Flat Wire Coil Shaft for Torque and Flexibility in Catheters
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Solution Overview
Problem
Elongate medical devices require high tensile and compressive forces for advancement and retraction while maintaining flexibility and torque response, but conventional designs compromise flexibility with increased stiffness.
Innovation Solution
A shaft design featuring a flat wire coil configuration with a higher wire height than width, providing a wider surface area for contact and improved radial strength, flexibility, and kink resistance, enhanced by a lubricious liner, braid layer, and jacket for additional support.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional shaft designs increase stiffness to provide high tensile and compressive forces, then strength is improved, but flexibility decreases
Solution Approach 1:
The shaft employs a composite structure combining a liner, flat wire coil, and jacket made from different materials with complementary properties. The liner provides flexibility and lubricity, the flat wire coil provides radial strength and kink resistance, and the jacket provides tensile strength and structural integrity. This composite construction allows the shaft to simultaneously achieve high strength and flexibility that cannot be obtained with a single material.
Solution Approach 2:
Different portions of the shaft have different structural characteristics optimized for their specific functions. The flat wire coil is positioned radially outward to provide localized radial strength and kink resistance where needed, while the liner maintains flexibility throughout. The variable pitch configuration allows different sections of the coil to provide different levels of support along the shaft length.
2Strength
If conventional shaft designs increase overall structure stiffness to meet torque performance requirements, then torque performance is improved, but flexibility decreases
Solution Approach 1:
The composite construction with the flat wire coil embedded between the liner and jacket creates a structure that resists torque through the coordinated action of multiple layers. The flat wire coil's radial positioning and flat cross-section provide torque resistance while the flexible liner and jacket maintain overall shaft flexibility, allowing the shaft to transmit torque without becoming overly stiff.
Solution Approach 2:
The flat wire coil is positioned radially outward from the liner, creating a distributed reinforcement structure that extends in the radial dimension. This radial positioning allows the coil to provide torque resistance through its orientation and spacing, while maintaining flexibility along the longitudinal axis of the shaft.
3Ease of manufacture
If conventional shaft designs use traditional coil configurations, then manufacturing is simplified, but radial strength and kink resistance are reduced
Solution Approach 1:
The flat wire coil has an asymmetric flat cross-section rather than a symmetric round cross-section. This asymmetry is oriented with the flat face radial to the shaft axis, creating a configuration that maximizes radial strength and kink resistance. The asymmetric shape provides larger contact surface area between coil windings, preventing collapse while maintaining manufacturability through standard coiling processes.
Solution Approach 2:
The flat wire coil is integrated as part of a composite shaft structure, where its specific geometric properties work in conjunction with the liner and jacket materials to achieve enhanced radial strength and kink resistance. The composite construction compensates for any manufacturing complexity by distributing functional requirements across multiple components.
4Device complexity
If conventional shaft designs use round wire coils, then structural simplicity is maintained, but compression strength and contact surface area are reduced
Solution Approach 1:
The flat wire coil uses a flat cross-section instead of a round cross-section, creating an asymmetric geometry that provides larger surface area for contact between windings when compressed axially. This flat configuration increases the contact surface area by approximately 37% compared to a round wire of equivalent area, significantly improving compression strength and load distribution.
Solution Approach 2:
The flat wire coil orientation introduces a radial dimension to the wire cross-section, with the flat face positioned radially outward. This dimensional change allows the coil to distribute compressive loads across a larger surface area, improving compression strength without significantly increasing overall shaft diameter or complexity.
Data Source
AI summary
In various examples, a shaft for an elongate medical device extends along a shaft length. The shaft includes a shaft axis, an outer surface, and an inner surface. The inner surface defines an inner lumen. A liner forms the inner surface of the shaft. A coil is disposed around and outwardly from the liner. The coil is formed from a flat wire. The flat wire includes a wire width and a wire height, wherein the wire height is greater than the wire width. The wire height extends substantially radially with respect to the shaft and the wire width extends substantially longitudinally with respect to the shaft. A jacket is disposed around and outwardly from the coil. The jacket forms the outer surface of the shaft.