T-Bar Self-Expanding Stent Structure for Catheter Loading
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Solution Overview
Problem
Self-expanding stents made from thin-walled nitinol tubes face challenges during loading into delivery systems due to potential deformation and collapse, especially as they are manufactured to smaller diameters, compromising their structural integrity and manufacturing processes.
Innovation Solution
A stent framework with a specific T-bar structure and geometry, featuring wider columns and slots to enhance longitudinal support and circumferential flexibility, allowing for simultaneous circumferential and longitudinal compression during loading, thereby reducing the risk of deformation and cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If stents are made from thinner walled tubes to enable smaller diameters, then the stent can be manufactured to smaller sizes, but the stent becomes more prone to deformation and collapse during loading
Solution Approach 1:
The stent framework is divided into multiple cells with struts arranged in a segmented pattern. This segmentation allows the structure to be both lightweight (using thin-walled tubes) and mechanically robust through the distributed strut architecture that resists deformation during loading.
Solution Approach 2:
The stent combines thin-walled nitinol tube material with a reinforced strut framework. This composite construction uses the shape memory properties of nitinol while the strut network provides additional structural support to prevent collapse during the loading process.
2Ease of operation
If stents are compressed and loaded into catheters simultaneously circumferentially and longitudinally, then the stent can be delivered through the delivery system, but the stent is at risk of substantial deformation or collapse
Solution Approach 1:
The stent is pre-formed with a specific configuration where cells are spaced to allow longitudinal compression. During loading, the stent is first compressed circumferentially and then longitudinally in a controlled sequence, with the cell structure designed to accommodate this preliminary compression without collapsing.
Solution Approach 2:
The stent design incorporates specific geometric parameters including cell spacing, strut thickness, and column dimensions that are optimized to withstand the dual compression loading. The column width is specifically designed to be greater than strut width to provide buckling resistance during the loading process.
3Strength
If the column width is increased to provide longitudinal support, then the stent rigidity improves, but the circumferential flexibility may be compromised
Solution Approach 1:
The T-bar structure features localized variations in geometry where the column portion provides longitudinal support where needed, while the top bar portion maintains circumferential flexibility. The curved edge on the top bar specifically allows for flexible cell separation while the column provides rigid longitudinal support, creating different mechanical properties in different locations of the same structure.
Solution Approach 2:
The T-bar structure resolves the rigidity-flexibility contradiction by adding a dimensional element (the vertical column portion) that provides longitudinal support without interfering with circumferential movement. The column extends in the longitudinal dimension to provide rigidity, while the top bar in the circumferential dimension maintains flexibility through its curved edge design.
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
The T-bar structure maintains stent performance by providing adequate longitudinal rigidity and flexibility, facilitating successful loading into delivery systems without compromising radial stiffness or flexibility, and preventing fractures during expansion and heat-setting operations.
Implementation Method 1
The column has a minimum width perpendicular to the long axis that is wider than a maximum width of each of the struts, and the column defines at least one slot. The top bar has a curved edge on a side opposite from the column, and the curved edge straddles the long axis.
Implementation Method 2
putting the stent into a loading configuration, which includes simultaneously compressing the self expanding stent circumferentially and longitudinally while sliding the stent into the catheter
Implementation Method 3
One class of self expanding stents are typically cut from a thin walled nitinol tube
Data Source
AI summary
A stent comprises a framework that includes a sequence of cells that each occupy a discrete segment of the stent length, and each of the cells includes a plurality of struts with ends connected at respective vertices. An adjacent pair of the cells are attached to one another by a plurality of T-bars that each include a column defining a long axis that extends parallel to the stent axis, and a top bar attached to one end of the column. An opposite end of the column is attached to a first cell, and the top bar is attached at opposite ends to a second cell of the adjacent pair of cells. The top bar includes a curved edge on an opposite side from the column, and the curved edge straddles the long axis.