Comparative study of novel in situ decorated porous chitosan-selenium scaffolds and porous chitosan-silver scaffolds towards antimicrobial wound dressing application.

Dermal defects caused by trauma or disease are challenging to treat due to difficult-to-treat infections that impair wound healing. Due to the widespread emergence of drug-resistant bacteria and dwindling discoveries of new antibiotics, there is currently an urgent need to introduce novel antimicrobials effective against antibiotic-resistant bacteria without causing damage to host tissues. As selenium (Se) and silver (Ag) are known for their antimicrobial properties, we investigated the separate loading of these materials into porous chitosan/PVA (CS) scaffolds through a simple in situ deposition method to create two distinct wound dressing materials (CS-Se and CS-Ag). Scaffolds with Se nanostructures and scaffolds containing Ag nanostructures were characterized and their activities against S. aureus - (a Gram-positive bacterium), E. coli - (a Gram-negative bacterium) and Methicillin-Resistant S. aureus (MRSA) - (a multi-drug resistant bacterium) were compared. The release of Ag and Se in vitro was shown to depend strongly on the release medium used (deionised water, mammalian or bacterial culture media). Ag-loaded scaffolds showed a significant reduction in CFUs and cytotoxicity towards fibroblasts while Se-loaded scaffolds showed abilities to damage bacterial cell membrane and non-toxicity to fibroblast. Overall, in this study we have demonstrated simple, in situ immobilization porous CS scaffolds with either Se or Ag nanostructures which could be used to suit different wound healing applications.

Low cytotoxic trace element selenium nanoparticles and their differential antimicrobial properties against S. aureus and E. coli.

Antimicrobial agents that have no or low cytotoxicity and high specificity are desirable to have no or minimal side effects. We report here the low cytotoxicity of polyvinyl alcohol-stabilized selenium (Se) nanoparticles and their differential effects on growth of S. aureus, a gram-positive bacterium and E. coli, a gram-negative bacterium. The nanoparticles were synthesised through redox reactions in an aqueous environment at room temperature and were characterised using UV visible spectrophotometry, transmission electron microscopy, dynamic light scattering and x-ray photoelectron spectroscopy. The nanoparticles showed low toxicity toward fibroblasts which remained more than 70% viable at Se concentrations as high as 128 ppm. The nanoparticles also exhibited very low haemolysis with only 18% of maximal lysis observed at a Se concentration of 128 ppm. Importantly, the nanoparticles showed strong growth inhibition toward S. aureus at a concentration as low as 1 ppm. Interestingly, growth of E. coli was unaffected at all concentrations tested. This study therefore strongly suggests that these nanoparticles should be investigated further to understand this differential effect as well as for potential advanced antimicrobial applications such as S. aureus infection-resisting, non-cytotoxic coatings for medical devices.

Assembly and degradation of low-fouling click-functionalized poly(ethylene glycol)-based multilayer films and capsules.

Nano-/micrometer-scaled films and capsules made of low-fouling materials such as poly(ethylene glycol) (PEG) are of interest for drug delivery and tissue engineering applications. Herein, the assembly and degradation of low-fouling, alkyne-functionalized PEG (PEG(Alk) ) multilayer films and capsules, which are prepared by combining layer-by-layer (LbL) assembly and click chemistry, are reported. A nonlinear, temperature-responsive PEG(Alk) is synthesized, and is then used to form hydrogen-bonded multilayers with poly(methacrylic acid) (PMA) at pH 5. The thermoresponsive behavior of PEG(Alk) is exploited to tailor film buildup by adjusting the assembly conditions. Using alkyne-azide click chemistry, PEG(Alk)/PMA multilayers are crosslinked with a bisazide linker that contains a disulfide bond, rendering these films and capsules redox-responsive. At pH 7, by disrupting the hydrogen bonding between the polymers, PEG(Alk) LbL films and PEG(Alk) -based capsules are obtained. These films exhibit specific deconstruction properties under simulated intracellular reducing conditions, but remain stable at physiological pH, suggesting potential applications in controlled drug release. The low-fouling properties of the PEG films are confirmed by incubation with human serum and a blood clot. Additionally, these capsules showed negligible toxicity to human cells.