Enhanced antibacterial activity of starch-alginate beads by a synergistic effect between Cu2+ and Zn2+ ions with a potential wound dressing application

Abstract

The synthesis and characterisationof starch/alginate composite beads, crosslinked with Cu2+, Zn2+,and Cu:Zn mixtures were investigated, focusing on their potential application inexudative wound dressings. Hydrogel beads were prepared using the externalgelation method and then dried via freeze-drying to create cryogels andair-drying to create xerogels. Microstructural characterisation was performed usingSEM and EDS, showing the typical porous structure with a homogeneousdistribution of cations across the beads. Unimetallic beads exhibited higherequilibrium water uptake compared to Cu:Zn bimetallic beads (500 % vs. 300 %).After the swelling study, the total amount of Cu2+ released was significantlybelow the maximum allowed level as a safeguard against copper toxicity. Allbeads demonstrated excellent antimicrobial activity against E. coli, S. aureus, and P. aeruginosa.Bimetallic materials, particularly cryogels with equal or greater amount ofzinc relative to copper, were particularly effective against P. aeruginosa. Hence, the synthesisedbimetallic starch-alginate materials presented superior water absorptioncapacity and significantly enhanced antibacterial response compared to unimetallicbeads, due to the synergistic effect between Cu2+ and Zn2+ions, making then suitable for use in exudative wound dressings.