Silver-doped phosphate coacervates and remote Cold Atmospheric Plasma effluent to inhibit bacteria associated with wound infections
Creators: name: Nikolaou, Athanasios
Publisher: name: University of Surrey
Year: 2023

description: There is a great demand from patients requiring skin repair due to poorly healed acute or chronic wounds. These patients usually suffer from constant inflammation and are at high risk of life-threatening infections. Therefore, new treatments that rapidly stimulate healing and simultaneously prevent bacterial infections are urgently needed. In this thesis, two novel chemistry-based methods are presented, designed and aimed to stimulate the growth of human keratinocyte cells and simultaneously inhibit pathogenic bacteria associated with wound infections. The first method is based on the use of silver-doped Phosphate-based Coacervate (PC_Ag) as a novel material, investigating its cytocompatibility and antibacterial efficacy against pathogenic bacteria. The second method explores the antibacterial activity of Reactive Oxygen and Nitrogen Species (RONS) produced by a Remote Cold Atmospheric Plasma (ReCAP) effluent. Phosphate-based coacervate (PC) gels have recently been the subject of increased interest because of their great potential as controlled delivery systems in tissue regeneration. Being bioresorbable, they dissolve over time and simultaneously release therapeutic species in a controlled manner.[1] A particularly interesting class of therapeutic species are metallic ions, a promising alternative to conventional antibiotics due to their strong antibacterial efficacy and low bacterial resistance.[2] This work investigates the therapeutic potential of PC gels containing different loadings of the antibacterial ion Ag+. Dissolution tests in deionised water and cell media have demonstrated that the controlled release of Ag+ results in a significant antibacterial activity against Gram positive and Gram negative bacteria (up to a 7-log bacterial reduction) associated to wound infections. Other species that might also play a role in tissue regeneration[3], such as P, Ca2+ and Na+, were also released from the gels in a controlled manner. Biocompatibility studies have demonstrated that the viability of human keratinocytes (HaCaT cells) increases when exposed to our PC_Ag gels.<br>
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description: The ReCAP effluent refers to a prototype patented device sponsored by Fourth State Medicine Ltd (FSM).[4] ReCAP effluent is a gas flow containing RONS that are previously generated in a CAP device with a dielectric barrier discharge.[5] RONS are known to be able to inhibit bacteria; thus, we have investigated the antibacterial effect of the ReCAP effluent when administered to pathogenic bacteria at several exposure times and different Reactive Nitrogen Species (RNS) and Reactive Oxyge Species (ROS) (i.e. H2O2, NO3-, NO2-) ratios. The pathogens included Staphylococcus aureus, Enterococcus faecalis, Escherichia coli and Pseudomonas aeruginosa, and the antibacterial monitoring was conducted at a cellular and molecular level using Fluorescence-Activated Cell Sorting (FACS), Scanning Electron Microscopy (SEM) and quantitative Reverse Transcriptase-PCR (qRT-PCR). Data showed that the abundance of RNS triggers the appearance of punch-like holes and membrane depolarization in bacterial cells, resulting in a bactericidal effect. In contrast, ROS-enriched effluents induce a more bacteriostatic action associated with increased permeability and biofilm formation. The final part of the PhD work investigates synergies between the ReCAP effluent and the PC_Ag gels. PC_Ag gels were initially exposed to ReCAP effluent and then challenged against S. aureus and E. coli, reference organisms for Gram-positive and Gram-negative bacteria, respectively. Results showed that gels exposed to RONS displayed a significant, enhanced antibacterial activity against the two bacteria. Our results indicate that PC_Ag gels and the ReCAP effluent are very promising alternatives to current wound healing treatments. PC_Ag gels are capable to inhibit Gram-positive and Gram-negative bacteria associated with wound infections as well as improve skin cell viability. <br>