New Nickel-Titanium alloys for biomedical applications

Abstract

Nitinol is a shape memory alloy with unique shape memory characteristics and superelasticity. The understanding of these properties as well as its main applications in the biomedical field are the central object of study of this final degree project. Special emphasis is placed on cardiac devices composed of this alloy such as heart valves and coronary stents. Due to its distinctive properties, the use of these nitinol-based devices has allowed to successfully treat certain cardiovascular pathologies, such as interventricular communication and peripheral vascular diseases. However, surface roughness of nitinol stents represents an important factor to consider since it considerably affects its biocompatibility. The friction of the implant in contact with the vascular tissue can cause the adhesion of proteins and therefore, lead to thrombus formation. With the aim of improving its biocompatibility, effective surface treatments in reducing surface roughness of nitinol stents are explored. Among many alternatives, the electrochemical procedure known as electropolishing is analysed in detail in this project. To test the effectiveness of this surface treatment, an experimental procedure based on the electropolishing of nitinol stents under different conditions is performed. A meticulous characterization process of the surface of the samples is then carried out. The optimal polishing conditions are determined, thus achieving a considerable reduction in the surface roughness of nitinol stents.