Segmented Durometer Sheath for Kink Resistance
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Solution Overview
Problem
Introducer sheaths used in medical procedures are prone to kinking, especially when navigating the vascular system, which renders them unusable and requires repeated access sites, causing time delays and potential life-threatening situations, especially during emergency procedures.
Innovation Solution
A flexible, kink-resistant introducer sheath design featuring an inner tube with a coil and an outer tube with segments of decreasing durometer from the proximal to the distal end, providing sufficient stiffness for navigation while maintaining flexibility for accessing small vessels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the sheath wall thickness is increased to improve kink resistance, then the level of kink resistance is improved, but the entry hole size must be increased
Solution Approach 1:
The outer tube is divided into multiple segments with different durometer values along its length. The proximal segment has higher durometer for kink resistance, while distal segments have lower durometer for flexibility and smaller entry hole requirement. This segmentation allows the sheath to have varying mechanical properties along its length, resolving the contradiction between overall kink resistance and entry hole size.
Solution Approach 2:
Different portions of the sheath are assigned different material properties (durometer values). The proximal portion maintains higher stiffness for structural support and kink resistance, while the distal portion becomes progressively more flexible. This local differentiation of material properties allows the sheath to satisfy both requirements without increasing overall wall thickness.
2Duration of action of stationary object
If the sheath remains positioned in the patient's body for an extended period to perform hemofiltration or dialysis, then the procedure effectiveness is improved, but the sheath becomes prone to kinking due to repeated use or patient movement
Solution Approach 1:
The segmented outer tube structure with varying durometer values provides distributed mechanical support along the sheath length. During extended positioning, the higher durometer proximal segment resists kinking from repeated manipulation and patient movement, while the flexible distal segments accommodate physiological movements without transmitting kink forces to the critical proximal regions, maintaining reliability over extended duration.
Solution Approach 2:
The sheath design allows dynamic adaptation to different usage conditions. The gradient of durometer values enables the sheath to be more rigid when subjected to external forces (resisting kinking) while remaining flexible enough to accommodate natural body movements during extended positioning, thus maintaining reliability throughout the procedure duration.
3Ease of operation
If the sheath is made small in diameter to facilitate vascular access, then the ease of insertion is improved, but the sheath becomes particularly prone to being bent and kinked during emergency procedures
Solution Approach 1:
The segmented construction with proximal high-durometer segments provides structural reinforcement at the critical regions where kinking would occur, while maintaining overall small diameter. The segmentation allows strategic placement of stiffer material only where needed for kink resistance, rather than requiring uniform thickness increase throughout the entire sheath, thus preserving ease of insertion while improving bending resistance.
Solution Approach 2:
The sheath employs a composite structure combining multiple materials with different durometer values in a gradient arrangement. This composite design creates a sheath that is stiffer than any single material would allow at the proximal end (resisting kinking) while maintaining thin-wall construction overall (easy insertion), effectively resolving the contradiction between diameter and kink resistance.
4Adaptability or versatility
If the sheath is used to deliver an implantable medical device into smaller vessels branching off from major vessels, then the adaptability to different vascular configurations is improved, but the sheath may not have enough flexibility at the point where flexibility is required
Solution Approach 1:
The gradient of decreasing durometer from proximal to distal segments creates local quality variation that perfectly matches the functional requirements. The distal segments with lowest durometer provide maximum flexibility exactly where the sheath needs to conform to small branch vessels, while the proximal segments maintain structural integrity for device delivery, thus improving adaptability without sacrificing necessary flexibility.
Data Source
AI summary
A flexible kink-resistant introducer sheath (10). The introducer sheath includes an inner liner (31), a coil (33) and an outer tube (33). The inner liner includes a passageway (30) extending longitudinally therethrough, where a catheter (50) can be advanced through the passageway. The coil (33) has a plurality of turns positioned longitudinally and compression fitted around the inner liner (31), where the turns have a predetermined spacing therebetween. The outer tube (20) is positioned longitudinally around the coil (33) and the inner liner (31), and is connected to the inner liner through the spaces between the turns. A diameter difference between the inner liner and the catheter is in a range of about 0.0005 to about 0.004 inch (0.013 to about 0.10 mm).