Polymer Stent Flared Loop Bends Prevent Fish-Mouthing
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Solution Overview
Problem
Current stent technologies face challenges in delivery due to 'fish-mouthing' phenomena, where loop ends are forced into the stent lumen during compression, making full expansion difficult, and long-term storage of polymer stents is complicated due to self-expansion issues with polymeric materials.
Innovation Solution
Incorporating flared end loops with secondary bends or curved radii in polymer stents to prevent kinking during delivery and using a stent packaging system that maintains stents in an expanded state for storage, along with adhesives and coatings for improved retention and compatibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If stents are compressed for delivery through catheters, then the stent can be delivered to the target site, but loop ends are forced into the stent lumen causing fish-mouthing and preventing full expansion
Solution Approach 1:
The stent is divided into multiple struts with distinct geometries - body struts and loop struts. The loop struts are specifically designed with flared ends and secondary bends that differ from the body struts, allowing the loop ends to flare outward during compression rather than being forced into the lumen. This segmentation of function between different strut types resolves the fish-mouthing problem while maintaining deliverability.
Solution Approach 2:
The loop ends are designed with flared geometries and secondary bends that create curved, non-linear paths. Instead of straight loop ends that would be forced into the lumen during compression, the flared and bent configurations allow the loop ends to navigate around each other and expand fully at the deployment site, preventing fish-mouthing while enabling catheter delivery.
2Ease of operation
If polymer stents are made self-expanding, then the stent can deploy automatically at the target site, but long-term storage is complicated due to self-expansion issues
Solution Approach 1:
The patent employs shape memory polymers that can change their physical state between a compressed configuration for storage and an expanded configuration for deployment. By controlling temperature or other environmental parameters, the polymer transitions from a rigid compressed state during storage to a flexible expanded state at the target site, enabling both stable long-term storage and automatic self-expansion deployment.
Solution Approach 2:
The stent is pre-formed in its expanded configuration with the desired geometric features (flared loop ends, secondary bends) before storage. During storage, it is compressed into a smaller diameter using the shape memory effect or external constraints. At deployment, the pre-programmed memory causes automatic expansion back to the original configuration, eliminating the need for balloon inflation while maintaining storage stability.
3Ease of operation
If flared end loops are added to prevent kinking, then stent delivery is improved, but device complexity increases
Solution Approach 1:
The flared end loops and secondary bends are applied locally only to the loop struts rather than the entire stent structure. The body struts maintain a simpler geometry optimized for radial strength and vessel support, while only the loop portions have the additional flared and bent features necessary for preventing fish-mouthing. This localized application of complexity resolves the delivery problem without unnecessarily complicating the overall stent design.
Data Source
AI summary
Polymers have many positive properties which make them beneficial as a material used in a vascular—and neurovascular—implant, such as a stent. Stents comprising polymers, methods of making stents comprising polymers, packaging for stents, and adhesives, coatings and other materials used on stents are described. Also described are stents with flared ends having bends.