Catheters are used for cardiovascular, urological, gastrointestinal, neurovascular, and ophthalmic applications. They may be left inside the body either temporarily or permanently to allow for drainage, drug administration, or access by surgical instruments. Accordingly, catheters may be inserted into vessels, skin tissue, body cavities or the brain. Thus, depending on their use and intended location in the body, their tubes vary in diameter and stiffness and come with or without balloons that hold them in place.
Breakage or separation of any catheter can be catastrophic. Polyurethane material degradation during in vivo may cause deterioration of the mechanical properties of medical catheters. The best way to ensure that catheters are safe, retain their quality, and perform successfully is to subject them to a series of tests to measure their mechanical properties and durability.
Catheter mechanical tests include:
Ballon Cycle Fatigue – Balloons must withstand multiple inflations during clinical use to avoid inducing device failure or vessel damage.
Ballon Rated Burst Pressure – Measuring the maximum pressure a balloon can withstand before bursting is known as the rated burst pressure (RBP).
Flexibility/Kink Resistance – Measuring the ability of the device to bend in order to accommodate a predetermined clinically relevant radius or angle it will be required to negotiate during access and delivery.
Coating Friction Test – Lubricity/Pinch Test – The purpose of this test is to assess the lubricity and durability of coatings applied to catheters. The most common test used for measuring surface coating friction is a pinch test, where catheters are pinched between two pads with a known normal/pinching force while using a linear actuator to pull and push the catheter through the pads. Cycling the catheter between the pads multiple times will result in increasing friction readings due to coating degradation.
Peak Tensile Force / Tensile Bond Strength – Measuring the maximum force during uniaxial tensile tests to determine the bond strength at locations where adhesives, thermal fusion, or other joining methods are used for bonding components of the delivery system.
Three-Point Bending – The rigidity of a catheter is measured using a three-point bend test. The sample rests on two lower supports and a force is applied at a constant displacement rate midway between the supports. The test stops when the displacement reaches 0.2 x span length.
Torque Strength – Rotate the proximal end of the catheter while the distal end is fixed and routed through a tortuous path simulating anatomical conditions. Record the number of turns to failure.
Torsional Bond Strength – Determine the torque required to cause failure of the joints and/or fixed connections in the catheter system.