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