On the Determination of Magnesium Degradation Rates under Physiological Conditions

Abstract

The current physiological in vitro tests of Mg degradation follow the procedure stated according to the ASTM standard. This standard, although useful in predicting the initial degradation behavior of an alloy, has its limitations in interpreting the same for longer periods of immersion in cell culture media. This is an important consequence as the alloy’s degradation is time dependent. Even if two different alloys show similar corrosion rates in a short term experiment, their degradation characteristics might differ with increased immersion times. Furthermore, studies concerning Mg corrosion extrapolate the corrosion rate from a single time point measurement to the order of a year (mm/y), which might not be appropriate because of time dependent degradation behavior. In this work, the above issues are addressed and a new methodology of performing long-term immersion tests in determining the degradation rates of Mg alloys was put forth. For this purpose, cast and extruded Mg-2Ag and powder pressed and sintered Mg-0.3Ca alloy systems were chosen. DMEM Glutamax +10% FBS (Fetal Bovine Serum) +1% Penicillin streptomycin was used as cell culture medium. The advantages of such a method in predicting the degradation rates in vivo deduced from in vitro experiments are discussed.

Quantitative characterization of degradation processes in situ by means of a bioreactor coupled flow chamber under physiological conditions using time‐lapse SRµCT

“…The degradation rate DR i at time t = i was determined as in accordance with Ref. . In Eq.…”

A simple model for long‐time degradation of magnesium under physiological conditions

“…(1); blue line: measured data at higher times). [8] [Color figure can be viewed at wileyonlinelibrary.com] FIGURE 2 Degradation rate versus time for Mg-0.3Ca, powder pressed and sintered, exposed to DMEM Glutamax + 10% FBS cell culture medium (red curve: calculated data according to Eqs. (1) and (2); blue dots: approximated data by step-wise numerical differentiation of measured data.…”

“…(1) and (2); blue dots: approximated data by step-wise numerical differentiation of measured data. [8] [Color figure can be viewed at wileyonlinelibrary.com] Displacement of the Mg surface due to Mg-flux into the layer is exactly the mean degradation depth h in Eq. (1) being proportional to the mass loss m Mg of the magnesium.…”

“…In a previous paper, it has been shown that the degradation behavior of Mg‐0.3Ca under physiological conditions can be mostly described by linear degradation over the course of several weeks and high degradation rates at the beginning, the degradation rate decreasing during the first days toward the long‐time degradation rate, see Figures and . This decrease is in agreement with the usual behavior of magnesium alloys concerning the corrosion‐rate according to ASTM NACE/ASTM G31‐12a .…”

“…Degradation rate versus time for Mg‐0.3Ca, powder pressed and sintered, exposed to DMEM Glutamax + 10% FBS cell culture medium (red curve: calculated data according to Eqs. and ; blue dots: approximated data by step‐wise numerical differentiation of measured data [Color figure can be viewed at wileyonlinelibrary.com]…”