Abstract
Four formulations have been used to produce different poly(2-hydroxyethyl methacrylate) (PHEMA) thin films, containing singlet oxygen photosensitizer Rose Bengal (RB). The polymers have been characterized employing Thermogravimetric Analysis (TGA), Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) and UV-vis Absorption Spectroscopy. When irradiated with white light (400–700 nm) films generated singlet oxygen (1O2), as demonstrated by the reactivity with 1O2 trap 9,10-dimethylanthracene (DMA). Material with the highest RB loading (polymer A4, 835 nmol RB/g polymer) was able to perform up to ten cycles of DMA oxygenation reactions at high conversion rates (ca. 90%). Polymer A4 was also able to produce the complete eradication of a Pseudomonas aeruginosa planktonic suspension of 8 log10 CFU/mL, when irradiated with white light (total dose 72 J/cm2). The antimicrobial photodynamic effect was remarkably enhanced by adding potassium iodide (100 mM). In such conditions the complete bacterial reduction occurred with a total light dose of 24 J/cm2. Triiodide anion (I3−) generation was confirmed by UV-vis absorption spectroscopy. This species was detected inside the PHEMA films after irradiation and at concentrations ca. 1 M. The generation of this species and its retention in the matrix imparts long-lasting bactericidal effects to the RB@PHEMA polymeric hydrogels. The polymers here described could find potential applications in the medical context, when optimized for their use in everyday objects, helping to prevent bacterial contagion by contact with surfaces.
Highlights
Infections by microorganisms cause the death of 13 million people worldwide annually [1], and the situation is worsening due to the emergence of antibiotic-resistant strains [2]
The development of this scientific discipline started with studies on photosensitization in solution, this approach being termed as antimicrobial photodynamic inactivation, among other denominations [15,16]
Electron or energy transfer can take place to the surrounding ground state oxygen. This process leads to the formation of radical species and/or singlet oxygen (1O2, via type II mechanism), which induce the killing of pathogenic microorganisms
Summary
Infections by microorganisms cause the death of 13 million people worldwide annually [1], and the situation is worsening due to the emergence of antibiotic-resistant strains [2]. An alternative strategy that is receiving increasing attention is the use of visible light to activate materials via the encapsulation of a photosensitizer capable of converting the absorbed energy into cytotoxic species. The mechanism of photosensitization implies the absorption of light by a molecule that is activated to an excited state. Electron or energy transfer can take place (type I and II mechanisms, respectively) to the surrounding ground state oxygen. This process leads to the formation of radical species (hydroxyl radical, superoxide anion, via type I mechanism) and/or singlet oxygen (1O2, via type II mechanism), which induce the killing of pathogenic microorganisms. Polymeric matrix recently used in aPDI include, among others, polystyrene nanofibers [28], polylactic acid [29], polyolefin thermoplastic elastomers [30], pyridinium modified Merrifield resins [31], polyether block amide [32], chitosan [33], wool keratine [34], cellulose [35], nylon [36] and polyacrylonitrile [36]
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