Polymer Scaffold Retention on Delivery Balloon
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Solution Overview
Problem
Polymeric scaffolds for drug-eluting medical devices face challenges in retaining structural integrity and retention force on delivery balloons due to their non-linear and unpredictable mechanical properties, which differ significantly from metallic stents, leading to issues like fracture and misalignment during crimping and deployment.
Innovation Solution
A crimping process that involves pressurizing the balloon during the crimping of the scaffold, heating it to a temperature just below the glass transition temperature of the polymer, and applying dwell periods with varying balloon pressures to enhance retention force, allowing for final alignment and stress relaxation, thereby increasing the scaffold's retention force on the balloon.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the scaffold is crimped to reduce its diameter for delivery, then the scaffold can be delivered through narrow vessels, but the retention force between the scaffold and balloon decreases
Solution Approach 1:
The patent applies parameter changes by heating the polymer scaffold to a temperature just below its glass transition temperature during crimping. This temperature parameter change makes the polymer more compliant and ductile, allowing it to be crimped to smaller diameters while maintaining sufficient retention force through controlled molecular chain mobility without permanent damage.
Solution Approach 2:
The patent employs periodic action through dwell periods during the crimping process. The scaffold is crimped to a reduced diameter, held there for a dwell period to allow stress relaxation and molecular rearrangement, then slightly expanded and re-crimped. This periodic cycling enables progressive diameter reduction while maintaining structural integrity and retention force.
2Stability of the object's composition
If the scaffold is made from brittle polymer material to be bio-absorbable, then the scaffold can degrade after implantation, but the scaffold is prone to fracture during crimping and deployment
Solution Approach 1:
The patent changes the temperature parameter to just below the glass transition temperature of the polymer, transforming the material from a brittle state at room temperature to a more ductile and compliant state during crimping. This temporary parameter change allows the brittle polymer to undergo plastic deformation without fracturing, then returns to its stronger state after cooling for reliable deployment and controlled degradation.
Solution Approach 2:
The patent applies beforehand cushioning by using dwell periods where the scaffold is held at the reduced diameter for extended times. This allows stress relaxation and molecular chain rearrangement to occur before the next crimping step, preventing stress concentration and fracture in the brittle polymer material during the crimping process.
3Length of moving object
If the scaffold is crimped to a small diameter for delivery, then the scaffold can navigate tortuous anatomy, but misalignment and structural damage occur during crimping
Solution Approach 1:
The patent uses periodic action with multiple crimping and expansion cycles separated by dwell periods. The scaffold is crimped to a reduced diameter, held for a dwell period to allow structural stabilization and alignment correction, then slightly expanded to allow realignment before the next crimping step. This periodic process prevents permanent misalignment and structural damage while achieving the necessary small delivery diameter.
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 process significantly increases the retention force of the crimped polymer scaffold on the balloon, ensuring stable deployment and reduced risk of dislodgment, with a minimum 0.5 lb increase in retention force and a diameter reduction of at least 2.5 times without significant loss of strength, addressing the brittleness and temperature sensitivity of polymer materials.
Implementation Method 1
crimping the scaffold to the balloon while the balloon is pressurized
Implementation Method 2
heating the scaffold to a temperature close to, but below the glass transition temperature (Tg) of the polymer material
Implementation Method 3
applying balloon pressure during dwell periods (i.e., balloon pressure is applied when the scaffold diameter is held constant)
Data Source
AI summary
A medical device includes a scaffold crimped to a catheter having an expansion balloon. The scaffold is crimped to the balloon by a process that includes inflating the delivery balloon during a diameter reduction to improve scaffold retention and maintaining an inflated balloon during the diameter reduction and prior and subsequent dwell periods.