Guidewires are most commonly made out of nickel-titanium, also known as Nitinol, or stainless steel. Typical tension testing of Nitinol wire is completed to ASTM F2516 standards. For both, Nitinol and stainless steel, wire pull to failure testing is also common to measure elongation and strength properties of the material. In addition to tension testing for quantifying the material properties, guidewire manufacturers, especially in the cardiovascular industry, are interested in quantifying the frictional forces of guidewire to simulate the action of the product being pushed through a patient's body. This type of test is often referred to as tortuosity testing. For many companies, establishing testing requirements for simulating a guidewire's use in surgery can seem like a daunting task. One of the main challenges with this test is the customization required in the software to control the machine in such a way that simulates a surgeon inserting a guidewire into a patient.
Despite the perceived complexity of tortuosity testing, the test can actually be quite simple. Our solution is to use a horizontally mounted 6800 Series testing system, a lower pneumatic side action grip that can be toggled with air pressure to open and close, and a tortuous path membrane designed to simulate the patient's body. Standard Bluehill® Universal software equipped with the TestProfiler module is required to program simple cyclic testing with the control tied to toggling the pneumatic grip. A test method can be set up to close the grip, use the Instron® crosshead to push the guidewire into the membrane, and measure the frictional force with a force transducer or load cell. Once the guidewire is pushed far enough, the pneumatic grip can be programmed to open, move back to the starting position, and then repeat the test sequence from the beginning.