Antimicrobial properties of light-activated polyurethane containing indocyanine green

The aim of this study was to produce novel antimicrobial polymers containing the light-activated antimicrobial agent indocyanine green (ICG). The novel materials were prepared by swelling polyurethane in acetone containing water and ICG, followed by solvent evaporation. The uptake of ICG was dependent upon the ratio of acetone to water. Only at a ratio of 99 parts acetone to 1 part water was there any substantial colouration of the samples. When exposed to laser light from the near infrared spectrum (808 nm), polyurethane-containing ICG exhibited antimicrobial activity against Gram-positive bacteria; a 2 log₁₀ reduction was achieved against methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus epidermidis after 15 min exposure, corresponding to an energy dose of 31.83 J delivered at an energy density of 31.83 J/cm². Under the same conditions, Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) appeared to be less susceptible, the viable count being reduced by 0.5 log₁₀. Some of the physical properties of the resulting material were also investigated and it was found that the elasticity (Young's modulus) was reduced by approximately 60%. Furthermore, when the ICG-containing polymer was stretched, the breaking point occurred when the elongation was 6.7 times the initial value, while ICG-free polyurethane samples did not break following a 7-fold elongation. The contact angles for water droplets revealed that the ICG-containing polymer was more hydrophobic than untreated polyurethane. The results of this study show that ICG can be embedded in polyurethane to produce materials which when irradiated with near-infrared light can exert a bactericidal effect particularly against MRSA and S. epidermidis. Such materials may be useful for preparing intravenous catheters, which are often colonized by such organisms.