Antimicrobial Polymeric Surfaces Using Embedded Silver Nanoparticles.

Pathogens (disease-causing microorganisms) can survive up to a few days on surfaces and can propagate through surfaces in high percentages, and thus, these surfaces turn into a primary source of pathogen transmission. To prevent and mitigate pathogen transmission, antimicrobial surfaces seem to be a promising option that can be prepared by using resilient, mass-produced polymers with partly embedded antimicrobial nanoparticles (NPs) with controlled size. In the present study, a 6 nm thick Ag nanolayer was sputter deposited on polycarbonate (PC) substrate and then thermally annealed, in a first step at 120 °C (temperature below Tg) for two hours, for promoting NP diffusion and growth, and in a second step at 180 °C (temperature above Tg) for 22 h, for promoting thermal embedding of the NPs into the polymer surface. The variation in the height of NPs on the polymer surface with thermal annealing confirms the embedding of NPs. It was shown that the incorporation of silver nanoparticles (Ag NPs) had a great impact on the antibacterial capacity, as the Ag NP-embedded polymer surface presented an inhibition effect on the growth of Gram-positive and Gram-negative bacteria. The tested surface-engineering process of incorporating antimicrobial Ag NPs in a polymer surface is both cost-effective and highly scalable.

Effect of Annealing Heat Treatment on the Composition, Morphology, Structure and Mechanical Properties of the W-S-N Coatings.

Alloyed-transition metal dichalcogenide (TMD) coatings have been under investigation as multi-environment lubricants for the past few decades. These coatings display very low coefficient of friction properties at elevated temperatures. Studies on the annealing of these low-friction coatings are missing in the literature. For the first time, in this study, the annealing of the W-S-N dry lubricant coatings was carried out to study its effects on the composition, morphology, crystal structure and hardness of the coatings. The W-S-N coatings were deposited by direct current (DC) reactive magnetron sputtering. The analysis was carried out for as-deposited, 200 °C and 400 °C annealed coatings. The as-deposited coatings have N content in the range of 0-25.5 at. %. The coatings are compact and the densification increased with the increase in N-alloying. All the coatings are crystalline except the highest N-alloyed coating which is X-ray amorphous. A maximum hardness of 8.0 GPa was measured for the coating alloyed with 23 at. % N. Annealing did not affect the composition and morphology of the coatings, while some variations were observed in their crystal structure and hardness. The maximum hardness increased from 8 GPa to 9.2 GPa after 400 °C annealing of the 23 at. % N-alloyed coating.

Immobilization of Streptavidin on a Plasmonic Au-TiO2 Thin Film towards an LSPR Biosensing Platform.

Optical biosensors based on localized surface plasmon resonance (LSPR) are the future of label-free detection methods. This work reports the development of plasmonic thin films, containing Au nanoparticles dispersed in a TiO2 matrix, as platforms for LSPR biosensors. Post-deposition treatments were employed, namely annealing at 400 °C, to develop an LSPR band, and Ar plasma, to improve the sensitivity of the Au-TiO2 thin film. Streptavidin and biotin conjugated with horseradish peroxidase (HRP) were chosen as the model receptor-analyte, to prove the efficiency of the immobilization method and to demonstrate the potential of the LSPR-based biosensor. The Au-TiO2 thin films were activated with O2 plasma, to promote the streptavidin immobilization as a biorecognition element, by increasing the surface hydrophilicity (contact angle drop to 7°). The interaction between biotin and the immobilized streptavidin was confirmed by the detection of HRP activity (average absorbance 1.9 ± 0.6), following a protocol based on enzyme-linked immunosorbent assay (ELISA). Furthermore, an LSPR wavelength shift was detectable (0.8 ± 0.1 nm), resulting from a plasmonic thin-film platform with a refractive index sensitivity estimated to be 33 nm/RIU. The detection of the analyte using these two different methods proves that the functionalization protocol was successful and the Au-TiO2 thin films have the potential to be used as an LSPR platform for label-free biosensors.

Cr-Based Sputtered Decorative Coatings for Automotive Industry.

The present work aims to study the impact of O and N addition on Cr-sputtered coatings on plastic (polycarbonate, PC) used in automobile parts, as a promisor alternative for auto part metallization, while eliminating the usage of toxic hexavalent chromium. The coatings were deposited using DC magnetron sputtering from a single pure Cr target in a reactive atmosphere (N2 and/or O2). The deposition of the coatings was performed maintaining the total pressure constant and close to 1 Pa by tuning Ar pressure while reactive gases were added. The target current density was kept at JW = 20 mA·cm-2. Structural characterization revealed a mixture of α-Cr, δ-Cr, ß-Cr2N, and CrN crystalline structures as well as amorphous oxides. The coating hardness ranged from 9 GPa for the CrON coating to 15 GPa for the CrN coating. All deposited coatings showed a particularly good interface adhesion; adjusting the amount of O and N made it possible to tune the optical properties of the Cr-based coatings as desired. The promising results open future industrialization of sputtered Cr-based coatings for automotive industries.

Robust LSPR Sensing Using Thermally Embedded Au Nanoparticles in Glass Substrates.

The poor adhesion and chemical and thermal stability of plasmonic nanostructures deposited on solid surfaces are a hindrance to the longevity and long-term development of robust localized surface plasmon resonance (LSPR)-based systems. In this paper, we have deposited gold (Au) nanolayers with thicknesses above the percolation limit over glass substrates and have used a thermal annealing treatment at a temperature above the substrate's glass transition temperature to promote the dewetting, recrystallization, and thermal embedding of Au nanoparticles (NPs). Due to the partial embedding in glass, the NPs were strongly adherent to the surface of the substrate and were able to resist to the commonly used cleaning procedures and mechanical adhesion tests alike. The reflectivity of the embedded nanostructures was studied and shown to be strongly dependent on the NP size/shape distributions and on the degree of NP embedding. Strong optical scattering bands with increasing width and redshifted LSPR peak position were observed with the Au content. Refractive index sensitivity (RIS) values between 150 and 360 nm/RIU (concerning LSPR band edge shift) or between 32 and 72 nm/RIU (concerning LSPR peak position shift) were obtained for the samples having narrower LSPR extinction bands. These robust LSPR sensors can be used following a simple excitation/detection scheme consisting of a reflectance measurement at a fixed angle and wavelength.

On the Microstructural, Mechanical and Tribological Properties of Mo-Se-C Coatings and Their Potential for Friction Reduction against Rubber.

Friction and wear contribute to high energetic losses that reduce the efficiency of mechanical systems. However, carbon alloyed transition metal dichalcogenide (TMD-C) coatings possess low friction coefficients in diverse environments and can self-adapt to various sliding conditions. Hence, in this investigation, a semi-industrial magnetron sputtering device, operated in direct current mode (DC), is utilized to deposit several molybdenum-selenium-carbon (Mo-Se-C) coatings with a carbon content up to 60 atomic % (at. %). Then, the carbon content influence on the final properties of the films is analysed using several structural, mechanical and tribological characterization techniques. With an increasing carbon content in the Mo-Se-C films, lower Se/Mo ratio, porosity and roughness appeared, while the hardness and compactness increased. Pin-on-disk (POD) experiments performed in humid air disclosed that the Mo-Se-C vs. nitrile butadiene rubber (NBR) friction is higher than Mo-Se-C vs. steel friction, and the coefficient of friction (CoF) is higher at 25 °C than at 200 °C, for both steel and NBR countersurfaces. In terms of wear, the Mo-Se-C coatings with 51 at. % C showed the lowest specific wear rates of all carbon content films when sliding against steel. The study shows the potential of TMD-based coatings for friction and wear reduction sliding against rubber.

Nanotribological Investigation of Sliding Properties of Transition Metal Dichalcogenide Thin Film Coatings.

Transition metal dichalcogenide (TMD)-based coatings are known for their low friction performance, which is attributed to the formation of a tribolayer consisting almost exclusively of pure well-ordered TMD. However, the formation of such a tribolayer and its wear track coverage is still unknown. In this study, we employed surface mapping and nanotribological techniques to study the properties of the wear tracks of composite W-S-C coatings. Our analysis revealed that the as-deposited coating consisted of two phases, with significantly different nanoscale frictional properties. We attributed the phases to nanocrystalline WS2 (low friction) and amorphous solution of carbon and WS2 (high friction). The two phases wear at different rates, especially at lower loads, where we observed faster depletion of nanocrystalline WS2. In the wear track, sparse flat WS2 flakes were identified, suggesting that the recrystallization of the WS2 phase occurs only at the spots where the contact pressure is the highest.

Mechanical Properties and Vacuum Tribological Performance of Mo-S-N Sputtered Coatings.

MoS2 is the most widely used dry lubricant for low friction applications in vacuum environments. However, due to its lamellar nature it exfoliates during sliding, leading to high wear, high coefficient of friction (COF), and low stability. Here, we report the mechanical properties and the vacuum (10-4 Pa) tribological performance of nitrogen-alloyed transition-metal-dichalcogenide (TMD-N) coatings. The coatings were deposited using a hybrid deposition method, that is, reactive direct current (DC) sputtering of MoS2 target assisted by an additional plasma source. The tribological tests were performed at relatively low contact stresses to replicate real industrial needs. The interaction between different mating surfaces (coating versus steel, coating versus coating) has been reported. Additionally, the effects of loads on the sliding properties were also studied for coating versus coating interactions. A maximum hardness of 8.9 GPa was measured for the 37 atom % N-alloyed coating. In all mating conditions, the pure MoS2 coating had COF in the range of 0.1-0.25 and the least specific wear rates were found to be 3.0 × 10-6 mm3/N·m for flat and 2.5 × 10-6 mm3/N·m for cylinder. As compared to MoS2 coating, the COF and specific wear rates decreased with N additions. The COF was in the range of 0.05-0.1 for Mo-S-N coatings, while coating versus coating displayed the lowest specific wear rates (8.6 × 10-8 mm3/N·m for flat and 4.4 × 10-8 mm3/N·m for cylinder). Finally, the increase in load resulted in a decrease of COF, but an increase in the wear rate was observed. The detailed mechanism behind the behavior of the COF for the different mating conditions was presented and discussed. This work brings some important issues when testing transition metal dichalcogenide-based coatings under low contact stress conditions more appropriate for simulating real service applications.

Antibacterial Effects of Bimetallic Clusters Incorporated in Amorphous Carbon for Stent Application.

The purpose of this work is the development of Ag/a:C and Ag-Au/a:C coatings for ureteral stents, to provide them with antimicrobial characteristics. Silver was selected because of its well-known antibacterial properties, while gold was included to assess its capacity to accelerate the silver ion release forming a galvanic couple between Au and Ag. Thus, the metallic (Ag) and bimetallic clusters (Ag-Au) were produced by three different configurations: (i) unbalanced magnetron sputtering (conventional sputtering), (ii) plasma gas condensation process, and by (iii) a combination between both previous approaches. Coatings with Ag-Au bimetallic clusters were characterized by transmission electron microscopy (TEM) in order to study the arrangement (alloy, core-shell, and galvanic couple) of these particles in the carbon matrix. Inductively coupled plasma optical emission spectroscopy (ICP-OES) was used to quantify the Ag ions released through artificial urine from the different coatings deposited on thermoplastic polyurethane tape (one of the materials used in the manufacture of the ureteral stent ). Then, the antibacterial and cytotoxicity properties of Ag and Ag-Au/a:C coatings were evaluated. TEM shows that a biphasic structure was not detected, thus not allowing to anticipate the establishment of a galvanic couple. The ICP-OES results demonstrate that the silver ionization is mainly a function of the amount of silver incorporated in the amorphous carbon (a:C) matrix, and the formation of a bimetallic alloy has a detrimental effect on release of the silver ions. The antibacterial activity was regulated by the silver ionization mechanisms because the coatings with higher Ag release had a higher antibacterial activity.

Au-WO3 Nanocomposite Coatings for Localized Surface Plasmon Resonance Sensing.

Localized surface plasmon resonance (LSPR) gas sensors are gaining increasing importance due to their unique tuneable functional properties. Au-WO3-x nanocomposite coatings, in particular, can be outstandingly sensitive to many different gases. However, a proper understanding of their optical properties and the way in which those properties are correlated to their structure/microstructure, is still needed. In this work, Au-WO3 nanocomposite coatings, with Au contents between 0-11 atomic percent, were grown using reactive magnetron co-sputtering technique and were characterized concerning their optical response. The precipitation of Au nanoparticles in the oxide matrix was promoted through thermal annealing treatments until 500 °C. Along with the Au nanoparticles' morphological changes, the annealing treatments stimulated the crystallization of WO3, together with the appearance of oxygen-deficient WO3-x phases. Through theoretical simulations, we have related the LSPR effect with the different structural and morphological variations (namely, size and distribution of the nanoparticles and their local environment), which were a function of the Au content and annealing temperature. Our results suggest that local voids were present in the vicinity of the Au nanoparticles, for all temperature range, and that they should be present in a wide variety of Au-WO3 nanocomposites. A theoretical study concerning the refractive index sensitivity was carried out in order to predict the optimal coating design parameters for gas sensing experiments.

Local Response of Sialoliths to Lithotripsy: Cues on Fragmentation Outcome.

Lithotripsy methods show relatively low efficiency in the fragmentation of sialoliths compared with the success rates achieved in the destruction of renal calculi. However, the information available on the mechanical behavior of sialoliths is limited and their apparently tougher response is not fully understood. This work evaluates the hardness and Young's modulus of sialoliths at different scales and analyzes specific damage patterns induced in these calcified structures by ultrasonic vibrations, pneumoballistic impacts, shock waves, and laser ablation. A clear correlation between local mechanical properties and ultrastructure/chemistry has been established: sialoliths are composite materials consisting of hard and soft components of mineralized and organic nature, respectively. Ultrasonic and pneumoballistic reverberations damage preferentially highly mineralized regions, leaving relatively unaffected the surrounding organic matter. In contrast, shock waves leach the organic component and lead to erosion of the overall structure. Laser ablation destroys homogeneously the irradiated zones regardless of the mineralized/organic nature of the underlying ultrastructure; however, damage is less extensive than with mechanical methods. Overall, the present results show that composition and internal structure are key features behind sialoliths' comminution behavior and that the organic matter contributes to reduce the therapeutic efficiency of lithotripsy methods.

Complex frictional analysis of self-lubricant W-S-C/Cr coating.

Transition metal dichalcogenides belong to one of the most developed classes of materials for solid lubrication. However, one of the main drawbacks of most of the self-lubricating coatings is their low load-bearing capacity, particularly in terrestrial atmospheres. In our previous work, alloying thin films based on tungsten disulfide with non-metallic interstitial elements, such as carbon or nitrogen, has been studied in order to improve tribological performance in different environments. Excellent results were reached with the deposited coatings hardness, in some cases, more than one order of magnitude higher than single W-S films. In this work, W-S-C films were deposited with increasing Cr contents by co-sputtering chromium and composite WS2-C and targets. Two films were prepared with approx. 7 and 13 at.% of Cr. Alloying with chromium led to dense films with amorphous microstructure; the hardness and adhesion was improved. Sliding tests were carried out in dry and humid air using a pin-on-disc tribometer with 100Cr6 steel balls as a counterpart. To analyse the sliding process, the surfaces in the contact were investigated by X-ray photoelectron spectroscopy (bonding), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. Surface and sub-surface structural modification of the coating and composition of the transferred tribolayer are discussed in detail. High friction in humid air was attributed to the absence of a well-ordered WS2 sliding interface. On the other hand, the existence of such an interface explained the very low friction observed in dry air.