Corrosion Resistance of Tantalum-Based Coatings on Medical Implants
Modern medicine widely uses implants and stents, which should ensure long-term operation in the patient's body, causing minimal harm. Various metals and compounds used to make implants and stents have the necessary mechanical properties, but the presence of metal in the human body can lead to undesirable consequences (increased exudation, formation of excess fibrosis, rejection reaction).
To solve this problem, thin-film coatings are widely studied for medical devices based on oxides and nitrides of transition group metals. Coatings of tantalum (Ta), tantalum nitride (TaN), tantalum oxynitride (TaON), and tantalum oxide (Ta2O5) demonstrate high corrosion resistance and characteristic biocompatibility. Currently, it is necessary to justify the use of tantalum-based coating materials for use in surgical practice.
This paper reports the results of a comparative experimental study of corrosion resistance of Ta-based bioinert coatings on metal samples. The idea of the research is to find the optimal coating for medical implants balancing corrosion resistance of oxides, high hardness of nitrides and ductility of metals. Biochemical and morphological substantiation of the use of tantalum-based coatings in surgical practice will be carried out at the following step of research through in vivo experiments using laboratory animals. Here we present the results of the corrosion resistance estimation of different Ta-based coatings studied using potentiostatic measurements.
Polished plates of medical stainless steel (AISI 304) measuring (1.5x1.5) cm and 2 mm thick were made for the application of Ta-based coatings. Such model implants are planned to be used for implantation in laboratory animals in the future. Various implants were coated with Ta, Ta2O5, TaN, and TaON (thickness of about 2 μm) by reactive magnetron sputtering using the multifunctional Cluster Ion-Plasma System (CIPS) [1-2], which consists of compatible sources of fluxes of metal atoms, ions, chemically active particles for a complex effect on the growing film.
Subsequently, coated and uncoated implants were tested for corrosion resistance. Polarization curves were measured in saline solution. The measurement results show that the tantalum oxide exhibits excellent insulating properties, but this result is not stable. The reason for this is that tantalum oxide is hard and brittle and the corrosion current is mainly due to defects in the coating. Tantalum, being a ductile metal, has the fewest defects and shows the most stable results. In this case, the corrosion current is only slightly inferior to the values for the oxide. Tantalum nitride has the highest corrosion current, while oxynitride shows intermediate results.
Thus, from the results of the research presented in this paper, it can be concluded that tantalum-based coatings can become one of the most practical ways to improve the durability and stability of biomedical implants and reduce the risk of post-surgery complications.
Tantalum-based coating, oxynitride, implants
This research was supported by the National Research Foundation of
Ukraine in the framework of the project 2021.01/0204
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[2] S. Yakovin, A. Zykov, S. Dudin, N. Yefymenko, " Synthesis of thin-film Ta2O5 coatings by reactive magnetron sputtering", Problems of Atomic Science and Technology. Series “Plasma Physics”, no 6, p. 248-251 (2016)