Abstract
Silver-particle-incorporated polyurethane films were evaluated for antimicrobial activity towards two different bacteria: Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Distributed silver particles sourced from silver nitrate, silver lactate and preformed silver nanoparticles were mixed with polyurethane (PU) and variously characterized by field emission scanning electron microscopy (FESEM), fourier transform infra-red (FTIR) spectroscopy, X-ray diffraction (XRD) and contact angle measurement. Antibacterial activity against E.coli was confirmed for films loaded with 10% (w/w) AgNO3, 1% and 10% (w/w) Ag lactate and preformed Ag nanoparticles. All were active against S. aureus, but Ag nanoparticles loaded with PU had a minor effect. The apparent antibacterial performance of Ag lactate-loaded PU is better than other Ag ion-loaded films, revealed from the zone of inhibition study. The better performance of silver lactate-loaded PU was the likely result of a porous PU structure. FESEM and FTIR indicated direct interaction of silver with the PU backbone, and XRD patterns confirmed that face-centred cubic-type silver, representative of Ag metal, was present. Young’s modulus, tensile strength and the hardness of silver containing PU films were not adversely affected and possibly marginally increased with silver incorporation. Dynamic mechanical analysis (DMA) indicated greater thermal stability.
Highlights
Implanted medical devices become increasingly vulnerable with time to microbial colonization
Silver is less prone to microbial resistance than antibiotics, especially if rapid bactericidal action is achieved [34]
Once silver does bind to microbial cells, it denatures crucial proteins, disrupts DNA and RNA, inhibits cell replication and, causes cell death
Summary
Implanted medical devices become increasingly vulnerable with time to microbial colonization. Gram-negative Escherichia coli (E. coli) and Pseudomonas aeruginosa, though infections tend to be more severe with S. aureus and E. coli [2] Such nosocomial pathogens colonize both the outer and inner surfaces of catheters and are characteristically multi-antibiotic-resistant. They can lead to bloodstream infection with high morbidity and mortality [3]. S. aureus is a common cause of infection, its pathogenicity being partly due to coagulase production This enables it to coagulate plasma in its microenvironment, helping to protect it from host defence mechanisms. Effectiveness cannot be guaranteed, even with a potent topical antibiotic, such as silver sulphadiazine [10], and alternatives are constantly needed In this context, it is notable that mupirocin, whilst much more potent against S. aureus, does not provide universal coverage [11].
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