Antibacterial activity and cytocompatibility of Cu-coated PETG for clear aligner applications

Prolonged wear of clear aligners may promote plaque accumulation and increase the risks of enamel demineralization and gingival inflammation. In this study, a copper (Cu) coating was fabricated on polyethylene terephthalate glycol (PETG) by magnetron sputtering, and its physicochemical properties, antibacterial activity, antibiofilm effect, and cytocompatibility were evaluated. Surface characteristics were analyzed by SEM, EDS, AFM, XRD, and FTIR, and mechanical properties were also assessed. Antibacterial and antibiofilm activities against Streptococcus mutans and Porphyromonas gingivalis were evaluated by CFU counting, MTT assay, and CLSM, while cytocompatibility was assessed by CCK-8 assay and cytoskeletal staining. The results showed that a relatively uniform Cu coating was successfully formed on the PETG surface without markedly affecting the main chemical structure or mechanical properties of PETG. Compared with pristine PETG, PETG/Cu composites exhibited evident antibacterial effects against both bacterial species, with the 45 s group showing the best performance, reaching antibacterial rates of approximately 60% against S. mutans and 80% against P. gingivalis, while also reducing bacterial adhesion and biofilm formation. No apparent cytotoxicity was observed under the tested in vitro conditions. These findings indicate that PETG/Cu composite coatings can endow PETG with antibacterial and antibiofilm properties while maintaining its basic performance, highlighting its potential for functional clear aligner applications.