In 2008, researchers at the University of Sheffield published work regarding the synthesis of a triblock copolymer which formed a biocompatible gel suitable for use in wound dressings.1Unexpectedly, these gels also exhibited antimicrobial activity towards a range of microorganisms.2 This work has recently been further studied in a collaboration between the Department of Chemistry, the School of Clinical Dentistry and the Department of Engineering Materials at the University of Sheffield. This study aimed to understand more about the relationship between the polymer structure or architecture and its antimicrobial activity. This exciting research has potential be used in the future to provide alternatives to standard antibiotic treatments in a society where they have become much overused and antibacterial resistance is a growing problem.3
The original material synthesised had an ABA structure comprising of blocks of 2-hydroxypropyl methacrylate (HPMA) and 2-(methacryloyloxy) ethyl phosphorylcholine (MPC).An analogous graft-copolymer has been synthesised where PHPMA chains have been attached onto a PMPC chain via RAFT polymerisation, a form of controlled free-radical polymerisation used frequently by the research group of Professor Steve Armes in the Department of Chemistry. As well as this, AB diblock copolymers of the same monomers have been synthesised and shown to form self-assembled ‘worm-gels’. This novel material is biocompatible and has also been used in this study to determine if it is due to the gel property of polymers with this composition which leads to their antimicrobial properties.
Biological assays with staphylococcus aureus have been carried out on all of these PHPMA-PMPC materials to determine more about the mechanism of antimicrobial activity. Results have shown that the ‘worm-gels’, although biocompatible gels, were not antimicrobial. However, the graft copolymer gels have been shown inhibit bacterial growth and further studies by transmission electron microscopy show that this is likely due to the hydrophobic PHPMA chains in the gel penetrating and therefore causing damage to the bacterial membrane. Another interesting property of this graft copolymer gel is its thermoreversible gelation behaviour, making it applicable in the formation of antibacterial smart wound dressings.
Original article: Antimicrobial Graft Copolymer Gels. A. C. Harvey, J. Madsen, C. W. I. Douglas, S. MacNeil, S. P. Armes, Biomacromolecules, 2016, 2710-2718
Article by Rheanna Perry; a PhD Student on the EPSRC Polymers, Soft Matter and Colloids CDT programme. For more information, please contact Dr Joe Gaunt at the Polymer Centre.
(1) Madsen, J.; Armes, S. P.; Bertal, K.; Lomas, H.; MacNeil, S.; Lewis, A. L. Biomacromolecules 2008, 9 (8), 2265–2275.
(2) Bertal, K.; Shepherd, J.; Douglas, C. W. I.; Madsen, J.; Morse, A.; Edmondson, S.; Armes, S. P.; Lewis, A.; MacNeil, S. J. Mater. Sci. 2009, 44 (23), 6233–6246.
(3) Harvey, A. C.; Madsen, J.; Douglas, C. W. I.; MacNeil, S.; Armes, S. P. Biomacromolecules 2016, 17 (8), 2710–2718.