Biodegradable metals for cardiovascular stent application: interests and new opportunities

Biocompatibility and biodegradability of Mg-Sr alloys: the formation of Sr-substituted hydroxyapatite

Magnesium is an attractive material for use in biodegradable implants due to its low density, non-toxicity and mechanical properties similar to those of human tissue such as bone. Its biocompatibility makes it amenable for use in a wide range of applications from bone to cardiovascular implants. Here we investigated the corrosion rate in simulated body fluid (SBF) of a series of Mg-Sr alloys, with Sr in the range of 0.3-2.5%, and found that the Mg-0.5 Sr alloy showed the slowest corrosion rate. The degradation rate from this alloy indicated that the daily Sr intake from a typical stent would be 0.01-0.02 mg day⁻¹, which is well below the maximum daily Sr intake levels of 4 mg day⁻¹. Indirect cytotoxicity assays using human umbilical vascular endothelial cells indicated that Mg-0.5 Sr extraction medium did not cause any toxicity or detrimental effect on the viability of the cells. Finally, a tubular Mg-0.5 Sr stent sample, along with a WE43 control stent, was implanted into the right and left dog femoral artery. No thrombosis effect was observed in the Mg-0.5 Sr stent after 3 weeks of implantation while the WE43 stent thrombosed. X-ray diffraction demonstrated the formation of hydroxyapatite and Mg(OH)₂ as a result of the degradation of Mg-0.5 Sr alloy after 3 days in SBF. X-ray photoelectron spectroscopy further showed the possibility of the formation of a hydroxyapatite Sr-substituted layer that presents as a thin layer at the interface between the Mg-0.5 Sr alloy and the corrosion products. We believe that this interfacial layer stabilizes the surface of the Mg-0.5 Sr alloy, and slows down its degradation rate over time.

Coronary stents: historical development, current status and future directions

INTRODUCTION

Coronary angioplasty with stenting has revolutionized the treatment of coronary artery disease. This article describes the history of coronary angioplasty and stenting, reviews the contemporary stents and recommendations and highlights the on-going work and potential future directions.

SOURCES OF DATA

This review examined the data on coronary stents available in PubMed.

AREAS OF AGREEMENT

Coronary artery stenting is the treatment of choice for patients requiring coronary angioplasty. Stents, and particularly drug-eluting stents, reduce the risk of restenosis, but may be associated with the hazard of late stent thrombosis. Dual anti-platelet treatment is recommended for patients receiving coronary stents.

AREAS OF CONTROVERSY

The selection of stents for various lesions and patients and the duration of anti-platelet therapy remain debated areas.

AREAS TIMELY FOR DEVELOPING RESEARCH

There are on-going preclinical and clinical studies to develop better stent platforms, more biocompatible polymers, novel anti-proliferative and anti-platelet drugs, pro-healing stents and bioresorbable scaffolds.

Corrosion Behavior of Fe-Mn-C Alloy as Degradable Materials Candidate Fabricated via Powder Metallurgy Process

Fe-Mn alloys are prospective degradable materials for coronary stents. Several methods and strategies are investigated to produce excellence properties for this application, such as addition of alloying elements. The study is focused on the corrosion behavior of novel Fe-Mn alloys, i.e. Fe-25Mn-1C and Fe-35Mn-1C fabricated by powder metallurgy process. Addition of carbon is intended to obtain the phase that has ability to easily degradable without compromising its mechanical properties. The results show that austenite phase formed from this process and corrosion rate increased in proportion with the manganese addition from 32.2 mpy (Fe-25Mn-1C) to 43.7 mpy (Fe-35Mn-1C) using polarization methods. The presence of porosity, which cannot be extinguished by sintering, makes the degradation favorable. The results of this study indicate that these alloys have prospective properties to be applied as degradable biomaterials.