Catheter Strain Relief Fitting Gradient Flexural Modulus
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Solution Overview
Problem
Elongate medical devices, such as catheters, are prone to kinking due to stress risers at the interface between the hub and the catheter shaft, leading to potential damage and risk to patients during manipulation.
Innovation Solution
A graduated strain relief fitting with a tapered profile and varying flexural modulus is introduced between the hub and the catheter shaft, featuring scalloped flexure joints and changing wall thickness to minimize stress risers and facilitate deflection without kinking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a rigid strain relief fitting is used to support the catheter shaft, then structural integrity is improved, but stress risers are created at the fitting interface leading to kinking
Solution Approach 1:
The fitting transitions from a rigid proximal portion to a flexible distal portion, with each section having different mechanical properties optimized for its specific function. The proximal portion provides structural support while the distal portion allows controlled deflection to prevent kinking.
Solution Approach 2:
The flexural modulus of the fitting material is varied along its length, creating a gradient from high stiffness near the hub to low stiffness at the catheter interface. This parameter change allows the fitting to provide support where needed while preventing stress concentration that causes kinking.
2Ease of operation
If the hub profile is enlarged to facilitate manipulation, then ease of operation is improved, but the profile change creates a sharp interface leading to stress risers
Solution Approach 1:
The strain relief fitting serves as an intermediary component between the hub and catheter shaft, absorbing and distributing the mechanical stresses generated during manipulation. It mediates the interface between the enlarged hub profile and the smaller catheter shaft, preventing stress concentration.
Solution Approach 2:
The fitting is positioned beforehand to cushion and distribute mechanical stresses before they can concentrate at the hub-catheter interface. Its flexible distal portion acts as a buffer that prevents sharp stress risers from forming during manipulation.
3Adaptability or versatility
If the catheter shaft is deflected to navigate tortuous paths, then adaptability is improved, but kinking and buckling occur due to enhanced stresses
Solution Approach 1:
The fitting's mechanical properties are made dynamic along its length, with the distal portion being more compliant to accommodate the dynamic deflections required for navigating tortuous paths. This allows the assembly to adapt to complex geometries without causing kinking.
Solution Approach 2:
Different portions of the fitting have different levels of flexibility optimized for their specific locations. The distal portion near the catheter shaft is made more flexible to allow deflection during navigation, while the proximal portion near the hub maintains higher stiffness for structural support.
Data Source
AI summary
A catheter assembly includes a catheter shaft having shaft proximal and distal portions. A hub is coupled with the catheter shaft proximate the shaft proximal portion. A graduated strain relief fitting is coupled between the catheter shaft and the hub. The graduated strain relief fitting includes at least a first flexural modulus proximate the hub and a fitting proximal portion. The graduated strain relief fitting includes a second flexural modulus proximate the catheter shaft and a fitting distal portion. The second flexural modulus is less than the first flexural modulus and less than or equal to a catheter shaft flexural modulus. The first and second flexural moduli are modulated with one or more of a taper, flexure joints, fitting frame of the fitting or material of the fitting body.