Microstructural changes within similar coronary stents produced from two different austenitic steels.

Area of Science:

• Biomaterials Science
• Cardiovascular Engineering
• Materials Science

Background:

• Coronary heart disease is a leading cause of death in industrialized nations, with coronary stents crucial for preventing vessel collapse.
• Current coronary stents predominantly use chromium-nickel-molybdenum steel (AISI 316L), offering strength, ductility, and corrosion resistance but raising concerns about nickel's allergenic potential.
• Alternative materials like cobalt-base L605 and tantalum alloys are expensive, limiting their widespread use.

Purpose of the Study:

• To evaluate newly developed austenitic high-nitrogen CrMnMoN-steels (AHNS) as a potential alternative to conventional stent materials.
• To assess the mechanical properties, corrosion resistance, and biocompatibility of AHNS compared to AISI 316L.
• To understand the implications of the oligocrystalline structure of thin-strut stents on their performance under deformation.

Main Methods:

• Literature review of existing studies on coronary stent materials and their properties.
• Analysis of traditional material tests comparing AHNS with AISI 316L.
• Consideration of the microstructural characteristics (oligocrystalline nature) of thin-strut stents (approx. 100 micrometers).
• Evaluation of material behavior under inhomogeneous plastic deformation experienced during crimping and dilation.

Main Results:

• Newly developed austenitic high-nitrogen steels (AHNS) demonstrate comparable or superior strength, ductility, corrosion resistance, and biocompatibility to AISI 316L.
• AHNS present a viable nickel-free alternative, mitigating concerns associated with nickel allergies.
• The oligocrystalline nature of thin stent struts means individual crystal grains significantly influence overall stent performance and failure.

Conclusions:

• Austenitic high-nitrogen CrMnMoN-steels are a promising alternative for coronary artery stents, offering excellent material properties and addressing nickel allergy concerns.
• The mechanical integrity of thin-strut stents is highly dependent on their microstructural features, specifically the behavior of individual crystal grains.
• Further research into the performance of AHNS under physiological conditions and during implantation procedures is warranted.