Controlling biofilm formation on dental implants : an experimental and computational study of natural compounds in layer-by-layer functionalised electrospun membranes

Abstract

Guided Bone Regeneration (GBR) after dental implant placement is at risk of failure should bacterial and biofilm growth occur around wound site. Current barrier membranes can maintain site structure, and incorporation of antibacterial components and antibiotics can provide a surface resistant to bacteria. This PhD project assessed the utility of natural compounds (Manuka Honey 400, Manuka Honey 550+, Tea Tree Oil, and Lemon Oil) for their efficacy as antimicrobial agents and for their biocompatibility, as an alternative to antibiotics. Two bacteria commonly associated with implant failure, Staphylococcus aureus NCTC 6571 and Porphyromonas gingivalis W50, were exposed to selected compounds to evaluate their minimum inhibitory and bactericidal concentrations. Mammalian neo-natal fibroblasts and osteoblasts hFOB1.19 were exposed to the same compounds to evaluate their cytotoxicity. All the selected compounds inhibited bacterial growth and were cytotoxic for the mammalian cells at different concentrations. Given its better biocompatibility, Manuka Honey (MH) 550+ was selected for further tests. This project then sought to provide a proof of concept of a physical barrier membrane, nanolayers of 20%w/v Manuka Honey 550+ were functionalised onto poly(ε-caprolactone) electrospun membranes via layer-by-layer assembly using in-house automation. Membranes were imaged, and characterised via scanning electron microscopy, Fourier transform infrared spectroscopy, and release profiles, before analysing cytotoxic and antimicrobial effects. Functionalised membranes showed good bonding up to 14 nanolayers. Inhibition of S. aureus and P. gingivalis was comparable to bare electrospun membranes, however MH membranes allowed greater proliferation of mammalian cells during initial growth period demonstrating their benefits as a therapeutic barrier membrane. Finally, an agent-based model was developed to provide qualitative comparisons to in vitro results mimicking a top-down view of an agar plate during bacterial growth that agreed qualitatively to the experimental results. The mathematical model shows a framework for simulating an antimicrobial membrane with defined parameters, which can be based on experimental measurements, and can be used in the development of an ideal membrane for the oral cavity during GBR.