Device for determination of the fatigue durability of intravascular stents

Metal stents used to restore the lumen of stenotic blood vessels remain in the human body for life after their implantation. Their high fatigue strength and durability are necessary conditions for the successful use of the implants. Devices intended for testing the fatigue durability of stents are most often based on using a polymer tube of changeable diameter which imitates the blood vessel into which the stent of the corresponding size is placed. The devices are often foreign made and rather expensive. The authors developed a relatively simple and not expensive research facility in which cyclic loading is realized by «rotating bending» scheme. A stent is placed inside the silicone tube having the diameter corresponding to that of the blood vessel in which the stent will be installed. The ends of the tube are fixed on the rotating shafts, which in turn are located in the bearings. Moving one of the bearings changes the bending radius of the tube R and, accordingly, the degree of deformation of the stent elements. The platform with the stent is located in the tank filled with saline solution. A radiator maintains a constant temperature inside the tank. The rotation frequency can be varied up to 60 Hz, five stents can be tested simultaneously. Cyclic loading is realized with a stress ratio equal to 1. We have tested two typical sizes of self-expanding stents made of the alloy based on titanium nickelide: the first being 8 mm in diameter and 60 mm in length, and the second one — 4 mm in diameter and 30 mm in length. The temperature of the saline solution was (37 ± 2)°C, the rotation frequency of the shaft — 50 Hz. The bending radius was R » 250 mm. Tests showed that the developed device can be effectively used for accelerated fatigue tests of stents.

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