FAQs
Q: What is durometer, flexural modulus and tensile strength?
A: Durometer is the measure of hardness for a material. Shore and Rockwell Durometer measure the resistance of plastics toward indentation. The higher the number the harder the material will be. Shore Hardness uses two different scales; Shore A or Shore D. Shore A is usually used for flexible materials and Shore D is used for semi-flexible materials. For catheters the durometer can vary from very stiff for maximum pushability to very flexible and soft for areas where invasive pushing could create damage. Durometer is important not only for the device in use but also for the manufacturing of the device. Some materials extrude better with particular zones of hardness.
Flexural modulus is the measure of a material’s bending stress relative to elongation under load. It provides an elastic measure of a material’s stiffness for a given test specimen and shape. The rigidity of a polymer tube is determined by the inherent stiffness of the material (modulus) and the cross sectional design of the catheter. Changing the dimensions of the cross section can have a profound impact on rigidity.
Tensile strength is the maximum stress that a material can withstand while being stretched or pulled before breaking. This is important to understand for extruding thin walled tubes as well as for the tube’s performance. Heat shrink, balloons, and high pressure braided tubing all rely heavily on the tensile strength characteristics of a material. Materials such as Polyimide and PEEK have the highest burst pressure performance of materials commonly used in vascular catheters. To improve these characteristics, tubes are often braided to add strength and reinforcement to the structure.
