Exploring ROS formation from ZnO/cellulose acetate composites films in Aqueous Solution: Light vs. Darkness

Abstract

The spectacular evolution of wearable/implantable medical devices in the last two decades has resulted in efficient medical treatments, higher life quality and expectancy. A threat to this bright future is the misuse/overuse of antibiotics resulting in antimicrobial resistance to pathogens [1]. A solution to this issue is the design of systems able to respond to microbe pathogens, by formulating materials composites coupling biocompatibility with switchable antibacterial properties. Accordingly, this work shows ZnO nanostructures (n-ZnO)/cellulose acetate composites that can produce bactericidal Reactive Oxygen Species (ROS) under simulated solar light. Both ZnO and cellulose acetate are bactericidal and biocompatible, having been found numerous applications in biomedical sciences [2]. The n-ZnO are synthesized by a rational approach (85°C, 60 hours) leading to n-ZnO assembled in micrometric flower-shaped grains. Different instrumental techniques (SEM, XPS, XRD, UV-Vis, thermogravimetry, cyclic-voltammetry and ζ-potential) permit to analyze their morphology and physico-chemical properties. n-ZnO/cellulose acetate composites films are prepared from n-ZnO dispersed at different weight percentages (1-15 w/w %) in cellulose acetate dissolved at 2 mg/mL in ethyl acetate. The dispersion is drop casted in a 4 cm diameter beaker and placed at 80°C for three hours to evaporate ethyl acetate, resulting in self-standing micrometer thick flexible films. Accordingly, n-ZnO fillers tune the water contact angle and the dielectric properties of the composites. The formation of ROS under simulated solar light is demonstrated by the photocatalytic degradation of the dye methylene blue (MB), showing an apparent degradation kinetics of 0.029 ± 0.002 min-1 (at 10 % W/W n-ZnO), along with an excellent reusability at the second and third cycles (0.041 ± 0.002 and 0.039 ± 0.002 min-1, respectively), whereas control experiments in the absence of light show a negligible MB photodegradation. Electrochemical Impedance spectroscopy (50 kHz - 1 Khz) is carried out on the aqueous solutions where the composites are soaked to monitor the release of ionic species in dark. The higher the n-ZnO filler concentration, the lower is the solution bulk impedance, as a result of zinc ionic species leaching in solution. References [1] E. Seebacha and K. Kubatzky, Chronic Implant-Related Bone Infections-Can Immune Modulation be a Therapeutic Strategy? Frontiers in Immunology, 2019, 10, 1724. [2] G. Arrabito, A. Delisi A., G. Giuliano, G. Prestopino, P.G. Medaglia, V. Ferrara, F. Arcidiacono, M. Scopelliti, D.F. Chillura Martino, B. Pignataro, Self-Cleaning Bending Sensors Based on Semitransparent ZnO Nanostructured Films, ACS Applied Engineering Materials, 2023, 1, 1384.