Recently, silver (Ag) and copper (Cu) have been incorporated into a titanium (Ti) surface to realize their antibacterial property. This study investigated both the durability of the antibacterial effect and the surface change of the Ag- and Cu-incorporated porous titanium dioxide (TiO2) layer. Ag- and Cu-incorporated TiO2 layers were formed by micro-arc oxidation (MAO) treatment using the electrolyte with Ag and Cu ions. Ag- and Cu-incorporated specimens were incubated in saline during a period of 0–28 days. The changes in both the concentrations and chemical states of the Ag and Cu were characterized using X-ray photoelectron spectroscopy (XPS). The durability of the antibacterial effects against Escherichia coli (E. coli) were evaluated by the international organization for standardization (ISO) method. As a result, the Ag- and Cu-incorporated porous TiO2 layers were formed on a Ti surface by MAO. The chemical state of Ag changed from Ag2O to metallic Ag, whilst that of Cu did not change by incubation in saline for up to 28 days. Cu existed as a stable Cu2O compound in the TiO2 layer during the 28 days of incubation in saline. The concentrations of Ag and Cu were dramatically decreased by incubation for up to 7 days, and remained a slight amount until 28 days. The antibacterial effect of Ag-incorporated specimens diminished, and that of Cu was maintained even after incubation in saline. Our study suggests the importance of the time-transient effects of Ag and Cu on develop their antibacterial effects.
Recently, biofilm formation caused by bacterial adhesion and colonization has been recognized as the major cause of failure in orthopedic and dental implant surgeries. In this study, a customized micro-arc oxidation (MAO) treatment technique was developed to obtain desirable antibacterial properties on Ti surfaces. The two-step MAO treatment was applied in the fabrication of specimens with Ag and with/without Zn in their surface oxide layer. In order to simulate practical usage, surface analyses and immersion tests were performed to evaluate the incorporation of Ag and Zn into the resulting oxide layer and ion release behavior, respectively. Additionally, the antibacterial properties of the specimens after long-term immersion in physiological saline were evaluated using Gram-negative facultative anaerobic bacteria. The MAO-treated specimens containing Ag and Zn exhibited excellent antibacterial properties against Escherichia coli, which were sustained even after 6 months of immersion in physiological saline to simulate practical usage. Moreover, the Ag ions released from the surface oxide indicate the antibacterial properties of the specimen in the early stage, while the release of the corrosion products of Zn demonstrates its antibacterial properties in the later stage.
This study investigates the interaction between E. coli bacteria and various surface states of Cu. Pure Cu was oxidized at 298 K, 673 K, and 1273 K, and its surface chemical state was characterized using X-ray photoelectron spectroscopy. The oxidized specimens were immersed in both bacteria-free and bacteria-containing solutions, and the release of Cu ions from each specimen was evaluated. As a result, the specimens, which existed as mainly Cu 0 or Cu + on the surface, exhibited the same corrosion behavior and promoted the elution of Cu ions due to the presence of E. coli in the immersion solution. In contrast, the release of Cu ions from the specimen that existed mainly as Cu 2+ did not change in the presence of bacteria. According to the XPS analyses before and after immersion in bacteria-free and bacteria-containing solutions, the generation of Cu 2+ on the surface was inhibited by the presence of E. coli, and promoted Cu ion elution. This study proposes that the specific corrosion behavior of Cu due to bacteria is beneficial for developing its antibacterial properties.
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