Antibacterial Property and Biocompatibility of Silver, Copper, and Zinc in Titanium Dioxide Layers Incorporated by One-Step Micro-Arc Oxidation: A Review

Abstract

Titanium (Ti) and its alloys are commonly used in medical devices. However, biomaterial-associated infections such as peri-implantitis and prosthetic joint infections are devastating and threatening complications for patients, dentists, and orthopedists and are easily developed on titanium surfaces. Therefore, this review focuses on the formation of biofilms on implant surfaces, which is the main cause of infections, and one-step micro-arc oxidation (MAO) as a coating technology that can be expected to prevent infections due to the implant. Many researchers have provided sufficient data to prove the efficacy of MAO for preventing the initial stages of biofilm formation on implant surfaces. Silver (Ag), copper (Cu), and zinc (Zn) are well used and are incorporated into the Ti surface by MAO. In this review, the antibacterial properties, cytotoxicity, and durability of these elements on the Ti surface incorporated by one-step MAO will be summarized. This review is aimed at enhancing the importance of the quantitative control of Ag, Cu, and Zn for their use in implant surfaces and the significance of the biodegradation behavior of these elements for the development of antibacterial properties.

Keywords: antibacterial properties; biofilm; coating; copper; implant; infection; micro-arc oxidation; silver; titanium; zinc.

Figure 1

Schematic diagram of the biofilm formation process. The dashed area represents the initial stages of biofilm formation.

Figure 2

(a) Schematic diagram of the formation of a porous oxide layer on the Ti substrate and the incorporation of antibacterial elements by micro-arc oxidation (MAO). (b) Scanning electron microscopy (SEM) images of the Ti surface before and after MAO; (c) cross-sectional views of Ag-incorporated porous oxide layer and element mapping results by electron probe micro analyzer (EPMA). Scale bar represents 10 µm; (d) X-ray photoelectron spectroscopy (XPS) survey scan spectra obtained from the specimen, with and without antibacterial elements. The spectra obtained from the control (specimen without antibacterial elements), Ag-, Cu-, and Zn-incorporated specimens are shown from the bottom to the top. Specimens were MAO-treated at 400 V using the electrolytes containing 150 mM of calcium acetate and 100 mM of calcium glycerophosphate with or without 2.5 mM of silver nitrate, 2.5 mM of copper chloride, or 2.5 mM of zinc chloride.

Figure 3

Conceptual diagram of the suitable concentration range (green-colored area) of antibacterial elements for the dual-functionalization of the Ti surface.

Figure 4

Changes in the concentration of Ag, Cu, and Zn in the oxide layer (a) and antibacterial effects (b) before and after incubation in saline for 28 days [97,102].