Medical grade titanium alloy, Ti-6Al-4V, with TiO₂ nanotubes (TiO₂-NTs) grown on the surface and then decorated with silver nanoparticles (Ag NPs) is proposed to enhance the antimicrobial properties of the bone/dental implants. However, the decoration with Ag NPs is not consistent and there are concerns about the direct contact of Ag NPs with human tissue. The aim of this study was to achieve a more even coverage of Ag NPs on TiO₂-NTs and determine their biocidal properties against Staphylococcus aureus, with and without a top coat of nano hydroxyapatite (nHA). The decoration with Ag NPs was optimised by adjusting the incubation time of the TiO₂-NTs in a silver ammonia solution, and using biocompatible δ-gluconolactone as a reducing agent. The optimum incubation in silver ammonia was 7 min, and resulted in evenly distributed Ag NPs with an average diameter of 47.5 ± 1.7 nm attached to the surface of the nanotubes. The addition of nHA did not compromise the antimicrobial properties of the materials; high-resolution electron microscopy showed S. aureus did not grow on the composite with nHA and with >80% biocidal activity measured by the LIVE/DEAD assay, also limited lactate production. Dialysis experiment confirmed the stability of the coatings, and showed a slow release of dissolved silver (3.27 ± 0.15 μg/L over 24 h) through the top coat of nHA.

Coating, as one of the significant applications in the building and construction sector, is crucial to prevent steel from reaching critical temperature and fire-induced structural collapse. This article reviews the current use of conventional coatings and assesses the potential use of novel geopolymer coatings on the metal substrate, particularly on the steel structure. The conventional passive fireproofing systems, including cement-based coatings and intumescent coatings, exhibit unavoidable limitations either due to the high thickness and weight or poor thermal and chemical resistance of the coating. Thus, innovations in conventional and novel coatings are constantly developing and growing rapidly. In recent years, geopolymer coatings have attracted much attention due to their higher mechanical strength and excellent resistance to chemicals and heat. Moreover, the green and environmentally friendly characteristics make geopolymer an admirable coating material for many applications. The main challenge that lies in the development of geopolymer coating is the interfacial bonding with the metal structure. Therefore, the influencing factors, including precursor materials, alkaline activator, and curing processes on the adhesion and thermal and chemical resistance of the geopolymer coating have been well explored. The performance comparison between these coatings indicates that geopolymer coating offers a superior mechanical and thermal performance, along with a substantially lower environmental impact compared with cement-based coating. This suggests that geopolymer coatings have great potential for fire protection on steel structures.

Purpose: This study aimed to decorate the surface of TiO₂ nanotubes (TiO₂ NTs) grown on medical grade Ti-6Al-4V alloy with an antimicrobial layer of nano zinc oxide particles (nZnO) and then determine if the antimicrobial properties were maintained with a final layer of nano-hydroxyapatite (HA) on the composite. Methods: The additions of nZnO were attempted at three different annealing temperatures: 350, 450 and 550 °C. Of these temperatures, 350°C provided the most uniform and nanoporous coating and was selected for antimicrobial testing. Results: The LIVE/DEAD assay showed that ZnCl₂ and nZnO alone were >90% biocidal to the attached bacteria, and nZnO as a coating on the nanotubes resulted in around 70% biocidal activity. The lactate production assay agreed with the LIVE/DEAD assay. The concentrations of lactate produced by the attached bacteria on the surface of nZnO-coated TiO₂ NTs and ZnO/HA-coated TiO₂ NTs were 0.13±0.03 mM and 0.37±0.1 mM, respectively, which was significantly lower than that produced by the bacteria on TiO₂ NTs alone, 1.09±0.30 mM (Kruskal–Wallis, P<0.05, n=6). These biochemical measurements were correlated with electron micrographs of cell morphology and cell coverage on the coatings. Conclusion: nZnO on TiO₂ NTs was a stable and antimicrobial coating, and most of the biocidal properties remained in the presence of nano-HA on the coating.