Microscopic bio‐corrosion evaluations of magnesium surfaces in static and dynamic conditions

Abstract

SummaryBiodegradable materials including biodegradable metals are continuously being investigated for the development of next generation cardiovascular stents. Predictive in vitro tests are needed that could evaluate potential materials while simulating in vivo conditions. In this manuscript we report the microscopic bio-corrosion evaluations of magnesium surfaces in static and dynamic conditions. A corrosion test bench was designed and fabricated and static and dynamic corrosion tests were carried out with samples of magnesium alloy. The fluid wall shear stress equation and the Churchill's friction factor equation were used to calculate the fluid velocity required to generate the desired shear stress on samples in the test bench. Static and dynamic corrosion tests at 24 and 72 h were carried out at 0.88 Pa shear stress mimicking the in vivo shear stress. Microscopic evaluations of the corroded surfaces were carried out by optical, scanning electron microscopy and energy dispersive X-ray spectroscopy to evaluate the corrosion behaviour and surface properties of the test samples. The surface and interface analysis of magnesium samples post test indicated that dynamic conditions prevented the build-up of corrosion by-products on the sample surface and the corrosion mechanism was uniform as compared to static conditions. The use of a masking element to restrict the exposed area of the sample didn't result in increased corrosion at the boundary. Thus, we have demonstrated the feasibility of the designed test bench as a viable method for bio-corrosion surface analysis under dynamic corrosion conditions for potential biodegradable cardiovascular stent materials.

Preliminary validation of a dynamic electrochemical biodegradation test bench in pseudo-physiological conditions

“…Tests were conducted in Phosphate Buffer Saline (PBS) at room temperature. These were comparable conditions, previously tested [22]. The standard static corrosion cell (Gamry Apparatus) was used for the control.…”

“…The sample was covered with Teflon mask to expose an even area of 1cm 2 . Previous testing has shown this method favorable, with no presence of uneven or crevice corrosion at the boundary [22]. Previous potentiodynamic experiments have shown 316L SS corrosion rates typically ranging around 0.049 mm/year within SBF at 37 ° C [24].…”

“…The dimensions of the rectangular channel that opened up over the exposed sample was as follows: length =29.5mm, width =14.2 mm, height = 7.2 mm (Figure 2). Further detail over the design and rationale of the dynamic test chamber design has been reported elsewhere [22].…”

“…Shear stress exerted by the dynamic motion of fluid can affect the corrosion displayed by the sample, and therefore possibly alter the corrosion behavior under working conditions [16, 17]. Previous work in our laboratory, demonstrated that magnesium (a potential biodegradable material for stent application) surfaces showed different corrosion behavior under flow conditions than in static conditions [22].…”

Preparation of Biodegradable Mg/β-TCP Biofunctional Gradient Materials by Friction Stir Processing and Pulse Reverse Current Electrodeposition

“…Their good biocompatibility, biodegradability and biological activity can avoid secondary surgery and promote bone cell proliferation, which attract extensive attention and research of Mg alloys [3,4,6]. However, Mg alloys have a very active electrochemical property and are corroded easily in chlorine-ion-bearing solution like the physiological environment of the human body, which significantly limits their clinical applications [7][8][9].…”