Structure and Surface Morphology Effect on the Cytotoxicity of [Al2O3/ZnO]n/316L SS Nanolaminates Growth by Atomic Layer Deposition (ALD)

Recently, different biomedical applications of aluminum oxide (Al2O3) and zinc oxide (ZnO) have been studied, and they have displayed good biocompatible behavior. For this reason, this study explores nanolaminates of [Al2O3/ZnO]n obtained by atomic layer deposition (ALD) on silicon (100) and 316L stainless steel substrates with different bilayer periods: n = 1, 2, 5, and 10. The intention is to correlate the structure, chemical bonds, morphology, and electrochemical properties of ZnO and Al2O3 single layers and [Al2O3/ZnO]n nanolaminates with their cytotoxic and biocompatibility behavior, to establish their viability for biomedical applications in implants based on the 316L SS substrate. These nanolaminates have been characterized by grazing incident X-ray diffraction (XRD), finding diffraction planes for wurtzite type structure from zincite. The chemical bonding and composition for both single layers were identified through X-ray photoelectron spectroscopy (XPS). The morphology and roughness were tested with atomic force microscopy (AFM), which showed a reduction in roughness and grain size with a bilayer period increase. The thickness of the samples was measured with scanning electron microscopy, and the results confirmed the value of ~210 nm for the nanolaminate samples. The electrochemical impedance spectroscopy analysis with Hank’s balanced salt solution (HBSS) evidenced an evolution of [Al2O3/ZnO]n/316L system corrosion resistance of around 95% in relation with the uncoated steel substrate as function of the increase in the bilayers number. To identify the biocompatibility behavior of these nanolaminate systems, the lactate dehydrogenase test was performed with Chinese hamster ovary (CHO) cells for a short system of life cell evaluation. This test shows the cytotoxicity of the multilayer compared to the single layers of Al2O3, ZnO, and 316L stainless steel. The lowest cytotoxicity was found in the single layers of ZnO, which leads to cell proliferation easier than Al2O3, obtaining better adhesion and anchoring to its surface.

Tuneable Functionalization of Glass Fibre Membranes with ZnO/SnO2 Heterostructures for Photocatalytic Water Treatment: Effect of SnO2 Coverage Rate on the Photocatalytic Degradation of Organics

The construction of a ZnO/SnO2 heterostructure is considered in the literature as an efficient strategy to improve photocatalytic properties of ZnO due to an electron/hole delocalisation process. This study is dedicated to an investigation of the photocatalytic performance of ZnO/SnO2 heterostructures directly synthesized in macroporous glass fibres membranes. Hydrothermal ZnO nanorods have been functionalized with SnO2 using an atomic layer deposition (ALD) process. The coverage rate of SnO2 on ZnO nanorods was precisely tailored by controlling the number of ALD cycles. We highlight here the tight control of the photocatalytic properties of the ZnO/SnO2 structure according to the coverage rate of SnO2 on the ZnO nanorods. We show that the highest degradation of methylene blue is obtained when a 40% coverage rate of SnO2 is reached. Interestingly, we also demonstrate that a higher coverage rate leads to a full passivation of the photocatalyst. In addition, we highlight that 40% coverage rate of SnO2 onto ZnO is sufficient for getting a protective layer, leading to a more stable photocatalyst in reuse.