Variable Stiffness Catheter Support Member
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Solution Overview
Problem
Medical catheters face challenges in navigating tortuous vasculature due to stiffness issues, which can lead to kinking, buckling, and reduced navigability, particularly at the distal end, affecting their ability to effectively access and treat vascular defects.
Innovation Solution
The catheter design incorporates a structural support member with variable stiffness along its longitudinal axis, achieved through cold working and subsequent heat treatment, allowing for customizable stiffness and increased ductility, particularly at the distal end, to enhance navigability and integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the structural support member is made stiff through cold working to provide buckling resistance in proximal and medial portions, then navigability through vasculature is improved, but stiffness at the distal end reduces catheter deflection and increases push force requirements
Solution Approach 1:
The structural support member is designed with variable stiffness along its length: proximal and medial portions maintain high stiffness through cold working to provide buckling resistance, while the distal end undergoes heat treatment to reduce stiffness and enable deflection for navigating tortuous vasculature. This local differentiation resolves the contradiction by providing strength where needed while maintaining ease of operation at the distal end.
Solution Approach 2:
The structural support member is effectively segmented into zones with different mechanical properties: a proximal zone with high residual stress for strength, a medial transition zone, and a distal zone with reduced residual stress for flexibility. This segmentation allows each portion to fulfill its specific functional requirement without compromising the others.
2Reliability
If the structural support member is made stiff through cold working to provide structural integrity, then the catheter can navigate through vasculature without kinking, but stiffness at the distal end inhibits positioning of the structural support member during manufacture and reduces deflection
Solution Approach 1:
Heat treatment is applied to the distal end of the structural support member before final assembly into the catheter. This preliminary softening action allows the distal end to be easily positioned and conform to the inner liner during manufacturing. After assembly, the heat-treated distal end maintains sufficient structural integrity for its intended function while being easier to manufacture.
3Strength
If the structural support member is made stiff through cold working to resist kinking, then buckling resistance is improved, but stiffness at the distal end reduces deflection and tracking through tortuous vasculature
Solution Approach 1:
The structural support member exhibits locally differentiated properties: proximal portions maintain high stiffness through cold working to resist kinking and provide structural strength, while the distal end undergoes heat treatment to enable deflection and conformability for tracking through tortuous vasculature. This local quality differentiation resolves the contradiction between kink resistance and adaptability.
4Strength
If a relatively small diameter structural support member with large cold work is used to provide strength, then buckling resistance is improved, but stiffness is high which reduces integration with adjacent components and increases push force
Solution Approach 1:
Heat treatment is applied to the distal end of the structural support member before assembly to temporarily reduce its stiffness. This preliminary softening action facilitates easier integration with adjacent catheter components such as the inner liner and outer jacket. After assembly, the structural support member maintains sufficient strength for buckling resistance while having been easier to integrate during manufacturing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the catheter to more easily conform to tortuous vasculature, reduce push force requirements, and maintain structural integrity during navigation, thereby improving its ability to access and treat vascular defects without compromising inner diameter or navigability.
Implementation Method 1
The stiffness and strength of the structural support member is due, at least in part, to cold working of a material, such as nitinol, forming the structural support member, such that the resulting structural support member has residual stress.
Implementation Method 2
One or more portions of the structural support member are heat treated to relieve stress from cold working and/or increase ductility in the structural support member.
Implementation Method 3
One or more portions of the structural support member are heat treated to relieve stress from cold working
Data Source
AI summary
In some examples a catheter includes an inner liner, an outer jacket, and a structural support member positioned between at least a portion of the inner liner and at least a portion of the outer jacket. A first portion of the structural support member has a first residual stress and a second portion of the structural support member has a second residual stress, greater than the first residual stress. The second portion of the structural support member includes a percent cold work greater than about 20%.