Smart&ThinFilms& for MedicalApplications · ) Fabrication methode allows realizationof6thin film6...

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Christian-Albrechts-Universität zu Kiel

Smart Thin Films for Medical Applications

Eckhard Quandt

Institute for Materials ScienceFaculty of Engineering University of Kiel Germany

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- Introduction

- Superelastic TiNi Thin Films for Medical Devices

- Magnetoelectric Composites for Biomagnetic Field Sensors

- Conclusions and Outlook

Outline

ThinFilms 2016, Singapore, July 13th, 2016

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- Introduction




Outline


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Smart Materials


MagneticFieldorStress

ElectricFieldor Stress

Temperatureor Stress

Ferroic Properties

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5

Smart Material Thin Films


• Inherent effects ⇒ can be down-scaled to micrometer or nanometerdimensions• Transduce electromagnetic and mechanical energies⇒ mechanismsfor actuators and sensors• Combination of different effects ⇒ natural or composite multiferroics• Cost-effective batch fabrication compatible to MEMS/NEMS

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Laboratories @ Kieler Nanolabor


LithographyMask Aligner, E-Beam, FIB

Cleanroom: 350 m2

Thin Film TechnologyMagnetron Sputtering, Evaporation, PLD, PECVD

EtchingIon Beam Etching, ReactiveIon Etching, Bosch ProcessWet Etching

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7

- Introduction


- Stent Technology- Thin Film Processing Route- Unique Features of Thin Film Devices- Examples of Applications



Outline


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Shape Memory Effects


1. Alloy that "remembers" its original shape

— after deformation returns to its original shape when heated

2. Superelasticity

— recovering of large strain

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Stent Technology


D. Stöckel, NDC

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Stent Fabrication: Traditional Process Flow


NiTi-Tube Laser-BeamCutting Deburring Honing

HeatTreatment Blasting Electro-

polishing

Limits:• Minimum tube thickness (approx. 50 µm)• Minimum feature size (approx. 20 µm)

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Strokes (#4 Killer in the U.S.)


Ischemic Stroke~ 300 of 100.000 people(i.e. ~ 725,000 strokes / year (US))~ 15% mortality rate~ 15 – 30% permanent handycapped

Intercerebral Hemorrhage: ~ 30 of 100.000 people in thedeveloped world are affected

Subarachnoid Hemorrhage(Cerebral Aneurysms): ~ 15 von 100.000 people(i.e. ~ 35.000 / year (US))high mortality rate

è Development of newtechnology essential

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Planar Thin Film Process


700 µm

20 µm

TiNi

Cu

Photo Resist

Substrate

(1) (2) (3)TiNi Thin FilmCu Sacrificial Layer

Photo Resist /UV Lithography

TiNi EtchingProcess

(7) Sacrificial LayerWet Etch

Removal of Photo Resist

TiNi DepositionCu Etching(4) (5) (6)

(4)

(7)Advanced Engineering Materials 15 (2013), 66-69

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Workflow for Thin Film Devices @ Acquandas


CAD Design UV- Lithography

Heat Treatment / Shape setting

Sputtering Process

Wafer afterSputtering Process

Sample Release by wet-chemical Etching

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Improved Mechanical Properties


0 10 20 30 400

500

1000

1500

σ / M

Pa

ε / %

Acquandas thick film(laser cut & surface finished)

Conventional sheet metal(laser cut & surface finished)

T= 35°C

Fracture strains of up to ~40%

0 1 2 3 4 5 60

1

2 NiTi Film Fracture NiTi Film Run out (10 Mio. cycles) NiTi Standard Fracture NiTi Standard Run out (10 Mio. cycles)

Alte

rnat

ing

Stra

in /

%

Mean strain / %

Alternating strains of up to ±1.5%

Advanced Engineering Materials 15 (2013), 66-69Journal of Materials Engineering and Performance 23, 2437-2445 (2014)

è Improvement of mechanical properties by a factor of 2.5

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Fatigue in Superelastic TiNiCu Films


0.00 0.01 0.02 0.030

100

200

300

400

TTest = 70 °CAf = 65 °C

cycle 1 cycle 10 cycle 50 cycle 100 cycle 200

stre

ss /

MPa

strain

Ti51Ni36Cu13

Ti54Ni34Cu12

TTest = 78 °CAf = 72 °C

0.00 0.01 0.02 0.03

a)

strain

b)

• Aquiatomic TiNi similar (even worse) compared to aquiatomic TiNiCu• Functional and structural fatigue behavior is strongly influenced by the Ti content

Science 348 (2015) 1004

near-‐aquiatomic Ti-‐rich

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Ultra-low Fatigue in Superelastic Ti-rich TiNiCu Films


Science 348 (2015) 1004

No functional fatigue for 107 full superelastic cycles

Fatigue test of the full superelastic transformation at 10 Hz

0,000 0,005 0,010 0,015 0,0200

100

200

300

400

TTest = 70 °CAf = 65 °C

stre

ss /

MP

a

strain

cycle 1 cycle 200 cycle 107

Ti54Ni34Cu12

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Crystallographic Compatibility


Y. Song et al., Nature 502, 85-88 (2013)

Cofactors (CCI and CCII)

The low fatigue Ti-rich sample satisfies the cofactor conditions better than the near equiatomic sample

J. Cui et al., Nature Materials 5, 286-290 (2006)

middle eigenvalue (λ2)0

412dettr 222 ≥−−− aUU

{ } 0cof 2 =−• nIUUa

Science 348 (2015) 1004

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Epitaxy in Phase Transformation


Occurrence of Ti2Cu precipitates only in the Ti-rich TiNiCu thin film

Science 348 (2015) 1004

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Advantages of Thin Film Technology


Miniaturization Complex Design Options

Integration ofFunctions Rapid Prototyping

Fatigue Life MaterialCombination

MicropatternedSurfaces

Excellent Biocompatibility

Cost effective(Batch process)

Simple Alloy Optimization

0,000 0,005 0,010 0,015 0,0200

100

200

300

400

TTest = 70 °CAf = 65 °C

stre

ss /

MPa

strain

cycle 1 cycle 200 cycle 107

Ti54Ni34Cu12

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Mechanical Thromboembolectomy


Deepak S Nair, MD (Vascular Neurology INI Stroke Center, OSF Saint Francis Medical Center)www.ini.org/.../Stroke-101-Deepak-S-Nair-MD.ppt

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Thin Film Stent Retriever


strut thickness: 30 µm

internal structure hight: 10 µm

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Transcatheter Aortic Valve Implantation


Edwards Lifescience

Minimal invasive implantation

• Developed to treat high riskpatients

• First ‚in human‘ in 2002• Today more than 60,000 implants worldwide

• Durability max. 15 years• Possible damage of leaflets due to high crimping forces• Leaflet thickness 200 –350 µm

Biological valve

NiTi thin film leaflets

• Long durability• High crimpability(superelasticity)• Leaflet thickness10 – 20 µm

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Fabrication of NiTi Thin Film Leaflets


Leaflet Forming & Annealing

Forming Annealing

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Patterned Leaflets


Fabrication of structuredheart valve leaflets

Diameter: 20 mmHeight: 18 mmFilm thickness: 10 and 15 µm

9.5 µm

24.6 µm

84.9 µm10 mm

1.

Cell seeding of smooth muscle cellsfor 7 days

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Performance in Comparison to Biological Valve


Opening Phase Closing Phase

TiNiFull 10 µm

TiNiMesh 10 µm

Porcine

Opening cycle ofheart valves at a heart rate of 70 bpm

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- Introduction



- Principle- General Features- Exchange-biased Sensors- Tuning Fork Sensors


Outline


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Development of a biomagnetic interface to measure the magnetic fieldsof heart and brain currents

• magnetoelectric composites (magnetostrictive, piezoelectric components) as magnetic field sensors

• magnetoelectric sensor (array) systems• medical applications of the biomagnetic interfaces

Focus of the Collaborative Research Centre 1261


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Magnetic Fields in Medicine


earth magnetic field

urban noise

magnetocardiography (MCG)

magnetoencophalography (MEG)

SQUID noise

Frequency

Challenges:• small signals• large noise level• no cooling

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Natural and Composite Magnetoelectric Effects


Composite magnetoelectric effectcan be described as a product property:

magnetostrictive property * coupling* piezoelectric property

Composite Magnetoelectric Effect in Thin Films

ThinFilms 2016, Singapore, July 13th, 2016 30

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General Features of Magnetoelectric Thin Film Sensors

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current noise ~ 1/f

voltage noise

amplification by mechanical resonancefrequency dependent noise sources

linear response over orders of magnitudeLOD minimum @ mechanical resonance

Appl. Phys. Lett. 2016(in press)

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Plate Capacitor vs. Interdigital Electrodes: αME


approximately factor 10 in effect size

-2 -1 0 1 2

0

500

1000

1500

2000

Bbias / mT

α /

mV/

Oe

-2 -1 0 1 2

0

50

100

150

200

Bbias

/ mT

α /

mV/

Oe

Appl. Phys. Lett., 103, 032902 (2013).

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Magnetoelectric Effect vs. Magnetic Bias Field

• Magnetoelectric effect directly related to magnetostrictivesusceptibility (piezomagnetic coefficient)

• Magnetic bias field needed: at H=0 ME effect almost vanishes

-4 -2 0 2 4-6

-4

-2

0

2

4

6

b (M

Pa)

µ0H (mT)-4 -2 0 2 4

dλ/d

H (a

.u.)

µ0H (mT)

-500

-250

0

250

500

αM

E (V

/cm

Oe)

bdλ/dHαME


Mag

neto

stric

tionλ

(a.u

.)

λ

ThinFilms 2016, Singapore, July 13th, 2016 34

Biased ME Sensors

External bias: • limits miniaturization• crosstalk in sensor arrays• adds additional noise source

X

Y

sensor array 3d sensor

HEB H

MFMAFM

FMAFM

TNéel < T < TCurie

T < TNéelExchange Coupling

Intrinsic bias via exchange bias:

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Si

Ta

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Exchange Biased Magnetoelectric Sensor

CuMnIr

magnetostrictive

AlN

TaCuMnIr

magnetostrictive

••• x times

AlN 2 µm

650 µm x 3 mm x 25 mm Si cantileverwith trench

Fe50Co50 or Fe70.2Co7.8Si12B10 tFM

Mn70Ir30 7 nm (111) textured

Cu 3 nmTa 7 nm

seed

total thickness of magnetostrictive layerapprox. 1 µm


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-5 0 5

-100

-50

0

50

100

αΜΕ

/ V /

cmO

e

µ0H / mT)

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Exchange Biased Magnetoelectric Sensor

Fe70.2Co7.8Si12B10

f = 1.2kHz

8 x (tFM = 130nm)<-> 1040nm FeCoSiB


Nature Materials 11 (2012), 523-529.

no bias field needed

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Tuning Fork Magnetoelectric Sensor


• vibrations cancel out• magnetic field induced strains add up

• high LoD in less shielded environments

single sensor

tuning fork

Sensors and Actuators A: 237 (2016), 91-95

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- Introduction




Outline


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- Superelastic TiNi thin films show unique properties

- Fabrication methode allows realization of thin film medicalimplants with new features that open up new application areas

- ME composites show a LoD below the pT range (at resonance)

- Exchanged biased sensors do not require a magnetic bias fieldfor operation

- Tuning fork sensors are less sensitive to vibrations and acousticnoise

Summary

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Acknowledgements


Team in Kiel, especially:

Dr. Rodrigo Lima de Miranda(CEO Acquandas)- SMA Technology -

Dr. Dirk Meyners- ME Composites -

Prof. Manfred Wuttig, University of Maryland

Smart&ThinFilms& for MedicalApplications · ) Fabrication methode allows realizationof6thin film6...

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