Substrate-Driven Cytocompatibility of Superhydrophobic SiO2 Coatings: A Comparative Interfacial Study on Glass and Al7075 Alloy

Understanding the interfacial biological response of superhydrophobic surfaces is critical for their safe deployment in sanitary and clinical environments. This study investigates the substrate-driven cytocompatibility of superhydrophobic silica nanoparticle (SiO2 NPs) coatings, functionally modified with 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFDTES) or 1H,1H,2H,2H-perfluorodecyltrimethoxysilane (PFDTMS). To elucidate the synergistic influence of the coating chemistry and the underlying material, the fluorinated systems were deposited on an inert glass substrate and an active structural aluminum alloy (Al7075). Wettability characterization confirmed superhydrophobicity, yielding water contact angles (WCA) > 150° and water sliding angles (WSA) ≤ 10° for all coated surfaces. Biological evaluations using primary fibroblasts, encompassing 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays (24 and 48 h) and hematoxylin and eosin (H&E) morphological staining, revealed a distinctly substrate-dependent cellular response. On glass substrates, PFDTMS coatings maintained a non-cytotoxic response, whereas PFDTES exhibited a time-dependent reduction in cell viability and adhesion, albeit remaining safely above the non-cytotoxicity threshold (>70%). Conversely, on the Al7075 alloy, both fluorinated coatings demonstrated high cell viability (>90%) and extensive cellular spreading, with PFDTES exhibiting a highly favorable early-stage interfacial interaction. These findings suggest that, within the evaluated model, the cytocompatibility of superhydrophobic treatments exhibits strong substrate dependence rather than being solely an intrinsic property of the functional coating. This comparative study provides experimental evidence for the strategic design and engineering of functionalized metallic interfaces in healthcare applications.