UHMW Bioabsorbable Polymer Stent Fatigue Resistance
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Solution Overview
Problem
Current polymeric stents face challenges with low fracture toughness and radial strength, leading to potential mechanical failure and recoil, especially in endovascular applications, due to their material properties and processing methods.
Innovation Solution
Development of stents using ultra-high molecular weight (UHMW) bioabsorbable polymers with inherent viscosity greater than 6 dl/g or weight average molecular weight greater than 1 million g/mole, fabricated through solvent processing methods to enhance mechanical properties such as radial strength, modulus, and fracture toughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional polymeric materials are used for stent fabrication, then the stent can be biodegradable and bioabsorbable, but the fracture toughness and radial strength are insufficient
Solution Approach 1:
The patent applies parameter changes by increasing the molecular weight of the polymeric material to ultra-high molecular weight (UHMW) ranges. Specifically, the polylactide polymer has a weight average molecular weight (Mw) greater than 1 million g/mole and number average molecular weight (Mn) greater than 500,000 g/mole. This molecular weight parameter change fundamentally alters the mechanical properties, providing high fracture toughness and elongation while maintaining biodegradability and bioabsorbability, thereby resolving the contradiction between strength and reliability.
2Duration of action of stationary object
If bioabsorbable polymers are used to allow complete degradation after treatment, then the device can disappear after treatment completion, but the material exhibits low fracture toughness
Solution Approach 1:
The patent resolves this contradiction by changing the molecular weight parameter to UHMW ranges (Mw > 1 million g/mole, Mn > 500,000 g/mole). This parameter change enables the polymer to maintain high fracture toughness and mechanical strength during the degradation period while preserving the complete biodegradation capability. The high molecular weight provides sufficient structural integrity throughout the treatment duration, allowing the stent to fulfill its mechanical support function before completely degrading into negligible residues.
3Strength
If typical molecular weight polymers are used, then the material can be processed easily, but the stent lacks sufficient toughness and radial strength
Solution Approach 1:
The patent applies parameter changes by utilizing UHMW polymers with specific molecular weight characteristics (Mw > 1 million g/mole, Mn > 500,000 g/mole) and inherent viscosity greater than 8 dl/g. These parameter changes provide sufficient toughness and radial strength for clinical performance. The processing challenges associated with such high molecular weights are managed through specialized manufacturing techniques including solvent processing, dip coating, and controlled extrusion, which enable fabrication of stents with the required mechanical properties.
4Strength
If the stent is made from polymeric material, then it can be biodegradable, but the radial strength is insufficient to withstand structural loads
Solution Approach 1:
The patent resolves this contradiction by changing the molecular weight parameter to ultra-high ranges. The UHMW polylactide with Mw > 1 million g/mole and Mn > 500,000 g/mole provides exceptional radial strength and structural integrity. This parameter change enables the polymeric stent to withstand the structural loads and radial compressive forces imposed during vessel support, while maintaining complete biodegradability. The high molecular weight creates a material that is sufficiently rigid to maintain stent size and shape throughout service life despite cyclic loading from the beating heart.
Data Source
AI summary
A stent made from an ultra high molecular weight bioabsorbable polymer is disclosed herein. The bioabsorbable polymer can have a Mw greater than 1 million g/mole or greater than 2 million g/mole. Methods of making the ultra high molecular weight polymer stent without degrading the molecular weight are further disclosed.