Performance assessment of braided venous stent designs through computational modeling

The application of stents in the venous system is increasing. Where arterial stents have been used and developed for many decades, specific venous stents have not received the same level of attention while their requirements are clearly distinct from arterial stents. Here, computational modelling has been used to quantify the performance of braided stents for the venous system and develop an optimization tool for their design.
Explicit finite element models have been created of venous stents which are modelled using beam elements. Beam elements provide an efficient alternative to full 3D solid elements and the braided wire stent geometry is very suited for this approach [1,2]. To avoid unphysical behavior, wire crossovers are modelled with a contact algorithm including friction. Crush resistance is evaluated using cylinder crush tests resembling May-Thurner syndrome type loading on free stents, Fig. 1, and stents deployed in an artificial vein. Chronic outward force is assessed and conformability is investigated by deploying the stent in a 90 degrees angled tube and assessing wall apposition. Based on performance parameters for venous stents, tests have been selected and suitable metrics defined. The created models have first been validated by comparing with bench test measurements, followed by an investigation of the influence of different
design parameters: stent length and diameter, wire diameter and amount,
winding angle, end type (open or looped).
Wire diameter and winding angle are found to be critical design factors for local crush resistance, while stents with looped ends exhibit significantly higher chronic outward force and better conformability. Friction is observed to play a key role in the deformation behavior of braided stents, Fig. 2 which is also affected by being deployed in a vein, Fig. 3.
Using validated computational modelling for the evaluation of stent performance provides a significant advantage in creating insight in the stent behavior. The modeling strategy proposed here allows for fast quantified evaluation of design features, facilitating optimal stent design.