Fourth-generation endovascular stent-graft: the concept of laminar flow.

The stent graft is a noncompliant system inserted in a semi-compliant structure. This generates a mismatch. The media also shows a composite movement and is oriented 45° resulting in an arterial spiral movement that contributes to maintaining the clockwise orientation of laminar flow with an 80° deflection. Our multilayer stent is constituted by a single Nitinol thread, worked on 3 surfaces in order to realize a proper exoskeleton that reproduces the architecture of the tunica media, in particular its flexo-torsional forces, thus restoring the energy transmission and the match between the wall and the blood flow. A first in vivo implantation was performed by using an experimental pig model in our veterinary department. The pig underwent general anesthesia and the right femoral artery was surgically exposed in order to accommodate a 12F long introducer sheath. Under fluoroscopy three multilayer stents were consecutively implanted from the aortic isthmus to the iliac bifurcation in an overlap fashion. All the intercostal artery and visceral branches were covered by the overlapped stents. The final control angiography revealed an optimal sealing of the implanted stent with an evident flexotorsional oscillatory movement, which follows the conical architecture of the thoracic aorta and the complete patency of all the branches that arise from the aorta. After two months, the multilayer showed a normal endothelialization process with an optimal adhesion to the aortic wall both proximally and distally without provoking any inflammatory response or thickness wall alterations. The perfect and homogenous endothelialization preserved the patency of all the collateral branches arising from the treated aorta, in particular all the intercostal arteries, celiac trunk, and renal arteries. The disease of the aorta essentially concerns the tunica media as it causes disruption of the media components. This exoskeleton works like a neo-tunica media, is perfectly endothelialized, and seems to optimally transmit the flexotorsional forces, restoring the match between wall and flow that represents the primary condition for laminar flow and branch perfusion.