Antimicrobial activity of cuprous oxide-coated and cupric oxide-coated surfaces.

BACKGROUND: Disease can be spread through contact with contaminated surfaces (fomites). For example, fomites have been implicated in the spread of meticillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa. Antimicrobial surface treatments are a potential method of reducing disease transmission from fomites, and broad-spectrum activity is desirable. AIM: To test cuprous oxide (Cu2O) and cupric oxide (CuO) coatings for antimicrobial activity against 12 micro-organisms including bacteria and fungi. METHODS: We fabricated two surface coatings. The Cu2O coating was fabricated in a simple two-step process using polyurethane to bind the active copper oxide particles; CuO was prepared by heat treatment of Cu2O particles in air to produce cupric oxide (CuO) and to cause early-stage sintering to form a continuous coating. The antimicrobial activity was examined with 10 µL of microbial suspension droplets followed by counting cells as colony-forming units (cfu). FINDINGS: The coatings rapidly killed nine different micro-organisms, including Gram-negative and Gram-positive bacteria, mycobacteria and fungi. For example, the Cu2O/PU coating killed 99.9997% of P. aeruginosa and 99.9993% of S. aureus after 1 h. Efficacy was not reduced after weekly cleanings. The antimicrobial activity of the Cu2O coating was unchanged after abrasion treatment, and the coatings were not cytotoxic to human cells. CONCLUSION: The combination of broad-spectrum antimicrobial activity, abrasion resistance, and low toxicity of the Cu2O coating suggests potential use in healthcare settings.

Modeling of confinement-induced phase transitions for surfactant layers on amphiphilic surfaces.

A self-consistent field model is used to consider a solution of positively charged surfactants up to its critical micellization concentration adsorbing onto two surfaces in close proximity. Each surface mimics a polystyrene sulfonate interface; that is, hydrophobic properties are combined with a (fixed) negative charge. We observe large and sudden changes in adsorption as a function of separation, which are not normally considered when interpreting surface force measurements. The parameters are chosen such that the adsorbed surfactant layer is of a monolayer type when the surfaces are far apart. A typical interaction curve is presented for a fixed surfactant chemical potential, which is extracted from the set of adsorption isotherms each with a fixed slit width. When the slit width approaches the thickness of the two surfactant layers, a first-order phase transition takes place, which is driven by the unfavorable hydrophobic-water contacts. At the transition, the average orientation of the surfactants switches from a high concentration of tails at the surface to a bilayer configuration where tail profiles from both sides merge in the center. The headgroups are pulled slightly away from the surface. The interaction force jumps from a weak electrostatic repulsion at large distances (two effectively positively charged surface layers repel each other) to a strong electrostatic attraction at short distances (the central surfactant bilayer is attracted to the oppositely charged surfaces). The amount of adsorbed surfactants tend to decrease with decreasing distance between the surfaces but suddenly increases at the transition. Because of this, we anticipate that in surface force experiments, for example, there is a hysteresis associated with this transition: the forces and also the adsorbed amounts depend not only on the distance between the surfaces but also on the history if nonsufficient equilibration times are implemented.

Confinement-induced phase transition and hysteresis in colloidal forces for surfactant layers on hydrophobic surfaces.

In this paper we consider surfactant solutions near a pair of interfaces. It is well-known that strong lateral interactions between surfactant molecules give rise to a step in the adsorption isotherm. In a self-consistent field theory, such a step in the adsorbed amount shows up as a van der Waals loop. The consequence of such a loop for surface force experiments is analyzed. From adsorption isotherms at fixed confinement we extract the relevant adsorbed amounts for a fixed chemical potential as a function of the confinement. A cusped structure is found for the relation between the interaction energy and the slit width: there is a confinement-induced first-order phase transition. The corresponding interaction curve has a kink at the binodal slit distance. Metastable branches as well as an unstable branch (bracketed by the two spinodal points) are presented. The metastability is expected to give rise to force hysteresis in, e.g., atomic force microscope or surface force apparatus experiments, distinctly different from those due to mechanical instabilities of the cantilever system.

Celery (Apium graveolens L.) parenchyma cell walls examined by atomic force microscopy: effect of dehydration on cellulose microfibrils.

Atomic force microscopy (AFM) was used to image celery (Apium graveolens L.) parenchyma cell walls in situ. Cellulose microfibrils could clearly be distinguished in topographic images of the cell wall. The microfibrils of the hydrated walls appeared smaller, more uniformly distributed, and less enmeshed than those of dried peels. In material that was kept hydrated at all times and imaged under water, the microfibril diameter was mainly in the range 6-25 nm. The cellulose microfibril diameters were highly dependent on the water content of the specimen. As the water content was decreased, by mixing ethanol with the bathing solution, the microfibril diameters increased. Upon complete dehydration of the specimen we observed a significant increase in microfibril diameter. The procedure used to dehydrate the parenchyma cells also influenced the size of cellulose microfibrils with freeze-dried material having larger diameters than air-dried material.

Organized Structure of Lithium Perfluorooctanesulfonate at the Graphite-Solution Interface

The structure of aggregates of lithium perfluorooctanesulfonate (LiFOS) adsorbed to the interface between graphite and aqueous solution have been measured. This fluorocarbon surfactant produces aggregates which are long ( approximately 100 nm) and thin ( approximately 5 nm), and about one molecule ( approximately 1.3 nm) deep. The aggregates lie in straight, parallel arrays on the surface with a characteristic repeat distance, or period, perpendicular to the long axis. As the bulk concentration of LiCl is increased, the period decreases, but as the bulk concentration of LiFOS is increased, the period increases. The decrease in period on addition of salt is similar to that observed for sodium dodecyl sulfate (SDS) and is explicable in terms of electrostatic forces. The increase in period on addition of surfactant is in sharp contrast to the behavior of SDS and may be due to a higher surfactant packing-parameter for LiFOS.

Van der Waals Epitaxial Growth of agr-Alumina Nanocrystals on Mica.

Lattice mismatch stresses, which severely restrict heteroepitaxial growth, are greatly minimized when thin alumina films are grown by means of van der Waals forces on inert mica substrates. A 10-nanometer-thick epitaxial film exhibits crystallographic sixfold symmetry, a lattice constant close to that of the basal plane [0001] of alpha-alumina (sapphire), and an aluminum: oxygen atomic ratio of 1:1.51 +/- 0.02 (measured by x-ray photoelectron spectroscopy), again the same as for bulk sapphire. The film is free of steps and grain boundaries over large areas and appears to be an ideal model system for studying adhesion, tribology, and other surface phenomena at atomic scales.

The case of the high-risk safety product.

After several days of meetings, J.F. Winchester, president of MDC Industries, felt no closer to a decision. MDC, a manufacturer of wall and ceiling panels, was considering whether to exercise an option to buy a new and safer wallboard technology. The product was being touted as revolutionary, but, Winchester wondered, could MDC afford to carry the flag? According to its inventor, Robert Goerner, Smoke-Safe would be a vast improvement over standard safety-rated wallboard. With almost the same flame-retardant properties, Smoke-Safe had the advantage of giving off almost no fumes or smoke in fire tests. And, Winchester knew, most fire-related deaths are from smoke, not flames. Indeed, the numbers were grimly persuasive: 82% of fire-related injuries involving standard panels were caused by smoke inhalation. What's more, Smoke-Safe would cost about the same to manufacture as MDC's current wallboard. But MDC had several other good options for spending the $5 million Goerner was asking; building plastics was only one of its profit centers. And the prospect of launching a campaign to change building codes in order to market Smoke-Safe, which could spark a fight with competitors, was daunting. Since its current wallboard gave MDC only 18% of the wallboard market, many industry insiders speculated whether MDC had the market clout to influence major cities to revise their codes. Six experts in marketing, law, and ethics advise MDC Industries on how it can balance ethical and business imperatives in making its decision.