Electrospun thermoplastic polyurethane/nano-Ag-coated clear aligners for the inhibition of Streptococcus mutan s and oral biofilm

Abstract The aim of this study is to develop a novel clear aligner coated with electrospun thermoplastic polyurethane (TPU) and a nano-silver-based antibacterial agent to inhibit Streptococcus mutans ( S. mutans ) growth and biofilm formation, addressing the risk of dental caries and enamel demineralization associated with bacterial accumulation on clear aligners. TPU/Ag-coated aligners were fabricated via electrospinning, incorporating silver nanoparticles (AgNPs) at concentrations of 0, 1, 2, and 5 wt%. The TPU/Ag-coated aligners were characterized for morphology, mechanical properties, adhesion stability, wettability, silver ion release kinetics, antibacterial efficacy, and cytotoxicity using human gingival fibroblasts. The TPU/Ag coatings exhibited uniform fiber morphology with AgNPs dispersed homogeneously. Mechanical tests revealed no significant differences in the modulus of elasticity between coated and uncoated aligners, although the breaking strength and elongation at break decreased slightly at higher AgNP concentrations. The TPU/Ag coating demonstrated good adhesion stability in both dry and wet conditions. Antibacterial assays showed a 5–6 log reduction in free S. mutans and a 44% reduction in biofilm metabolic activity for the 2 wt% group, with acceptable changes in mechanical properties and sustained silver ion release. Cytotoxicity assays confirmed biocompatibility, with cell viability >90% across all groups. The electrospun TPU/Ag-coated aligners with 2 wt% AgNPs effectively inhibit bacterial growth and biofilm metabolic activity without compromising mechanical integrity or biocompatibility. This approach offers a durable, clinically viable solution to mitigate caries risks during clear aligner treatment. Further in vivo studies are warranted to validate long-term safety and efficacy.