during storage time in all treatments except for strawberries coated (CF) at 4 °C, with 2.43 ± 0.2%. Regarding firmness, after 8 days of storage the greatest difference occurred in the fruit uncoated (UF) exposed to 30 °C decreased 30.93%, whereas the CF group showed a reduction of 2.04%, showing a significant difference between these treatments (p < 0.05). However, the CF at 4 °C had a value of 3.98 ± 0.3 N after eight days of storage, which is close to that of fresh fruit, indicating the effectiveness of the coating. In terms of microbiological results, the mesophilic and mold counts were lower in the treatment at 4 °C with coating (3.6 log CFU/g and 4.48 log CFU/g) than in the treatment stored at 30 °C (5.78 log CFU/g and 6.04 log CFU/g). The shelf-life estimate determined that CF stored at 4 °C could be preserved for 15 days and those stored at 30 °C for 6 days. Finally, sensory evaluation determined that CF stored at 4 °C were well-accepted in terms of attributes such as taste, sweetness, firmness, and flavor. These findings underscore the effectiveness of coating, not only in improving the storage quality of strawberries, but also in ensuring their sensory acceptance. Full article

Graphene and its derivatives are widely recognized as effective reinforcements due to their unique mechanical, thermal and lubrication performance. Incorporation of these reinforcements into polyamide-imide (PAI) coating matrix has shown significant potential for improving the tribological performance. Here, the mechanisms underlying the tribological improvement enabled by graphene oxide (GO) are investigated via frictional experiments and molecular dynamics simulations. It was found that the coefficient of friction (COF) of PAI coating is reduced upon the addition of GO over the range of 100–400 MPa and 20–100 mm/s, with a maximum reduction of ~25% achieved at 200 MPa and 60 mm/s. Simulations reveal that the friction reduction arises from strong adhesion interactions between the embedded GO sheets and PAI molecular chains, which inhibit the shear-induced mobility of the chains during the friction process. This mechanism enables a further reduction in the COF of the GO/PAI composite coating by increasing the interfacial adhesion through the tailored modulations of surface morphology and chemistry of the GO sheets. These findings pave the way for advancing the rational design and application of graphene-based composite coatings with highly improved tribological performance. Full article

Streptococcus canis is an opportunistic pathogen that colonises the mucosal surfaces and skin of its host. Though predominantly a veterinary pathogen affecting cats and dogs, S. canis has also been identified as the causative agent in severe human disease. IdeC is a secreted cysteine protease of S. canis that has a high specificity for IgG, cleaving at the hinge region. We show here that the protein binds back to the surface of the bacteria. Additionally, the protein contains a conserved Arg-Gly-Asp (RGD) motif, the minimal peptide sequence required for integrin binding. Several bacterial proteins containing RGD motifs have been implicated in adhesion and invasion of host cells. This RGD motif along with the ability of IdeC to bind back to the bacterial surface after secretion is the basis for this study into a potential secondary function of IdeC in adhesion and/or invasion. We used protein-coated latex beads to investigate the interaction of IdeC with epithelial and endothelial cells and, further, the extent to which the RGD motif is involved in this interaction by utilising an RGD->RGE recombinant protein. We also report here that the deletion of IdeC in S. canis results in a significant reduction in invasion into epithelial cells. Full article

Biofilms rapidly form on medical devices such as urinary catheters and surgical materials. These biofilms compromise patient safety and undermine infection prevention and control (IPC). Biofilms also reduce the effectiveness of antibiotics and disinfectants. As a result, they increase healthcare-associated infections and increase costs through device failure and the need for maintenance or replacement. Researchers are increasingly exploring biosurfactants (BSs) as surface coatings and cleaning additives to prevent microbial attachment and disrupt early biofilm formation on medical devices and healthcare-related surfaces. This review examines the translational potential of biosurfactants as preventive, disruptive, and adjunctive antibiofilm agents for medical devices and healthcare-related surfaces. Literature evidence on glycolipids (rhamnolipids, sophorolipids) and lipopeptides (surfactin) from static, flow-based, and microfluidic in vitro models that used clinically relevant materials, such as silicone and polydimethylsiloxane (PDMS), were examined. In our literature search, we focused on pathogens central to IPC, such as Staphylococcus aureus, Pseudomonas aeruginosa, Enterococcus spp., and Candida spp., and it was generally noted that BSs reduced microbial adhesion and delayed early biofilm formation on medical devices and healthcare-related surfaces. Significant evidence also suggests that they partially disrupt biofilms and improve antimicrobial penetration when co-applied, mainly through membrane disruption, destabilization of extracellular substances, interfering with quorum sensing, and synergistic and/or antagonistic interactions with other molecules. Their performance varied with class, formulation, hydrodynamic conditions, and microbial composition. BSs function better as preventive and adjunctive IPC tools than stand-alone antimicrobial agents and can help to reduce biofilm formation on devices and improve surface disinfection. However, translating this promise into practice demands more robust data on long-term safety, stability, and product quality. Full article

This study investigates the causes and mechanisms of a corrosion-induced perforation failure in P110 tubing from a nitrogen injection well in the Tahe Oilfield. A comprehensive analysis was performed using macroscopic examination, mechanical and chemical property testing, characterization of corrosion product morphology and composition, and electrochemical measurements. The results show that the tubing material met all relevant standard requirements, ruling out intrinsic material defects as a contributing factor. The primary cause of failure was the breakdown of the internal coating. Poor coating adhesion in the older tubing from the shallow section, combined with the tensile stress from the tubing’s suspended weight and the acidic service environment, led to coating blistering and disbondment, thereby exposing the underlying steel. In the presence of H₂S, CO₂, and O₂, severe electrochemical corrosion developed on the exposed metal surface. The process was further accelerated by a high concentration of Cl⁻, which promoted rapid localized corrosion and ultimately resulted in perforation. Based on these findings, several targeted mitigation strategies are proposed. These include optimizing the coating process to improve adhesion and modifying the corrosive environment. The recommendations provide practical guidance for corrosion control in similar oil and gas well applications. Full article