The Morphology, Structure, Mechanical Properties and Biocompatibility of Nanotubular Titania Coatings before and after Autoclaving Process

Abstract

The autoclaving process is one of the sterilization procedures of implantable devices. Therefore, it is important to assess the impact of hot steam at high pressure on the morphology, structure, and properties of implants modified by nanocomposite coatings. In our works, we focused on studies on amorphous titania nanotubes produced by titanium alloy (Ti6Al4V) electrochemical oxidation in the potential range 5–60 V. Half of the samples were drying in argon stream at room temperature, and the second ones were drying additionally with the use of immersion in acetone and drying at 396 K. Samples were subjected to autoclaving and after sterilization they were structurally and morphologically characterized using Raman spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) and scanning electron microscopy (SEM). They were characterized in terms of wettability, mechanical properties, and biocompatibility. Obtained results proved that the autoclaving of amorphous titania nanotube coatings produced at lower potentials (5–15 V) does not affect their morphology and structure regardless of the drying method before autoclaving. Nanotubular coatings produced using higher potentials (20–60 V) require removal of adsorbed water particles from their surface. Otherwise, autoclaving leads to the destruction of the architecture of nanotubular coatings, which is associated with the changing of their mechanical and biointegration properties.

Comprehensive Evaluation of the Biological Properties of Surface-Modified Titanium Alloy Implants

“…On the basis of our earlier works, we chose the anodic oxidation method as a surface modification of implants produced in 3D technology (SLS of Ti6Al4V ELI Grade 23 powder) [25]. Two types of amorphous coatings, which revealed suitable biointegration and antibacterial properties in preliminary studies, were selected for more comprehensive investigations, i.e., TNT5 (the ordered nanoporous) and TNT15 (the ordered nanotubular) [25,26]. Thanks to the anodic oxidation method, the TNT5 and TNT15 coatings covered the whole implant surface without cracks and gaps.…”

“…The type of produced coating has a direct impact on the surface wettability, its porosity, and roughness, as well as on the mechanical properties. Moreover, it was found that the substrates covered with the TNT layer are characterized by more vigorous cell growth (fibroblasts) and better integration of bone with the implant surfaces [20,25,26]. The enrichment of TNT coatings with silver nanoparticles (AgNPs) using chemical vapor deposition (CVD) and atomic layer deposition (ALD) techniques, allowing control of their size and dispersion, was another direction of our works [27][28][29][30].…”

“…From a practical point of view, the anodic oxidation of titanium-based implants' surface in the HF solution, leading to the formation of first-generation TiO 2 (TNT) nanotube coating, seems to be particularly interesting [22][23][24][25]. Depending on the value of the applied potential [U], this method allows the following to be obtained: (a) Ordered porous layers (U = 3-10 V), consisting of nanotubes with common walls; (b) ordered tube layers (U = 10-30 V), composed of separated titania nanotubes; and (c) oxide coatings with a sponge-like structure (above U = 30 V) [24,26]. Produced TNT coatings, as obtained, are amorphous and form a uniform oxide layer of a thickness c.a.…”

“…Our previous research [20,21,[24][25][26][27][28][29][30][31] focused on the development of technology to produce the bioactive coatings on the surface of Ti6Al4V alloy substrates, i.e., widely used material in the construction of orthopedic implants. However, in order to implement the developed nanocoatings into implant fabrication, it is necessary to estimate their bioactivity in detail.…”

Ti6Al4V foams having nanotubular surfaces for orthopaedic applications

“…Specifically, Macak et al used 1M (NH 4 ) 2 SO 4 electrolyte containing 0.5 wt % of NH 4 F to obtain self‐organized nanotubular oxide layers having thicknesses of several hundreds of nanometers. Radtke et al anodized Ti6Al4V alloy in the potential range of 5 to 60 V at room temperature for 30 minutes and observed nanotubes to possess diameters between 25 and 110 nm depending on the utilized potential. In vitro biological tests showed that anodized Ti6Al4V surfaces having nanotubular morphology enhanced bone cell adhesion, proliferation, alkaline phosphatase activity, collagen type I, and calcium mineral deposition compared with conventional Ti6Al4V samples .…”