Measurement of the Degradation Rate of Anodized AZ91 Magnesium Temporary Implants Using Digital Image Processing Techniques

Abstract

To be used as intracorporeal temporary orthopedic biomaterial, magnesium alloys have to be biocompatible but also to have an adequate and controlled corrosion rate. It means that its degradation accompanies the formation of bone tissue since it is expected that the material maintains its mechanical properties until it fulfills its function and then degrades in the body. The degradation of AZ91 magnesium alloy generates the release of hydrogen gas. It is important to quantify the hydrogen evolution since it is directly related to the Mg corrosion rate. Hydrogen evolution can be experimentally quantified with high associated errors. Digital image processing tools allow the evaluation frame by frame of the hydrogen release from the surface. In this work, we performed a set of digital image processing operations to determine the gas generation rate in the surface of metallic pieces of AZ91 magnesium alloy with and without a surface oxidation process, captured from an optical microscopy camera. The proposed approach detected gas bubbles in a region of interest and then it measured the present volume in each frame of the video sequence. Surface oxidized AZ91 samples showed a slow rate of hydrogen release at short immersion times, showing a retarding in corrosion or degradation of the sample at early times.