Antimicrobial activity of novel biocompatible wound dressings based on triblock copolymer hydrogels

Wound infection is a common complication often resulting in delayed healing with adverse clinical and financial consequences. Current antimicrobial treatments are far from ideal, side effects can include both bacterial resistance and toxicity. As a result, a great deal of effort over the last 20 years has been spent on investigating new forms of antimicrobial dressings. Here, we report the unexpected antimicrobial activity of a relatively new biocompatible thermo-responsive PHPMA-PMPC-PHPMA triblock copolymer gelator [where PHPMA denotes poly(2-hydroxypropyl methacrylate) and PMPC denotes poly(2-(methacryloyloxy)ethyl phosphorylcholine)]. In a radial diffusion assay, a 20% w/v copolymer gel produced an inhibitory zone up to six times greater than the corresponding control against Staphylococcus aureus. Similarly, in a broth inhibition assay the same copolymer reduced bacterial growth by 45% compared with control experiments conducted in the absence of any copolymer. Moreover, addition of the copolymer to a 3D-infected skin model reduced bacterial recovery by 38% compared to that of controls over 24-48 h. This is particularly relevant since these antimicrobial triblock copolymers were recently shown to be non-toxic when exposed to a tissue-engineered skin model. This antimicrobial activity was also successfully immobilised by grafting PMPC-PHPMA diblock copolymer brushes onto silicon wafers. Our results indicate that both PMPC-PHPMA diblock and PHPMA homopolymer brushes exhibit antimicrobial activity. Our hypothesis for the mode of action is that the moderately hydrophobic PHPMA chains penetrate the bacterial membrane, causing leakage of the cell contents. In summary, these gels and surfaces offer a promising new approach to antimicrobial dressings.