Degradation Kinetics and Ion Release in Mg-Al Alloy for Coronary Stents: In-Vitro and In-Vivo Studies

Investigating degradation behavior and aluminum release in Mg-9Al alloys for bioresorbable stent applications.

This project focuses on the in-vitro and in-vivo degradation behavior of Mg-9Al alloys, particularly their suitability for biodegradable cardiovascular stents. In collaboration with Prof. Roger Guillory II at the Medical College of Wisconsin, we evaluate corrosion behavior, hydrogen evolution, and aluminum release using a combination of electrochemical, microstructural, and biological methods.

Objectives

  • Study the degradation mechanisms of solutionized and peak-aged Mg-9Al alloys in vitro and in vivo.
  • Monitor hydrogen evolution and morphological degradation using SEM and CT.
  • Assess aluminum release trends to understand potential systemic biocompatibility risks.
  • Inform microstructural design strategies to control degradation rates in bioresorbable stents.

Methodology

Thermal processing of Mg-9Al alloy to create solutionized and peak-aged states for comparison.
  • In-vitro immersion testing in simulated body fluids was performed to study mass loss, pH changes, and surface morphology, with analysis via SEM/EDS.
  • Aluminum release from corroding samples was tracked over time using ICP QQQ, providing insights into alloy biocompatibility.
  • In-vivo studies involved subcutaneous implantation in murine models, with CT imaging used to monitor hydrogen bubble evolution as a proxy for degradation rate.
Hydrogen evolution tracked via in-vivo CT imaging reveals differences in degradation behavior across processing states.

Key Insights

  • Peak-aged microstructures, rich in Mg17Al12, show accelerated corrosion in vitro due to micro-galvanic effects.
  • Aluminum release, though elevated in vitro, is being carefully evaluated in vivo for its systemic effects.
  • In-vivo degradation proceeds more gradually, indicating that the biological environment buffers degradation aggressiveness.

Ongoing Work

Current work focuses on refining thermal processing routes to minimize Al-rich precipitate formation and improve biocompatibility without compromising mechanical integrity. These insights are being integrated into a framework for safer Mg-based bioresorbable devices.

Keywords: magnesium alloys, Mg-9Al, degradation, aluminum release, hydrogen evolution, CT imaging, SEM/EDS, MCW, β-Mg17Al12, bioresorbable stents