Design Information for Braid-Reinforced Catheter Shafts

Braided catheter shaft designs are typically used for applications that require high torque, burst pressure resistance, pushability, steerability, and kink resistance. These designs can be produced in a wide range of sizes from 2F through 24F depending on the application.

A common requirement for this type of shaft is to have an un-reinforced soft stem section welded to the distal end of the catheter. In addition to the un-reinforced stem, certain applications require an atraumatic tip as well to provide protection to the intimal tissue during insertion of the catheter. This tip is welded to the distal end of the stem section.

When designing braid reinforced shafts, a variety of materials can be specified for the liner and jacket materials to enhance the properties of the shaft depending on the performance characteristics that are to be achieved, (i.e. torque, kink resistance, and flexibility).

With respect to dimensions, a braided shaft has three elements, the inner liner, the braid and the outer jacket. These elements must be combined in order to achieve the required dimensions and there are some physical limitations that result. The liner and outer jacket thickness is typically limited to 0.002″ (0.05 mm) each although this is determined by the overall diameter of the shaft.

To determine the wall, the inner and outer polymer layer thickness must be added to twice the diameter of the braid wire (the braid crosses itself). For example, a braid wire of 0.001″ (0.03 mm) would yield a theoretical wall of 0.006″ (0.15 mm) by adding the liner thickness of 0.002″ (0.05 mm) to the wire diameter 0.001″ (0.03 mm) times 2 or 0.002″ (0.05 mm) added to the outer jacket thickness of 0.002″ (0.05 mm).

Often there are trade off’s required in the design depending on the performance requirements. For example, higher torque can be achieved with a higher pick count* but this will reduce the flexibility of the shaft. Likewise, a larger diameter braid wire can be specified to provide more stiffness and torque but this will impact the minimum wall thickness and flexibility. A flat braid wire will reduce the wall, increase the flexibility but this will also reduce the torque.

As a result, it is important when designing a braid reinforced catheter shaft to consider the performance requirements up front to assure that the design meets the needs of the user.

*Please note: The pick count is expressed in picks per inch of length (PPI), which represents the number of times the wire crosses for every inch of shaft length. The higher the PPI, the more wire coverage is achieved.

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