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PROCESSING OF MAGNESIUM ALLOYS FOR IMPLANTS
Norbert Hort
Magnesium Innovation Centre, Helmholtz-Zentrum Geesthacht
Res Metallica, 16th May 2019
KU Leuven
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THE HELMHOLTZ ASSOCIATION
19 centres
4,7 B€
40,000 employees
Research areas
Energy
Earth andEnvironment
Health
Aeronautics, Space, Transport
Matter
Key Technologies
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HELMHOLTZ CENTRE GEESTHACHTMission
From Application-oriented Fundamental Research to Innovation
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HELMHOLTZ CENTRE GEESTHACHT
Research locations in Geesthacht und Teltow
Institute of Materials Research
Magnesium Innovation Centre
Metallic Biomaterials
Materials Technology
Materials Physics
Materials Mechanics
Institute of Polymer Research
Institute of Coastal Research
Institute of Biomaterial Science (Teltow)
Outstations
Climate Service Center 2.0 (Hamburg)
at DESY (Hamburg)
at MLZ (FRM II Munich)
BCRT (Berlin)
950 employees
100 M€ annual budget
1/3 Coastal and
Climate Research
2/3 Materials Research
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MagIC – MAGNESIUM INNOVATION CENTRE
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Corrosion
and
Surface
ProtectionM. Zheludkevich
Wrought AlloysD. Letzig
MagICK.U. Kainer
Manufacturing
Light Metal
ComponentsN. Ben Khalifa
ProcessingN. Hort
Approx. 60 staff members
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MagIC – MAGNESIUM INNOVATION CENTREResearch Portfolio
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MagIC – MAGNESIUM INNOVATION CENTREModelling/Simulation Activities
Atoms Components
ContinuumModelling
Mould Filling
ContinuumModellingPhase Field
CALPHADThermodynamics
MolecularDynamics
Ab initio
ContinuumModelling
FEM
Magnesium
1s22s22p63s2
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TYPICAL MAGNESIUM APPLICATIONS
The bad news:
Magnesium
corrodes!
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TYPICAL MAGNESIUM APPLICATIONS
The good news:
Magnesium
corrodes!
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NEW MAGNESIUM APPLICATIONS
The good news:
Magnesium degrades
and is
Biocompatible!
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NEW MAGNESIUM APPLICATIONS?E. C. Huse, Chicago Medical Journal and Examiner, 1878
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DEGRADABLE MG ALLOYS FOR IMPLANTS
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Bone plate
Stent
(BIOTRONIK, Berlin, Germany)
Bone pin
Disadvantages still too fast degradation
form subcutaneous hydrogen bubblesloss mechanical integrity before healing
Advantages low Young’s modulus (reduce stress shielding effect)
Bone: 5-23 GPa, Mg: 45 GPa, Ti: 114 GPa, polymer (DL-PLA): 2.1 GPa
appropriate strength compared to bone excellent biodegradability
Mg→Mg2+ in body fluid300-350 mg Mg is needed daily, extra Mg2+ can be excreted by urineNo second surgery to save costs (especially good for children)
good biocompatibilityOsteoconductive (stimulates bone regeneration)
Prototype of biodegradable Mg based implants
(Small Animal Clinic, Hannover, Germany)
Challenges combination of good mechanical properties and
low degradation rate controlled homogeneous degradation
(Synthes GmbH)
Risks Peri-implant infections: 8%-44% Orthopedic implant: higher infection risk in post-operations Potential infection risk: degradable polymer and magnesium2
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WHAT AN ENGINEER WANTS TO KNOWRequirements of the implant
Degradable or not?
How fast can/has the implant to degrade?What does an engineer understand in strength and what does the clinician mean?
What is stiffness for the engineer and what for the clinician?
What is the „right“ degradation rate?
…
Basically, what is the property profile of a degradable implant?
Do we really speak the same language?
We have to learn each others requirements, limits and the proper way to express what engineers, biologists, clinicians need!
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TALKING TO A SURGEON
Give me a „GOOD“ alloy that is as
Strong as steel
Stiff as titanium
(not stiffness but strength was meant)
no real understanding of
materials science concepts
Degradable, but
how fast is fast
how slow is slow?
Musculo-sceletal: Juvenile/adult bone?
Cardio-vascular: high stiffness, strength, ductility
One alloy for all applications
What are the real requirements for degradable implants?
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COMMON LANGUAGE
western blot
dislocation
segregation
phases
CDNA real-time PCR …
ligature
suture
animal model
…
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PERMANENT VS DEGRADABLE IMPLANTS
What can be compared?
content of sugar
content of fruit acid
texture – mouth feeling
…
But taste?
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ALLOY DEVELOPMENT
You have to answer three questions for each requirement:
Yes, we can!
No, it does not work!
We do not know it right now!
Benchmarks VW(creep resistant alloys)
• Specified requirements
• Castability like AZ91
• RT strength like AZ91
• Corrosion resistance like AZ91
• Creep resistance like AE42
• Max. 20 % increase in costs compared to AZ91
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ALLOY DEVELOPMENT FOR AN IMPLANT
MeKo, HZGcoronary stent alloy (Resoloy®)
• yield stress > 200 MPa
• tensile strength 300 MPa
• elongation to fracture 30 %
• stable in service for 6 month
• fully degraded after 12 month
Benchmarks VW(creep resistant alloys)
• Specified requirements
• Castability like AZ91
• RT strength like AZ91
• Corrosion resistance like AZ91
• Creep resistance like AE42
• Max. 20 % increase in costs compared to AZ91
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MAGNESIUM PROCESSING
Selecting the right material
Primary Magnesium
Casting
Wrought Processing
Powder Metallurgy
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MAGNESIUM SOURCES
Magnesite MgCO3 : 28.8 % Mg(Ca, Si, Fe, Al, Mn, Ni)
Dolomite MgCO3 * CaCO3 : 28.8 % Mg(Fe, Mn, Al, Si)
Serpentine 3 MgO * 2 SiO2 * 2 H2O : 26.3 % Mg(Co, Mn, Cu, Fe, Al, Cr, Si)
BischofiteMgCl2 * 6 H2O : 12 % Mg(Cu, Zn, Ag, Mo, Si, Ca, Fe)
CarnalliteMgCl2 * KCl * 6 H2O : 8.8 % Mg(Ca, Si, Fe)
Salt water Mg2+
Ro
ck
Sa
lt
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PRIMARY PRODUCTION
Pidgeon Process
Low investment costs(1000 €/t)
Energy intensive
Personnel intensiv
Low environmental sustainability
Electrolysis
High investment costs(10,000 €/t)
High productivity
Mainly in western countries
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ALLOY DESIGN
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THE PERIODIC TABLE OF ELEMENTSOur Toolbox
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THE PERIODIC TABLE OF ELEMENTSAvailable Binary Phase Diagrams of Mg
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THE PERIODIC TABLE OF ELEMENTSUnsuitable Alloying Elements
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THE PERIODIC TABLE OF ELEMENTSSuitable Alloying Elements
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MAGNESIUM AND ITS ALLOYSProcessing: Casting
Sand casting
Permanent mould casting
Gravity die casting
High pressure die casting
Cold chamber HPDC
Warm chamber HPDC
Semi-Solid Processing
Thixocasting
Thixomoulding
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DIRECT CHILL PERMANENT MOLD CASTING
sonotrode
stirring device
mould
heating
melt
ultrasonic
device
sonotrode
melt
mold
water bath
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CASTING
Melt the metal/metals!
Pour it into a mould!
Let it freeze!
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MELTING MAGNESIUM
Steel is normally used for
Crucibles
Moulds
Tools
S235 (1.0253), P265 GH (1.04250),
X10CrAl18 (1.4742), X10CrAl7 (1.4713)…
because
Low solid solubility of Fe in Mg
Costs
Alternatives
Ti
W, Pt, Os …
Aluminiumtitanate Al2TiO5
Source: Ditta Musto, Italy
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Mg-GdDegradation Behaviour
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Mg-GdCompression
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Mg-GdTension
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Mg-GdAs cast – Heat Treated – Extruded: Mg10Gd
Str
ess
[M
Pa]
Elo
ng
ati
on
[%
]
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Mg-2Gd-x(Ag,Ca)
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Mg-2Gd-x(Ag,Ca)
Mg2GdxCa
Mg2Gd2AgxCa
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Mg-2Gd-x(Ag,Ca)
Mg2Gd2AgxCa
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Mg-2Gd-x(Ag,Ca)Phases
Alloy Predicted IMPs Exp. IMPs
Mg-2Gd Mg5Gd Mg5Gd
Mg-2Ag Mg4Ag Mg4Ag
Mg-0.8Ca Mg2Ca Mg2Ca
Mg-2Gd-2Ag Mg5Gd, Mg4Ag Mg5Gd, Mg52Gd3Ag5
Mg-2Gd-0.4Ca Mg5Gd, Mg2Ca Mg5Gd, Mg2Ca
Mg-2Gd-0.8Ca Mg5Gd, Mg2Ca Mg5Gd, Mg2Ca
Mg-2Gd-2Ag-0.4Ca Mg5Gd, Mg4Ag, Mg2Ca MgGdAgCa, Mg2Ca
phase predictions in binary alloys: okternary MgGdAg: partially ok; new phase was not predictedternary MgGdCa: okquaternary MgGdCaAg partially ok; new phase was not predicted
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MAGNESIUM AND ITS ALLOYSProcessing: Wrought
Extrusion
Rolling
Forging
Deep drawing
Wire drawing
…
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Mg-2Gd-xAgExtrusion
Increasing extrusion speed:=> grain size increases
Increasing Ag content=> almost no influence
Alloy Mg-2Gd-1Ag Mg-2Gd-2Ag
Extrusion speed [mm/s] 0,6 2,2 4,4 0,6 2,2 4,4
Grain size [μm] 10±1 25±1 38±3 8±1 25±3 38±4
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Mg-2Gd-xAgExtrusion
Ten
sile
Stre
ngt
hin
MPa
Extrusion speed in mm/s
UTS Mg2Gd-1Ag UTS Mg2Gd-2Ag
TYS Mg2Gd-1Ag TYS Mg2Gd-2Ag
Co
mp
resi
veSt
ren
gth
in M
Pa
Extrusion speed in mm/s
UCS Mg2Gd-1Ag UCS Mg2Gd-2Ag
CYS Mg2Gd-1Ag CYS Mg2Gd-2Ag
Alloy Mg-2Gd-1Ag Mg-2Gd-2Ag
Extrusion speed [mm/s] 0,6 2,2 4,4 0,6 2,2 4,4
Elongation to fracture [%] 46,8 ± 2,1 39,0 ± 1,1 36,2 ± 1,1 44,0 ± 1,6 36,8 ± 1,7 37,7 ± 1,6
Compression to fracture 19 ± 0,7 20 ± 0,5 21 ± 0,3 19 ± 0,5 20 ± 0,5 19 ± 1
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EXTRUDED Mg-2Gd-xAgDegradation
No influence of
Extrusion speed
Grain size
Ag content
Alloy Mg-2Gd-1Ag Mg-2Gd-2Ag
Extrusion speed [mm/s] 0,6 2,2 4,4 0,6 2,2 4,4
Degradation rate [mm/a] 0,28 ± 0,03 0,29 ± 0,07 0,31 ± 0,04 0,33 ± 0,35 0,28 ± 0,01 0,28 ± 0,02
Cell culture medium
Dulbecco's Modified Eagle Medium (DMEM)
10% Fetal Bovine Serum (FB)
1% Penicillin Streptomycin
7 days
𝐷𝑅 =𝛥𝑚 ∗ 𝑘
𝐴 ∗ 𝑡 ∗ 𝜌
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BINDER-BASED SINTERING TECHNOLOGIESBasic process chain
Sintering
Sintered part
Shaping
Green part
Fused Filament Fabrication(FFF, FDM)
Microextrusion
Screen printing
Composite ExtrusionModeling
Solvent jetting
(Binder jetting)
Machining
Injection Moulding(MIM)
Debinding
Brown part
Metal powder
Polymeric binder
Feedstock
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SHAPING TECHNOLOGIESExamples of typical techniques
Shaping process Feedstock Device Remark
FFF Filament 3D-(home)printer Low cost device
Microextrusion Paste Special 3D-printer Structured macro-porosity
Screen printing Paste Screens High resolution
Composite ExtrusionModeling
Granules CEM printer Rather novel
Solvent jetting Granules Ink jet like printer Rather low cost device
(Binder jetting) Powder + binder Ink jet like printer Powder bed (similar to SLM)
Machining Compacts Machining devices Simple, but limited in geometry and size
Injection moulding Granules Injection mouldingmachine
Mould needed,high numbers, precise
Screen printing
Fraunhofer IFAM Dresden
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METAL INJECTION MOULDING MIM
Element 22 GmbH
Tricumed GmbH HZG
DTC Orthodontics, China
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EFFECT OF CONSOLIDATION ON MICROSTRUCTURE
• Long time heattreatment
• Slow temperaturechanges
• Tendency for equilibriumstate
Melting
• Very short local melting• Very fast temperature
changes• Complicated heat
transfer• Tendency for non-
equilibrium state
Sintering
SLM/EBM
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SINTERING OF MAGNESIUM
Challenges
• Very reactive with respect to oxygen
• Oxide layer present on powder surface
• High vapour pressure
AZ81 Mg-0.9Ca
However, it works!
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SINTERING OF MAGNESIUM
AZ81 Mg-0.9Ca
Remaining oxides hinder/limit grain growth
FFF
5 mm
20 µm
MIM
Design: Conmed
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IN VITRO TESTINGMTT* Assay
NO Cells!
Interactions between Magnesium degradation and the testing
system in vitro has to be taken into regard!
* 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromid
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SUMMARY
Successfull implant materials development needs:
A common languageBiologist Engineer Clinician has to be established
A close collaboration
Suitable and reliable materials testingin vitro in vivo
Benchmarks
Property profiles
Carefull selection of
Alloying elements
Processing routes
for “robust” alloys
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ACKNOWLWDGEMENTS
Funding from
Helmholtz Virtual Institute VH-VI-523 (In vivo studies of biodegradablemagnesium based implant materials)
EU Grant Agreement No 289163, European Union, MagnIM – Tailoredbiodegradable magnesium implantmaterials
All people from MagnIM and VI
Colleagues, students and PhD studentsat MagIC
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THANK YOU FOR YOUR ATTENTION!
11th BiometalsAlicante, Spain, August 25-30, 2019www.biodegradablemetals.org
Euromat 2019Stockholm, SW, September 01-05, 2019euromat2019.fems.eu
149th TMS Annual Meeting 2020San Diego, CA, USAwww.tms.org/tms2020