Theoretical models for surface forces and adhesion and their measurement using atomic force microscopy

Transcending Lifshitz Theory: Reliable Prediction of Adhesion Forces between Hydrocarbon Surfaces in Condensed Phases Using Molecular Contact Thermodynamics

Lifshitz theory is widely used to calculate interfacial interaction energies and underpins established approaches to the interpretation of measurement data from experimental methods including the surface forces apparatus and the atomic force microscope. However, a significant limitation of Lifshitz theory is that it uses the bulk dielectric properties of the medium to predict the work of adhesion. Here, we demonstrate that a different approach, in which the interactions between molecules at surfaces and in the medium are described by a set of surface site interaction points (SSIPs), yields interaction free energies that are correlated better with experimentally determined values. The work of adhesion W(Lifshitz) between hydrocarbon surfaces was calculated in 260 liquids using Lifshitz theory and compared with interaction free energies ΔΔG calculated using the SSIP model. The predictions of these models diverge in significant ways. In particular, ΔΔG values for hydrocarbon surfaces are typically small and vary little, but in contrast, W(Lifshitz) values span 4 orders of magnitude. Moreover, the SSIP model yields significantly different ΔΔG values in some liquids for which Lifshitz theory predicts similar values of W(Lifshitz). These divergent predictions were tested using atomic force microscopy. Experimentally determined works of adhesion were closer to the values predicted using the SSIP model than Lifshitz theory. In mixtures of methanol and benzyl alcohol, even greater differences were found in the interaction energies calculated using the two models: the value of ΔΔG calculated using the SSIP model declines smoothly as the benzyl alcohol concentration increases, and values are well correlated with experimental data; however, W(Lifshitz) decreases to a minimum and then increases, reaching a larger value for benzyl alcohol than for methanol. We conclude that the SSIP model provides more reliable estimates of the work of adhesion than Lifshitz theory.

Pluronic P123/DMSO Lyotropic Liquid Crystal for Incorporating Bioactive Substances for Topical Application

Lyotropic liquid crystals (LLCs) have attracted considerably growing interest in drug delivery applications over the last years. The structure of LLC matrices is complementary to cell membranes and provides an efficient, controlled, and selective release of drugs. In this work, a complex of experimental methods was used to characterize binary LLCs Pluronic P123/DMSO and triple LLC systems Pluronic P123/DMSO/Ibuprofen, which are interesting as transdermal drug delivery systems. Liquid crystalline, thermal, and rheological properties of LLCs were studied. Concentration and temperature areas of the lyomesophase existence were found, and phase transition enthalpies were evaluated. Intermolecular interactions among the components were studied by infrared (IR) spectroscopy. In vitro studies of Ibuprofen (Ibu) release from various LLCs allow differentiation of its release depending on the polymer content. Atomic force microscopy and contact angle methods were used to characterize the surface morphology of the hydrophobic membrane, which was used as a stratum corneum model, and also evaluate the adhesion work of the LLCs. A complex analysis of the results provided by these experimental methods allowed revealing correlations between the phase behavior and rheological characteristics of the LLCs and release kinetics of ibuprofen. The proposed biocompatible systems have considerable potential for a transdermal delivery of bioactive substances.

Photoaged microplastics enhanced the antibiotic resistance dissemination in WWTPs by altering the adsorption behavior of antibiotic resistance plasmids

Growing concerns have raised about the microplastic eco-coronas in the ultraviolet (UV) disinfection wastewater, which accelerated the pollution of antibiotic resistance genes (ARGs) in the aquatic environment. As the hotspot of gene exchange, microplastics (MPs), especially for the UV-aged MPs, could alter the spread of ARGs in the eco-coronas and affect the resistance of the environment through adsorbing antibiotic resistant plasmids (ARPs). However, the relationship between the MP adsorption for ARPs and ARG spreading characteristics in MP eco-corona remain unclear. Herein, this study explored the distribution of ARGs in the MP eco-corona through in situ investigations of the discharged wastewater, and the adsorption behaviors of MPs for ARPs by in vitro adsorption experiments and in silico calculations. Results showed that the adsorption capacity of MPs for ARPs was enhanced by 42.7-48.0 % and the adsorption behavior changed from monolayer to multilayer adsorption after UV-aging. It was related to the increased surface roughness and oxygen-containing functional groups of MPs under UV treatment. Moreover, the abundance of ARGs in MP eco-corona of UV-treated wastewater was 1.33-1.55 folds higher than that without UV treatment, promoting the proliferation of drug resistance. DFT and DLVO theoretical calculations indicated that the MP-ARP interactions were dominated by electrostatic physical adsorption, endowing the aged MPs with low potential oxygen-containing groups to increase the electrostatic interaction with ARPs. Besides, due to the desorption of ARPs on MPs driven by the electrostatic repulsion, the bioavailability of ARGs in the MP eco-coronas was increased with pH and decreased with salinity after the wastewater discharge. Overall, this study advanced the understanding of the adsorption behavior of MPs for ARPs and provided inspirations for the evaluation of the resistance spread in the aquatic environment mediated by MP eco-coronas.

Effects of Temperature and Humidity on Energy Dissipation between Human Corneocytes and Nanoasperity Sliding Contacts

Human haptic perception relies on the ability of sensory receptors underneath the skin corneocyte layer to sense external load, where adhesion and friction play an essential role in nanoscale solid-solid contact. Energy dissipation present at the surface interface due to the change of separation distance during sliding contact was uncovered, but the energy dissipation of human finger skin cell-nanoprobe contact under humidity and temperature conditions has not been investigated yet. In this paper, the energy dissipation of skin corneocyte-nanoprobe interface under variation of both humidity, 0.05-80%RH, and temperature ranging from 25 to 40 °C is directly measured by atomic force microscopy (AFM). Analytical models of dissipation energy for this nanomaterial interface mechanism are developed, and the results are compared to the measured values. AFM measurements of dissipation energy reveal that the amount of dissipated energy caused by water meniscus stretching monotonically increases with humidity and temperature, resulting in adhesion and friction decreases. The purposed analytical model represents that dissipation energy trend.

Effects of tableting process parameters and powder lubrication levels on tablet surface temperature and moisture content

Punch sticking is a recurrent problem during the pharmaceutical tableting process. Powder moisture content plays a key role in the buildup of sticking; it evaporates due to increased tablet temperature, accumulates at the punch-tablet interface, and causes sticking through capillary force. This study investigated the effects of compaction pressure (CP), compaction speed (CS), and lubrication level (magnesium stearate (MgSt) ratio) on tablet surface temperature (TST) and tablet surface moisture content (TSMC). TST and TSMC were measured with an infrared thermal camera and near-infrared sensor, respectively. Microcrystalline cellulose was used as the tableting powder and MgSt as the lubricant. The low range of CS values (16-32 mm/s) considered in this study did not have significant effects on TST and TSMC. MgSt ratio had a significant positive effect on TST; this may be explained by the increase in powder blend effusivity with the addition of MgSt. However, MgSt ratio did not have a significant effect on TSMC. CP had a significant positive effect on both TST and TSMC. Increased CP induced higher heat generation through particle deformation and friction during the compaction phase, leading to increased TST. Furthermore, the water vapor diffusion rate through the powder bed might have increased due to the rise in thermal energy and led to further moisture accumulation at the tablet-punch interface, causing the significant positive effect of CP on TSMC. This result may explain the occurrence of sticking regardless of the CP applied during the tableting process.

Molecular Imprinting Technology Enables Proactive Capture of Nitrogen for Boosted Ammonia Synthesis under Ambient Conditions

Electrochemical nitrogen reduction reaction (NRR) is a burgeoning field for green and sustainable ammonia production, in which numerous potential catalysts emerge endlessly. However, satisfactory performances are still not realized under practical applications due to the limited solubility and sluggish diffusion of nitrogen at the interface. Herein, molecular imprinting technology is adopted to construct an adlayer with abundant nitrogen imprints on the electrocatalyst, which is capable of selectively recognizing and proactively aggregating high-concentrated nitrogen at the interface while hindering the access of overwhelming water simultaneously. With this favorable microenvironment, nitrogen can preferentially occupy the active surface, and the NRR equilibrium can be positively shifted to facilitate the reaction kinetics. Approximately threefold improvements in both ammonia production rate (185.7 µg h-1 mg-1 ) and Faradaic efficiency (72.9%) are achieved by a metal-free catalyst compared with the bare one. It is believed that the molecular imprinting strategy should be a general method to find further applicability in numerous catalysts or even other reactions facing similar challenges.

Non-contact non-resonant atomic force microscopy method for measurements of highly mobile molecules and nanoparticles

Atomic force microscopy (AFM) is nowadays indispensable versatile scanning probe method widely employed for fundamental and applied research in physics, chemistry, biology as well as industrial metrology. Conventional AFM systems can operate in various environments such as ultra-high vacuum, electrolyte solutions, or controlled gas atmosphere. Measurements in ambient air are prevalent due to their technical simplicity; however, there are drawbacks such as formation of water meniscus that greatly increases attractive interaction (adhesion) between the tip and the sample, reduced spatial resolution, and too strong interactions leading to tip and/or sample modifications. Here we show how the attractive forces in AFM under ambient conditions can be used with advantage to probe surface properties in a very sensitive way even on highly mobile molecules and nanoparticles. We introduce a stable non-contact non-resonant (NCNR) AFM method which enables to reliably perform measurements in the attractive force regime even in air by controlling the tip position in the intimate surface vicinity without touching it. We demonstrate proof-of-concept results on helicene-based macrocycles, DNA on mica, and nanodiamonds on SiO2. We compare the results with other conventional AFM regimes, showing NCNR advantages such as higher spatial resolution, reduced tip contamination, and negligible sample modification. We analyze principle physical and chemical mechanisms influencing the measurements, discuss issues of stability and various possible method implementations. We explain how the NCNR method can be applied in any AFM system by a mere software modification. The method thus opens a new research field for measurements of highly sensitive and mobile nanoscale objects under air and other environments.

Simultaneous quantification of Young's modulus and dispersion forces with nanoscale spatial resolution

Many advances in polymers and layered materials rely on a precise understanding of the local interactions between adjacent molecular or atomic layers. Quantifying dispersion forces at the nanoscale is particularly challenging with existing methods often time consuming, destructive, relying on surface averaging or requiring bespoke equipment. Here, we present a non-invasive method able to quantify the local mechanical and dispersion properties of a given sample with nanometer lateral precision. The method, based on atomic force microscopy (AFM), uses the frequency shift of a vibrating AFM cantilever in combination with established contact mechanics models to simultaneously derive the Hamaker constant and the effective Young's modulus at a given sample location. The derived Hamaker constant and Young's modulus represent an average over a small (typically <100) number of molecules or atoms. The oscillation amplitude of the vibrating AFM probe is used to select the length-scale of the features to analyse, with small vibrations able to resolve the contribution of sub-nanometric defects and large ones exploring effectively homogeneous areas. The accuracy of the method is validated on a range of 2D materials in air and water as well as on polymer thin films. We also provide the first experimental measurements of the Hamaker constant of HBN, MoT2, WSe2and polymer films, verifying theoretical predictions and computer simulations. The simplicity and robustness of the method, implemented with a commercial AFM, may support a broad range of technological applications in the growing field of polymers and nanostructured materials where a fine control of the van der Waals interactions is crucial to tune their properties.

Electric-Field-Induced Assembly of an Ionic Liquid-Water Interphase Enables Efficient Heavy Metal Electrosorption

Controlling ion desolvation, transport, and charge transfer at the electrode-electrolyte interface (EEI) is critical to enable the rational design of the efficient and selective separation of targeted heavy metals and the decontamination of industrial wastewater. The main challenge is to sufficiently resolve and interrogate the desolvation of solvated metal ions and their subsequent electroreduction at the EEI and establish pathways to modulate these intermediate steps to achieve efficient energy transfer for targeted reactive separations. Herein, we obtained a predictive understanding of modulating the desolvation and electrosorption of Pb2+ cations using the hydrophobic ionic liquid 1-ethyl-3-methylimidazolium chloride (EMIMCl) in aqueous electrolyte. We revealed the formation of a compact interphase layer consisting of EMIMCl-Pb complexes under an applied electric field using operando electrochemical Raman spectroscopy, atomic force microscopy, and electrochemical impedance spectroscopy measurements combined with classical molecular dynamics simulations. A lower negative potential was shown to result in the formation of a well-oriented layer with the positive imidazolium ring of EMIMCl lying perpendicular to the electrode and the hydrophobic alkyl chain extending into the bulk electrolyte. This oriented layer, which formed from a dilute concentration of EMIMCl added to the electrolyte, was demonstrated to facilitate desolvation of incoming solvated Pb2+ cations and decrease the charge transfer resistance for Pb electrodeposition, which has important implications for the selective removal of Pb from contaminated mixtures. Overall, our findings open up new opportunities to modulate ion desolvation using hydrophobic ionic liquids in aqueous electrolytes for efficient heavy-metal separation.

Structural stabilization of honeybee wings based on heterogeneous stiffness

Structural stabilization for a membrane structure under high-frequency vibration is still a recognized problem. In nature, honeybee wings with non-uniform material properties demonstrate excellent anti-interference ability. However, the correlation between the structural stabilization and mechanical properties of insect wings has not been completely verified. Here we demonstrate that the sclerotization diversity partially distinguishes the stiffness inhomogeneity of the wing structure. Furthermore, a wing cross-section model with diversity in elastic modulus is constructed to analyze the effect of stiffness distribution on stress optimization during flight. Our results demonstrate that the heterogeneous stiffness promotes the stress distribution and structural stabilization of the wing during flight, which may inspire more optimal designs for anisotropic high-strength membrane structures.

Strengthening Polylactic Acid by Salification: Surface Characterization Study

Polylactic acid (PLA) is one of the market's most commonly used biodegradable polymers, with diverse applications in additive manufacturing, specifically fused deposition modeling (FDM) 3D printing. The use of PLA in complex and sophisticated FDM applications is continually growing. However, the increased range of applications requires a better understanding of the material properties of this polymer. For example, recent studies have shown that PLA has the potential to be used in artificial heart valves. Still, the durability and longevity of this material in such a harsh environment are unknown, as heart valve failures have been attributed to salification. Additionally, there is a gap in the field for in situ material characterization of PLA surfaces during stiffening. The present study aims to benchmark different dynamic atomic force microscopy (AFM) techniques available to study the salification phenomenon of PLA at micro-scales using different PLA thin films with various salt concentrations (i.e., 10%, 15%, and 20% of sodium chloride (NaCl)). The measurements are conducted by tapping mode AFM, bimodal AFM, the force spectroscopy technique, and energy quantity analysis. These measurements showed a stiffening phenomenon occurring as the salt solution is increased, but the change was not equally sensitive to material property differences. Tapping mode AFM provided accurate topographical information, while the associated phase images were not considered reliable. On the other hand, bimodal AFM was shown to be capable of providing the topographical information and material compositional mapping through the higher eigenmode's phase channel. The dissipated power energy quantities indicated that how the polymers become less dissipative as salt concentration increases can be measured. Lastly, it was shown that force spectroscopy is the most sensitive technique in detecting the differences in properties. The comparison of these techniques can provide a helpful guideline for studying the material properties of PLA polymers at micro- and nano-scales that can prove beneficial in various fields.

Quantitative surface free energy with micro-colloid probe pairs

Measurement of the surface free energy (SFE) of a material allows the prediction of its adhesion properties. Materials can have microscale or sub-microscale surface inhomogeneities, engineered or random, which affect the surface macroscopic behaviour. However, quantitative characterization of the SFE at such length scales remains challenging in view of the variety of instruments and techniques available, the poor knowledge of critical variables and parameters during measurements and the need for appropriate contact models to derive the SFE from the measurements. Failure to characterize adhesion correctly may result in defective components or lengthy process optimization costing billions to industry. Conversely, for planar and homogeneous surfaces, contact angle (CA) measurements are standardized and allow for calculating the SFE using for example the Owen-Wendt model, relying only on the properties of the probing liquids. As such, we assessed and report here a method to correlate quantitative measurements of force-distance curves made with an atomic force microscope (AFM) and with silica and polystyrene (PS) colloidal probe pairs, with quantitative CA measurements and CA-derived SFE values. We measured five surfaces (mica, highly oriented pyrolytic graphite, thermally grown silica on silicon, silicon, and silicon with a super-hydrophobic coating), ranging from hydrophilic to super-hydrophobic, and found an excellent classification of the AFM measurements when these are represented by a set of principal components (PCs), and when both silica and PS colloidal probes are considered together. A regression of the PCs onto the CA measurements allows recovery of the SFE at the length scale of the colloidal probes, which is here ca. 1 micron. We found that once the PC-regression model is built, test sets of only ten AFM force-distance curves are sufficient to predict the local SFE with the calibrated silica and PS colloidal probes.

Antifungal Activity of Mycogenic Silver Nanoparticles on Clinical Yeasts and Phytopathogens

In this study, seven different silver nanoparticles (AgNPs) were obtained using the fungi species from the phylum Ascomycota, Aspergillus tubingensis, Aspergillus spp., Cladosporium pini-ponderosae, Fusarium proliferatum, Epicoccum nigrum, Exserohilum rostratum, and Bionectria ochroleuca, isolated from the Brazilian biodiversity, particularly from the mangrove and Caatinga biomes. The nanoparticles were coded as AgNP-AT, AgNP-Asp, AgNP-CPP, AgNP-FP, AgNP-EN, AgNP-ER, and AgNP-BO and characterized using spectrophotometry (UV-Vis), dynamic light scattering (DLS), zeta potential, transmission electron microcopy (TEM), and Fourier-transform infrared (FTIR) spectroscopy. All the AgNPs presented homogeneous size in the range from 43.4 to 120.6 nm (DLS) and from 21.8 to 35.8 nm (TEM), pH from 4.5 to 7.5, negative charge, and presence of protein coating on their surface. The antifungal activity of the AgNPs was evaluated on clinical strains of Candida albicans, and on the non-albicans species, Candida krusei, Candida glabrata, Candida parapsilosis, Candida tropicalis, and Candida guilliermondii, common in hospital infections, and against the phytopathogens Fusarium oxysporum, Fusarium phaseoli, Fusarium sacchari, Fusarium subglutinans, Fusarium verticillioides, and Curvularia lunata, which are species responsible for serious damage to agriculture production. The AgNPs were effective against the yeasts with MICs ranging from 1.25 to 40 µM and on the phytopathogens with MICs from 4 to 250 µM, indicating the promising possibility of application of these AgNPs as antifungal agents. The results indicated that the physicochemical parameters of the AgNPs, including the functional groups present on their surface, interfered with their antifungal activity. Overall, the results indicate that there is no specificity of the AgNPs for the yeasts or for the phytopathogens, which can be an advantage, increasing the possibility of application in different areas.

Experimental observation of metal-organic framework-polymer interaction forces and intercalation

We attach a MOF crystallite to an atomic force microscope cantilever to realize a system for rapidly and quantitatively studying the interaction between single-crystal MOFs and polymer films. Using this method, we find evidence of polymer intercalation into MOF pores. This approach can accelerate composite design.

Effect of decoration route on the nanomechanical, adhesive, and force response of nanocelluloses-An in situ force spectroscopy study

Although cellulose derivatives are widely applied in high-tech materials, the relation between their force responses and their surface chemical properties in a biological environment as a function of pH is unknown. Here, interaction forces of surface modified cellulose nanocrystals (CNCs), lignin residual cellulose nanocrystals (LCNCs), and 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose nanofibres (TCNFs) with OSO3-, COO- and lignin chemical groups were measured using in situ peak force quantitative nanomechanical mapping and force spectroscopy in salt solution at two pH values. We found that the forces acting between the tip and CNC or LCNC are steric dominated showing long range and slow decay as a result of their low surface charge density. High Mw lignin contributed to the increased repulsion range for LCNCs compared to CNCs. The repulsion measured for TCNFs at the very short range was electrostatic force dominating showing a steep decay attributed to its high surface charge density. In the case of TCNFs, electrostatic double layer force was also evidenced by the attraction measured at secondary minima. In all the three cases the electro steric interactions are pH dependent. Dissipation maps verified that the force behavior for each material was related to structural conformation restriction of the groups at compression. The slow decayed repulsion of CNCs or LCNCs is related to a weak restriction of conformational change due to small surface groups or high molecular weight bound polymers forming flat layers, whereas the steep repulsion of TCNFs is attributed to a strong conformation restriction of carboxylic groups occurred by forming extended structure. Our results suggest that the force responses of the materials were dominated by surface charges and structural differences. TCNFs showed superior nanomechanical and repulsion properties over CNCs or LCNCs at neutral pH.

Kinetics of polystyrene nanoplastic deposition on SiO2 and Al2O3 surfaces: Ionic strength effects

Nanoplastic pollution is an emerging environmental threat to the critical zone. The transport of nanoplastic particles in subsurface environments can be determined mainly by soil minerals because they provide surfaces that interact with nanoplastic particles. However, the interactions between mineral surfaces and nanoplastics are poorly understood. In this study, the deposition kinetics of polystyrene-nanoplastic particles onto representative oxide surfaces SiO2 and Al2O3 at circumneutral pH were investigated using a quartz crystal microbalance, with variations in the ionic strength (0.1-100 mM) of the well-dispersed nanoplastic particles suspension. While polystyrene-nanoplastic particles deposited minimally on the SiO2 surface at an ionic strength of < 100 mM (∼10 ng/cm2), substantial deposition occurred at 100 mM (3.7 ± 0.4 μg/cm2). On the Al2O3 surface, a significant amount of polystyrene-nanoplastic particle was deposited from the lowest ionic strength (4.5 ± 0.8 μg/cm2). The deposition mass at 100 mM NaCl was two times higher (7.2 ± 0.2 μg/cm2) than on the SiO2 surface, while the deposition rates were similar between the two surfaces (10-15 Hz/min). Our results indicate that alumina most likely exerts a stronger influence than quartz on the transport of nanoplastic particles in soils and groundwater aquifers. The deposition kinetics strongly depends on the mineral surface and solution ionic strength, and these quantitative results can serve as validation data in developing transport modeling of nanoplastic in subsurface environments.

Nanomechanical and Vibrational Signature of Chikungunya Viral Particles

Chikungunya virus (CHIKV) belongs to the genus Alphaviridae, with a single-stranded positive-sense RNA genome of 11.8 kbp encoding a polyprotein that generates both non-structural proteins and structural proteins. The virus is transmitted by the Aedes aegypti and A. albopictus mosquitoes, depending on the location. CHIKV infection leads to dengue-like musculoskeletal symptoms and has been responsible for several outbreaks worldwide since its discovery in 1952. Patients often experience fever, headache, muscle pain, joint swelling, and skin rashes. However, the ultrastructural and mechanical properties of CHIKV have not been fully characterized. Thus, this study aims to apply a physical approach to investigate CHIKV's ultrastructural morphology and mechanical properties, using atomic force microscopy and Raman spectroscopy as the main tools. Using nanomechanical assays of AFM and a gold nanoparticles substrate for Raman signal enhancement, we explored the conformational plasticity, morphology, vibrational signature, and nanomechanical properties of the chikungunya virus, providing new information on its ultrastructure at the nanoscale and offering a novel understanding of the virus' behavior upon mechanical disruptions besides its molecular composition.

Effects of interfacial dynamics on the damping of biocomposites

A damping model is developed based on the mechanism of interfacial interaction in nanoscale particle reinforced composites. The model includes the elasticity of the materials and the effects of interfacial adhesion hysteresis. Specific results are given for the case of bio-based PA610 polyamide reinforced by nanocrystalline cellulose (CNC), based on a previous study that showed this composite possesses very high damping. The presence of hydrogen bonding at the interface between the particle and matrix and the large interfacial area due to the filler's nano size are shown to be the main causes of the high damping enhancement. The influence of other parameters, such as interfacial distance and stiffness of the matrix materials are also discussed. The modeling work can be used as a guide in designing composites with good damping properties.

Gripping adhesive principles in the design of effectors

This article presents a basic study of knowledge in the research and development of specific gripping elements based on the principle of adhesion. It summarizes the use of materials with a high degree of surface adhesion in the design of gripping elements usable in industry to provide stable gripping of objects during automatic manipulation. The principle of a combined element proposed by the authors, where the gripping force is derived through both vacuum and adhesion, is presented. The conditions of operation in an active or completely passive mode without the need to connect an energy source are discussed in detail. In the active mode, a significant increase in gripping forces is demonstrated compared to standard vacuum elements, which has a positive effect on the amounts of compressed air consumed and the level of grip safety in production processes. To ensure the optimal function of the adhesive gripping elements, the design of a specifically designed fluid position compensator and an active system for disturbing the adhesive gripping forces is presented. The functionality of the designed element is demonstrated through several laboratory tests under various conditions, and the results clearly confirm an increase in gripping forces in the axial and in particular the radial direction of the load. The research includes the design of a computer model of deformation-adhesive contact, respecting the time dependence of the deformation of the adhesive layer and the gradual loss of contact with the object.

Article highlights:o

Experimental study presents use of PU materials in adhesive and combined gripping elements.

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Adhesive contact theory is applied for a numerical simulation and prepared computer model is subsequently verified.

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Authors present new proprietary solution of gripping element applicable in industrial robotics.

Anticancer peptides mechanisms, simple and complex

Peptide therapy has started since 1920s with the advent of insulin application, and now it has emerged as a new approach in treatment of diseases including cancer. Using anti-cancer peptides (ACPs) is a promising way of cancer therapy as ACPs are continuing to be approved and arrived at major pharmaceutical markets. Traditional cancer treatments face different problems like intensive adverse effects to patient's body, cell resistance to conventional chemical drugs and in some worse cases the occurrence of cell multidrug resistance (MDR) of cancerous tissues against chemotherapy. On the other hand, there are some benefits conceived for peptides usage in treatment of diseases specifically cancer, as these compounds present favorable characteristics such as smaller size, high activity, low immunogenicity, good biocompatibility in vivo, convenient and rapid way of synthesis, amenable to sequence modification and revision and there is no limitation for the type of cargo they carry. It is possible to achieve an optimum molecular and functional structure of peptides based on previous experience and bank of peptide motif data which may result in novel peptide design. Bioactive peptides are able to form pores in cell membrane and induce necrosis or apoptosis of abnormal cells. Moreover, recent researches have focused on the tumor recognizing peptide motifs with the ability to permeate to cancerous cells with the aim of cancer treatment at earlier stages. In this strategy the most important factors for addressing cancer are choosing peptides with easy accessibility to tumor cell without cytotoxicity effect towards normal cells. The peptides must also meet acceptable pharmacokinetic requirements. In this review, the characteristics of peptides and cancer cells are discussed. The various mechanisms of peptides' action proposed against cancer cells make the next part of discussion. It will be followed by giving information on peptides application, various methods of peptide designing along with introducing various databases. Future aspects of peptides for employing in area of cancer treatment come as conclusion at the end.

Solid state of inhalable high dose powders

High dose inhaled powders have received increased attention for treating lung infections. These powders can be prepared using techniques such as spray drying, spray-freeze drying, crystallization, and milling. The selected preparation technique is known to influence the solid state of the powders, which in turn can potentially modulate aerosolization and aerosolization stability. This review focuses on how and to what extent the change in solid state of high dose powders can influence aerosolization. It also discusses the commonly used solid state characterization techniques and the application of potential strategies to improve the physical and chemical stability of the amorphous powders for high dose delivery.

Wetting dynamics under periodic switching on different scales: characterization and mechanisms

The development of substrates with a switchable wettability is proceeding and the limit of switching frequencies and contact angle differences between substrate states has developed in the past years. In this paper we investigate the behavior of a droplet on a homogeneous substrate, which is switched between two wettabilities for a large range of switching frequencies. Here, we are particularly interested in the dependence of the wetting behavior on the switching frequency. We show that results obtained on the particle level via molecular dynamics simulations and on the continuum level via the thin-film model are consistent. Predictions of simple models as the molecular theory of wetting (MKT) and analytical calculations based on the MKT also show good agreement and offer deeper insights into the underlying mechanisms.

Activated Sintering of Cr2O3-Based Composites by Hot Pressing

The paper presents and discusses questions on structure formation during the sintering process of Cr₂O₃-based composites using the hot pressing method, when a chemical reaction between the components takes place. The task was difficult because Cr₂O₃ decomposes when sintered at temperatures above 1300 °C. The proposed novel method allowed for interaction between aluminum and chromia, thus avoiding the decomposition of the latter. Here, ultrafine aluminum powder played the role of the active agent forming a liquid phase and reacting with Cr₂O₃. The appearance of the solid solutions of (Cr,Al)₂O₃ with different stoichiometry of Cr and Al depended on the aluminum content in the initial mixture. The solid solution significantly strengthened boundaries between composite phases, resulting in the composite material of high fracture toughness between 5 and 7 MPa m^½ and bending strength of ca. 500 MPa. The best mechanical properties exhibited the cermet with 22 wt.% of the restored chromium.

Atomic force microscopy probing interactions and microstructures of ionic liquids at solid surfaces

Ionic liquids (ILs) are room temperature molten salts that possess preeminent physicochemical properties and have shown great potential in many applications. However, the use of ILs in surface-dependent processes, e.g. energy storage, is hindered by the lack of a systematic understanding of the IL interfacial microstructure. ILs on the solid surface display rich ordering, arising from coulombic, van der Waals, solvophobic interactions, etc., all giving near-surface ILs distinct microstructures. Therefore, it is highly important to clarify the interactions of ILs with solid surfaces at the nanoscale to understand the microstructure and mechanism, providing quantitative structure-property relationships. Atomic force microscopy (AFM) opens a surface-sensitive way to probe the interaction force of ILs with solid surfaces in the layers from sub-nanometers to micrometers. Herein, this review showcases the recent progress of AFM in probing interactions and microstructures of ILs at solid interfaces, and the influence of IL characteristics, surface properties and external stimuli is thereafter discussed. Finally, a summary and perspectives are established, in which, the necessities of the quantification of IL-solid interactions at the molecular level, the development of in situ techniques closely coupled with AFM for probing IL-solid interfaces, and the combination of experiments and simulations are argued.

Modeling the temporal evolution and stability of thin evaporating films for wafer surface processing

The interaction of thin evaporating fluid films with solids is studied using the example of water on LiTaO3 (LTO). Adsorption energies are computed by ab initio DFT and used to calculate the Gibbs free energy of adsorption of water on LTO. Integrating the disjoining pressure, consisting of molecular and structural components, with respect to film thickness gives an expression for the Gibbs free energy. In this way, parameters for the disjoining pressure can be calculated by fitting its integral to the Gibbs free energy computed by ab initio DFT. A combination of literature-known models for spin drying and evaporation is utilized to describe the temporal evolution of the water layer. The vapor above the water layer is modeled by diffusion and a mass balance is applied at the water-air interface. For thick initial layers, an analytical approximation is derived which only depends on fluid and ambient conditions but not on properties of the substrate.

Assembly of planar chiral superlattices from achiral building blocks

The spontaneous assembly of chiral structures from building blocks that lack chirality is fundamentally important for colloidal chemistry and has implications for the formation of advanced optical materials. Here, we find that purified achiral gold tetrahedron-shaped nanoparticles assemble into two-dimensional superlattices that exhibit planar chirality under a balance of repulsive electrostatic and attractive van der Waals and depletion forces. A model accounting for these interactions shows that the growth of planar structures is kinetically preferred over similar three-dimensional products, explaining their selective formation. Exploration and mapping of different packing symmetries demonstrates that the hexagonal chiral phase forms exclusively because of geometric constraints imposed by the presence of constituent tetrahedra with sharp tips. A formation mechanism is proposed in which the chiral phase nucleates from within a related 2D achiral phase by clockwise or counterclockwise rotation of tetrahedra about their central axis. These results lay the scientific foundation for the high-throughput assembly of planar chiral metamaterials.

The formation of nanostructures with chiral symmetry often requires chiral directing agents at a smaller length scale. Here, the authors report the self-assembly of 2D chiral superlattices from achiral tetrahedron-shaped building blocks.

Effect of TiO2 Nanoparticles on Capillary-Driven Flow in Water Nanofilters Based on Chitosan Cellulose and Polyvinylidene Fluoride Nanocomposites: A Theoretical Study

In this study, a novel concept of nanofiltration process of drinking water based on capillary-driven nanofiltration is demonstrated using a bio-based nanocomposites’ nanofilter as free power: a green and sustainable solution. Based on Lifshitz and Young–Laplace theories, we show that the chitosan (CS), cellulose acetate (CLA), and Polyvinylidene fluoride (PVDF) polymer matrixes demonstrate hydrophobic behavior, which leads to the draining of water from nanopores when negative capillary pressure is applied and consequently prevents the capillary-driven nanofiltration process. By incorporating 10%, 20%, and 30% volume fraction of titanium dioxide (TiO₂) nanoparticles (NPs) to the polymers’ matrixes, we demonstrate a wetting conversion from hydrophobic to hydrophilic behavior of these polymer nanocomposites. Subsequently, the threshold volume fraction of the TiO₂ NPs for the conversion from draining (hydrophobic) to filling (hydrophilic) by capillary pressure were found to be equal to 5.1%, 10.9%, and 13.9%, respectively, for CS/TiO₂, CLA/TiO₂, and PVDF/TiO₂ nanocomposites. Then, we demonstrated the negligible effect of the gravity force on capillary rise as well as the capillary-driven flow for nanoscale pore size. For nanofilters with the same effective nanopore radius, porosity, pore shape factor, and tortuosity, results from the modified Lucas–Washburn model show that the capillary rise as well as the capillary-driven water volume increase with increased volume fraction of the TiO₂ NPs for all nanocomposite nanofilter. Interestingly, the capillary-driven water volume was in range (5.26–6.39) L/h·m² with 30% volume fraction of TiO₂ NPs, which support our idea for capillary-driven nanofiltration as zero energy consumption nano-filtration process. Correspondingly, the biodegradable CS/TiO₂ and CLA/TiO₂ nanocomposites nanofilter demonstrate capillary-driven water volume higher, ~1.5 and ~1.2 times, respectively, more than the synthetic PVDF/TiO₂ nanocomposite.

An expert opinion on respiratory delivery of high dose powders for lung infections

INTRODUCTION

High dose powder inhalation is evolving as an important approach to to treat lung infections. It is important to its identify applications, consider the factors affecting high dose powder delivery, and assess the effect of high dose drugs in patients.

AREA COVERED

Both current and pipeline high dose inhalers and their applications have been summarized. Challenges and opportunities to high dose delivery have been highlighted after reviewing formulation techniques in the context of factors affecting aerosolization, devices, and patient factors.

EXPERT OPINION

High dose inhaled delivery of antimicrobials is an innovative way to increase treatment efficacy of respiratory infections, tackle drug resistance, and the scarcity of new antimicrobials. The high dose inhaled technology also has potential for systemic action; however, innovations in formulation strategies and devices are required to realize its full potential. Advances in formulation strategies include the use of excipients or the engineering of particles to decrease the cohesive property of microparticles and their packing density. Similarly, selection of a synergistic drug instead of an excipient can be considered to increase aerosolization and stability. Device development focused on improving dispersion and loading capacity is also important, and modification of existing devices for high dose delivery can also be considered.

Amino Acids Improve Aerosolization and Chemical Stability of Potential Inhalable Amorphous Spray-dried Ceftazidime for Pseudomonas aeruginosa Lung Infection

Pseudomonas aeruginosa infection is common in cystic fibrosis as well non-cystic fibrosis bronchiectasis. The pathogen presents challenges for treatment due to its adaptive antibiotic-resistance, mainly pertaining to its biofilm-forming ability, as well as limitations associated with conventional drug delivery in achieving desired therapeutic concentration in the infection site. Hence, therapeutic approach has shifted towards the inhalation of antibiotics. Ceftazidime is a potent antibiotic against the pathogen; however, it is currently only available as a parenteral formulation. Here, spray-dryer was employed to generate inhalable high dose ceftazidime microparticles. In addition, the use of amino acids (valine, leucine, methionine, phenylalanine, and tryptophan) to improve aerosolization as well as chemical stability of amorphous ceftazidime was explored. The particles were characterized using X ray diffraction, infrared (IR) spectroscopy, calorimetry, electron microscopy, particle size analyzer, and next generation impactor. The chemical stability at 25 °C/<15% was assessed using chromatography. All co-spray dried formulations were confirmed as monophasic amorphous systems using calorimetry. In addition, principal component analysis of the IR spectra suggested potential interaction between tryptophan and ceftazidime in the co-amorphous matrix. Inclusion of amino acids improved aerosolization and chemical stability in all cases. Increase in surface asperity was clear with the use of amino acids which likely contributed to the improved aerosol performance, and potential interaction between amino acids and ceftazidime was plausibly the reason for improved chemical stability. Leucine offered the best aerosolization enhancement with a fine particle fraction of 78% and tryptophan showed stabilizing superiority by reducing chemical degradation by 51% over 10 weeks in 1:1 molar ratio. The protection against ceftazidime degradation varied with the nature of amino acids. Additionally, there was a linear relationship between degradation protection and molar mass of amino acids or percentage weight of amino acids in the formulations. None of the amino acids were successful in completely inhibiting degradation of ceftazidime in amorphous spray-dried powder to prepare a commercially viable product with desired shelf-life. All the amino acids and ceftazidime were non-toxic to A549 alveolar cell line.

Experimental observations of the effects of intermolecular Van der Waal forces on entropy

An experimental effort was conducted to measure the change in internal energy of non-ideal carbon dioxide as its volume rapidly expanded with the sudden opening of a valve from one to two compressed gas cylinders. This was achieved by measuring the mass heat capacity of the gas cylinders and the manifold-valve, and measuring the change in temperature from the sudden doubling of volume of the non-ideal carbon dioxide. It was determined that an empirical equation for the change in internal energy of a non-ideal fluid was more accurate than previous methods used for estimating the change in internal energy by estimating the change in entropy. With this empirical equation, a theoretical ideal Stirling cycle heat engine that exceeds the Carnot efficiency was realized by utilizing non-ideal carbon dioxide as a working fluid.

Nonlinear charge regulation for the deposition of silica nanoparticles on polystyrene spherical surfaces

HYPOTHESIS

We describe the deposition behavior of monodispersed silica nanoparticles on polystyrene spherical particles by using modified pairwise DLVO (Derjaguin-Landau-Verwey-Overbeek) interaction force profiles at pH values between two and twelve. Our modified model contains a new nonlinear charge regulation parameter that considers redistribution of ions, which allows us to realistically express the electrical double layer (EDL) interaction forces.

EXPERIMENTS

Silanol-terminated silica nanoparticles (7.6 ± 0.4 nm), l-lysine-covered silica nanoparticles (7.8 ± 0.4 nm), and polyallylamine hydrochloride-covered polystyrene (PAH/PS) particles (348 ± 1 nm) were synthesized. Then, each type of silica nanoparticle was deposited on the PAH/PS particles at a range of pH values.

FINDINGS

Our new regulation parameter describes the realistic redistribution of charges governed by pH, total salt concentration, ionic strength of solution, and separation distance of particles. We find that this regulation parameter can be roughly approximated from the absolute values of theoretically calculated surface charge density and potential distributions, as well as experimentally measured ζ-potentials. Morphological analysis using electron microscopy of the experimental systems shows that the modified pairwise DLVO interaction forces exceptionally describe the deposition behavior of the silica nanoparticles physically adsorbed on the PAH/PS particle substrates.

Tuning the Charge and Hydrophobicity of Graphene Oxide Membranes by Functionalization with Ionic Liquids at Epoxide Sites

Functionalization of graphene oxide (GO) membranes is generally achieved using carboxyl groups as binding sites for ligands. Herein, by taking advantage of the ability of imidazolium-based ionic liquids (ILs) to undergo an epoxide ring-opening reaction, a new approach of GO modification was established, in which ILs were bonded to the abundant epoxides on GO without sacrificing the carboxyl groups. Computational methods confirmed this unique configuration of ILs on GO, which enabled the dispersion of IL/GO flakes in water for facile casting into laminate membranes. Compared with neat GO, the ILs in IL/GO membranes served as spacers that substantially reduced the multi-valent cation mobility, simultaneously facilitated ion desolvation, and increased the water flux across the membrane. Our studies found that the higher separation efficiency of IL/GO membranes may be attributed to the synergistic modification of the hydrophobicity and surface charge. Specifically, the protonated nitrogen of the imidazolium cations altered the surface charge of GO, thereby generating electrostatic repulsion that enhanced the selectivity of cation rejection. On the other hand, the increased length of the alkyl chains bound to the imidazolium rings was found to increase the hydrophobicity of GO, which, in turn, aided the fine-tuning of the water desolvation/transport dynamics at the GO/IL interface to achieve a high water flux. Additionally, the water retention was reduced on the hydrophobic planes, which inhibited GO swelling during aqueous separations. Molecular dynamics simulations revealed increased water diffusivity when ILs were intercalated within GO layers. We establish that without requiring a high energy input, functionalization of GO membranes with ILs may be a promising approach to achieve efficient ion separation and critical material recovery.

Doxorubicin-Conjugated Zinc Oxide Nanoparticles, Biogenically Synthesised Using a Fungus Aspergillus niger, Exhibit High Therapeutic Efficacy against Lung Cancer Cells

This study reports the therapeutic effectiveness of doxorubicin-conjugated zinc oxide nanoparticles against lung cancer cell line. The zinc oxide nanoparticles (ZnONPs) were first synthesised using a fungus, isolated from air with an extraordinary capability to survive in very high concentrations of zinc salt. Molecular analysis based on 18S rRNA gene sequencing led to its identification as Aspergillus niger with the NCBI accession no. OL636020. The fungus was found to produce ZnONPs via the reduction of zinc ions from zinc sulphate. The ZnONPs were characterised by various biophysical techniques. ZnONPs were further bioconjugated with the anti-cancer drug doxorubicin (DOX), which was further confirmed by different physical techniques. Furthermore, we examined the cytotoxic efficacy of Doxorubicin-bioconjugated-ZnONPs (DOX-ZnONPs) against lung cancer A549 cells in comparison to ZnONPs and DOX alone. The cytotoxicity caused due to ZnONPs, DOX and DOX-ZnONPs in lung cancer A549 cells was assessed by MTT assay. DOX-ZnONPs strongly inhibited the proliferation of A549 with IC50 value of 0.34 μg/mL, which is lower than IC50 of DOX alone (0.56 μg/mL). Moreover, DOX-ZnONPs treated cells also showed increased nuclear condensation, enhanced ROS generation in cytosol and reduced mitochondrial membrane potential. To investigate the induction of apoptosis, caspase-3 activity was measured in all the treated groups. Conclusively, results of our study have established that DOX-ZnONPs have strong therapeutic efficacy to inhibit the growth of lung cancer cells in comparison to DOX alone. Our study also offers substantial evidence for the biogenically synthesised zinc oxide nanoparticle as a promising candidate for a drug delivery system.

Neutrally charged nanosilver antimicrobial effects: A surface thermodynamic perspective

Nanosilver (AgNP) has a large surface area that contributes to enhanced interactions with bacteria, as well as silver ion release. The actual AgNP antimicrobial effect is determined by the AgNP size. AgNPs with smaller diameters showed better antimicrobial effects because smaller AgNPs had larger surface areas, which led to greater silver ion release and stronger attachment to bacteria. The attachment of AgNPs to bacterial surfaces is attributed to the attractive interactions between the AgNPs and bacteria, which is also a function of the size of AgNPs. Although the antimicrobial activity of AgNPs has been extensively studied, there is a gap between antimicrobial effects of AgNPs on bacteria and their subsequent attachment. To fully understand the antimicrobial effectiveness of different-sized AgNPs, this study investigated the dynamic process of AgNP-bacteria interactions in aqueous media, including AgNP aggregation, AgNP attachment, and antimicrobial effects. AgNP-AgNP and AgNP-bacteria interactions were quantified based on DLVO and surface chemistry theories, which were used to interpret subsequent AgNP aggregation, AgNP-bacteria attachment and AgNP antimicrobial observations.

Novel Bioengineered Antibacterial and Anticancer ZnO Nanoparticles

Transition metal oxide NPs have delivered wide applications in various fields. Therefore, in this study, a novel fungus, Alternaria sp. (NCBI Accession No: MT982648) was isolated and characterized from the vicinity of medicinal plants. Eventually, in this method extracted proteins from isolated fungus were utilized to synthesize highly biocompatible zinc nanoparticles (ZnO NPs). The various physical techniques including UV-visible spectroscopy, TEM, HR-TEM, XRD, DLS, zeta potential, and FTIR were used to characterize particles. The UV-visible absorption (λ_Max) and binding energy for the as-synthesized particles were found to be 329 nm and 3.91 eV, respectively. Further, the polydispersed particles were revealed to have regular crystallinity with hexagonal wurtzite phase of ZnO with the spacing of ~2.46 Å under XRD and HR-TEM. The average size of a particle under TEM was found to be ~18 nm. The evaluation of various surface functional groups of particles was done by FTIR. The average hydrodynamic diameter of particles was found to be ~57 d. nm with 0.44 particle distribution index whereas the nanoemulsion stability was explained by Zeta potential (-9.47 mV). These particles were found to exhibit potential antibacterial and anticancer activities. They were found to be bactericidal against S. abony (MIC 5.73 μg/mL); B. pumilis (MIC 6.64 μg/mL); K. pneumonia (MIC 14.4 μg/mL); E. coli (MIC 8.7 μg/mL); B. subtilis (MIC 5.63 μg/mL) and S. aureus (MIC 12.04 μg/mL). Further, they are also found to be concentration-dependent anticancer and inhibited the growth of A549 cells (IC₅₀-65.3 μg/mL) whereas they were found to demonstrate no any cytotoxicity against NRK normal kidney cell line. The internalization of particles into the nucleus (i.e., nuclear fragmentation and DNA damage) was confirmed by DAPI staining. The intracellular particles were found to generate excessive ROS. Further, the anticancer potential was also estimated by noticing a hike in oxidative stress parameters, cell viability, cell morphology, and change in mitochondrial membrane potential. We effectively synthesized potentially potent antibacterial and anticancer novel bioengineered ZnO NPs.

Nanoscopic Study of Water Uptake on Glass Surfaces with Organic Thin Films and Particles from Exposure to Indoor Cooking Activities: Comparison to Model Systems

Water uptake by thin organic films and organic particles on glass substrates at 80% relative humidity was investigated using atomic force microscopy-infrared (AFM-IR) spectroscopy. Glass surfaces exposed to kitchen cooking activities show a wide variability of coverages from organic particles and organic thin films. Water uptake, as measured by changes in the volume of the films and particles, was also quite variable. A comparison of glass surfaces exposed to kitchen activities to model systems shows that they can be largely represented by oxidized oleic acid and carboxylate groups on long and medium hydrocarbon chains (i.e., fatty acids). Overall, we demonstrate that organic particles and thin films that cover glass surfaces can take up water under indoor-relevant conditions but that the water content is not uniform. The spatial heterogeneity of the changes in these aged glass surfaces under dry (5%) and wet (80%) conditions is quite marked, highlighting the need for studies at the nano- and microscale.

Swelling-based preparation of polypropylene nanocomposite with non-functionalized cellulose nanofibrils

Dispersion of nanofillers in a polymer matrix is one of the most important steps in preparing polymer nanocomposites. However, hydrophobic polymers and hydrophilic nanofillers are intrinsically incompatible, making it difficult to mix them homogeneously. Here, we propose the swelling-based particle adsorption method (SPA) providing a simple route to disperse cellulose nanofibrils (CNFs) within incompatible polypropylene (PP) matrix without surface functionalization of CNFs. The SPA enables CNFs to adsorb onto the surface of PP particles using a small amount of solvent. PP/CNFs composite films fabricated from the SPA showed increased Young's modulus by 80%, which agrees well with a theoretical prediction proving nano-dispersed. Furthermore, simply mixing a bit of polypropylene-graft-maleic anhydride can improve the tensile strength by 30% and the elongation at break by 10-fold than that of PP/CNFs composites. The SPA can be universally applied to any incompatible polymer-nanofiller pairs for the fabrication of nanocomposite materials.

Optimization of Methionine in Inhalable High-dose Spray-dried Amorphous Composite Particles using Response Surface Method, Infrared and Low frequency Raman Spectroscopy

The influence of amino acids, other than leucine, in improving aerosolization of inhalable powders has not been widely explored. This detailed study focused on the use of methionine, another promising endogenous amino acid, in high dose spray-dried co-amorphous powders by investigating the influence of methionine proportion (0 - 20% ^w/_w), and feed concentration (0.2 - 0.8% ^w/_v) on aerosolization of kanamycin, a model drug, using a design of experiment approach. Low frequency Raman spectroscopy was used to assess the stability of the powders stored at 25 °C/53% relative humidity over 28 days. An increase in concentration of methionine was associated with an increase in fine particle fraction (FPF), with the highest FPF of 84% being achieved at 20% ^w/_w and 0.2% ^w/_v feed concentration. With an increase in feed concentration, both yield and particle size increased for all formulations; the FPF did not change except for kanamycin only formulation in which it decreased. During storage at high humidity, similar aerosolization stabilities were offered by different proportions of methionine although methionine crystallized out in all formulations. Furthermore, the crystallization was accompanied by surface enrichment of methionine on the particles. This study suggests that there is a direct relationship between methionine content and aerosolization for kanamycin-methionine amorphous matrices but feed concentration has little effect. In addition, methionine proportion has no effect on physical stability of such matrices at high humidity.

Theoretical and Experimental Analysis of Surface Roughness and Adhesion Forces of MEMS Surfaces Using a Novel Method for Making a Compound Sputtering Target

Achieving a compound thin film with uniform thickness and high purity has always been a challenge in the applications concerning micro electro mechanical systems (MEMS). Controlling the adhesion force in micro/nanoscale is also critical. In the present study, a novel method for making a sputtering compound target is proposed for coating Ag–Au thin films with thicknesses of 120 and 500 nm on silicon substrates. The surface topography and adhesion forces of the samples were obtained using atomic force microscope (AFM). Rabinovich and Rumpf models were utilized to measure the adhesion force and compare the results with the obtained experimental values. It was found that the layer with a thickness of 500 nm has a lower adhesion force than the one with 120 nm thickness. The results further indicated that due to surface asperity radius, the adhesion achieved from the Rabinovich model was closer to the experimental values. This novel method for making a compound sputtering target has led to a lower adhesion force which can be useful for coating microgripper surfaces.

Fruit Derived Potentially Bioactive Bioengineered Silver Nanoparticles

INTRODUCTION

Protein-derived biogenic syntheses of inorganic nanoparticles have gained immense attention because of their broad spectrum of applications. Proteins offer a reducing environment to enable the synthesis of nanoparticles and encapsulate synthesized nanoparticles and provide them temporal stability in addition to biocompatibility.

METHODS

In the present study, Benincasa hispida fruit proteins were used to synthesize silver nanoparticles (AgNPs) at 37 °C over five days of incubation. The synthesis of AgNPs was confirmed by UV-Vis spectroscopy, TEM, zeta potential, and DLS analyses. Further, these NPs depicted antibacterial and antibiofilm effects. Additionally, the anticancer activities of nanoparticles were also tested against the lung cancer cell line (A549) with respect to the normal cell line (NRK) using MTT assay. Further, the estimation of ROS generation through DCFH-DA staining along with a reduction in mitochondrial membrane potential by Mito Tracker Red CMX staining was carried out. Moreover, nuclear degradation in the AgNPs treated cells was cross-checked by DAPI staining.

RESULTS

The average size of AgNPs was detected to be 27 ±1 nm by TEM analysis, whereas surface encapsulation by protein was determined by FTIR spectroscopy. These NPs were effective against bacterial pathogens such as Escherichia coli, Staphylococcus aureus, Salmonella enteric, and Staphylococcus epidermis with MICs of 148.12 µg/mL, 165.63 µg/mL, 162.77 µg/mL, and 124.88 µg/mL, respectively. Furthermore, these nanoparticles inhibit the formation of biofilms of E. coli, S. aureus, S. enteric, and S. epidermis by 71.14%, 73.89%, 66.66%, and 64.81%, respectively. Similarly, these nanoparticles were also found to inhibit (IC50 = 57.11 µM) the lung cancer cell line (A549). At the same time, they were non-toxic against NRK cells up to a concentration of 200 µM.

DISCUSSION

We successfully synthesized potentially potent antibacterial, antibiofilm and anticancer biogenic AgNPs.

Different Evolution Behaviors of Adhesion Force with Relative Humidity at Silica/Silica and Silica/Graphene Interfaces Studied using Atomic Force Microscopy

The influence of relative humidity (RH) on adhesion forces demands clarification. Adhesion forces at silica/silica and silica/graphene interfaces were measured on an atomic force microscope to investigate the evolution behaviors with RH and the contact time dependence at a certain RH. For the silica/silica interface, the adhesion force at a location by decreasing RH is independent of RH, but increases as a whole with RH both at a location and in the force volume mode by increasing RH. However, for the silica/graphene interface at a location, the adhesion force remains unchanged with RH as a whole by reducing RH and tends to decrease as a whole by increasing RH. In the force volume mode, the adhesion force at the silica/graphene interface is independent of RH. For the silica/silica interface, the adhesion force increases logarithmically with dwell time at a low RH and remains unchanged at a high RH. However, for the silica/graphene interface, the force is not dependent on RH at low and high RHs. The results can serve to further understand the mechanisms and behaviors of adhesion forces and promote the anti-adhesion design for small-scale silicon-based structures.

GenX is not always a better fluorinated organic compound than PFOA: A critical review on aqueous phase treatability by adsorption and its associated cost

Hexafluoropropylene oxide dimer acid (GenX) has been marketed as a substitute for perfluorooctanoic acid (PFOA) to reduce environmental and health risks. GenX and PFOA have been detected in various natural water sources, and adsorption is recognized as a typical treatment process for PFOA removal. In this paper, comparisons of GenX and PFOA adsorption are evaluated, including adsorption potential, adsorption mechanisms, and associated costs. A detailed literature review suggests that anion-exchange resins are more effective in removing GenX than activated carbon. GenX removal efficiency through activated carbon (30%) is lower than that of PFOA (80-95%), while GenX and PFOA removal efficiencies by anion exchange resins are similar (99%). Unconventional adsorbents, such as ionic fluorogels and covalent organic frameworks can effectively remove GenX from water. The review reveals that GenX adsorption is more challenging, requiring almost 4 times the treatment cost of its predecessor, PFOA. Annual operation and maintenance costs for GenX adsorption (initial concentration of GenX and PFOA = 0.2 µg.L^-1) by GAC for treating 10,000 m³ per day is almost US$1,000,000 per year, but only around US$240,000 per year for PFOA. Desorption of GenX in the presence of PFOA highlights GenX's inferior treatability by adsorption. It is believed that GenX is a more environmentally friendly compound than PFOA, but this environmental friendliness comes with the price.

Exceptional Elasticity of Microscale Constrained MoS2 Domes

The outstanding mechanical performances of two-dimensional (2D) materials make them appealing for the emerging fields of flextronics and straintronics. However, their manufacturing and integration in 2D crystal-based devices rely on a thorough knowledge of their hardness, elasticity, and interface mechanics. Here, we investigate the elasticity of highly strained monolayer-thick MoS₂ membranes, in the shape of micrometer-sized domes, by atomic force microscopy (AFM)-based nanoindentation experiments. A dome's crushing procedure is performed to induce a local re-adhesion of the dome's membrane to the bulk substrate under the AFM tip's load. It is worth noting that no breakage, damage, or variation in size and shape are recorded in 95% of the crushed domes upon unloading. Furthermore, such a procedure paves the way to address quantitatively the extent of the van der Waals interlayer interaction and adhesion of MoS₂ by studying pull-in instabilities and hysteresis of the loading-unloading cycles. The fundamental role and advantage of using a superimposed dome's constraint are also discussed.

Formation of a colloidal band via pH-dependent electrokinetics

Electroosmosis on nonuniformly charged surfaces often gives rise to intriguing flow behaviors, which can be utilized in applications such as mixing processes and designing micromotors. Here, we demonstrate nonuniform electroosmosis induced by electrochemical reactions. Water electrolysis creates pH gradients near the electrodes that cause a spatiotemporal change in the wall zeta potential, leading to nonuniform electroosmosis. Such nonuniform EOFs induce multiple vortices, which promote the continuous accumulation of particles that subsequently form a colloidal band. The band develops vertically into a "wall" of particles that spans from the bottom to the top surface of the chamber. Such a flow-driven colloidal band can be potentially used in colloidal self-assembly and separation processes irrespective of the particle surface properties. For instance, we demonstrate these vortices can promote rapid segregation of soft colloids such as oil droplets and fat globules.

Improving and evaluating the adhesion and stability of make-up by enhancing the affinity between skin/make-up layer

PURPOSE

upMake-up clumps, bumps and collapses are the three factors that determine how well make-up has been performed. The purpose of this study is to reduce the three factors mentioned above by using amphiphilic substances to increase the affinity between the skin and the make-up layer. In addition, it aims to evaluate the improvement of the make-up layer by developing an objective make-up layer evaluation method.

METHODS

Experiments were performed in an attempt to increase the affinity between the skin and the make-up layer by minimizing the difference in surface energy between the two. Multiple types of artificial skin (leather and bio-skin) were used and treated to form the liquid foundation layer. Qualitative evaluation of the make-up layer was conducted by analyzing the surface, cross-section, and fracture area of the make-up layer, using the evaluation method proposed in this study.

RESULTS

After applying this method and taking measurements by 3D surface analysis, the surface roughness of the make-up layer reduced by 46%, and the maximum thickness of the make-up layer reduced by about 50% in comparison with the control group (method not applied). In the case of the make-up layer to which this method was applied, two-dimensional cross-sectional Scanning Electron Microscope (SEM) image analysis confirmed that agglomeration was reduced, and the thickness of the make-up layer was also reduced by an average of 54%. According to this result, the technique of increasing the affinity between the skin and the make-up layer reduces the level of aggregation of make-up and encourages the formation of a uniform and thin make-up layer. Also, the fracture area after motion simulation was reduced by 33%. These results indicate that the method of increasing the affinity between skin/make-up membranes positively affects the formation of a uniform make-up layer.

CONCLUSION

Increasing the affinity by reducing the surface energy between the skin and the make-up layer plays an important role in forming a thin and uniform make-up layer by improving the problems of lifting, agglomeration, and collapse of the make-up. In addition, it has been confirmed that through this method, the quality of consumer experience related to make-up satisfaction can be improved. The results show that objective analyses of make-up help the understanding of the quality of consumer experience on make-up.

The potential of metal epoxy composite (MEC) as hybrid mold inserts in rapid tooling application: a review

Purpose

Rapid tooling (RT) integrated with additive manufacturing technologies have been implemented in various sectors of the RT industry in recent years with various kinds of prototype applications, especially in the development of new products. The purpose of this study is to analyze the current application trends of RT techniques in producing hybrid mold inserts.

Design/methodology/approach

The direct and indirect RT techniques discussed in this paper are aimed at developing a hybrid mold insert using metal epoxy composite (MEC) in increasing the speed of tooling development and performance. An extensive review of the suitable development approach of hybrid mold inserts, material preparation and filler effect on physical and mechanical properties has been conducted.

Findings

Latest research studies indicate that it is possible to develop a hybrid material through the combination of different shapes/sizes of filler particles and it is expected to improve the compressive strength, thermal conductivity and consequently increasing the hybrid mold performance (cooling time and a number of molding cycles).

Research limitations/implications

The number of research studies on RT for hybrid mold inserts is still lacking as compared to research studies on conventional manufacturing technology. One of the significant limitations is on the ways to improve physical and mechanical properties due to the limited type, size and shape of materials that are currently available.

Originality/value

This review presents the related information and highlights the current gaps related to this field of study. In addition, it appraises the new formulation of MEC materials for the hybrid mold inserts in injection molding application and RT for non-metal products.

Mathematical Modelling of a System for Solar PV Efficiency Improvement Using Compressed Air for Panel Cleaning and Cooling

The efficiency of solar photovoltaic (PV) panels is greatly reduced by panel soiling and high temperatures. A mechanism for eliminating both of these sources of inefficiencies is presented by integrating solar PV generation with a compressed air system. High-pressure air can be stored and used to blow over the surface of PV panels, removing present dust and cooling the panels, increasing output power. A full-system mathematical model of the proposed system is presented, comprised of compressed air generation and storage, panel temperature, panel cleaning, and PV power generation. Simulation results indicate the benefit of employing compressed air for cleaning and cooling solar PV panels. For a fixed volume of compressed air, it is advantageous to blow air over the panels early in the day if the panel is soiled or when solar radiation is most abundant with the highest achievable flow rate if the panel is clean. These strategies have been shown to achieve the greatest energy captures for a single PV panel. When comparing the energy for air compression to the energy gain from cleaning a single PV over a two-week period, an energy ROI of 23.8 is determined. The system has the potential to eliminate the requirement for additional manual cleaning of solar PV panels.