Spiral Laminar Flow™ Technology in a Self-expanding Nitinol Stent: Investigation on the Manufacturing Process

Self-expanding Nitinol stenting is the preferred treatment for peripheral artery disease (PAD). Among the long-term complications, in-stent restenosis shows with high incidence, and it’s believed to be caused by altered flow dynamics induced by the presence of the device.

Spiral laminal flow (SLF^TM) technology consists in a helical ridge placed on the inner surface of the device which allows to recover the natural helical blood flow pattern to improve downstream flow, reduce forces and turbulence caused by stenting and prevent disease progression.

This study considered a Nitinol stent design inspired by a commercially-available device for femoropopliteal arteries and investigated the feasibility of SLF^TM manufacturing approach. The SLF^TM technology was provided in two steps:

• Ridge Deformation (RD) with an ad hoc tool to create the helical ridge;
• Heat Treatment (HT) in a furnace to set the shape (T*[°C], t*[min]).

To assess potential mechanical modifications induced during RD and HT, four stents progressively underwent different process steps (S1=ref, S2=HT, S3=RD+HT, S4=RD+HT) and were subjected to standard bench tests (parallel plate crush, radial compression) and visual inspection (digital and SEM microscope).

It was found that HT generally caused a slight reduction of the mechanical performance both in parallel plate and radial compression tests, however, within acceptable ranges for stent applications. The RD is believed to be the reason that caused a fracture in one of the devices, thus further modification of the RD tool and optimisation of heat treatment parameters (T[°C], t[min]) will be put in place to solve the issue.