Design of Lined, Reinforced Catheter Shafts

Fluoropolymer lined, braided catheter shaft designs are typically used for applications that require liner lubricity, torque, 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 segments of varying durometer and/or material types along the length of the shaft. These segments will provide a change in the stiffness of the shaft from the proximal to the distal end. In addition, the use of a very low durometer material at the very distal end can provide an atraumatic tip to protect the intimal tissue during insertion of the catheter. All of these segments are fused together during the assembly process to form a continuous outer jacket.

The primary feature of the lined catheter is the inclusion of a PTFE, FEP, or other fluoropolymer liner. This liner provides the catheter shaft with a high degree of lubricity on the inner diameter that facilitates the passage of other diagnostic or therapeutic devices through the inner lumen. In addition, fluoropolymers are resistant to many chemicals, which make this construction ideal for some types of drug delivery systems as well.

With respect to dimensions, a lined 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; there are some physical limitations that result. The liner can be produced as thin as 0.001″ (0.03 mm) and the outer jacket thickness is typically limited to 0.002″ (0.05 mm) minimum although these will change depending on the overall diameter of the shaft to be manufactured.

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 0.005″ (0.13 mm) by adding the liner thickness of 0.001″ (0.03 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 offs 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.

Lined catheter shafts offer a high degree of design flexibility making it easy to include other features into the product such as radiopaque marker bands and reinforcing coils. The marker bands are encapsulated in the wall of the catheter shaft and provide excellent radiographic visualization for the identification of tip or other locations while placed in vitro. The coil reinforcement can be added as a segment after the braid or as the sole reinforcing member in the shaft and this coil provides much better kink resistance than a braided shaft alone.

Using our proprietary process, Teleflex Medical OEM is able to provide shafts incorporating multiple lumens, each with its own fluoropolymer liner. These shafts are used in the construction of articulating tip catheters, providing a lubricious liner for the pull wire(s) channel(s).

*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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