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

Abstract

used in many applications such as cosmetics, agriculture, and the food industry owing to their biodegradability and low toxicity compared to chemical surfactants 8−10) . In addition to these benefits, biosurfactants have properties that are suitable for cosmetic applications, such as compatibility with human skin and skin surface moisturizing 10) .Furthermore, consumers pay more attention to natural products when considering environmental sustainability 11) . Therefore, biosurfactants have scope to be further deployed in the cosmetic industry. For instance, in addition to their potential skin benefits, the eco-friendly characteristics of biosurfactants have attracted attention for cleaning applications and their potential applications in haircare 12) .Sophorolipids are biosurfactants that possess both capacities for the disruption 13−16) and removal 17) of biofilms. Owing to the high complexity of biofilms, it is challenging to understand which of their components should be target-Abstract: 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 β-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 β-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 β-glucan film. The second process involves the removal of the β-glucan film from the sensor surface. Furthermore, it is suggested that sophorolipids interfere with the hydration of the β-glucan film and suppress increases in its viscosity. This is expected to be an essential factor for the removal of the β-glucan film. Sophorolipids, therefore, show potential for use in cosmetics as an eco-friendly agent for biofilm removal.

Interaction between Sophorolipids and β-glucan in Aqueous Solutions

“…Moreover, the overall reaction was exothermic, which might be the result of demicellization of sophorolipids or the presence of other exothermic interactions, such as hydrogen bonding. Our previous study suggested that sophorolipids interfere with the hydration bonds between the β-glucan molecules during β-glucan film removal, as evaluated using a quartz crystal microbalance with dissipation monitoring measurements 22) . Hence, hydrogen bonding may also be involved in this interaction.…”

“…Sophorolipids is a type of biosurfactants, which have been reported to be effective in the disruption 17−20) and removal 21) of biofilms. In our previous study on polysaccharides in EPS, which was focused on their contributions to the adhesion and mechanical stability of biofilms, we found that sophorolipids contributed on the removal of model EPS generated by a β-glucan 22) using quartz crystal microbalance with dissipation monitoring measurements. β-glucan forms triple helix in aqueous solution 23) .…”

Quantification of Enzymatic Biofilm Removal Using the Sauerbrey Equation: Application to the Case of Pseudomonas protegens

“…Recently, Kaga et al 37 studied the removal of a β-glucan film by surfactants, showing that QCM-D allows to assess the BF removal in real time, by monitoring the viscoelasticity of the β-glucan films. However, since experiments were performed under flow in a liquid environment, the data treatment becomes more complex.…”

Enhanced Removal of Photoresist Films through Swelling and Dewetting Using Pluronic Surfactants

“…Additionally, by simultaneously measuring energy dissipation, it provides valuable information about the viscoelasticity of the adsorbed layer. QCM-D can also be used to monitor the cleaning dynamics, as long as the shear wave is still present in the adsorbed film, and this technique has been applied in several recent studies. ,− However, despite its compatibility with QCM-D, the removal dynamics in the electronics industry, which demands high-precision cleanliness, is still unclear. This emphasizes the potential of QCM-D as an analysis platform for evaluating new cleaning methods using interfacial technology.…”