Investigating the Antibacterial Effectiveness of Zinc Particles in Different Forms within Alginate-Based Hydrogels Incorporating Nanocellulose

In contrast to zinc oxide (ZnO), the antibacterial potential of zinc hydroxyacetate (Zn-HA) remains unexplored. In this study, we fabricated alginate/TEMPO-oxidized nanocellulose (AT) hydrogels containing three types of zinc particles (Zn Ps): Zn-HA, Zn-N (ZnO nanoparticles), and Zn-C (commercial ZnO). The antibacterial efficacy of these hydrogels was assessed and compared. The integration of Zn Ps into AT hydrogels was achieved through a facile method, resulting in the formation of composite hydrogels with layered three-dimensional structures. The addition of Zn Ps reduced the mechanical properties and swelling ability of the hydrogels. The antibacterial activities of the Zn Ps and hydrogels were evaluated using the disc diffusion method. Surprisingly, Zn-HA exhibited significantly stronger antibacterial efficacy against both E. coli and S. aureus, with the zone of inhibition (ZOI) ranging from 11 mm to 19.7 mm compared to Zn-C and Zn-N (ZOI of 8.3–9.3 mm). This improved antibacterial activity might be attributed to the higher release of Zn2+ from Zn-HA (7.5 mg/100 mL compared to 0.8 and 1.2 mg/100 mL), as evidenced by the zinc dissolution study. The antibacterial activity of the AT hydrogels was significantly enhanced by the inclusion of Zn-HA but not Zn-C or Zn-N. All hydrogels exhibited mild toxicity to human skin fibroblasts. In summary, our findings challenge the expectation that ZnO (Zn-C and Zn-N) would have better antibacterial properties due to their smaller particle sizes in comparison to Zn-HA microparticles. Additionally, our results indicate that converting Zn-HA to ZnO is unnecessary to impart antibacterial properties to the hydrogels. Thus, AT hydrogels containing Zn-HA (ATZ-HA) can potentially be used as advanced antibacterial materials, possibly for use in wound dressings. Synthesis of alginate/TOCN (AT) hydrogels incorporating different forms of zinc particles, i.e., zinc hydroxyacetate (Zn-HA), commercial ZnO (Zn-C), and ZnO nanoparticles (Zn-N). Zn-HA displayed significantly stronger antibacterial efficacy against E. coli and S. aureus compared to Zn-C and Zn-N. Zn-HA enhanced the antibacterial efficiency of AT hydrogels, but it reduced their mechanical, crystallinity, and swelling properties. AT hydrogels containing Zn-HA (ATZ-HA) hold the potential as advanced antibacterial materials, possibly for wound dressings.