Mechanistic insights into graphene coatings for oral biofilm inhibition and osteoblast compatibility

Abstract

The initial adhesion of bacterial cells to implant surfaces is a critical step in biofilm formation. Biofilms are complex microbial communities that are much more tolerant to conventional antimicrobial treatments than planktonic cells, often requiring mechanical disruption in addition to antimicrobial treatment. Once established, these biofilms and their self-produced extracellular matrix are difficult to eradicate. As a result, there is growing interest in engineering implant surfaces that can effectively disrupt bacterial adhesion and subsequent biofilm formation. Various surface-modification strategies, including antimicrobial agents and nanomaterial-based coatings, have been investigated. Among these, graphene-based coatings have shown promising antimicrobial properties. However, the mechanisms of their bactericidal activity remain insufficiently understood. We evaluated the antimicrobial efficacy of vertically aligned graphene (VG) coatings against Streptococcus mutans, employing electron microscopy and transcriptomics analysis to elucidate the mode of action. These coatings inhibited biofilm formation through a multifaceted mechanism: (i) reducing bacterial colonization; (ii) mechanical disruption of bacterial membranes by nanoscale protrusions; (iii) modulating expression of the genes associated with membrane integrity, transport, oxidative stress, and cell division. Importantly, the coatings inhibited bacterial adhesion and biofilm formation without affecting osteoblast growth or proliferation. These results indicate that VG coatings could offer a dual benefit by enhancing antimicrobial activity while being compatible for osseointegration, indicating their potential as candidates for next-generation biomedical implants.