In-vitro Evaluation Method to Measure the Radial Force of Various Stents

Endovascular treatments of stenosis in carotid artery often utilize a self-expanding stent. There are a variety of stents commercially available. The radial force of a stent is a key parameter to characterize its mechanical property, but there is no reliable evaluation to standardize the force measurement. In measuring the radial force accurately, the stent deformation has to be uniform for the whole structure so as to ensure the force balance. Here we aim to develop such a measuring system of stent radial force, and compare the results with those obtained by conventional techniques. A developed device consisted of a tubular stent holder and a load measuring system. The Precise, Protege and Easy Wall stents with a diameter (D) of 10 mm were placed by a delivery system. Radial forces were measured with D = 8, 6, 5, and 4 mm at a temperature of 37 degrees. Maintaining the circular shape of stents was found to influence substantially the magnitude of radial force. The value increased about 80 % at maximum for those measured by conventional techniques. These data show that the radial force has to be uniformly applied in a circumferential direction. Also, the Easy Wall stent showed a distinct tendency in contrast to the Precise and Protege stent. The Easy Wall stent was found to be placed with eliminating the axial variation of mesh geometries. These results indicate that the radial force measurements of stents have to ensure the uniform mesh geometry in both the axial and circumferential direction. It was concluded that our device can ensure the reliable measurement of stent radial forces.