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Author: Mike Schultz, VP of Innovation and Development, Spectrum Plastics Group

Minimally invasive surgery (MIS) using steerable catheter systems represents an expanding market in the healthcare sector. As the types of catheter-based procedures continue to increase, doctors and therapists need tools and technology to increase access and performance, and the steerable catheter market opens the door to innovation.

MIS procedures, especially for cardiovascular and neurovascular applications, must often travel through tortuous paths to access more distant blood vessels and specific target anatomical structures. The success of these procedures depends on an advanced catheter system that delivers the treatment to a precise location through a narrow access point (such as the femoral artery). As MIS procedures become more sophisticated and complex, doctors need to enhance the control and maneuverability of catheters to accurately locate and deploy treatments without damaging surrounding tissues.

The most important design considerations for steerable catheters are:

Build a steerable/deflectable catheter

A typical steerable/deflectable catheter consists of four key parts:

Generally, the handle is made of rigid plastic, which provides a comfortable grip and precise translation of user actions. The proximal part of the shaft closest to the handle is made of a relatively hard polymer, which provides excellent torque response and minimal flexibility. The catheter body gradually becomes more flexible from the handle to the distal tip, which is the most flexible part of the device. The corresponding length and stiffness of each section can vary according to the specific anatomy and procedure for which the catheter is designed.

The deflection of the distal end is controlled by the user operating the wheel or slider on the handle. The wheel is connected to one or more wires that extend along the length of the catheter body to the distal end; when the wheel rotates, it creates tension in the wire, which causes the flexible distal tip to deflect in a specific direction.

Designing a steerable catheter requires a comprehensive understanding of the surgery, the anatomy to be navigated, and the range of motion/deflection required for treatment. For example, what is the bending angle and the deflection plane? How much deflection is required, and what is the best bending radius for the anatomy?

Flexibility is controlled by polymer type, hardness, and density of coiled or braided reinforcements in various parts of the catheter. The high-density braid at the distal end maximizes flexibility; the lower-density braid makes the proximal shaft stiffer. A variety of hardness materials can be used along the catheter body to form a gradual change in flexibility. Achieving a balance between torque and flexibility requires careful modeling and testing. Generally, the higher the flexibility, the lower the torque, so a well-defined design input is the key to allowing the designer to determine with certainty how to optimize performance so that the device can easily reach the target anatomy. Other reinforcement structures can also be added, such as a machined hypodermic syringe with a special bending mode to enhance deflection or more specific curve configurations.

A closed pull wire extending along the outside of the central catheter lumen controls the deflection of the distal tip. The number and position of the lines determine the user's degree of control over the deflection of the distal tip. Typical configurations are: one-way (one-way), two-way (two-way) and four-way (four-way). The four-way catheter has four pull wires extending from the distal end to the proximal handle to control the curved drive in the two motion planes. When tension is applied to the wire, friction will increase, so it is usually necessary to choose a low-friction coating, such as PTFE, for the wire, the inner surface of the lumen, or both.

The internal target into the body is obtained through a sheath set consisting of an access sheath and a dilator, which is inserted percutaneously into the selected blood vessel. The dilator is then removed from the lumen of the sheath, leaving the sheath as a port into which the catheter or delivery system is inserted to begin the operation. The main entry point for most cardiovascular and neurovascular surgeries is the femoral artery (groin) or radial artery (wrist). Emerging surgeries that rely on steerable catheters include transseptal interventions in the heart, such as cardiac ablation, mitral valve repair, and pulmonary vein isolation.

The dilator/sheath consists of a hemostatic valve that controls blood flow and a central tubular sheath, usually made of soft low-friction materials, such as Pebax, high-density polyethylene (HDPE) or fluorinated ethylene propylene (FEP) for Easy to insert, and the transition tip of the sheath. The transition from the sheath body to the tip must be seamless, with no irregularities that would cause friction. Hydrophilic coatings, especially for larger or longer devices, can also be applied and become very slippery once wetted.

The dilator is usually of single stiffness because it may not need to advance through highly tortuous anatomical structures. Dilators that must penetrate further and/or must conform to the tortuous anatomy usually adopt a multi-stiffness structure, with a rigid proximal end and a highly flexible distal end. The sheath is usually made of FEP because of its flexibility and low coefficient of friction. In the case of larger diameter/thin wall access sheaths, coiled reinforcements can be used to maximize kink resistance while allowing flexibility. The flexible polymer marking tape can be loaded with tiny tungsten particles, which makes the device visible under fluoroscopy. The distal hole can be drilled with a laser to help irrigate or flush the dilator. Depending on the surgical application, the distal tip can adopt a variety of geometric designs, which can be through grinding, radio frequency dielectric heating, or both.

Access to the target anatomy is a critical part of the success of any surgery. Therefore, the sheath, dilator, and steerable catheter assembly must be optimized to ensure that they provide a safe, simple, and reliable path for the treatment device. Any cutting-edge equipment must use the most advanced materials and design, which is very important. Spectrum Plastics Group has decades of experience and an in-depth understanding of the materials, design, and processes used to access and convey systems. Our experienced development engineers and powerful design control system will ensure that your equipment is optimized to achieve the highest performance, quality and manufacturability.

Spectrum has extensive experience in designing and manufacturing steerable/deflectable catheters and dilators/sheaths. Spectrum not only customizes catheters for specific customer needs, we also provide ready-made steerable catheters, catheter subassemblies, dilators/sheaths and other catheter components online at webstore.spectrumplastics.com, which can be used to accelerate the design and development of your next project .

Content sponsored by Spectrum Plastics Group

Filing basis: Sponsored content tagged as: Spectral Plastic

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