Antimicrobial actions of zinc oxide microcrystals: from design… to ‘’ziotape’’

Abstract

ZnO is a versatile material exhibiting reconfigurable morphologies and significant antibacterial activity towards gram positive and negative microorganisms, connected with their high surface to volume ratio and their physicochemical properties. Several models are suggested for explaining the mechanisms of bacterial growth inhibition for nanostructured ZnO, leveraging electrostatic interactions between ZnO and cell walls affecting bacterial cell integrity, release of antimicrobial Zn2+ ions, which is connected to accumulation of ZnO into bacteria cells and finally ROS formation [1]. However, ZnO nanoparticles are usually detrimental to cell viability, so new ZnO based synthetic strategies are needed to better control the ZnO biocidal effects. To bridge this knowledge gap, in this work, we engineered a new synthetic approach based on the wet synthesis of ZnO to exploit experimental design allowing for improving synthesis yield (obtained at temperatures < 90 °C) [2], photocatalysis efficiency and the antibacterial properties of the microcrystals. The resulting ZnO-based microcrystals stabilized in a biocompatible amino-functionalized cellulose solid supports or microcrystalline matrices matrix allow for a prolonged (>24 hours) antibacterial activity based on dual mechanical/chemical routes. In the former, a direct disruptive mechanical interaction occurs with bacteria due to impaling with asymmetrical functionalized ZnO diffusing from the cellulose in presence of external stimuli (fuel or light) [3], that facilitate their motion and interaction with bacteria. For the latter, the zinc release in solution might modify the zinc homeostasis, leading to reactive oxygen species (ROS). Antimicrobial assays are carried out with two reference strains (Escherichia coli and Staphylococcus aureus) with different structural/physiological features, highlighting both the time and concentration dependency of ZnO microcrystals in killing bacteria. Showing the technological relevance of the research, we also demonstrate the scalability of this approach towards antibacterial products dispersed in cellulose matrix and we present it as Ziotape, antimicrobial modulable ZnO-based adhesive patches to be applied on surfaces. These "smart" supports incorporate antibacterial properties that might allow to reduce the use of antimicrobials, disinfectants, drugs or creams. Currently we are carrying out experiments trying to elucidate the antibacterial mechanisms of ZnO microcrystals: in fact, besides a direct disruptive mechanical interaction with bacteria due to ZnO particles diffusion from the cellulose in presence of external stimuli (fuel or light), also the zinc release in solution might be critical modifying the zinc homeostasis and leading to reactive oxygen species (ROS). Electrostatic interactions between ZnO microparticles and cell walls affecting bacterial cell integrity have been also described [4,5]. References: [1] T. Vitasovic, G. Caniglia, N. Eghtesadi, M. Ceccato, E.D. Bo̷jesen, U. Gosewinkel, G. Neusser, U. Rupp, P. Walther, C.Kranz, E.E. Ferapontova, ACS Applied Materials & Interfaces 2024, 16(24), 30847-30859. DOI:10.1021/acsami.4c04682 [2] V. Errico, G. Arrabito, E. Fornetti, C. Fuoco, S. Testa, G. Saggio, S. Rufini, S. Cannata, A. Desideri, C. Falconi, C. Gargioli, ACS Applied Materials & Interfaces 2018, 10(16), 14097-14107. DOI:10.1021/acsami.7b19758 [3] G. Arrabito, G. Prestopino, P.G. Medaglia, V. Ferrara, G. Sancataldo, G. Cavallaro, F. Di Franco, M. Scopelliti, B. Pignataro, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2024, 698, 134526. DOI:10.1016/j.colsurfa.2024.134526 [4] R. Brayner, R. Ferrari-Iliou, N. Brivois, S. Djediat, M.F. Benedetti, F. Fiévet Nano Letters 2006, 6(4), 866-870. DOI:10.1021/nl052326h [5] N. Jones, B. Ray, K.T. Ranjit, A.C. Manna, FEMS Microbiology Letters, 2008, 279(1), 71–76. DOI:10.1111/j.1574-6968.2007.01012