Variable Stiffness Catheter for Intravascular Stent Graft Deployment
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Solution Overview
Problem
Intravascular deployment of stent grafts faces challenges due to interference between components of the delivery apparatus, leading to incomplete or failed deployment, often caused by buckling of the graft cover when navigating tortuous anatomy, which can result in binding with the stent stop and prevent retraction of the graft cover.
Innovation Solution
A delivery system with a variable stiffness member is introduced, which is positioned adjacent to the stent graft within the graft cover to allow buckling to occur at a location that does not interfere with the stent stop, and runners are provided to prevent binding by allowing the buckled graft cover to slide over the stent stop, maintaining the graft cover's diameter and enabling complete deployment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the graft cover is made thin-walled to enable retraction during deployment, then the ease of operation is improved, but the graft cover becomes susceptible to buckling under axial, rotational, and bending loads
Solution Approach 1:
A variable stiffness member is introduced as an intermediary element between the graft cover and the stent stop. This member has a stiffness profile that varies along its length, with a lower stiffness region positioned to allow controlled buckling of the thin-walled graft cover away from the stent stop, while higher stiffness regions provide structural support. The intermediary member thus enables the graft cover to be thin-walled for easy retraction while preventing harmful buckling that would interfere with deployment.
2Adaptability or versatility
If the graft cover buckles to accommodate tortuous anatomy, then the adaptability is improved, but the buckled graft cover may bind with the stent stop preventing complete deployment
Solution Approach 1:
The variable stiffness member exhibits local quality variations along its length, with a lower stiffness region specifically positioned to allow localized buckling of the graft cover. This localized buckling accommodates tortuous anatomy while the higher stiffness regions of the variable stiffness member ensure that the buckling occurs in a controlled manner that does not interfere with the stent stop. The local quality differentiation thus enables adaptability to tortuous pathways while maintaining reliability of complete deployment.
3Strength
If the middle member provides rigid support to carry axial and bending loads during tracking, then the strength is improved, but the graft cover is more likely to buckle when forces exceed its buckling strength
Solution Approach 1:
The middle member is designed with variable stiffness characteristics rather than uniform rigidity. The stiffness profile is engineered to provide adequate load carrying capacity during tracking while having reduced stiffness in specific regions that allow the graft cover to buckle in a controlled manner when necessary. This dynamic stiffness distribution enables the system to adapt to varying mechanical conditions, providing strength when needed while preventing harmful buckling through strategic flexibility.
Data Source
AI summary
An intravascular delivery catheter includes a middle member or manipulator to ameliorate the effect of buckling of the graft cover during the tracking or positioning of the delivery device within a body flow lumen to deploy an exclusion device, such a stent graft. The delivery device/catheter includes a region or regions of lower resistance to bending than other portions of the delivery device, which are positioned, within the delivery device, to preferentially bend the delivery system at locations where buckling will have minimal effect upon the deployment of the exclusion device from the delivery system. The preferential bending is accomplished, by providing a middle member/manipulator that is a rod with laterally oriented slots, having different depth and spacing configurations, or by using a wire coil as a portion of the middle member where the variable stiffness is created either by providing a variable/multiple coil diameter or by using a wire having a variable diameter along its length while the wire coil diameter is relatively uniform.