Comparison of Biomechanical Properties of the iCover and VBX Stent Grafts When Used as Bridge Stents in Fenestrated Endografts: An In Vitro Study

Abstract

Objective:

The objective of this study was to compare in vitro the different biomechanical properties of 2 balloon-expandable covered stents, VBX (Viabahn VBX, W.L. Gore & Associates, Flagstaff, AZ) and iCover (iVascular, Barcelona, Spain), as bridging stents in fenestrated aortic endoprostheses.

Methods:

Three biomechanical tests were performed to evaluate a total of 12 stents (6 VBX 6 × 59 mm and 6 iCover 6 × 57m). First, a 3-point bending test was performed with a calibrated dynamometer to evaluate the bending strength of the 40% and 150% deformation of the system in its crimped state and the force necessary to deform the expanded stent by 40% with respect to its initial diameter. Then the stents were expanded to their nominal diameter inside a 6-mm-diameter handmade fenestration and flared up to 8 and 10 mm. The whole set was fixed in the dynamometer to carry out the pullout-force (perpendicular dislocation) and shear-stress-force (axial dislocation) tests. The resulting forces were recorded via the force transducer. Load, deformation, and displacement data were recorded in newtons. The results of each stent test were examined under the microscope, and both stent types were compared.

Results:

Higher forces were required to bend the crimped VBX (16.24 N [IQR, 13.87-17.47 N] for the iCover and 19.01 N [IQR, 16.01-19.50 N] for VBX; P < 0.001), but lower forces were necessary for the expanded VBX compared with the iCover (0.36 N [IQR, 0.1-0.49 N] and 1.01 N [IQR, 0.97-1.09 N], respectively; p = 0.004). Pullout forces were 3.56 N (IQR, 3-4.1 N) and 7.07 N (IQR, 6.86-7.28 N) for the 8-mm flare and 7.29 N (IQR, 6.13-8.45 N) and 14 N (IQR, 12.05-15.95 N) for the 10-mm flare for the iCover and VBX, respectively (P = 0.333 for both comparisons). The shear-stress forces needed to dislocate the 6-mm iCover and VBX axially with a 10-mm flare to 50%, 100%, and 200% were 0.88, 1.61, and 3.55 N for the iCover and 0.71, 1.43, and 2.51 N for the VBX (P = 0.343, P = 0.486, and P = 0.486, respectively).

Conclusion:

After evaluating the stents under in vitro conditions, the VBX and iCover stents showed similar results in terms of biomechanical properties, which demonstrates their competence in in vitro conditions. Further in vitro comparisons with other stent grafts are required.

Clinical Impact

The BECS used in FEVAR / BEVAR must ensure some properties to avoid the most frequent complications derived from the failure of these bridging stents (stenosis, thrombosis, stent integrity, dislodgement or endoleaks) that represent the most common cause for reintervention. This paper adds to the limited data available, information to the clinician after comparing some properties of two BECS used in these techniques that demonstrate their competence in in-vitro conditions.