Electrochemical Aspects in Biomedical Alloy Characterization: Electrochemical Impedance Spectrosopy

Abstract

Metals and alloys are widely used as biomedical materials and are essential for orthopaedic implants, bone fixations, artificial joints, external fixations... since they can substitute for the function of hard tissues in orthopaedic. In particular, toughness, elasticity, rigidity, and electrical conductivity are important properties for metallic materials used in medical devices. Because the most important property of biomaterials is safety and biocompatibility, corrosion-resistant materials such as stainless steel, cobalt-chromium-molybdenum alloys and titanium alloys are commonly employed. However, there is still a significant concern associated with biomedical alloys related to the production of metal particles and ions (Fleury et al., 2006; Okazaki & Gotoh, 2005) which can lead to cellular toxicity (Germain et al., 2003; Catelas et al., 2001; Horowitz et al., 1998), metal hypersensitivity (Granchi et al., 2005; Hallab et al., 2000), and chromosomal changes (Masse et al., 2003). Corrosion of orthopedic biomaterials is a complex multifactorial phenomenon that depends on geometric, metallurgical, mechanical and physico-chemical parameters, thus a firm understanding of these factors and their interactions is required in order to comprehend how and why implant materials fail (corrode, degrade). Electrochemical measurements are powerful in situ methods that allow analyzing the interface properties and corrosion behaviour between metal biomaterials (passive oxide film) and the involved body fluids. Within this group of techniques, the Electrochemical Impedance Spectroscopy (EIS) is a useful tool which provides information about the interface, its structure, passive film properties and the reactions taking place on the interface electrolyte/oxide passive film. The impedance spectroscopy is a technique that permits the measurement of uniform corrosion and passive dissolution rates, the elucidation of reaction mechanisms, the characterization of surface films and it is also used for testing coatings or surface modifications. The aim of the present chapter is to describe the EIS technique and its potentiality in the fundamental understanding of the processes occurring at the metal/human body interface in bio-systems. The chapter will be mainly focused on its application in characterizing CoCrMo biomedical alloys.