Poly(vinyl alcohol) and Methylglyoxal Hybrid Fibres for Antibacterial Wound Dressing Materials

Various bioactive wound dressing materials exist on the market that are designed to aid recovery and comfort of patients with chronic wounds. However, one of the persistent issues is the control of bacterial activity in the wound, which can influence infection rates, efficacy of wound healing and odour generation. A key requirement of a wound dressing is to facilitate a moist wound-healing environment and simultaneously control the growth of bacteria using an antibacterial agent. Manuka honey is currently utilised in bioactive wound dressing materials as an antibacterial agent via the direct impregnation or coating of honey onto a suitable material. It provides a unique antibacterial potency, attributable to one of its constituents, methylglyoxal (MGO). Commercially, there have been relatively few examples of electrospun fabric components being integrated into advanced wound care products. However, many studies have explored the potential of electrospun webs as part of a novel wound dressing material, due to their inherent nano and micro-fibrous structure, which provides a high surface area available for active delivery. In this research, synthetic MGO was evaluated for its effectiveness as a novel antibacterial agent, when encapsulated into an electrospun poly(vinyl alcohol) (PVA) hydrogel forming web. In the first phase of this research, the antibacterial activity of both Manuka honey and synthetic MGO when applied as a topical coating to a nonwoven fabric was assessed via two British standard methods using Gram positive and Gram negative bacteria in-vitro. BS EN ISO 20743:2007 was employed as a quantitative method to establish if Manuka honey and synthetic MGO provided an antibacterial effect at equivalent MGO concentrations. It was found that concentrations of 0.0054 mg cm -2 of MGO in the form of Manuka honey and synthetic MGO was sufficient to achieve 100% reduction in bacteria for both Gram positive and Gram negative strains. Further tests were then carried out using BS EN ISO 20645:2004, which assessed the zone of inhibition using a seeded bacteria agar plate. In this case, higher concentrations between 0.0170 mg cm -2 and 0.1 mg cm -2 were required to facilitate a good antibacterial effect. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) was also assessed for MGO in liquid form against the three most prevalent wound pathogens, Staphylococcus. aureus, Pseudomonas. aeruginosa and Enterococcus. faecalis. Concentrations similar to that found in the literature, between and 128 mg L -1 and 1024 mg L were shown to provide either a bacteriostatic or bactericidal effect. Most importantly, the MIC and MBC of MGO against Enterococcus. faecalis was reported for the first time. -1. The encapsulation of synthetic MGO in electrospun PVA fibres was explored using both needle and free surface (needleless) electrospinning technologies, with a successful outcome. It was found that an 11.22 wt % MGO solution with 16% (w/v) PVA was most favourable for producing fibres free from beads when using needle electrospinning. A higher PVA concentration of 20% (w/v) was required to achieve bead free fibres using free surface electrospinning. Two different collector materials were utilised during free surface electrospinning, where an aluminium foil collector was found to produce a smaller mean fibre diameter when compared with a less conductive polypropylene spundbond substrate. Characterisation of the as-spun webs was determined via Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (NMR), where the presence of MGO in the PVA webs was confirmed by the characteristic carbonyl groups associated with MGO’s keto-aldehyde groups. A continuation of the zone of inhibition method highlighted that concentrations of MGO between 1.14 mg cm -2 and 1.50 mg cm -2 were required to have an antibacterial effect in-vitro. Finally the release behaviour of MGO from the electrospun webs was investigated using high performance liquid chromatography (HPLC). Crosslinking of the PVA/MGO webs with glutaraldehyde (GA), in the form of a vapour and a novel plasma technique showed promising results for controlling the release rate of MGO from the fibres. Prior to crosslinking, 93.7% of the MGO was released from the PVA fibres within 30 minutes. After crosslinking the amount of MGO released was considerably reduced over a period of 24 h, with a maximum of 75% released. The novel plasma crosslinking technique was further confirmed using FTIR and it is believed this is the first time this technique has been employed.