BioresorbableMagnesium Alloys for Orthopaedic Trauma Surgery · - Magnesium Elektron (materials...
Transcript of BioresorbableMagnesium Alloys for Orthopaedic Trauma Surgery · - Magnesium Elektron (materials...
David J. Browne
Professor, Materials Science and Engineering
Vice-Principal for Research, Innovation & Impact
College of Engineering & Architecture
School of Mechanical & Materials Engineering
University College Dublin
Ireland
Bioresorbable Magnesium Alloys for Orthopaedic
Trauma Surgery
MedTecGalway
4-5 October 2017
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Selected Extracts from Presentation
• The full presentation was delivered at the meeting in Galway on Wednesday afternoon, 4 October 2017.
• Some content, including illustrations, and unpublished results, is removed here due to confidentiality and copyright concerns.
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Outline of Presentation
• the Problem
• the Conventional Solution
• the Problem with the Conventional Solution
• the New Solution - conventional new solution
- novel new solution
• Outlook and remaining challenges
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The Conventional Solution
• Biomedical Implants
• Metallic Plates, screws, pins
• Materials: stainless steel, titanium alloys (Ti-6-4)
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Problems with Conventional Solution
• Appropriate mechanical properties – sy
– E
• Corrosion and fatigue
• Built-in redundancy
• Chronic pain; patient discomfort
• Removal surgery – difficulty, additional trauma, risk of infection
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The New Solution - conventional
• Biodegradable metallic devices
• Mg-based
• Mg in the body; dissolution
• Other alloying elements
• Y, RE, Zr
• Ca and Zn
• Corrosion rate
• H2 evolution
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The New Solution in practice
Property Matching
Properties Cortical bone MgZnCa BMGsCrystalline Mg
alloysTi-6Al-4V Stainless Steel
Synthetic
Hydroxyapatite
Density (g/cm3) 1.8-2.1 2.0-2.8 1.74-2.2 4.4-4.5 7.9-8.1 3.1
Elastic Modulus (GPa) 3-30 22-50 41-45 110-117 189-205 73-117
Compressive Yield Strength (MPa) 130-180 400-1190 100-560 758-1117 170-310 600
Fracture Toughness (MPa1/2) 3-6 NA NA 55-115 50-200 0.7
Meagher, P. et al.,
Adv. Mater., 28, 2016, 5755-5762Recommended adult allowances (mg/day):
Mg: 420
Ca: 1000
Zn: 10
Approx. 25g of Mg naturally present in adults.
Mg helps bone growth, inhibits inflammation
and prevents clot formation.
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The New Solution – practice and problems
• Industry uptake
- Syntellix (device design and manufacture) Magnezix®
- Magnesium Elektron (materials development and supply) SynerMag®
• Current clinical situation: Germany, Korea, China
• Problem with corrosion rate
• Mg + 2H2O → Mg(OH)2 + H2 (gas)
• Excessive hydrogen evolution: sub-cutaneous bubbles
• Excessive mineral supply rate (Mg, Ca, Zn)
• Bone not healed by the time implant loses strength
• Need a more corrosion-resistant material
• Novel solution: bulk metallic glass
Metallic Glass = Amorphous Metal
Ref: Maukawa, E. et al., J. Biomed. Mater. Res., 104B, 2016, 1282-1289
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• Hard
• Strong
• Wear resistant
• Corrosion resistant (zero microstructure)
• Biocompatible
• High precision replication – sharpness
• Tough in micro-parts
100 mm
Bulk (>1 mm) amorphous metal = bulk metallic glass
Mg-22Zn-5Ca can be produced in both crystalline and
glassy forms
The New Solution - novel
Amorphous Metal Properties
Corrosion comparison
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5 mm
5 mm
10 mm f crystalline samples
after 10 days in DMEM
Samples immersed in DMEM for indirect and direct cellular response testing, and observation of alloy corrosion.
Immersion in DMEM for 24 h, at 37 oC, and 5% CO2 to form an elution medium.
Medium transferred to wells containing healthy human dermal fibroblasts.
The cells were cultured for 24 and 48 h for indirect exposure. The samples were transferred to separate wells for 24 and 48 h direct cell exposure.
Total 3 mm f sample time in DMEM: 48h, 72 h.
BMG
Crystalline
48 h 72 h
Byrne, J. et al.,
European Cells and Materials, 30 (3), 2015, 75
Cytotoxicity comparison
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5 mm
CytoTox 96® assay on 24 h samples, measures the release of lactate dehydrogenase (LDH) signallingthe loss of membrane integrity and thus levels of cell death.
Copper and stainless steel coupons, of the same size, had been used as controls.
There was little significant difference in cytoxicity (direct or indirect) between conventional and metallic glass Mg alloy after 24 h.
The alloy contained trace elements, including rare earths.
Byrne, J. et al.,
European Cells and Materials, 30 (3), 2015, 75
Conclusions of initial study
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5 mm
• A pre-alloyed Mg-Zn-Ca alloy was cast in amorphous form relatively easily, and exhibited a critical casting diameter of 3 mm.
• The original crystalline variant of the alloy corroded significantly faster than the metallic glass.
• The crystalline structure of the Mg alloy does not impact on relative cytotoxicity, however further studies are warranted with a purer ingot of this material.
• Composition of the alloy for the initial investigation was chosen because of its glass forming ability
• This is not typical of commercial (crystalline) Mg alloys
• Following work included comparison of the Bulk Metallic Glass alloy with a biomedical grade crystalline alloy (WE43).
Conventional Mg biomedical alloy
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5 mm
• Further work was required to compare the BMG with a commercial Mg alloy
• Corrosion under stress also relevant
• WE 43 was chosen. Aluminium-free casting alloy being investigated as implant material.
Results yet to be published.
Outlook and Challenges
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5 mm
For their many advantages, the use of Mg alloys in orthopaedic surgery will
continue to grow.
Alloy composition remains to be optimised (for both C and A forms).
Improved understanding is needed of:
- Strength and ductility
- Cytotoxicity
- Fatigue
- Corrosion/resorption
- In vivo behaviour
- Manufacturing processes (incl. additive) §
Li, J. et al.,
Chem. Commun., 53, 2017, 8288-8291
§ www.I-Form.ie