Nanostructured surface modification for enhanced biocompatibility of Ti-based implant materials
Creators: name: QADIR, Muhammad Mehran
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400302
subject: Biomaterials
classificationCode: 401607
subject: Metals and alloy materials

description: The nanostructured surface modification of metallic materials has attracted significant attention in the scientific community for numerous applications over the last decade.  For biomaterials in particular, nanotubular (NT) oxide structures have garnered substantial interest due to their unique biological characteristics. Here, however, many questions remain regarding the exact interaction of these surfaces with the biological environment. Therefore, the present work was undertaken to probe the impact of these surfaces on the response of osteoblast-like cells, and improve the properties of a newly developed ß-phase Ti-35Zr-28Nb alloy. To investigate this, NT oxide layers were fabricated on Ti-35Zr-28Nb alloy and commercially pure titanium (CP-Ti). Different manufacturing parameters were trialed through use of the Taguchi optimization method to first identify the target parameters necessary to produce a variety of nanotube coatings with differing wall thicknesses (Wt), inner diameters (Di), lengths (Ln) and outer diameters (Do). Additionally, the CP-Ti NT surface was also investigated as a substrate for further coating by hydroxyapatite (HA) via physical vapor deposition magnetron sputtering (PVDMS). These surfaces were then used to investigate the relationships of Wt, Di, Ln and Do with the chemical and physical properties, surface roughness (Ra), and hydrophilicity of the surfaces, along with the overall cellular response.
From this, the applied voltage was identified as the most effective parameter for controlling the growth of TiO2-Nb2O5-ZrO2 NTs based on signal-to-noise (S/N) ratio analysis. Using these findings, an optimised surface was produced with the largest Di of the investigated NT surfaces, at 75.9 nm, achieved using an ethylene-glycol based electrolyte with an applied voltage of 40 V, water content of 5%, and anodization time of 120 min. Pareto ANOVA and confirmation test results therefore confirmed that the Taguchi method was successful in optimizing the larger Di for TiO2-Nb2O5-ZrO2 NTs. and achieving a surface with greater Ra and hydrophilicity.
It was found that for both TiO2 and TiO2-Nb2O5-ZrO2 NT surfaces, the highest cell viability was found on the oxide layers with the largest Di, and that hydrophilicity (as determined by contact angle θ) influenced the cellular response; in the TiO2 case, there was a direct correlation between Ra, θ and cellular viability, while for the TiO2-Nb2O5-ZrO2 surfaces, cell viability and adhesion density was sensitive to the surface energy (γ) above an apparent threshold of ~ 70 mJ/m2. The impact of Ra on cellular response was less clear in this system, however, with no significant response to Ra seen in the TiO2-Nb2O5-ZrO2 case.
After the deposition of a HA coating on TiO2 via PVDMS, the surface showed a significantly increased Ra, and decreased θ, compared to the fabricated TiO2 nanotube and bare CP-Ti surfaces. MTS assay results confirmed that the HA-coated TiO2 nanotubular surfaces provided an enhanced environment for the attachment and growth of osteoblast-like cells, with significant increases in cell adhesion and viability over both the fabricated TiO2 nanotubular surfaces and the pure CP-Ti.