Synthesis and characterization of sustainable Zn(II) and ZnO/chitosan Schiff base hydrogel for antimicrobial application

A significant amount of interest in Schiff bases (SBs) produced from metal-based hydrogels and chitosan has recently been garnered for their biological applications. We successfully synthesised a new hydrogel by crosslinking chitosan with 2,3,4-trihydroxybenzaldehyde (THB) to produce chitosan Schiff base (CSB) and subsequently created its Zn(II) metal composite and ZnO nanoparticles. Two different concentrations of Zn(II) ions (1% w/v and 1.5% w/v) and mass ratio of (CS: THB) of 1.0:0.25, 1.0:0.5, 1.0:1.0 and 1.0: 1.5 were studied. The structure and characteristics of the composite hydrogels are characterised using various techniques. The synthesised CSB and its nanocomposites were confirmed using XRD analysis, UV–Vis spectroscopy, and FTIR. The interactions among chitosan and metals, thermal stability, surface shape, and the elemental presence of metal ions in the hydrogels were analysed using FTIR, TGA, SEM, NMR, and EDX techniques. The synthesized CSB hydrogels were tested for their swelling manners at different temperatures ( 30, 45, and 60 °C) and pH ( 4, 7, 10). The antimicrobial applications were also investigated. The results indicate that the most significant degree of swelling occurs at low pH levels. The ZnO@CSB nanocomposite hydrogel has a swelling degree of 267%, whereas the Zn(II)@CSB nanocomposite hydrogel has a swelling degree of 260%. The antimicrobial tests demonstrated that all hydrogels and their nanocomposites possess potential antimicrobial activity against Staphylococcus aureus, Escherichia coli, and Candida albicans. From the results, all samples demonstrate higher antimicrobial activity against Candida albicans than against bacterial strains. The ZnO@CSB nanocomposite hydrogel exhibited the maximum inhibition rate at 19 mm, compared with the Zn(II)@CSB nanocomposite hydrogel at 15 mm. Furthermore, the hydrogel that was synthesized displayed significant values of tensile strength as well as elongation at break. Finally, these innovative hydrogels can be promising candidates for sustainable biomedical applications and wound dressing materials.