Characterization and Antimicrobial Activity of Hafnium Nanostructures Fabricated by Physical Vapor Deposition Through a Colloidal Mask

ABSTRACT With the prevalence of biomaterial‐related infections and the rapid emergence of antibiotic‐resistant strains of bacteria, the need for functional biomaterial coatings that have antibacterial properties has drastically increased over the past few decades. Recently, there has been interest in coatings of group IV transition metals such as hafnium (Hf) and zirconium due to their resistance to corrosion and inherent hardness. Here we fabricate nanostructured Hf surfaces via physical vapor deposition through a colloidal template made from either silica (Si) or polystyrene (PS) particles. The physical properties of the Hf structures were characterized by atomic force microscopy (AFM), while chemical characterization was carried out using water contact angles (WCAs) and X‐ray photoelectron spectroscopy (XPS). We show that the properties of the final Hf structures are heavily influenced by the composition and size of the colloid used as the template layer. The use of inorganic Si‐based colloidal templates resulted in an inverse structure with relatively low Hf content (0.9–7.9 Atom%), whereas polymeric PS‐based templates resulted in a multilayer system comprised of the PS‐template layer underneath the deposited Hf layer, resulting in a much higher Hf content (8.6–22.3 Atom %). Moreover, antibacterial analysis against Gram‐positive Staphylococcus aureus revealed that surfaces produced using the 0.093 µm PS template (PS0.093) provided an 87% killing efficiency along with a 98.6% reduction in adherent cells compared to flat control surfaces. On the contrary, the antibacterial tests again Gram‐negative Escherichia coli showed significant killing efficiency and antiadhesive behavior across a range of nanostructures. The results demonstrate that the nanoscale surface properties of structured Hf coatings play a role in the ability of Hf to be antibacterial, with potential to be used on medical implants.