Improved Fracture Resistance
Improved biomechanical performance reduces the risk of stent fracture
Femoropopliteal stenting in longer lesions has been associated with a significantly higher risk of Nitinol stent fracture, with a recent report on the STELLA study in long lesions (mean length 220 mm) indicating a fracture rate of 17.7%.2 While a review of recent studies might lead to an impression of declining stent fracture rates, Veryan believes that stent fracture is presently under-reported and the actual incidence is most likely obscured by study design and methods of reporting. Based on comment and guidance from advisers and regulators, Veryan expects that stent fracture will continue to be the Achilles’ heel of straight laser-cut Nitinol stent designs, particularly in longer lesions.
PROBLEM AND SOLUTION
Problem: Axial Compression in SFA When Knee Bends
Ansel VIVA 2009, VIBRANT Study 1-Year Interim Results, BMS.
Solution: 3D Helical Stent to Accommodate Compression
The unique helical shape of the BioMimics 3D stent confers important mechanical performance and biomechanical compatibility advantages over straight Nitinol stents. During knee bending, due to the helical centreline, the BioMimics 3D stent accommodates femoropopliteal arterial shortening by distributing the compressive strain across the entire stent whereas strain in a straight stent in compression becomes localized increasing the risk of fracture. Comparisons of fracture resistance in an anatomically representative model have shown that the BioMimics 3D stent was more fracture resistant than six different, commercially available, CE-Marked stents. Veryan has shown that 3D helical geometry may be imposed during the manufacture of other straight Nitinol stents to improve their fracture resistance.
Test replicates compression on 150mm stents deployed in an anatomically representative model. The BioMimics 3D stent (top of picture) allows an even strain distribution. The competitor straight stent (bottom of picture) kinks, creating high strain regions that lead to potential fracture sites
Performance of 6 different commercially available CE-marked Nitinol stents compared to BioMimics 3D (Successive 106 cycles of increasing % compression / 6 mm x 120-150mm stents)
2 J.-M. Davaine et al. / European Journal of Vascular and Endovascular Surgery 44 (2012) 432-441