Synthesis, physiochemical characterization and antibiofilm effects of morin-loaded nanoemulsions for application in endodontics

Considering the scarcity of medications with a wide range of therapeutic effects for the endodontic treatment, this study aimed to synthesize two morin (Mo) derivatives and test their cytotoxicity and effect on multispecies biofilm, in solution and loaded in nanoemulsions (NE). Minimum inhibitory and bactericidal concentration (MIC/MBC) of Mo, penta-acetylated Mo (Ac-Mo), Mo complexed with strontium (Sr-Mo) and control chlorhexidine digluconate (CHX) were determined against Enteroccocus faecalis, Actinomyces israelii, Streptococcus mutans, Lactobacillus casei, Fusobacterium nucleatum. NE were physiochemically characterized by analysis of droplet size and polydispersity index using dynamic light scattering, by determination of zeta potential, by Nanoparticle Tracking Analysis, and by Fourier Transform Infrared Spectroscopy analysis. NE containing Mo, its derivatives (at 2 mg/mL), and CHX (at 0.5 mg/mL) were evaluated against multispecies biofilms by bacterial counts, scanning electron microscopy, and confocal microscopy. The cytotoxicity of the compounds and NE was also determined in fibroblasts (L929) using resazurin assays. The data were statistically evaluated (p < 0.05). All compounds were considered potentially bactericidal against the bacteria tested. The values of MBC ranged from 0.25 to 1 mg/mL. Metabolic activity of fibroblasts was higher than 70% after treatment with compounds up to 0.25 mg/mL. Data from physiochemical characterization confirmed the successful formation of stable, uniformly dispersed nanoemulsion suitable for drug delivery applications. The highest bacterial reduction in multispecies biofilms was observed in NE + Ac-Mo, followed by NE + Mo, CHX, and NE + Sr-Mo groups. All NE diluted at 12.5% did not affect fibroblast metabolism after 24 h of treatment. Although in different concentrations, morin and its derivatives, either alone or loaded in nanoemulsions, were bactericidal (up to 1 mg/mL) and demonstrated antibiofilm effect (at 2 mg/mL). They also were cytocompatible at lower concentrations (0.25 mg/mL). Nanoemulsion containing penta-acetylated morin could be an alternative intracanal medication for reducing residual bacteria between short-term clinical appointments in endodontic approaches.