Interaction between Sophorolipids and ß-glucan in Aqueous Solutions.

Skin disorders, including acne vulgaris, atopic dermatitis, and rosacea, are characterized by the presence of biofilms, which are communities of microorganisms. The mechanical stability of biofilms is attributed to one of their constituents-polysaccharides-which are secreted by microorganisms. Sophorolipids are biosurfactants with biofilm disruption and removal abilities and are expected to become alternatives for classical petrochemical-based surfactants in cosmetics. In this study, we investigated the influence of sophorolipids on ß-glucan such as dispersion status, interaction mechanism, and configuration change as a model polysaccharide of biofilm in aqueous solution. Dynamic light scattering measurements showed that sophorolipids interfere with the aggregation of ß- glucan in aqueous solutions. In contrast, sodium dodecyl sulfate (SDS), which is used as a typical surfactant reference, promotes the aggregation of ß-glucan. The interaction between sophorolipids and ß-glucan were investigated using surface tension measurements and isothermal titration calorimetry (ITC). Surface tension increased only near critical micelle concentration (CMC) region of sophorolipids in the presence of ß-glucan. This suggests that the interaction occurred in the solution rather than at the air-liquid interface. Moreover, the results of ITC indicate that hydrophobic interactions were involved in this interaction. In addition, the results of optical rotation measurements indicate that sophorolipids did not unfold the triple helical structure of ß-glucan. ß-glucan dispersion was expected to be caused steric hindrance and electrostatic repulsion when sophorolipids interacted with ß-glucan via hydrophobic interactions owing to the unique molecular structure of sophorolipids attributed by a bulky sugar moiety and a carboxyl functional group. These results demonstrated unique performances of sophorolipids on ß-glucan and provided more insights on the efficacy of sophorolipids as good anti-biofilms.

Removal of a Model Biofilm by Sophorolipid Solutions: A QCM-D Study.

Biofilms are communities of microorganisms that have been widely studied because they can cause hospital-acquired infections and skin disorders. Polysaccharides secreted by microorganisms are constituents of biofilms, contributing to their adhesion and mechanical stability. Sophorolipids are biosurfactants with the ability to disrupt and remove biofilms. Biosurfactants have been targeted as potential substitutes for classical petrochemical-based surfactants in cosmetics. In this study, we fabricate a ß-glucan film as a model biofilm, and quartz crystal microbalance with dissipation monitoring (QCM-D) measurements are used to assess the biofilm removal. The viscoelasticity of the ß-glucan films is monitored while sophorolipid solutions are introduced into the system, and we found that the film removal performance increases with the sophorolipid concentration. In addition, Δf (change in frequency)-ΔD (change in energy dissipation) plot analyses reveal that two processes are involved in the removal mechanism. The first process involves the adsorption of water (hydration) on the ß-glucan film. The second process involves the removal of the ß-glucan film from the sensor surface. Furthermore, it is suggested that sophorolipids interfere with the hydration of the ß-glucan film and suppress increases in its viscosity. This is expected to be an essential factor for the removal of the ß-glucan film. Sophorolipids, therefore, show potential for use in cosmetics as an eco-friendly agent for biofilm removal.

Control of particle alignment in water by an alternating electric field.

We attempted to align a large number of silica particles dispersed in aqueous solution by controlling the alternating electric field between the two electrodes (400 microm apart). Relatively large particles (9.9 microm) were found to align forming strings in the direction parallel to the electric field while relatively small particles (2.0 and 4.9 microm) were observed to align making stripes in the direction perpendicular to the field. The number of stripes formed by particles between the electrodes increased with increasing frequency of the alternating field. This peculiar perpendicular particle alignment appeared when the contribution to particle alignment of electroosmotic flow exceeded that of dielectric polarization and the osmotic flow was found to be stronger around the particles than in the vicinity of the electrode surface.

Three-dimensional arrangements of polystyrene latex particles with a hyperbolic quadruple electrode system.

An attempt was made to arrange polystyrene latex particles (2, 5, and 10 microm in diameter) dispersed in aqueous media making use of their dielectrophoresis and electrophoresis with a hyperbolic quadruple electrode system. Application of a high-frequency ac field enabled the particles to arrange themselves between the electrodes forming a particle monolayer due to the negative dielectrophoretic force. Simultaneous application of high-frequency ac and dc fields caused the particles to gather in the region surrounded by the electrodes to form particle multilayers. Appropriate choice of the way of applying an electric field thus allowed the reversible control of particle arrangements (monolayer, multilayer, dispersion). Reapplication of an ac field to the particle layers produced highly dense particle multilayers.