The inhibitory effects of biomimetic strategies on Streptococcus mutans biofilm formation

Abstract

Introduction: Dental caries is one of the most prevalent chronic diseases globally, which is significantly impacting patients' quality of life if left untreated. In the oral environment, acid-producing oral plaque biofilm interacts with tooth mineral, leading to tooth mineral loss and accelerating the progression of dental caries. Clinical investigations have demonstrated that Streptococcus mutans (S. mutans) has important implications in caries formation, as it metabolizes sucrose into acid, thereby facilitating caries progression. Thus, it is important to control cariogenic biofilm to inhibit tooth demineralisation for early caries management. Traditional anticaries therapies are often associated with side effects and the development of drug resistance. In contrast, antibacterial biomimetic strategies aimed at controlling biofilm-related diseases should exhibit low toxicity and ensure stable clinical transitions. In vitro studies on single-species biofilms may provide a preliminary understanding of their inhibitory effects on biofilm formation. Aims: To evaluate the antibacterial effects of various biomimetic strategies including graphene oxide (GO), graphene quantum dots (GQDs), Ti-Cu alloy, and titanium nitride (TiN) nanoparticles under near-infrared (NIR) light irradiation. Methods: Following synthesis, the antibacterial efficiency of these materials was assessed through various tests, including anti-planktonic S. mutans, anti-biofilm S. mutans, and anti-S. mutans adhesion assays. The anti-planktonic and anti-adhesion efficiencies were evaluated using colony-forming unit counts, scanning electron microscopy, and Live/Dead staining. Crystal violet staining was employed to assess anti-biofilm capabilities. The antibacterial mechanisms were investigated by measuring reactive oxygen species levels and adenosine triphosphate concentrations to elucidate bacterial cell responses. Additionally, biocompatibility was evaluated by examining the proliferation of different cell lines. To investigate the ability to improve remineralization, GO- and GQDs-coated tooth slices were immersed in a biofilm-challenged environment with artificial saliva/biofilm cycling. Mineral changes were assessed by measuring mineral concentration variations and examining the surface morphology of regenerated crystals. Results: GO, GQDs, modified Ti-Cu alloy, and TiN nanoparticles under NIR light irradiation demonstrated significant anti-caries efficacy by inhibiting bacterial growth and biofilm formation (P<0.05), achieving an antibacterial rate exceeding 99.0%. Various antibacterial mechanisms were identified to enhance antibacterial activity, including the generation of oxidative stress, membrane destabilization, cytoplasmic fluid leakage, and cell death. In a biofilm-challenged environment, groups treated with GQDs and GO exhibited significant inhibition of S. mutans, resulting in reduced lesion depth and improved hydroxyapatite crystal structure compared to control groups (P<0.05). This indicated that GO- and GQDs-coated tooth slices are more resistant to subsequent acid challenges. High biocompatibility and low toxicity levels suggested that these biomimetic strategies are safe and effective agents for dental caries prevention. The development of biocompatible antimicrobial materials could enhance the success rate of caries prevention. Conclusion: Biomimetic strategies evaluated in this thesis were highly biocompatible and effective in inhibiting S. mutans proliferation. Further studies on biomimetic strategies are necessary to evaluate the antimicrobial activities, bioactivity, and biocompatibility in the caries model which imitates the complex structures of oral cavities, the microbiological effect of oral biofilm, and the hydrodynamic instability of saliva. More comprehensive results may encourage in vivo investigations on biomimetic materials for caries prevention.