Abstract
Wounded skin, in patients with underlying disease, can become inflamed and unable to heal (1). The economic burden of chronic wounds is significant and expected to rise substantially in the future. Current treatments are often ineffective, and even when successful there is a high recurrence rate (2).
Growth factors and cytokines are critical for generating an efficient wound healing response, and may potentially be exploited to improve wound healing (3). However to-date, delivery of growth factors and cytokines to wounds has been largely unsuccessful, likely due to increased levels of proteolysis in the wound environment (4).
Orf virus is a zoonotic parapoxvirus which encodes homologues of two proteins that are important in wound healing; vascular endothelial growth factor A (VEGF-A) and interleukin 10 (IL-10). Orf viral VEGF (VEGF-E) increases angiogenesis and endothelial cell migration and proliferation thus accelerating wound closure, while the viral IL-10 (ovIL-10) limits inflammation and reduces scarring (5, 6). These viral proteins are therefore promising wound therapeutics; however a delivery system is required which will protect these proteins from degradation while also enabling their controlled release at physiological concentrations.
We hypothesised that emulsion electrospun nanofibres would be a suitable platform for VEGF-E and ovIL-10 delivery to wounds. This study aimed to develop methods to incorporate the viral proteins into nanofibres and to evaluate their release and bioactivity.
Various FDA-approved synthetic polymers were tested for their ability to form electrospun nanofibres, the morphologies of which were confirmed by scanning electron microscopy (SEM). By loading the fibres with a fluorescently labelled test protein (ovalbumin) we were able to determine the release rate for each nanofibre and found that a fibre comprised of a poly(ethylene)oxide and poly(ɛ-caprolactone) (PEO:PCL) blend produced nanofibres with suitable protein release kinetics.
To enhance detection, VEGF-E and ovIL-10 were conjugated with near infrared (NIR) markers. Labelling VEGF-E did not significantly affect its bioactivity. Labelling of ovIL-10 however, did significantly but not completely reduce its bioactivity. The labelled proteins were then incorporated into the PEO:PCL nanofibres. Confocal scanning laser microscopy was used to demonstrate protein localisation within the core of the fibres, however a continuous core-shell structure was not observed. In solution, VEGF-E (8%) and ovIL-10 (19%) were released within 2 hr, and released proteins were intact when visualised using SDS-PAGE. Following release, VEGF-E bioactivity was confirmed using a receptor binding ELISA. SEM confirmed that Keratinocytes adhered to fibres, while MTT assays indicated that cells grown on the fibres were viable.
This work identified and characterised a method by which VEGF-E and ovIL-10 can be encapsulated into biocompatible nanofibres to both protect the proteins and control their release. Future studies will optimise the release kinetics and therapeutic utility of the nanofibres, in the hope that this will translate into enhanced healing of various types of wounds, particularly chronic wounds.