Variable Radius Stent for Constant Conductance Flow
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Solution Overview
Problem
Existing stents do not provide adequate flow to prevent restenosis and re-occlusion in the arterial and venous systems, as they fail to maintain smooth laminar blood flow with uniform velocity, leading to potential re-narrowing of vessels.
Innovation Solution
A stent design with a portion that maintains constant conductance flow, where the radius expands with length such that r4/l remains constant, ensuring increased and consistent flow rates by adjusting the geometric factor r4/L along the stent length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a traditional uniform diameter stent is used, then the stent structure is simple and easy to manufacture, but the blood flow rate is insufficient and restenosis occurs
Solution Approach 1:
The stent transitions from a uniform diameter design to a variable diameter design where different sections have different radii. Specifically, the stent includes a first section with radius r1 and a second section with radius r2, where r1 ≠ r2. This local variation in geometric properties optimizes blood flow characteristics in different regions, increasing overall flow rate while preventing restenosis, at the cost of increased structural complexity.
2Productivity
If the stent radius is increased to enhance flow, then the conductance increases, but the stent length also increases which may cause foreshortening and deployment inaccuracies
Solution Approach 1:
The stent employs specific mathematical relationships between radius and length parameters to optimize flow while controlling foreshortening. The design satisfies the condition that r1^4/L1 ≥ r2^4/L2, where r1 and r2 are radii of different sections and L1 and L2 are their corresponding lengths. This parameter optimization ensures adequate volumetric flow rate (Q ∝ r^4/L) while maintaining deployment accuracy by controlling the degree of expansion.
3Ease of operation
If a self-expanding stent is used, then the deployment is simpler, but the auto expansion is weak and requires pre-dilatation and post-dilatation
Solution Approach 1:
The stent is designed with dynamic expansion characteristics, transitioning from a compressed delivery state to an expanded deployed state. The variable diameter configuration (different radii in different sections) is achieved through controlled expansion, allowing the stent to adapt its geometry during deployment. This dynamic approach enables adequate expansion reliability while maintaining relatively simple deployment procedures.
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 stent design enhances blood flow by maintaining constant conductance, reducing the risk of restenosis and re-occlusion, as demonstrated by increased flow rates compared to traditional uniform diameter stents, particularly in low-pressure areas of the venous system.
Implementation Method 1
A stent that contains a portion of the stent that has increased flow or 'unitary,' or constant conductance flow, where the radius r of the portion expands with the length l so that so that r4/l remains constant in the portion
Data Source
AI summary
The invention includes an expandable stent having a tubular shape when expanded, the shape including a portion t where the stent radius grows with stent length so that the growth in the portion is constant conductance growth or near-constant conductance growth. The invention includes sheaths that will encase the stent to restrict the growth of the stent to the desired expanded shape. The invention also includes expandable stent balloons that expand the stent to the desired shape configuration with constant or near constant conductance portion. The balloons can include a similar sheath or sleeve to restrict the balloon's growth to the desired shape. The stent radius growth can be piecewise, and is not necessarily 4th order growth, but can be such that rn/l is a constant in the portion, where n>4.