Investigating the bending properties of cardiovascular catheters and stents via three-point bending test setup

Abstract The bending properties of catheters and stents have a big influence on their success during clinical application. Whereas bending stiffness directly affects the trackability of catheters, stents underlie bending when used for renal, superficial femoral or femoro-popliteal arteries, respectively. A three-point bending test setup according to ASTM F2606 was implemented into a universal testing machine and was validated regarding influence parameters such as accuracy of force measurement, test speed and span length. The bending stiffness can be calculated from the initial linear portion of the force-deflection curve. Furthermore, a multi-cycle approach was developed to evaluate the bending properties at large deformations revealing the deflection depending peak load as well as deflection depending elastic recovery rate after unloading. Within this study samples with a length of 120 mm from the proximal region of a commercial coronary balloon catheter were used. Influence of test speed was not significant. However, bending stiffness increased with increasing span length. For multi-cycle measurements a constant test speed and constant span length was used. Test results showed an increasing plastic deformation and peak load as well as a decreasing elastic recovery rate as expected. The presented test method can be used for catheters as well as stents with a length diameter ratio of at least 4:1.