Polymeric Stent Retention via Variable Diameter Sheath
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Solution Overview
Problem
Polymeric stents face challenges in retaining structural integrity and maintaining mechanical properties during crimping and balloon expansion due to their non-linear and unpredictable behavior, which differs significantly from metallic stents, leading to issues like fracture and limited retention force on the balloon.
Innovation Solution
A method involving a tubular sheath with specific diameter configurations to crimp and deploy polymeric scaffolding, where the middle portion matches the stent diameter and the end portions expand beyond the stent to enhance retention force by increasing balloon material penetration and contact with the stent ends.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If polymeric scaffolding is crimped tightly over a delivery balloon without additional retention structures, then the device complexity is reduced, but the retention force is insufficient and the scaffolding may dislodge during transit
Solution Approach 1:
A retention structure is introduced as an intermediary component between the polymeric scaffolding and the delivery balloon. This retention structure engages with both the scaffolding and the balloon, providing enhanced retention force while maintaining relative simplicity of the overall device architecture
Solution Approach 2:
The retention structure utilizes a balloon-expandable framework that transitions from a compressed delivery configuration to an expanded deployed configuration. This flexible framework provides adaptive retention, conforming to the scaffolding in the delivery state and providing enhanced engagement when expanded
2Strength
If the scaffolding is made with thicker and wider struts to compensate for low strength-to-weight ratio, then the structural integrity is improved, but the scaffolding occupies more space and requires larger delivery system
Solution Approach 1:
The scaffolding is designed with a segmented framework structure consisting of multiple struts and connectors. This segmentation allows for optimized distribution of mechanical loads across multiple elements, providing sufficient structural integrity while maintaining a compact overall volume for delivery
Solution Approach 2:
The scaffolding employs a three-dimensional framework architecture that provides structural strength through spatial configuration rather than simply increasing strut thickness. This dimensional approach allows adequate mechanical support with reduced material volume
3Force
If the end portions of the balloon are expanded beyond the outer diameter of the crimped scaffolding, then the retention force is increased through greater balloon material penetration, but the scaffolding may become damaged or the balloon may rupture
Solution Approach 1:
The balloon is designed with differentiated regions: a first portion with a first diameter that engages the crimped scaffolding, and a second portion with a second diameter that expands beyond the scaffolding outer diameter. This local quality differentiation allows the second portion to provide enhanced retention through greater tissue penetration while the first portion maintains safe engagement with the scaffolding
Solution Approach 2:
The balloon expandability is utilized to dynamically change the diameter of the second portion from a compressed state during delivery to an expanded state during deployment. This parameter change allows the balloon to provide increased retention force when needed while maintaining a compact, safe configuration during transit
Data Source
AI summary
A medical device includes a polymer stent crimped to a catheter having an expansion balloon. The stent is crimped to the balloon by a process that includes heating the stent to a temperature below the polymer's glass transition temperature to improve stent retention without adversely affecting the mechanical characteristics of the stent when later deployed to support a body lumen. A variable diameter sheath with a central portion that prevents expansion of the stent when the balloon is pressurized and larger diameter ends is disposed over the crimped stent-balloon assembly. The balloon is pressurized and the larger diameter ends of the sheath allow the balloon beyond the ends of the stent to expand. The balloon is then depressurized.