Bioerodible Magnesium Microstructure for Crack-Resistant Stents
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Solution Overview
Problem
Existing bioerodible magnesium alloys for endoprostheses face challenges with limited ductility and bioerosion rates, leading to stent cracking and impractical use in balloon-expandable designs due to coarse grain sizes and large secondary phase precipitates.
Innovation Solution
A bioerodible magnesium alloy with a microstructure comprising equiaxed Mg-rich solid solution-phase grains and continuous or discontinuous second-phase precipitates, refined through high-strain processes like ECAE, to enhance ductility and corrosion resistance, with a coating for controlled bioerosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional bioerodible magnesium alloys are used, then the material can be implanted, but the coarse grain sizes and large secondary phase precipitates cause limited ductility and stent cracking
Solution Approach 1:
The patent applies severe plastic deformation (SPD) processing techniques to fundamentally change the microstructural parameters of the magnesium alloy. This includes reducing grain size from conventional coarse dimensions to ultra-fine scales (average grain diameter ≤ 10 μm, with some embodiments achieving ≤ 5 μm), and reducing secondary phase precipitate sizes from large to fine dimensions (average diameter ≤ 2 μm, with some embodiments ≤ 1 μm). These parameter changes in grain size and precipitate size directly improve ductility and eliminate stent cracking while maintaining the bioerodible nature of the material
Solution Approach 2:
The patent creates a refined composite microstructure within the magnesium alloy by controlling the distribution and size of secondary phase precipitates. The ultra-fine grain structure combined with finely dispersed secondary phases (such as Al-containing beta-phase precipitates in grain boundaries) creates a composite-like microstructure that enhances mechanical properties. This refined composite structure provides both the ductility needed for balloon expansion and the strength to prevent stent cracking
2Ease of operation
If the bioerodible material is designed for temporary presence, then surgical removal is avoided, but the mechanical integrity is lost at a specific time
Solution Approach 1:
The patent designs the magnesium alloy with dynamic mechanical properties that evolve over time through controlled bioerosion. The ultra-fine grain structure and refined precipitate distribution create a material that maintains high mechanical integrity during the required support period, then progressively degrades as intended. The bioerosion rate is controlled through the microstructure refinement, allowing the stent to maintain strength when needed and then safely erode to avoid surgical removal, transitioning from a load-bearing structure to eroding particles
3Ease of manufacture
If existing bioerodible materials are used, then endoprostheses can be formed, but the erosion products and rate of release are problematic
Solution Approach 1:
The patent changes the microstructural parameters (grain size ≤ 10 μm, precipitate size ≤ 2 μm) to control the bioerosion behavior of the magnesium alloy. The ultra-fine grain structure and finely dispersed precipitates create a more uniform and controlled erosion pattern, producing smaller erosion products that are more easily absorbed by the body. The refined microstructure slows the erosion rate to match the desired temporary presence duration, preventing premature loss of mechanical integrity while ensuring complete bioerosion without harmful accumulation of large debris products
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 microstructured magnesium alloy exhibits improved mechanical properties, including ductility and controlled bioerosion, allowing for successful crimping and expansion of stents without fracturing, with tailored mechanical properties and degradation rates.
Implementation Method 1
performing at least one high-strain process on the ingot or billet to form a microstructure comprising equiaxed Mg-rich solid solution-phase grains
Implementation Method 2
continuous or discontinuous second-phase precipitates in grain boundaries between the Mg-rich solid solution-phase grains
Implementation Method 3
Any suitable bioerodible magnesium alloy formulation capable of having magnesium-rich solid solution grains and second-phase precipitates that offer cathodic protection or promote the formation of a protective film to the grains
Implementation Method 4
offer cathodic protection or promote the formation of a protective film to the grains
Data Source
AI summary
A bioerodible endoprosthesis includes a bioerodible magnesium alloy. The bioerodible magnesium alloy has magnesium and one or more additional alloying elements, including aluminum. The alloy has a microstructure comprising equiaxed Mg-rich solid solution phase grains having an average grain diameter of less than or equal to 5 microns and continuous or discontinuous second-phase precipitates in grain boundaries between the Mg-rich solid solution-phase grains, the second-phase precipitates having an average longest dimension of 0.5 micron or less.