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 characterization of starch/alginate composite beads, crosslinked with Cu²⁺, Zn²⁺, and Cu:Zn mixtures were investigated, focusing on their potential application in exudative wound dressings. Hydrogel beads were prepared using the external gelation method and then dried via freeze-drying to create cryogels and air-drying to create xerogels. Microstructural characterization was performed using SEM and EDS, showing the typical porous structure with a homogeneous distribution of cations across the beads. Unimetallic beads exhibited higher equilibrium water uptake compared to Cu:Zn bimetallic beads (500 % vs. 300 %). After the swelling study, the total amount of Cu²⁺ released was significantly below the maximum allowed level as a safeguard against copper toxicity. All beads demonstrated excellent antimicrobial activity against E. coli, S. aureus, and P. aeruginosa. Bimetallic materials, particularly cryogels with equal or greater amount of zinc relative to copper, were particularly effective against P. aeruginosa. Hence, the synthesized bimetallic starch-alginate materials presented superior water absorption capacity and significantly enhanced antibacterial response compared to unimetallic beads, due to the synergistic effect between Cu²⁺ and Zn²⁺ ions, making then suitable for use in exudative wound dressings.

Keywords: Alginate; Antibacterial activity; Starch.