Abstract
Crystallization alters the characteristics of TiO2 nanosurfaces, which consequently influences their bio-performance. In various biomedical applications, the anatase or rutile crystal phase is preferred over amorphous TiO2. The most common crystallization technique is annealing in a conventional furnace. Methods such as hydrothermal or room temperature crystallization, as well as plasma electrolytic oxidation (PEO) and other plasma-induced crystallization techniques, present more feasible and rapid alternatives for crystal phase initiation or transition between anatase and rutile phases. With oxygen plasma treatment, it is possible to achieve an anatase or rutile crystal phase in a few seconds, depending on the plasma conditions. This review article aims to address different crystallization techniques on nanostructured TiO2 surfaces and the influence of crystal phase on biological response. The emphasis is given to electrochemically anodized nanotube arrays and their interaction with the biological environment. A short overview of the most commonly employed medical devices made of titanium and its alloys is presented and discussed.
Highlights
Titanium-based alloys are considered as more biocompatible metallic biomaterials compared to stainless steel, cobalt–nickel, and chromium alloys, due to their low ion release when exposed to human body liquids [1], low elastic modulus [2], and relatively high strength to density ratio, as well as corrosion resistance [3]
The biocompatibility of titanium (Ti) arises from its high reactivity with oxygen when Ti is exposed to air, which leads to the formation of a chemically stable passivating oxide layer
Treatment with oxygen plasma of pure titanium foils, and TiO2 nanotubes with different lengths and diameters formed on the surface of a Ti substrate with the process of electrochemical anodization, initiated the transition of the amorphous phase to an anatase/rutile crystal structure depending on the plasma treatment conditions
Summary
Titanium-based alloys are considered as more biocompatible metallic biomaterials compared to stainless steel, cobalt–nickel, and chromium alloys, due to their low ion release when exposed to human body liquids [1], low elastic modulus [2], and relatively high strength to density ratio, as well as corrosion resistance [3]. With the development of nanotechnology, it has been shown that surface features significantly influence the amount and type of adhered proteins, as well as their conformational state, which further dictate their interaction with cells. Besides other characteristics, such as surface morphology, chemistry, charge, wettability, and the crystal structure of TiO2 nanosurfaces highly affect the material’s bio-performance. The selective growth of ECs over SMCs was observed, while platelet adhesion was significantly reduced This was achieved where both electrochemical anodization (nanostructured surface) and gaseous plasma treatment (the formation of high quality titanium oxide) were combined. Various crystallization methods and the mechanisms involved will be discussed
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