Bioabsorbable Stent Thin Struts Fatigue Strength
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Solution Overview
Problem
Current biodegradable stents made from polymers face challenges in achieving adequate radial strength, fatigue resistance, and low recoil while maintaining thin strut thickness, which is essential for minimizing vascular injury and ensuring proper deployment and expansion within the body.
Innovation Solution
A biodegradable stent with thin struts (thickness of 130 μm or less) is developed using a bioabsorbable polymer like PLLA, where the polymer tube is axially and radially expanded in multiple stages under controlled temperature and pressure conditions to enhance mechanical properties, combined with a scaffold design that balances strength, flexibility, and degradation rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the strut thickness is reduced to minimize vascular injury, then the vascular injury is reduced, but the radial strength and fatigue resistance deteriorate
Solution Approach 1:
The patent applies parameter changes by controlling the molecular weight of the bioabsorbable polymer (specifically PLLA with weight average molecular weight of 500,000 to 1,000,000 g/mol) and optimizing processing parameters such as extrusion temperature, drawing ratio, and heat treatment conditions to achieve the desired balance between thin strut thickness and mechanical strength
Solution Approach 2:
The patent utilizes composite material properties by selecting specific bioabsorbable polymers (PLLA, PLGA, or PCL) with optimized molecular characteristics and combining them with appropriate scaffold designs to achieve both thin strut dimensions and adequate mechanical performance for vascular support
2Strength
If the polymer molecular weight is increased to enhance mechanical strength, then the radial strength is improved, but the degradation rate decreases
Solution Approach 1:
The patent optimizes the weight average molecular weight parameter within a specific range (500,000 to 1,000,000 g/mol) to achieve the desired balance between mechanical strength and degradation rate, avoiding both too low (insufficient strength) and too high (too slow degradation) values
Solution Approach 2:
The patent employs feedback control in the manufacturing process by monitoring and adjusting processing parameters (extrusion temperature, drawing ratio, heat treatment) based on the achieved molecular weight and mechanical properties to ensure consistent performance and controlled degradation
3Length of moving object
If the stent is expanded to high radial stress to achieve desired diameter, then the lumen expansion is sufficient, but the polymer structure deteriorates
Solution Approach 1:
The patent optimizes the radial expansion ratio parameter (300%-500%) and controls the expansion temperature (below glass transition temperature) to achieve sufficient lumen diameter while preventing polymer structure deterioration and maintaining structural integrity
Solution Approach 2:
The patent applies preliminary actions by pre-heating the polymer tube to a controlled temperature below its glass transition point before expansion, and by using gradual multi-stage expansion protocols to prepare the material for deformation without causing structural damage
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 achieves high fatigue and radial strength, low recoil, and sufficient shape stability, allowing for effective vascular support until healing is complete and eventual absorption, reducing vascular injury and the need for prolonged antiplatelet therapy.
Implementation Method 1
radially and axially expanding the tube inside a mold while the tube is heated to a processing temperature
Implementation Method 2
On expansion, the stent material attains plastic deformation and hence the stent does not recoil back to its original shape
Data Source
AI summary
This invention discloses a process for preparation of a balloon expandable biodegradable polymer stent with thin struts (strut thickness 130 μm or less, preferably 100-110 μm) with high fatigue and radial strength. The invention discloses a process for the preparation of a biodegradable polymer stent which involves deforming an extruded biodegradable polymer tube axially at a first predefined temperature by applying an axial force for a first predefined time interval. The process further includes radially expanding the axially stretched tube at a second predefined temperature by pressurizing the tube with an inert gas in one or more stages, the pressure applied in each successive stage being higher than the pressure applied in a previous stage.