Braid-Free Microcatheter Coil Assembly for Lesion Crossability
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Solution Overview
Problem
Existing microcatheters face challenges in achieving a desirable combination of small crossing profiles, optimal flexibility, effective torque transmissibility, and bi-directional torquing response, particularly in navigating complex vasculature such as below-the-knee lesions.
Innovation Solution
The microcatheters feature a unique coil assembly with multiple layers of coils wound in different directions, combined with a polymer coating that decreases in hardness from proximal to distal, and includes gaps between coil filars to enhance flexibility while maintaining axial force transmission and torque capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If microcatheters are designed with high flexibility to traverse tortuous vasculature, then flexibility is improved, but pushability and torque transmission deteriorate
Solution Approach 1:
The catheter is divided into multiple sections with different flexibility characteristics. The distal portion contains a coil assembly with varying wire diameters and coil densities to provide graduated flexibility, while the proximal portion maintains higher stiffness for pushability. This segmentation allows the catheter to exhibit flexible behavior at the tip for navigation while maintaining structural integrity and force transmission from the operator's hand.
Solution Approach 2:
Different sections of the catheter are assigned different mechanical properties tailored to their specific functions. The distal tip region incorporates softer materials and looser coil winding for enhanced flexibility and conformability to vessel walls, while the shaft maintains higher stiffness for torque transmission and pushability. This local differentiation resolves the contradiction by providing flexibility where needed without compromising overall force transmission.
2Adaptability or versatility
If microcatheters are designed with small crossing profiles to access distal vessels, then crossing capability is improved, but structural integrity and torque response deteriorate
Solution Approach 1:
The catheter employs a nested construction where the coil assembly is embedded within a polymer jacket, which itself is contained within a larger catheter structure. Multiple layers of coils with different wire diameters are nested concentrically, with inner coils providing flexibility and outer coils providing structural support. This nested arrangement maximizes the strength-to-profile ratio by distributing mechanical loads across multiple nested layers.
Solution Approach 2:
The catheter utilizes composite construction combining metal coils (nitinol or stainless steel) with polymer materials (Pebax, Hytrel, or polyurethane). The metal coils provide high strength-to-weight ratio and superelasticity for torque response, while the polymer jacket provides flexibility and protects the metal structure. This composite approach enables small crossing profiles while maintaining adequate structural integrity and torque transmission.
3Force
If microcatheters use braided construction to provide structural support, then pushability is improved, but flexibility and torque response deteriorate
Solution Approach 1:
The invention extracts and eliminates the braided construction from the catheter design, replacing it with a coil assembly embedded in a polymer jacket. This removal of the braid eliminates the conflicting mechanical properties that braids impose (high radial strength but poor flexibility and torque response). The coil-polymer composite achieves pushability through axial stiffness of the coils and polymer reinforcement without the detrimental effects of braided construction on flexibility and torque transmission.
4Length of moving object
If microcatheters are designed for antegrade access to achieve long traversal distance, then reach is improved, but pushability and kink resistance requirements increase device complexity
Solution Approach 1:
The catheter incorporates dynamic mechanical properties that adapt along its length. The coil assembly features varying wire diameters and coil densities from proximal to distal, creating a gradient of flexibility that allows the catheter to dynamically adjust to vascular geometry. This dynamic design enables long traversal distances through tortuous vessels while maintaining manageable complexity through progressive rather than abrupt transitions in mechanical properties.
Data Source
AI summary
Embodiments of the disclosed microcatheters comprise an inner tube that extends from a distal tip to a proximal hub. The microcatheter comprises a first inner coil wound around a length of the inner tube, a second middle coil wound around the first coil and in a different winding direction than the winding direction of the first coil, and a third outer coil wound around a proximal portion of the second coil and in a different winding direction than the winding direction of the second coil. The first and second coils terminate distally together at a common location that is spaced proximally from the distal tip and the third coil terminates proximally from the termination location of the first and second coils. Gaps may be provided between groups or sections of wire filars forming the coils for flexibility. Outer polymer materials are provided around the coils, wherein the polymers comprise decreasing hardness moving from proximal to distal along the microcatheter.