Stent Graft Dimpling to Reduce Crimping Forces
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Solution Overview
Problem
Stent grafts face challenges during crimping due to axial stretching of the graft material, which introduces resistance and increases the risk of tearing, especially when the graft must accommodate the metallic stent's crimping operation without adequate material compliance.
Innovation Solution
The introduction of dimples in the graft material, created by a dimple tool, provides localized additional material to accommodate stretching, allowing the stent graft to crimp without axial stretching of the fabric, thereby reducing the risk of tearing and improving the crimping process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the graft material is continuously bonded to the metallic stent frame, then the structural integrity is improved, but the graft material must stretch during crimping which increases resistance and risk of tearing
Solution Approach 1:
The patent applies different bonding characteristics to different regions of the graft-stent interface. Specifically, the graft is bonded to the stent frame at certain locations but left unbonded at other locations, creating zones of flexibility. This allows the bonded regions to maintain structural integrity while the unbonded regions accommodate stretching and crimping motions without tearing.
Solution Approach 2:
The continuous graft-stent interface is segmented into discrete bonding zones and unbonded zones. This segmentation allows different portions of the graft to have different degrees of freedom during crimping, enabling the structure to deform without creating excessive stress concentrations that would lead to tearing.
2Ease of operation
If highly compliant graft material is selected to reduce stretching resistance, then the crimping process is improved, but the graft strength is weakened increasing vulnerability to tearing and bursting
Solution Approach 1:
Instead of using compliant material throughout, the patent creates local zones of flexibility through selective unbonding. The graft material itself can remain strong and compliant, but the bonding pattern creates localized regions that can stretch during crimping while other regions maintain structural strength.
Solution Approach 2:
The bonding is segmented into discrete regions rather than being continuous. This allows the graft to exhibit different mechanical properties in different zones - strong and rigid where bonded, flexible and compliant where unbonded - thereby achieving both strength and ease of crimping.
3Force
If the apex angle of stent struts is reduced to reduce stretching severity, then the crimping resistance is reduced, but the diametral reduction is reduced unless struts are lengthened which reduces radial stiffness
Solution Approach 1:
The patent extracts the flexibility requirement from the stent geometry (apex angle modification) and relocates it to the bonding pattern. By creating unbonded zones in the graft, the system achieves flexibility during crimping without needing to modify the stent strut geometry, thereby preserving radial stiffness.
Solution Approach 2:
The unbonded graft zones act as intermediaries that absorb the deformation during crimping. Instead of the stent struts themselves needing to have flexible geometry, the unbonded graft material serves as a mediator that accommodates the motion, allowing the struts to maintain their optimal rigid geometry for both crimping and radial support.
Data Source
Figure 1A~1B
Figure 2
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AI summary
A stent-graft assembly is provided for a variety of medical treatments. The stent-graft assembly includes a stent disposed to and attached between an inner layer of graft material and an outer layer of graft material. One of both of the graft layers includes one or more of a depression, dimple or detent that increases the localized surface area of the graft in one or more portions of the stent otherwise susceptible to graft stretching in the absence of the depression, dimple or detent. There is also described a method of forming dimples in selective locations on one or port graft layers in one or more locations relative to a portion of the stent where a portion of the graft may be susceptible to stretching or tearing during crimping or loading operations.