Developing a single dressing containing both antifungal and antibacterial drugs for treating mixed infections in diabetic foot ulcers

The prevalence of chronic wounds such as diabetic foot ulcers (DFUs) is growing at an epidemic rate in the United Kingdom, with a high cost burden for the National Health Service and are prone to infections. Mixed bacterial-fungal infections are more complicated than single microbe infections with enhanced severity of DFUs. Moreover, recently developed medicated dressings target only either bacterial or fungal infection. This study therefore aims to develop advanced bioactive calcium alginate-based dressings that will deliver therapeutically relevant doses of broad-spectrum antibiotic and antifungal drugs to target mixed infections in DFUs. The therapeutic calcium alginate (CA) based dressings were prepared as films and wafers by solvent casting and freeze-drying technique respectively, with ciprofloxacin (CIP) and fluconazole (FLU) as model antibacterial and antifungal drugs respectively. The dressings were physically characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and texture analysis. Further functional characterization for exudate handling properties included porosity, water absorption (Aw), equilibrium water content (EWC), swelling index (Is), water vapour transmission rate (WVTR), evaporative water loss (EWL) and moisture content, drug dissolution by HPLC, in vitro antimicrobial and cell viability (biocompatibility) studies. Further, the exudate handling, antimicrobial and cell viability properties of the dressings were compared with commercial silver and CA based Algisite Ag® and hydrogel Actiformcool®. The drug loaded films were transparent, flexible, uniform, durable and elastic while drug loaded wafers were soft, uniform texture and thickness, and pliable in nature. SEM investigation showed differences in surface morphology between films (continuous sheets) and wafers (porous matrix). XRD confirmed the presence of calcium carbonate in the dressings and FTIR showed that the addition of drug caused the shift of peaks towards a higher wavenumber due to hydrogen bonding formation. Wafers showed better wound dressing properties than films and the commercial dressings for swelling, EWC (91 ̶ 95%), Aw (1085 ̶ 2377%) and moisture content (9 ̶ 17%) due to high porosity. The dressings showed initial fast release followed by sustained drug release which completely eradicated all causative bacteria (Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus) and reduced fungal load (Candida albicans) 10 fold within 24 h. Moreover, the medicated dressings were found to be highly biocompatible (> 70% cell viability over 72 h) with human primary adult keratinocytes and showed maximum wound closure (in vitro scratch assay) within 7 days. CA wafers and films appeared to be potential delivery systems for delivering antimicrobial agents to mixed infected DFUs.