Deflectable Catheter with Anisotropic Bending Stiffness
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Solution Overview
Problem
Catheters with distal deflectable segments often experience inconsistent and unpredictable movement due to their isotropic bending stiffness, leading to unintended out-of-plane movement, which complicates precise placement during medical procedures.
Innovation Solution
A catheter with a distal deflectable segment that exhibits anisotropic bending stiffness, featuring a significantly higher stiffness in one plane (reinforced plane) compared to another (sweeping plane), utilizing stiffening elements with higher Young's modulus materials to restrict out-of-plane movement while allowing controlled in-plane deflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a distal deflectable segment with isotropic bending stiffness is used, then the catheter can deflect in all directions, but the catheter tip exhibits inconsistent and unpredictable movement with unintended out-of-plane movement
Solution Approach 1:
The deflectable segment is designed with non-uniform wall thickness, creating regions of different bending stiffness. The wall thickness varies along the circumferential direction, with thinner walls in the sweeping plane direction (allowing easier deflection) and thicker walls in the reinforced plane direction (resisting out-of-plane movement). This local variation in quality enables the catheter to deflect controllably in the desired plane while maintaining resistance to unintended movements.
Solution Approach 2:
The deflectable segment introduces asymmetric structural features through non-uniform wall thickness distribution. The thickness profile is asymmetric with respect to the two principal planes, creating different area moments of inertia (Ix ≠ Iy). This asymmetry ensures that the catheter has different bending stiffness characteristics in orthogonal directions, allowing controlled deflection in one plane while preventing deflection in the other plane.
2Ease of operation
If the distal deflectable segment is made soft and flexible to facilitate movement through body cavities, then catheter insertion is easier, but the catheter tip cannot maintain consistent deflection plane
Solution Approach 1:
The deflectable segment incorporates local quality variations through non-uniform wall thickness. The overall segment remains soft and flexible for easy navigation, but specific regions have increased thickness to provide localized reinforcement. This creates a gradient of stiffness properties that balances navigability with deflection control, allowing the catheter to be both easy to insert and reliable in maintaining deflection plane.
Solution Approach 2:
The deflectable segment can be constructed using composite material structures with different mechanical properties. By combining materials or structural configurations with different stiffness characteristics in a layered or distributed manner, the segment achieves both flexibility for navigation and directional stiffness for controlled deflection, resolving the contradiction between ease of insertion and deflection reliability.
3Ease of operation
If pull wires are used to deflect the catheter, then the catheter can be guided to desired locations, but out-of-plane movement occurs making precise placement difficult
Solution Approach 1:
The non-uniform wall thickness creates localized stiffness variations that guide the pull wire-induced deflection along a predictable path. The thinner regions naturally accommodate the bending caused by pull wire tension, while thicker regions resist deviation from the intended deflection plane. This local quality differentiation ensures that pull wire actuation produces consistent, planar deflection without out-of-plane movement, improving positioning accuracy.
Solution Approach 2:
The anisotropic stiffness structure provides inherent feedback by resisting deflection attempts in the reinforced plane while allowing deflection in the sweeping plane. When pull wires are actuated, the structural asymmetry immediately provides resistance feedback that guides the deflection back into the intended plane, preventing cumulative out-of-plane deviations and ensuring accurate tip placement.
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 design ensures consistent and predictable deflection within a designated sweeping plane, enhancing the controllability and precision of catheter placement during medical procedures, reducing the likelihood of out-of-plane movement and improving procedural accuracy.
Implementation Method 1
a first bending stiffness for deflection in a first plane and a second bending stiffness for deflection in a second plane
Implementation Method 2
utilizing stiffening elements with higher Young's modulus materials to restrict out-of-plane movement
Data Source
AI summary
A guidable, or steerable, or deflectable catheter is provided that includes a proximal portion and a distal portion for insertion into a body cavity. A selectively deflectable segment having an anisotropic bending stiffness for deflection in individual planes is incorporated into the distal portion of the catheter shaft. Upon actuation of pull wires, the distal deflectable segment may be deflected to move/sweep the distal catheter tip through a sweeping plane. The anisotropic bending stiffness of the distal deflectable segment permits in-plane movement of the distal catheter tip in the sweeping plane while resisting any out-of-plane movements. In one arrangement, stiffening elements are selectively disposed within the distal deflectable segment such that the out-of-plane bending stiffness is largely increased and greater than the in-plane bending stiffness for deflection in the sweeping plane. In another arrangement, the cross section of a distal deflectable segment is altered to produce anisotropic area inertias of moment about its centroidal axes, and thus anisotropic bending stiffnesses.