Design and production of biodegradable cardiovascular stents in magnesium

Amongst other cardiovascular stent materials such as stainless steel, titanium, Ni-Ti shape memory alloys or polymers, magnesium stands out as a promising new option in terms of three essential features: biocompatibility, biodegradability, and good mechanical properties. Magnesium, as an element already present in the human body, is highly compatible to the body tissues; due to its relatively low corrosion resistance in human body fluids its degradation is intrinsic and as a metal it exhibits good mechanical properties in terms of strength and recoil properties. Overall, this combination of properties would result in a less intrusive treatment of cardiovascular pathologies. In addition to the medical aspects, Mg stents need to be studied in terms of design and manufacturability owing to the use of Mg as innovative material for the biomedical sector. This would involve the selection of the appropriate Mg alloy, the design of the adequate stent mesh, the manufacturing of the semi-finished tubular material and the reproduction of the stent mesh on it. This work reports the study of extrusion, laser micromachining and chemical etching of AZ31 magnesium alloy for the manufacturing of cardiovascular stents with a novel mesh design. Primarily a new conceptive stents was investigated and a 3D stent mesh was modelled with optimised mechanical properties in terms of scaffolding ability. Second, high-temperature properties and extrusion behaviour of AZ31 alloy were studied by hot compression testing in the temperature range 350-450°C. Hollow, small diameter tubes were then extruded from the same alloy according to the parameters defined by the hot-compression tests. At this point a pulsed fiber laser system operating in nanosecond pulse regime was employed for the micromachining phase. Finally, chemical etching was applied to remove spatter and complete the scrap separation from the stent geometry.