REPOSITORY > RESULTS

Abstract

In this study, multifunctional polymer-based composite coatings were developed to combine either (i) the contact-based antibacterial activity of magnesium oxide (MgO) with the bioactive properties of magnesium ions (the dissolved form of MgO), or (ii) the antibacterial properties of vanadium pentoxide (V₂O₅), mediated by biomimetic myeloperoxidase-like catalytic activity, with the bioactivity of low concentrations of vanadate ions (the dissolved form of V₂O₅). I investigated the correlations between (i) antibacterial activity and (ii) the mechanisms controlling metal oxide dissolution kinetics within polymer-based coatings and the structural properties of the processed materials.
The appropriate design of the MgO surface is crucial at both the nanoscale and the atomic scale because of its contact-based antibacterial mechanism. I confirmed that nanotexturing the surfaces of MgO microrods improved their antibacterial activity against _Escherichia coli_ (_E. coli_, ATCC 47076). Optimal nanotexturing of the MgO microrods was achieved by calcination at 900 °C (MgO 900), making them more potent antibacterial agents than commercially available MgO nanoparticles (MgO NPs). This difference could not be explained by differences in morphology or specific surface area. Rather, it resulted from a lower abundance of low-coordinated oxygen atoms on the MgO surface, which improved its resistance to hydrolysis and enhanced its antibacterial activity. Regarding reactive oxygen species (ROS), I demonstrated that their generation was a by-product of either (i) MgO hydrolysis or (ii) interactions between MgO and bacteria, rather than an inherent property of MgO.
The catalytic properties of one-dimensional (1D) nanostructured V₂O₅ were related to its structural characteristics. I confirmed that pure orthorhombic V₂O₅ nanowires exhibited stronger myeloperoxidase-mimicking antibacterial activity than intercalated (MH₂O, K) MₓV₂O₅ nanoribbons. The unique ability of V₂O₅ to exhibit self-sustained antibacterial activity, without requiring H₂O₂ in the surrounding environment, based on its myeloperoxidase-like catalytic activity, was discovered and described.
The ability of different polymeric carriers and metal oxide particle morphologies to modulate the in vitro stability of the prepared metal oxide/polymer matrix composite coatings was assessed. I highlighted the correlation between the strength of interactions at the metal oxide/polymer interface and the stability of the composites under simulated physiological conditions. The appropriate choice of metal oxide particle morphology enabled control over both particle agglomeration and metal oxide dissolution. One-dimensional anisotropic particles exhibited reduced agglomeration compared with isotropic particles, improving their processing characteristics. In addition, using 1D particles instead of isotropic particles eliminated the initial burst release of dissolved metal ions.
The optimal properties were obtained with a poly(lactide-co-glycolide) (PLGA) polymer matrix, which enabled partially exposed 1D metal oxide particles to remain at the coating surface upon exposure to the surrounding medium. This was crucial for effectively preventing the colonisation of the surface by _Staphylococcus epidermidis_ (NCIMB 8853), while ensuring that no harmful effects on red blood cells occurred.