Analysis of nitinol coils expanded using an angioplasty balloon catheter

The rupture of vulnerable plaques is associated with life-threatening cardiovascular events such as heart attacks and strokes. While promising medicine therapies could regress the plaque burden and prevent their rupture, no drug delivery device is currently available to deliver medicine directly, efficiently, and effectively into the arterial wall. In this study, a novel device is proposed and analysed. It comprises of a hollow nitinol coil element coupled to a catheter balloon. Finite element analyses were used to determine key geometric constraints of the coil element, including the wire diameter and number of revolution of coils. A catheter balloon inflation model was developed and validated against inflation experiments using corresponding balloons. Different coil geometries were affixed to the balloon model and inflated. It was observed that the balloon sustained an increasing deformation as the wire diameter and number of revolutions increased. Foreshortening of the coil, similar to stent expansion, was also observed. The device will need to be designed to accommodate for the foreshortening of the coil. It was concluded that any number of coil revolution between 0.5 and 3 could be used with a wire diameter of 0.18 mm or smaller. If the wire diameter is larger than 0.18 mm, then only a half revolution coil could be used without obstructing the balloon inflation. From a clinical perspective, smaller wires are more advantageous as they allow for easier navigation to the target lesion due to their smaller diameter and increased flexibility.