Electrochemical Short-Time Testing Method for Simulating the Degradation Behavior of Magnesium-Based Biomaterials

Abstract

In regenerative medicine, degradable, magnesium-based biomaterials represent a promising material class. The low corrosion resistance typical for magnesium is advantageous for this application since the entire implant degrades in the presence of the aqueous body fluids after fulfilling the intended function, making a second operation for implant removal obsolete. To ensure sufficient stability within the functional phase, the degradation behavior must be known for months. In order to reduce time and costs for these long-time investigations, an electrochemical short-time testing method is developed and validated, accelerating the dissolution process of a magnesium alloy with and without surface modification based on galvanostatic anodic polarization, enabling a simulation of longer immersion times. During anodic polarization, the hydrogen gas formed by the corrosion process increases linearly. Moreover, the gas volume shows a linear relationship to the dissolving mass, enabling a defined dissolution of magnesium. As a starting point, corrosion rates of both variants from three-week immersion tests are used. A simplified relationship between the current density and the dissolution rate, determined experimentally, is used to design the experiments. Ex situ µ-computed tomography scans are performed to compare the degradation morphologies of both test strategies. The results demonstrate that a simulation of the degradation rates and, hence, considerable time saving based on galvanostatic anodic polarization is possible. Since the method is accompanied by a changed degradation morphology, it is suitable for a worst-case estimation allowing the exclusion of new, unsuitable magnesium systems before subsequent preclinical studies.

Keywords

• biodegradable implant
• magnesium alloy
• WE43
• plasma electrolytic oxidation
• immersion test
• galvanostatic polarization