Development of biodegradable magnesium alloy stents with coating

Abstract

Biodegradable stents are attracting the attention of many researchers in biomedical and materials research fields since they can absolve their specific function for the expected period of time and then gradually disappear. This feature allows avoiding the risk of long-term complications such as restenosis or mechanical instability of the device when the vessel grows in size in pediatric patients. Up to now biodegradable stents made of polymers or magnesium alloys have been proposed. However, both the solutions have limitations. The polymers have low mechanical properties, which lead to devices that cannot withstand the natural contraction of the blood vessel: the restenosis appears just after the implant, and can be ascribed to the compliance of the stent. The magnesium alloys have much higher mechanical properties, but they dissolve too fast in the human body. In this work we present some results of an ongoing study aiming to the development of biodegradable stents made of a magnesium alloy that is coated with a polymer having a high corrosion resistance. The mechanical action on the blood vessel is given by the magnesium stent for the desired period, being the stent protected against fast corrosion by the coating. The coating will dissolve in a longer term, thus delaying the exposition of the magnesium stent to the corrosive environment. We dealt with the problem exploiting the potentialities of a combined approach of experimental and computational methods (both standard and ad-hoc developed) for designing magnesium alloy, coating and scaffold geometry from different points of views. Our study required the following steps: i) selection of a Mg alloy suitable for stent production, having sufficient strength and elongation capability; ii) computational optimization of the stent geometry to minimize stress and strain after stent deployment, improve scaffolding ability and corrosion resistance; iii) development of a numerical model for studying stent degradation to support the selection of the best geometry; iv) optimization of the alloy microstructure and production of Mg alloy tubes for stent manufacturing; v) set up, in terms of laser cut and surface finishing, of the procedure to manufacture magnesium stents; vi) selection of a coating able to assure enough corrosion resistance and computational evaluation of the coating adhesion. In the paper the multi-disciplinary approach used to go through the steps above is summarized. The obtained results suggest that developed methodology is effective at designing innovative biomedical devices

The current trends of Mg alloys in biomedical applications—A review

“…Bartosch et al concluded that the use of Mg stents is safe but the research on Mg stents should be expanded to large stent designs for large vessels and applications other than just coronary stents . There are a number of studies on the mechanical and degradation analysis of Mg‐based stents which will be discussed in detail in the “Computational Models” section.…”

New methods for in vivo degradation testing of future stent materials

“…Most research was done on established materials like WE43, AZ31 or modifications of such alloys. Different magnesium alloys, surface modifications and coatings with or without anti‐proliferative substances have been analyzed in vitro as well as in vivo . Recently, Biotronik achieved CE‐marking for their degradable coronary stent “Magmaris.”…”

A Computational Study to Investigate Debonding in Coated Bioresorbable Stents

“…Hybrid bioresorbable stents (HBSs), like magnesium alloy stents coated with a degradable polymer, are a very promising solution for coronary artery diseases. 1,2 The magnesium alloy substrate will be resorbed by the body after they have completed their function, 3 limiting long term complications related to the body inflammatory response caused by permanent implants. Furthermore, the polymer coating can improve the desired degradation kinetics, ensuring a protective action from the corrosive environment which can cause too fast degradation of stent substrates.…”