Computational and experimental mechanical performance of a new everolimus-eluting stent purpose-built for left main interventions.

Left main (LM) coronary artery bifurcation stenting is a challenging topic due to the distinct anatomy and wall structure of LM. In this work, we investigated computationally and experimentally the mechanical performance of a novel everolimus-eluting stent (SYNERGY MEGATRON) purpose-built for interventions to large proximal coronary segments, including LM. MEGATRON stent has been purposefully designed to sustain its structural integrity at higher expansion diameters and to provide optimal lumen coverage. Four patient-specific LM geometries were 3D reconstructed and stented computationally with finite element analysis in a well-validated computational stent simulation platform under different homogeneous and heterogeneous plaque conditions. Four different everolimus-eluting stent designs (9-peak prototype MEGATRON, 10-peak prototype MEGATRON, 12-peak MEGATRON, and SYNERGY) were deployed computationally in all bifurcation geometries at three different diameters (i.e., 3.5, 4.5, and 5.0 mm). The stent designs were also expanded experimentally from 3.5 to 5.0 mm (blind analysis). Stent morphometric and biomechanical indices were calculated in the computational and experimental studies. In the computational studies the 12-peak MEGATRON exhibited significantly greater expansion, better scaffolding, smaller vessel prolapse, and greater radial strength (expressed as normalized hoop force) than the 9-peak MEGATRON, 10-peak MEGATRON, or SYNERGY (p < 0.05). Larger stent expansion diameters had significantly better radial strength and worse scaffolding than smaller stent diameters (p < 0.001). Computational stenting showed comparable scaffolding and radial strength with experimental stenting. 12-peak MEGATRON exhibited better mechanical performance than the 9-peak MEGATRON, 10-peak MEGATRON, or SYNERGY. Patient-specific computational LM stenting simulations can accurately reproduce experimental stent testing, providing an attractive framework for cost- and time-effective stent research and development.

Characterization of an NbTaWZr alloy designed for magnetic resonance angiography compatible stents.

The majority of stent materials are not fully compatible with magnetic resonance imaging due to their ferromagnetic or paramagnetic compositions. This leads to image artifact which can obscure clinical data in the vicinity of the stent. An Nb-28Ta-3.5W-1.3Zr alloy has been developed specifically to provide reduced magnetic susceptibility and therefore reduce image artifact. This study reports on initial surface characterization, corrosion behaviour, endothelial cell response and MR image performance. Surface analysis confirms the presence of a niobium oxide with some tantalum oxide also present. Electrochemical corrosion testing demonstrates the oxide to be stable with no evidence of film breakdown. Leaching of metallic ions during a 60-day immersion test shows low levels of release, comparable to cobalt-chromium L605. A short term endothelial cell adhesion study shows that the Nb-28Ta-3.5W-1.3Zr may be similar to stainless steel for supporting cell growth. The MR artifact assessment shows that the material has significantly reduced artifact compared to stainless steel. In summary, results from this initial study show that the Nb-28Ta-3.5W-1.3Zr meets many on the criteria expected of a stent material and that improved MR imaging behaviour is also obtained.