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Silver is an antimicrobial commonly used within wound care chiefly in advanced dressings or in a topical cream form, such as silver sulfadiazine (SSD). Although silver is effective at controlling the growth of many common wound bacteria, it can be cytotoxic and can build up in tissue, stalling the healing process. Here, we demonstrate the development of an on-demand release system for delivery of silver from a composite hydrogel comprising sodium polyacrylate particles dispersed in a cryo-crosslinked polyvinyl alcohol carrier gel. Application of cold atmospheric plasma (CAP) jet to the silver loaded hydrogel resulted in controlled release of silver. This release is thought to occur due to the formation of nitrous acids in the hydrogel by the CAP, resulting in protonation of carboxylate groups in the hydrogel and subsequent gel de-swelling due to the reduction in interchain charge repulsion. The location of silver within the sodium polyacrylate particles was probed using scanning electron microscopy and EDX imaging. The released silver inhibited the growth of Enterococcus faecalis, Pseudomonas aeruginosa, and Staphylococcus aureus and significantly reduced the viable cell count of the P. aeruginosa biofilm.

We present the concept of a versatile drug-loaded composite hydrogel that can be activated using an argon-based cold atmospheric plasma (CAP) jet to deliver both a drug and CAP-generated molecules, concomitantly, in a tissue target. To demonstrate this concept, we utilized the antibiotic gentamicin that is encapsulated in sodium polyacrylate (PAA) particles, which are dispersed within a poly(vinyl alcohol) (PVA) hydrogel matrix. The final product is a gentamicin-PAA-PVA composite hydrogel suitable for an on-demand triggered release using CAP. We show that by activating using CAP, we can effectively release gentamicin from the hydrogel and also eradicate the bacteria effectively, both in the planktonic state and within a biofilm. Besides gentamicin, we also successfully demonstrate the applicability of the CAP-activated composite hydrogel loaded with other antimicrobial agents such as cetrimide and silver. This concept of a composite hydrogel is potentially adaptable to a range of therapeutics (such as antimicrobials, anticancer agents, and nanoparticles) and activatable using any dielectric barrier discharge CAP device.

The study compares how acetyl donor molecules tetraacetylethylenediamine (TAED) and pentaacetate glucose (PAG) improve the antibacterial efficacy of solutions activated with a low-temperature atmospheric-pressure argon plasma jet. Plasma activation of solubilised TAED and PAG produce solutions with different chemical compositions and oxidative potentials. Both acetyl donor molecules enhance the hydrogen peroxide (H2O2) concentration in solution with TAED being more effective compared to PAG. However, PAG is more effective at forming peracetic acid (PAA) from reaction of its acetyl donor groups with plasma generated H2O2. The enhanced oxidative potential of plasma activated TAED and PAG solutions were shown to significantly improve bactericidal activity against common wound pathogens Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus compared to plasma activated water produced without acetyl donors. Furthermore, the oxidative capacity of plasma activated PAG was least affected by the bacterial oxidative defence enzyme catalase, attributed to the high concentration of PAA produced in this formulation. Overall, the above data show that acetyl donors may help improve next generation of antimicrobial formulations produced by plasma, which might help combat increasing problems of antimicrobial resistance.

The main bactericidal components of cold atmospheric plasma (CAP) are thought to be reactive oxygen and nitrogen species (RONS) and UV-radiation, both of which have the capacity to cause DNA damage and mutations. Here, the mutagenic effects of CAP on Escherichia coli were assessed in comparison to X- and UV-irradiation. DNA damage and mutagenesis were screened for using a diffusion-based DNA fragmentation assay and modified Ames test, respectively. Mutant colonies obtained from the latter were quantitated and sequenced. CAP was found to elicit a similar mutation spectrum to X-irradiation, which did not resemble that for UV implying that CAP-produced RONS are more likely the mutagenic component of CAP. CAP treatment was also shown to promote resistance to the antibiotic ciprofloxacin. Our data suggest that CAP treatment has mutagenic effects that may have important phenotypic consequences.

We explore how to configure an argon atmospheric-pressure plasma jet for enhancing its production of hydrogen peroxide (H2O2) in deionised water (DIW). The plasma jet consists of a quartz tube of 1.5 mm inner diameter and 3 mm outer diameter, with an upstream internal needle electrode (within the tube) and a downstream external cylindrical electrode (surrounding the tube). The plasma is operated by purging argon through the glass tube and applying a sinusoidal AC voltage to the internal needle electrode at 10 kV (peak-peak) with a frequency of 23.5 kHz. We study how the following operational parameters influence the production rate of H2O2 in water: tube length, inter-electrode separation distance, distance of the ground electrode from the tube orifice, distance between tube orifice and the DIW, argon flow rate and treatment time. By examining the electrical and optical properties of the plasma jet, we determine how the above operational parameters influence the major plasma processes that promote H2O2 generation through electron-induced dissociation reactions and UV photolysis within the plasma core and in the plasma afterglow; but with a caveat being that these processes are highly dependent on the water vapour content from the argon gas supply and ambient environment. We then demonstrate how the synergistic action between H2O2 and other plasma generated molecules at a plasma induced low pH in the DIW is highly effective at decontaminating common wound pathogens Gram-positive Staphylococus aureus and Gram-negative Pseudomonas aeruginosa. The information presented in this study is relevant in the design of medical plasma devices where production of plasma reactive species such as H2O2 at physiologically useful concentrations is needed to help realise the full clinical potential of the technology.

Herein, we report a series of di-anionic supramolecular self-associating amphiphiles (SSAs). We elucidate the antimicrobial properties of these SSAs against both methicillin resistant Staphylococcus aureus and Escherichia coli. In addition, we show this class of compound to form both intra- and intermolecular hydrogen bonded macrocyclic structures in the solid state.

We investigate the ability to disrupt and limit growth biofilms of Pseudomonas aeruginosa using application of cold atmospheric pressure (CAP) plasma. The effect of the bio-film's exposure to a helium (CAP) jet was assessed at varying time points during biofilm maturation. Results showed that the amount of time during biofilm growth that CAP pressure was applied has a crucial role on the ability of biofilms to mature and recover after CAP exposure. Intervention during the early stages of biofilm formation (0-8 h) results in a 4-5-log reduction in viable bacterial cells (measured at 24 h of incubation) relative to untreated biofilms. However, CAP treatment of biofilm at 12 h and above only results in a 2-log reduction in viable cells. This has potentially important implications for future clinical application of CAP to treat infected wounds.