Antimicrobial Effect of Mucoadhesive Films Prepared with Biogenic Silica Nanoparticles ^†

Mucoadhesive films can be used to extend the action of different bioactive compounds in the oral cavity. Biogenic silica nanoparticles (SiOxNPs) release silicic acid that promotes wound healing and connective tissues repair [1]. Due to its mucoadhesive properties, sodium alginate is widely used in the biomedical field, as well as in the food industry [2]. The aim of this study was to optimize the preparation of mucoadhesive films with entrapped biosilica nanoparticles and to investigate their antimicrobial effect in order to use them for further applications, such as obtaining oral health products. We used a three factors-two levels optimization plan for film preparation. The films were prepared with alginate or polyvinyl alcohol (PVA) as a main component and glycerol and sorbitol as additives as well as biosilica nanoparticles as the active compound. Two of the tested properties of the films were tensile stiffness represented by the Young’s modulus or elastic modulus, and ultimate tensile strength. Antibacterial activity of the films was assessed through the diffusimetric method. Films with a diameter of 6 mm and sterilized by UV were placed on a previously inoculated medium with a microbial suspension of known CFU (1.5 × 10⁸ colony forming unit). The Petri dishes were incubated at 37 °C overnight. Bactericidal effect of the films was quantified by measuring the diameter of the clear circle formed around the spot. The analysis of the experimental data with Design-Expert pointed out to a link between the Young’s modulus and ultimate tensile strength, which represents the desirability factor. The films with entrapped biogenic silica nanoparticles in sodium alginate showed an apparent increase in antimicrobial activity against Gram-negative bacteria in comparison with the films without SiOxNPs. A similar effect was observed in the case of polyvinyl alcohol. However, there was no noticeable effect against Gram-positive bacteria. Flexible and elastic yet sufficiently stiff films were prepared using three factors-two levels optimization. Both SiOxNPs/sodium alginate and SiOxNPs/PVA films were effective against Gram-negative bacteria.