Abstract
Nitinol is widely used in the production of medical devices, especially the ones that are designed for minimally invasive treatment, such as stents to restore vascular patency, stent grafts to eliminate aneurysms, and cava filters to trap blood clots. One of the most important characteristics that determines the reliability of the functioning of such products in the human body is the state of the surface layer. The higher the surface quality, the less negative impact is on the circulatory system, the walls of blood vessels and the higher the biological compatibility of the product. Electrochemical polishing methods are mainly used to improve the surface quality of nitinol products. The disadvantage of the applied electrochemical methods is the need to use aggressive electrolytes that contain toxic components, such as hydrofluoric acid, sulfuric acid, perchloric acid, nitric acid, methanol. As an alternative to the existing methods of electrochemical polishing, we have developed electrolytic-plasma polishing (EPP), a new highly efficient process for improving the surface quality of nitinol products. The most important advantage of the method over traditional electrochemical polishing is the use of aqueous salt solutions with a concentration of 4 % as electrolytes. Based on the results of the studies performed, the most rational EPP mode was established, the use of which during polishing of nitinol provides surface cleaning from scale, polishing with a decrease in the roughness parameter Ra by 0.344 µm and an increase in pitting potential by 33 %.
Highlights
The nitinol alloy is a promising biomaterial due to its distinctive properties, such as shape memory, super elasticity, high corrosion resistance and biocompatibility [1]
As an alternative to the existing methods of electrochemical polishing, we have developed electrolytic-plasma polishing (EPP), a new highly efficient process for improving the surface quality of nitinol products
In this work, using the example of a nitinol stent-element included in the design of a stent-graft, we investigated the effect of EPP on the surface characteristics in order to establish technological parameters that allow achieving a high quality surface treatment, corrosion resistance, provided that the radial stiffness sufficient for its performance is maintained
Summary
The nitinol alloy is a promising biomaterial due to its distinctive properties, such as shape memory, super elasticity, high corrosion resistance and biocompatibility [1]. Through these properties, nitinol is a suitable material for the manufacture of various biomedical products. Due to spontaneous surface passivation even at room temperature, nitinol provides sufficient corrosion resistance and biocompatibility for effective use as an implant [2, 3]. Various methods have been studied to improve the quality of nitinol surface, based on mechanical polishing and electrochemical polishing [4,5,6,7].
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