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Abstract
Infection of surgical implants is a costly and life-threatening problem which threatens to become more prevalent as implanted devices become more common. Antibiotic treatment is often unsuccessful due to the formation of biofilms, and is a contributing factor to bacterial resistance to antibiotics. A promising strategy to combat implant infection is anti-infective surface coating technology, and antimicrobial peptides (AMPs) offer an exciting avenue in this regard.
The ideal implant surface not only resists microbial colonisation, but also encourages host tissue integration. Certain peptide sequences can be employed towards this aim, such as arginine-glycine-aspartic acid (RGD).
This thesis tests a range of novel peptide sequences, based on the synthetic AMP melimine and in some cases incorporating RGD, for antimicrobial activity and cytotoxicity. The peptides tested also contain a single cysteine residue, which allows site-directed attachment through a unique sulfhydryl (-SH) group. A plasma polymer coating method described in this thesis renders any desired surface suitable for peptide coating, by the addition of free amine (-NH3) groups and the use of an amine-to-sulfhydryl maleimide linker.
A highly cationic 18-residue peptide, C Mel4, was identified as antimicrobial and biocompatible. In soluble form, C-Mel4 was lethal to common device-related bacterial pathogens including a methicillin-resistant Staphylococcus aureus (MRSA) isolate, and was toxic to mammalian cells only at high concentrations. When applied as a surface coating, C-Mel4 reduced adhesion of the same bacterial pathogens by approximately 60% and no toxicity was observed.
The in vitro responses of human dermal fibroblasts and epidermal keratinocytes to surfaces coated with C-Mel4 and other peptides were studied. Cells formed focal adhesions and stress fibres in contact with C-Mel4 and other peptide-coated surfaces.
C-Mel4 is an excellent candidate for further testing, including determination of the precise molecular mechanisms of mammalian tissue interaction; examination of the immune response to the peptide coating; and determination of the stability of the peptide coating over extended periods.