ICF Mechanical Property Optimisation of Magnesium Alloy Wires for Bioresorbable Vascular Scaffolds for the Treatment of Peripheral Arterial Disease

This project aims to develop a novel magnesium-lithium-yttrium alloy wire with the optimum mechanical properties required for manufacture of bioresorbable vascular scaffold (BVS) medical devices for the treatment of peripheral artery disease (PAD). Through altering the alloy composition, process temperature and strain rate during wire drawing and forming, this project will investigate how a more favourable microstructure can be generated for optimum mechanical properties with cost effectiveness.

The work will be conducted in close collaboration with SME company Lumenology who will apply the knowledge gained into the manufacturing processes of their BVS device.

BVS are an emerging technology which address an unmet clinical need for an effective treatment of PAD. There is no consensus on the best treatment approach because open surgery, endovascular interventions, or hybrid strategies all have significant drawbacks. Thus the outlook for patients with PAD is poor, and, without limb amputation in severe cases of PAD, the 5-year mortality rate is as high as 65%.1

PAD is mainly caused by atherosclerosis causing narrowing and damage leading to restricted blood flow. Atherosclerosis is generally treated with angioplasty (balloon catheters) and permanent metallic stents. Balloon catheters force open blocked arteries and stents provide structure while the artery heals.

Stents are compacted onto balloon catheter delivery systems, fed through the arteries to the blockage and inflated to a larger diameter. Minimisation of the compacted device/balloon system diameter is key to ensure easy delivery and safe expansion.

Current stents are effective for treating the coronary arteries, however implementation for long PAD lesions, particularly in arteries below-the-knee (BTK), has been associated with arteries re-occluding early and stent breakages. Temporary BVS devices are a potential solution for the treatment of BTK arteries. A BVS must provide acute structural support equivalent to stents to widen and allow the artery to heal but subsequently be safely absorbed, removing the long-term complications associated with permanent stents.

Magnesium alloys are the most promising candidate material for temporary BVS devices because they have appropriate mechanical properties whilst degrading safely, within a suitable timeframe. One limitation of magnesium alloys is that they exhibit relatively poor ductility compared to the materials used in permanent stents. Consequently, current magnesium based BVS devices have larger delivery diameters compared to permanent stents.

The mechanical properties of magnesium alloys are strongly influenced by the alloy's microstructure. Benchtop testing demonstrates that Lumenology's current BVS device exhibits impressive mechanical performance. However, during forming, the internal microstructure is significantly deformed, reducing ductility and thus limiting the minimum achievable compaction diameter.

This project aims to improve the ductility of magnesium-lithium-yttrium alloy wire by regulating the characteristics of the microstructure through modifying the alloy composition and processing conditions during device manufacture. This will allow the full potential of magnesium alloy wire based BVS devices to be unlocked, opening the door to revolutionising the treatment of PAD.

If successful, Lumenology's BVS device with optimised microstructure and mechanical properties will be able to be compacted to smaller diameters making it easier and safer to deliver into diseased arteries. Reduction of the diameter of the device/balloon system will be instrumental in progressing towards a successful first in-human clinical trial. This would allow Lumenology to bring the device to the market to start treating the millions of patients suffering from PAD who currently have limited treatment options and increased risk of death.