Catheter Design: Expert Guidelines for Achieving Optimal Performance

In catheter design, the functional requirements of the application allow the designer to identify performance requirements such as flexibility, lubricity, kink resistance, column or push strength, and torque transfer characteristics. Development of an optimal catheter design requires a strong understanding of catheter technologies to achieve the desired characteristics. This document offers a layer-by-layer approach to design considerations for your device.

Layer-By-Layer Design Considerations

At its simplest form, a reinforced catheter design is composed of an inner liner layer, a central reinforcing layer, and an outer polymeric overlayer.

Inner Layer – Liners
When selecting a liner material, it is essential to consider both the benefits of a material and its design considerations. There are trade-offs with any material. The key is to understand what is critical for the catheter’s application.

Central Layer – Reinforcement
There are two distinct types of catheter reinforcement: braid and coil. With both, Teleflex Medical OEM can offer you novel technologies for increasing the tensile yield of a reinforced catheter. These include the incorporation of longitudinal, reinforcing components in a variety of materials such as flexible, high-tensile, advanced fibers.

Braid Reinforcement
Excellent torque control is the primary driver of a braided catheter design. This can be achieved with braid reinforcement. Manipulation of the distal tip of a catheter, by twisting the proximal end, requires good torque transmission with little “whip”. A relatively linear response is a desired catheter characteristic for end-use applications.

The wire size, profile, density (PPI), and braid configurations can be engineered to provide a great balance of pushability with good torque control. In some cases, multiple braid layers are necessary to meet the level of manipulation that is required.

• The pitch of the braid pattern can also be modified, by section along the length of the catheter, to vary both the catheter flexibility and hoop strength.
• Materials used in the reinforcement can be metallic or non-metallic. As for metallics, the most popular is stainless steel. Nitinol, due to its kink resistance, is becoming popular in microcatheters.

Please note:Teleflex Medical OEM has experience with specialty braid wire options to impart radiopacity. Non-metallic materials, in fiber form, are available and often used in cases where MRI or potential field generation can be an issue, such as radiofrequency (RF) procedures.

Coil Reinforcement
Outstanding hoop strength, kink resistance, and good pushability are characteristics of coil reinforcement.

• Teleflex Medical OEM can provide discreet, coil-reinforced catheters, on a PTFE liner, using a laid-up assembly process. This is generally limited to a single pitch along the length of the catheter.
• We have developed proprietary technology for continuous, coil-reinforced assembly that allows the coil pitch to be varied along the length (variable pitch coiling). This allows differing amounts of flexibility and kink-resistance along the catheter shaft.
• Our catheter team can also provide proprietary multi-filar based, continuous-coil solutions which can improve the tensile strength of a coiled structure.
• A continuous-coil design, using an HDPE liner, is one of the most cost-effective, composite designs available for a catheter.

Outer Layer – Polymeric Overlayers
This selection of the outer layer material strongly influences tensile yield, stiffness, and catheter pushability. The outer layer may be multiple materials or durometers.

To perform effectively, a reinforced shaft needs strong adhesion between the inner and outer layers. Delamination between these two layers can compromise the catheter’s functional performance. This limits the choice of outer layer materials to polar materials, because they can adhere directly to either an etched surface or a tie layer.

Polar materials are also beneficial for adding a hydrophilic coating on the outer layer, as they provide better adhesion. Hydrocoating helps minimize endothelial damage (damage to the inner lining of the blood vessels) and makes it easier to place a catheter.

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