Assessment of Galvanostatic Anodic Polarization to Accelerate the Corrosion of the Bioresorbable Magnesium Alloy WE43

Abstract

In the field of surgery, bioresorbable magnesium is considered a promising candidate. Its low corrosion resistance, which is disadvantageous for technical application, is advantageous for surgery since the implant fully degrades in the presence of the water-based body fluids, and after a defined time the regenerating bone takes over its function again. Therefore, knowledge of the corrosion behavior over several months is essential. For this reason, an in vitro short-time testing method is developed to accelerate the corrosion progress by galvanostatic anodic polarization without influencing the macroscopic corrosion morphology. The initial corrosion rate of the magnesium alloy WE43 is calculated by detection of the hydrogen volume produced in an immersion test. In a corresponding experimental setup, a galvanostatic anodic polarization is applied with a three-electrode system. The application range for the polarization is determined based on the corrosion current density from potentiodynamic polarization. To correlate the initial corrosion rate, and accelerated dissolution rate, the corrosion morphologies of both test strategies are characterized by microscopy images, as well as energy dispersive X-ray spectroscopy and Fourier-transform infrared spectroscopy. The results demonstrate that the dissolution rate can be increased in the order of decades with the limitation of a changed corrosion morphology with increasing polarization. With this approach, it is possible to characterize and exclude new unsuitable magnesium alloys in a time-efficient manner before they are used in subsequent preclinical studies.

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

“…Thus, the performed experiments confirmed that it is possible to control the dissolution rate through galvanostatic polarization. The linear relationship between immersion time and hydrogen volume for constant current densities as well as the relationship between increasing current density and increasing HER agree with the literature [24,26] and could also be demonstrated in our own preliminary work on embedded samples [31]. The lower HER for the PEO specimens shows that the qualitative dissolution behavior of this second variant can be controlled by this test strategy.…”

“…The starting point was an experimentally determined mathematical relationship (Equation ( 6)) between the dissolution rate . m diss and the galvanostatic current density i [31]. This relationship was determined on embedded samples and can be assumed to be a two-dimensional (2D) case.…”

“…The aim was the simulation of the corrosion rates m corr of a magnesium alloy with and without surface treatment from three-week immersion tests. The starting point was an experimentally determined mathematical relationship (Equation ( 6)) between the dissolution rate m diss and the galvanostatic current density i [31]. This relationship was determined on embedded samples and can be assumed to be a two-dimensional (2D) case.…”

“…For both variants, the suitable property profile of degradation resistance and biocompatibility are known [29,30]. The starting point is an experimentally determined relationship between the dissolution rate and the current density [31] and the time-dependent corrosion rates from three-week immersion tests [30]. The aim is to reproduce the hydrogen evolution and thus the degradation behavior of the immersion tests in three days through a systematic design of the current densities.…”