Iron Lumen Stent Preform Microstructure for Plasma Nitriding
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Solution Overview
Problem
Current nitriding methods for iron-based stents face challenges such as low production efficiency, toxicity risks, and unsuitable mechanical properties for certain applications, particularly in achieving the required balance of radial strength and plasticity for coronary and peripheral stents.
Innovation Solution
A lumen stent preform made of pure iron or iron alloy with specific impurity and alloy content, processed to achieve a hardness of 160-250HV0.05/10 and a deformed microstructure, suitable for plasma nitriding, which enhances radial strength and corrosion rate while maintaining plasticity, using a method that includes drawing and plasma nitriding within a controlled temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If gas nitriding method is used to improve stent strength, then stent hardness increases, but production efficiency becomes too low for large-scale use
Solution Approach 1:
The patent replaces gas nitriding (chemical diffusion process) with plasma nitriding (physical plasma process), achieving faster nitrogen penetration into the iron alloy surface while maintaining improved hardness and strength
Solution Approach 2:
The patent changes the nitriding process parameters by using plasma state nitrogen at controlled temperatures (200-500°C) and pressures, enabling shorter treatment times compared to conventional gas nitriding while achieving the required surface hardness
2Strength
If salt-bath nitriding method is used to improve stent strength, then stent hardness increases, but toxic molten cyanide salts are required causing high clinical risk
Solution Approach 1:
The patent eliminates the harmful cyanide salts by using plasma nitriding with nitrogen and hydrogen gases, converting a toxic chemical process into a safe physical plasma process that leaves no toxic residues on the implantable stent
Solution Approach 2:
The patent uses an inert or controlled plasma atmosphere (nitrogen-hydrogen mixture) instead of toxic molten salts, creating a safe processing environment that prevents contamination of the medical device with harmful substances
3Strength
If gas nitriding or salt-bath nitriding is used, then stent strength improves, but compound layers become very thick (≥0.01 mm) unfavorable for subsequent polishing and fine structure design
Solution Approach 1:
The patent applies plasma nitriding with controlled parameters to achieve partial nitriding - forming a thin compound layer (much thinner than 0.01 mm) that provides sufficient surface hardness while leaving the bulk material properties intact and the surface suitable for fine polishing and complex structure fabrication
Solution Approach 2:
The patent controls the plasma nitriding parameters (temperature, pressure, gas composition, treatment time) to precisely control the thickness and composition of the compound layer, achieving optimal balance between surface hardness and surface quality for subsequent manufacturing steps
4Reliability
If pure iron stent is used to ensure biocompatibility, then corrosion rate is slow, but mechanical properties are lower compared to stainless steel or cobalt chromium stents
Solution Approach 1:
The patent creates a composite structure with a pure iron or iron alloy base material (providing biocompatibility and controlled corrosion) combined with a plasma-nitrided surface layer (providing enhanced hardness and strength), achieving both biocompatibility and improved mechanical properties
Solution Approach 2:
The patent applies plasma nitriding to create local quality enhancement - the bulk material remains soft and biocompatible pure iron/iron alloy, while the surface layer gains high hardness and strength through nitrogen penetration, providing different properties where needed
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 solution provides a stent with improved radial strength and corrosion rate, meeting the mechanical property requirements of conventional lumen stents, and allows for commercial-scale production of stents with enhanced mechanical properties.
Implementation Method 1
The plasma nitriding method has high nitriding efficiency, which uses nitrogen and hydrogen as treatment gas
Implementation Method 2
the nitriding treatment on pure iron/iron alloys can, on one hand, improve the stent strength (characterized by hardness or radial strength)
Implementation Method 3
the lumen stent preform has a hardness of 160-250HV0.05/10, and has a microstructure that is a deformed structure having a grain size number greater than or equal to 9 or a deformed structure after cold machining
Data Source
AI summary
A lumen stent preform is provided using a plasma nitriding technology, a preparation method thereof, a method for preparing a lumen stent by using the preform, and a lumen stent obtained according to the method. The preform is manufactured by using pure iron or an iron alloy containing no strong nitrogen compound, has a hardness of 160-250HV0.05/10, and has a microstructure that is a deformed structure having a grain size number greater than or equal to 9 or a deformed structure after cold machining. Alternatively, the preform is an iron alloy containing a strong nitrogen compound, and has a microstructure that is a deformed structure having a grain size number greater than or equal to 9 or a deformed structure after cold machining. The lumen stent preform meets the requirements of a conventional stent for radial strength and plasticity, so that plasma nitriding is applicable to commercial preparation of a lumen stent.