Development of Functionalized Coatings on Ti6Al4V through Surface Modification to Enhance the Corrosion Resistance and Antibacterial Activity

Abstract

Titanium alloy-based implants are among the most widely used biomaterials in orthopedic and dental applications. Many researchers created various surface structures using surface modification methods to improve the interaction of biomaterial surfaces with tissues. Still, the utilization of implantable metals presents several significant challenges that need to be addressed such as corrosion resistance, antibacterial activity, and bone-implant interaction. Biomedical metallic materials, generally corrode and the ions released from their surfaces are toxic and allergenic to tissues. Implant loosening is a condition that is caused by the wear particles released into body fluid from an implant, which evokes undesired immune responses and inflammatory responses resulting in osteolysis in the bone implant interface. As a result, good corrosion resistance is required to achieve satisfactory osseointegration and inflammatory responses. Bacterial infection remains a major impediment to the utility of medical implants. Implants related to bacterial infections involve multiple surgical procedures; removal of the implant, continuous use of antibiotics, and patient rehabilitation. Coating is an effective method that can be used to enhance the biological, antibacterial, and electrochemical properties of orthopedic and percutaneous implants. Keeping this in view, the present research work aims to enhance the corrosion property and antibacterial ability of Ti6Al4V through surface modification and coating. The primary focus of this research was to create the TiO2 (titanium dioxide) highly ordered nanotube arrays on a Ti6Al4V surface to improve surface roughness, antibacterial activity, and biocompatibility for its use in biomedical applications. In this approach, the anodic oxidation process was carried out in the organic bath solution, which is composed of ethylene glycol, NH4F, and ultrapure water. The process was carried out at a constant voltage of 30 V under different anodic oxidation time durations of 3 h, 4 h, and 5 h. Surface roughness of polished Ti6Al4V, TiO2 30 V 3 h, TiO2 30 V 4 h, and TiO2 30 V 5 h are 2.77 nm, 16.92 nm, 19.75 nm, and 22.01 nm respectively. The early-stage assessment of the antimicrobial efficacy of oxidized specimens was conducted quantitatively against Bacillus subtilis and Escherichia coli after a 24 h period of growth. MG-63 human osteoblast-like cells were employed to investigate cell studies. Cell viability on various surfaces was assessed through 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and adhesion assays, demonstrating an enhanced in vitro response to crystalline nanotubes. Overall, this work demonstrates the importance of using multifunctional TiO2 nanotubes to provide a synergistic impact on antibiofilm, antibacterial, and enhanced osseointegration. Furthermore, the investigation introduces a novel approach involving a chitosan-coated Ag-loaded TiO2 nanotubular surface, specifically designed for medical implant applications. In the first phase, Ag-loaded TiO2 nanotubular surfaces with different weight percentages of silver were fabricated at a constant voltage of 2 V under varied time durations of 1 min, 2 min, and 3 min. In the second phase, cathodic electrophoretic deposition (EPD) was used to coat the samples with chitosan by applying 10 V for 5 min as a constant process parameter for coating all the samples. The composition and morphology features of in-house fabricated chitosan- coated Ag-loaded TiO2 nanotubular surfaces were studied by different techniques. Corrosion resistance of the functionalized coated samples was assessed through open circuit potential (OCP), potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) techniques. The results evidenced that chitosan-coated Ag-loaded (2 V 2 min) TiO2 nanotubular surface (TNT-Ag2.2/Ch) showed the best performance as a coating system when compared to an uncoated surface. Overall, the TNT-Ag2.2/Ch coated sample showed 5 times better results when compared with icorr values. The biological studies also suggested the TNT- Ag2.2/Ch sample has better antibacterial activity and biocompatibility compared to the other samples. Additionally, the research introduces a copper to incorporate into the TiO2 nanotubular surface. In this, Cu-loaded TiO2 nanotubular surfaces with different weight percentages of copper were fabricated at a constant voltage of 2 V under varied time durations of 30 s, 60 s, and 90 s through electrochemical deposition (ECD). Then chitosan was deposited over the Cu-loaded TiO2 nanotubular surfaces through cathodic electrophoretic deposition (EPD) by applying 10 V for 5 min as a constant process parameter for coating all the samples. The structural and corrosion properties are characterized by various techniques. The scanning electron microscope (SEM) and an energy-dispersive X-ray spectrometer (EDXS) characterizations suggest that the deposition of the copper amount is elevated with the extension of the coating duration. The contact angle measurements confirmed the hydrophilic nature of all working samples. Contact angle values for polished Ti6Al4V, TiO2 30 V 4 h, TNT-Cu2/30/Ch, TNT-Cu2/60/Ch, and TNT-Cu2/90/Ch were 61.63°, 18.48°, 76.58°, 73.95°, and 68.30°, respectively. Corrosion rates, as determined by PDP curves, The TNT-Cu2/90/Ch sample exhibited a remarkably low corrosion rate of 0.0611 mm per year and a high corrosion protection efficiency of 79.81%. The biological studies also suggested the TNT-Cu2/90/Ch sample has better antibacterial activity and biocompatibility compared to the other samples. Finally, comparative studies are carried out to suggest the overall better anticorrosive and antibacterial surface among all the treated surface samples the corrosion and antibacterial studies are conducted. The samples polished Ti6Al4V, TiO2 30 V 4 h, TNT-Ag2.2/Ch, and TNT-Cu2/90/Ch are analyzed to optimize the best anticorrosive and antibacterial activity surface. The results evidenced that the TNT-Ag2.2/Ch sample showed better corrosion resistance and antibacterial activities.