Bioabsorbable Stent with Directional Solidification
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Solution Overview
Problem
Conventional magnesium-based absorbable metal stents face issues with poor control over degradation rate and fragmentation, leading to premature mechanical failure and potential embolization of radio-markers, which can cause serious infarction in coronary vessels, and existing absorbable polymer stents lack sufficient radial stiffness for effective artery opening.
Innovation Solution
The development of bioabsorbable stents with directional solidification to form single crystal or columnar crystal microstructures that degrade primarily through surface erosion, combined with a hybrid design using absorbable metal and polymer technologies, where metal segments are connected by flexible polymer connectors to prevent galvanic reactions and include biostable radio-opaque segments for stability and drug delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If conventional polycrystalline magnesium alloys are used for absorbable stents, then the stent can be fully absorbed by tissue, but the degradation rate is poor and fragmentation occurs leading to premature mechanical failure
Solution Approach 1:
The patent changes the microstructural parameters of the magnesium alloy from conventional polycrystalline to single crystal or columnar grain structures through directional solidification. This parameter change in crystal structure eliminates grain boundaries that serve as corrosion pathways, thereby controlling the degradation rate to match the required absorption time while maintaining mechanical integrity throughout the stent's functional life.
Solution Approach 2:
The patent creates a non-uniform microstructure with columnar grains oriented perpendicular to the stent surface, providing different properties at different locations. The grain structure is optimized locally at the surface for controlled corrosion resistance while maintaining bulk mechanical strength, resolving the contradiction between gradual absorption and sustained mechanical reliability.
2Loss of substance
If conventional polycrystalline magnesium alloys are used, then the stent degrades through corrosion, but corrosion proceeds along grain boundaries causing cavitation and cracking that shortens functional life
Solution Approach 1:
The patent fundamentally changes the microstructural parameter from polycrystalline to single crystal/columnar grain structure, eliminating grain boundaries that facilitate rapid corrosion. This parameter change slows the degradation rate by forcing uniform surface corrosion rather than grain boundary attack, thereby extending the functional life of the stent while maintaining controlled substance loss.
3Ease of manufacture
If radio-marker segments are added to absorbable stents for visualization, then the stent can be tracked, but the radio-markers may embolize and cause infarction in coronary vessels
Solution Approach 1:
The patent extracts the radio-marker function from separate embolizable segments and integrates it into the continuous absorbable metal structure through biostable radio-opaque segments. This extraction of the harmful radio-marker component and its reintegration into the structurally sound absorbable framework eliminates embolization risk while preserving visualization capability.
Solution Approach 2:
The patent creates a composite structure combining absorbable metal with biostable radio-opaque segments, merging the beneficial properties of both materials. The absorbable metal provides controlled degradation and mechanical support, while the biostable segments provide permanent radio-opacity for tracking without embolization risk, as they are integrated into the structurally sound framework.
4Duration of action of stationary object
If absorbable polymer stents are used, then the stent can be fully absorbed, but they lack sufficient radial stiffness for effective artery opening
Solution Approach 1:
The patent creates a composite stent structure where absorbable metal segments provide high radial stiffness for effective artery opening, while the overall design maintains absorbability. The metal segments are connected by flexible polymer connectors that allow controlled degradation, combining the strength benefits of metal with the absorbability benefit of polymers.
Solution Approach 2:
The patent segments the stent into alternating absorbable metal segments and flexible polymer connectors. The metal segments provide the necessary radial stiffness for artery opening, while the polymer connectors provide flexibility and controlled degradation. This segmentation allows each component to optimize its function while contributing to overall absorbability.
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
This approach results in controlled strength retention and degradation, preventing premature mechanical failure, reducing embolization risks, and enabling effective drug delivery while ensuring the stent is fully absorbed within 6 months, allowing endothelial healing and vaso-motion recovery.
Implementation Method 1
processing by directional solidification and the formation of single crystal or poly-columnar crystal micro-structures
Implementation Method 2
The resulting structure degrades primarily by surface erosion
Implementation Method 3
Corrosion can proceed along grain boundaries due to localized galvanic reactions between Mg and more noble metals
Data Source
AI summary
A bioabsorbable implant including an elongated metallic element including more than 50% a metal substantially free of rare earth metals, with the elongated metallic element defining at least a portion of the bioabsorbable implant.