Prolonged use of clear aligners promotes bacterial colonization and biofilm formation, which can compromise orthodontic outcomes. There is a clear clinical demand for approaches that can suppress pathogenic activity while preserving the fundamental functional and material characteristics of the aligners. To address this need, a novel strategy of fabricating metal–organic framework (MOF) coatings on aligners was adopted. Metal–organic frameworks (MOFs) have emerged as promising antibacterial coating materials by combining antimicrobial metal ions with biocompatible organic ligands. Three distinct porphyrin-based MOFs (Ag-, Cu-, and Ce-TCPP) were synthesized and fabricated as coatings on clear aligner surfaces via a coordination-driven self-assembly approach. The coated aligners were comprehensively assessed in vitro to determine their antibacterial performance, anti-inflammatory potential, biocompatibility, and key physical characteristics. Among the three coatings, Ag-TCPP showed the most favorable overall antibacterial and anti-biofilm performance in the present experimental system and facilitated macrophage polarization toward an anti-inflammatory M2-like phenotype. Ag-TCPP exhibited a significant inhibition zone of 6.75 ± 0.25 mm and reduced biofilm biomass by 72.2%. All MOF coatings exhibited excellent biocompatibility, and their application did not compromise the aligners’ mechanical integrity or aesthetic properties (light transmittance). This study reports the successful development of a novel metal–organic framework (MOF)-based coating strategy for clear aligners. Among the formulations investigated, the Ag-TCPP coating exhibited outstanding antibacterial and immunomodulatory performance while maintaining the critical mechanical integrity and aesthetic qualities of the aligner. The findings of this work offer a practical approach to designing multifunctional orthodontic devices that may reduce biofilm-related complications and improve clinical outcomes.

Objectives: Microplastics (MPs) released from clear aligner materials may affect periodontal cell responses. This study aimed to investigate whether clear aligner-associated MPs (CAF-MPs) induce oxidative stress and macrophage extracellular trap formation (METosis) in a periodontal co-culture model. Material and Methods: CAF-MPs with different particle sizes were prepared from thermoplastic clear aligner membranes and characterized using scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy. A Transwell co-culture system consisting of RAW264.7 macrophages and MC3T3-E1 osteoblasts was established to model macrophage-osteoblast interactions relevant to periodontal cellular responses following CAF-MP exposure. METosis, intracellular reactive oxygen species (ROS) production, mitochondrial membrane potential (MMP), inflammatory cytokine expression, and nuclear factor erythroid 2-related factor 2/heme oxygenase-1 (Nrf2/HO-1) signaling activity were assessed using immunofluorescence staining, quantitative real-time polymerase chain reaction, and Western blotting. Deoxyribonuclease I (DNase I) treatment was used to evaluate the potential contribution of extracellular DNA/METs to CAF-MP-associated cellular responses. Results: CAF-MPs-induced METosis, and different particle size fractions showed endpoint-specific effects on oxidative stress, mitochondrial dysfunction, inflammatory activation, and Nrf2/HO-1 signaling. CAF-MP exposure increased ROS accumulation, disrupted MMP, enhanced pro-inflammatory cytokine expression, and suppressed Nrf2/HO-1 antioxidant signaling in co-cultured MC3T3-E1 cells. DNase I partially attenuated these effects, suggesting that DNase I-sensitive extracellular DNA/METs may contribute to CAF-MP-associated oxidative stress and antioxidant signaling impairment. However, DNase I degradation of extracellular DNA does not uniquely prove METosis as the exclusive upstream driver, and direct particle-induced oxidative injury or soluble leachate-mediated effects cannot be fully excluded. Conclusion: CAF-MPs can induce METosis and oxidative stress-related responses in in vitro macrophages stress-related responses. DNase I-sensitive extracellular DNA/METs may partially contribute to CAF-MP-induced ROS accumulation and Nrf2/HO-1 suppression.