Investigation of Covarine Particle Behavior in a Microfluidic Mixer with Artificial Saliva

Abstract

Covarine is a commonly used ingredient in tooth whitening toothpastes. Different technologies have been employed to incorporate covarine into toothpaste formulations, resulting in various forms of the product. These technologies include the use of bigger flakes, two-phase pastes, and microbeads. The present investigation aimed to evaluate the behavior of covarine particles in Colgate Advanced White toothpaste, where covarine is present in the form of microbeads with a size of 200 microns after mixing with artificial saliva (AS) in both microfluidic mixer and Comsol simulations. The microfluidic mixer was designed with 400-micron wide channels arranged in a serpentine form with 30 serpentines. The mixer also featured a Y-shaped design with two inlets: one for the flow of AS and the other for the flow of toothpaste and its various dilutions with AS. The microfluidic mixer has been fabricated as a layered design, incorporating a middle layer created through the utilization of SLA 3D printing technology (LF-SLA) on a Formlabs Form3 3D printer. For this purpose, a flexible transparent resin with a shore hardness of 80A, specifically the Formlabs' Flexible 80A resin, was employed. To enclose the microfluidic chip, transparent PMMA layers were employed on the top and bottom sides, which were cut using a CO2 laser CNC machine, MBL 4040RS (Minoan Binding Laminating, Belgrade, Serbia). For simulation purposes using COMSOL, parameters were obtained from the datasheets of both the toothpaste and AS. All parameters that were not available in the datasheets, such as particle size, density, viscosity, etc., were measured in the laboratory to ensure accurate simulations. During the experiments conducted on a real microfluidic mixer, observations of covarine particles were made using an optical profilometer. By combining experimental data from microfluidic chips with computational simulations, researchers can gain a more comprehensive understanding of the behavior of covarine particles, elucidating their interactions with saliva and the formation of microfilms on the enamel surface.