Plastic strains during stent deployment have a critical influence on the rate of corrosion in absorbable magnesium stents

Abstract

Magnesium stents are a promising candidate in the emerging field of absorbable metallic stents (AMSs). In this study, the mechanical and corrosion performance of dog-bone specimens and a specific stent design of a magnesium alloy, WE43, are assessed experimentally in terms of their corrosion behaviour and mechanical integrity. It is shown that plastic strains that are induced in the struts of the stent during stent deployment have a critical influence in directing subsequent corrosion behaviour within the material. In addition, the deployment and scaffolding characteristics of the magnesium stent are elucidated and contrasted with those of a commercial stainless steel stent. The magnesium stent is found to support higher levels of cyclic strain amplitude than the stainless steel stent, even prior to degradation, and this may play a role in reducing in-stent restenosis. This study provides new insights into the experimental performance of a current AMS design and material whilst demonstrating the critical influence of plastic strain on the corrosion performance and scaffolding ability of an AMS.

A strain-mediated corrosion model for bioabsorbable metallic stents

“…The value of ߮ for each element was dependent on both the magnitude of elemental ε p1 and the simulated corrosion time, t, and was estimated from a table of values that were established in experimental corrosion tests briefly described below and given in detail in [22].…”

“…The corrosion model was calibrated based on the results of the experiment described in a previous work [22]. Briefly, the corrosion-induced loss of mechanical integrity and mass loss of WE43 alloy dog-bone specimens was determined for three specimen groups, each having a different magnitude of plastic strain, namely 0%, In representing the deformation of the material in the FE model, finite deformation kinematics was assumed.…”

“…Therefore, in this study the corrosion model parameters were established from experimental calibration procedures that involved mechanical and corrosion testing of magnesium specimens and stents with materials processing, surface treatments and loading regimes that were relevant to coronary stents [22].…”

In Vitro Corrosion and Biological Assessment of Bioabsorbable WE43 Mg Alloy Specimens

“…The greatest reduction in yield stress and UTS was observed for the dog-bone specimens, as shown in Figure 3a. Mechanical testing on dog-bone samples has already been published in an earlier study [12]. Wire specimens were also tested using a similar protocol, whereby mechanical strength testing was performed to determine the corrosion-induced loss of mechanical integrity of the specimens over time.…”

“…Thus, it is important that material characterisation testing for small-scale medical devices is conducted on the device itself or on a sample of the device material in the final or finished form. However, few studies have been published that examine the in vitro corrosion performance of WE43 stent precursor tubes and stents [10][11][12][13] and WE43 wires suited for use as orthopaedic implants [14][15][16]. While some data relating to the performance of WE43 dog-bone specimens was presented in our previous study [12], the main aim of this study is to compare and contrast the in vitro corrosion and biological performance of WE43 specimens prepared from stent precursor tubes and wires.…”