Extruded Magnesium-Calcium Alloys for Biodegradable Implant Strength
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Solution Overview
Problem
Current magnesium-based alloys for biomedical applications face challenges such as low mechanical strength, rapid degradation, and excessive hydrogen gas evolution, particularly due to the presence of rare-earth elements and zinc, which can lead to implant-related complications like pain, failure, and tissue damage.
Innovation Solution
A method for producing magnesium-calcium alloys through a single extrusion step at specific temperature and ram speed ranges, optimizing extrusion ratios to achieve improved mechanical properties, including high tensile strength and ductility, while avoiding zinc and rare-earth elements to reduce degradation and hydrogen evolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If magnesium alloys containing rare-earth elements and zinc are used to increase degradation resistance, then degradation resistance improves, but biocompatibility deteriorates due to toxic effects on immune cells and accumulation in bones and organs
Solution Approach 1:
The invention extracts and removes harmful rare-earth elements and zinc from the magnesium alloy composition, retaining only safe elements like calcium that provide beneficial effects. This extraction resolves the contradiction by eliminating toxic components while preserving degradation resistance through alternative safe alloying strategies.
Solution Approach 2:
The invention changes the compositional parameters of the magnesium alloy by specifying precise ranges of safe elements (0.1-1.0 wt% calcium, 0.01-0.5 wt% zirconium, 0.01-0.1 wt% hafnium) to achieve both degradation resistance and biocompatibility. This parameter optimization resolves the contradiction by finding the optimal composition within safe element constraints.
2Strength
If magnesium alloys with high calcium and zinc content are used to achieve mechanical strength, then mechanical strength improves, but degradation rate increases becoming too high or close to tolerable limit
Solution Approach 1:
The invention optimizes the parameters of calcium content (0.1-1.0 wt%) and adds small amounts of zirconium and hafnium to achieve the right balance between mechanical strength and degradation rate. This parameter optimization resolves the contradiction by finding the optimal composition that provides sufficient strength while maintaining acceptable degradation rates.
Solution Approach 2:
The invention creates a composite alloy system combining magnesium with carefully selected amounts of calcium, zirconium, and hafnium. This composite approach resolves the contradiction by leveraging the synergistic effects of multiple elements to achieve both mechanical strength and controlled degradation.
3Strength
If multiple extrusion steps are used to achieve improved mechanical properties, then mechanical properties improve, but manufacturing complexity and processing time increase
Solution Approach 1:
The invention performs preliminary alloying during the first extrusion step by adding zirconium and hafnium to the magnesium-calcium billet before extrusion. This preliminary action resolves the contradiction by achieving the desired mechanical properties in a single extrusion step rather than requiring multiple sequential extrusions.
Solution Approach 2:
The invention merges multiple functions into a single extrusion step: alloying, microstructure refinement, and mechanical property enhancement are all achieved simultaneously in one process. This merging resolves the contradiction by eliminating the need for separate multiple extrusion steps while maintaining improved mechanical properties.
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 method produces alloys with tailored mechanical properties, such as ultimate tensile strength ranging from 100 MPa to 500 MPa and elongation at fracture from 2% to 50%, enhancing biocompatibility and reducing degradation rates, making them suitable for biodegradable implants with improved safety and efficacy.
Implementation Method 1
The billet is extruded at least once at an extrusion temperature in the range of 250° C. to 450° C. and at a ram speed in the range of 0.01 mm/s to 1 mm/s and at an extrusion ratio in the range of 20 to 150
Implementation Method 2
The alloy preferably comprises an intermetallic phase of Mg2Ca. It is furthermore preferred that the intermetallic phase of Mg2Ca is present in a mole fraction in the range of 0% to 1.5%
Implementation Method 3
Hydrogen gas is a reaction product of Mg and water (1 mole Mg leads to 1 mole H2) that diffuses safely through tissues when evolving moderately
Data Source
AI summary
A method of producing an alloy including magnesium and calcium, preferably an implantable medical device having magnesium and calcium, includes the steps of generating a billet including magnesium and calcium, and extruding the billet. The billet is extruded at least once at an extrusion temperature in the range of 250° C. to 450° C. and at a ram speed in the range of 0.01 mm/s to 1 mm/s and at an extrusion ratio in the range of 20 to 150 and preferably at an extrusion ratio in the range of 35 to 150.