Abstract

Chronic wounds are difficult to treat, require frequent changing of dressings and are slow to heal. Inflammatory status persists in chronic wounds because they are associated with fluids that impair cell growth. Electrospun poly(vinyl alcohol) (PVA) fibers are proven effective at absorbing excess fluid from wounds. Appropriate drugs can also be embedded in such fibers for release into wounds via diffusion to accelerate wound healing. However, to better control the release of antiinflammatory drugs into wounds, controlled drug delivery mechanisms are required.

The goal of this project is to use the unique properties of upconverting nanoparticles (UCNPs) to trigger drug release from electrospun fibers. These nanoparticles absorb near-infrared radiation and emit UV-radiation via an upconversion process. Since the UCNPs are born to have oleates on their surface, a variety of hydrophilic coatings have been screened to stabilize the UCNPs in an aqueous environment. Furthermore, our triggering mechanism relies on the sensitivity of onitrobenzyl (ONB) linkages towards the UV light emitted by the UCNPs. Poly(ethylene glycol) (PEG) was were conjugated through the photo-labile ONB molecules with levofloxacin, an antimicrobial drug whose release can be controlled via exposure of the UCNPs to infrared light. Preliminary drug release tests have shown that the drug conjugated ONB molecules can be cleaved by UV light and by the emission of UCNPs upon excitation with near-infrared light. The photolabile conjugated drug (hvL-PEG) and UCNPs were embedded in electrospun and crosslinked PVA fibers as a model system for a wound healing dressing. The UCNP/hvL-PEG electrospun fibers show high antibacterial activity against the Gram-positive bacteria Staphylococcus aureus and Gram-negative bacteria Escherichia coli.