Steerable Catheter Pull Ring Segmentation for Canting and Leak Prevention
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Solution Overview
Problem
Existing steerable catheters face challenges in navigating through small vessels and tight bends due to issues with the pull ring assembly, such as undesirable canting and potential leak paths, as well as weak spots from unraveling braided filaments under tensile stress.
Innovation Solution
A pull ring assembly with a stepped design, featuring a larger proximal segment and a smaller distal segment, where the steering member extends through the braided layer and alongside the pull ring, reducing the transition section length and minimizing canting, and embedding the pull ring between polymeric layers to enhance structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the pull ring inner diameter is made larger than the braided layer outer diameter to allow assembly, then the pull ring can be installed over the braided layer, but this creates a long transition section that causes undesirable canting and potential leak paths
Solution Approach 1:
The pull ring is divided into multiple axial segments (first pull ring segment, second pull ring segment, third pull ring segment) with different radial extensions. The first segment extends furthest radially to engage the braided layer, the second segment engages the inner polymeric layer, and the third segment engages the outer polymeric layer. This segmentation allows each segment to perform its specific function while eliminating the need for a large overall inner diameter, thus preventing canting and leak paths.
Solution Approach 2:
Different segments of the pull ring have different radial extensions tailored to their specific engagement requirements. The first pull ring segment has a greater radial extension to securely engage the braided layer, while subsequent segments have progressively smaller extensions. This local differentiation of geometric properties allows precise control over the transition section length, eliminating undesirable canting while maintaining assembly feasibility.
2Shape
If the pull wire transition section is made longer to accommodate the pull ring, then the pull ring can be properly positioned, but this increases stiffness and causes undesirable canting of the pull ring
Solution Approach 1:
The pull ring is segmented axially into multiple sections with varying radial extensions. This segmentation allows the pull ring to be positioned precisely without requiring a long transition section. The first segment engages the braided layer at its full radial extension, while subsequent segments engage inner and outer polymeric layers at progressively reduced extensions, enabling compact positioning and maintaining steerability.
Solution Approach 2:
The pull ring assembly engages multiple layers of the catheter shaft (braided layer, inner polymeric layer, outer polymeric layer) simultaneously through different segments. This composite engagement distributes the mechanical interaction across multiple materials and layers, reducing the need for a long transition section and minimizing canting while ensuring proper positioning.
3Ease of manufacture
If the braided layer filaments are cut to form an opening for the pull wire, then the pull wire can extend through the braided layer, but this creates weak spots that may unravel under tensile stress
Solution Approach 1:
The pull ring is divided into multiple segments that engage different layers of the catheter shaft. The first segment engages the braided layer, while subsequent segments engage the inner and outer polymeric layers. This segmentation distributes the mechanical load across multiple engagement points, reducing stress concentration at any single location and preventing filament unraveling while still allowing opening formation.
Solution Approach 2:
The multi-segment pull ring design provides distributed engagement with the braided layer and polymeric layers before tensile stress is applied to the pull wire. This beforehand cushioning through distributed mechanical engagement prevents stress concentration at the opening location, reducing the risk of filament unraveling under load.
Data Source
AI summary
A steerable delivery apparatus for an implantable medical device comprises a shaft extending distally from the handle, the shaft having a steering-member lumen extending through a length of the shaft, and a steering member extending through the steering-member lumen, the steering member having a proximal end portion and a distal end portion. A pull ring is disposed along a distal end portion of the shaft, the pull ring comprising a proximal segment having a first diameter and a distal segment having a second diameter smaller than the first diameter. The distal end portion of the steering member is fixed to the distal segment of the pull ring, and an adjustment mechanism is further provided in the handle, the mechanism operatively coupled to the proximal end portion of the steering member and configured to adjust tension in the steering member so as to adjust a curvature of the shaft.