Post on 17-Jun-2020
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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
- 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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Smart Materials
ThinFilms 2016, Singapore, July 13th, 2016
MagneticFieldorStress
ElectricFieldor Stress
Temperatureor Stress
Ferroic Properties
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Smart Material Thin Films
ThinFilms 2016, Singapore, July 13th, 2016
• 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
ThinFilms 2016, Singapore, July 13th, 2016
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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- Introduction
- Superelastic TiNi Thin Films for Medical Devices
- Stent Technology- Thin Film Processing Route- Unique Features of Thin Film Devices- Examples of Applications
- Magnetoelectric Composites for Biomagnetic Field Sensors
- Conclusions and Outlook
Outline
ThinFilms 2016, Singapore, July 13th, 2016
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Shape Memory Effects
ThinFilms 2016, Singapore, July 13th, 2016
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
ThinFilms 2016, Singapore, July 13th, 2016
D. Stöckel, NDC
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Stent Fabrication: Traditional Process Flow
ThinFilms 2016, Singapore, July 13th, 2016
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.)
ThinFilms 2016, Singapore, July 13th, 2016
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
ThinFilms 2016, Singapore, July 13th, 2016
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
ThinFilms 2016, Singapore, July 13th, 2016
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
ThinFilms 2016, Singapore, July 13th, 2016
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
ThinFilms 2016, Singapore, July 13th, 2016
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
ThinFilms 2016, Singapore, July 13th, 2016
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
ThinFilms 2016, Singapore, July 13th, 2016
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
ThinFilms 2016, Singapore, July 13th, 2016
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
ThinFilms 2016, Singapore, July 13th, 2016
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
ThinFilms 2016, Singapore, July 13th, 2016
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
ThinFilms 2016, Singapore, July 13th, 2016
strut thickness: 30 µm
internal structure hight: 10 µm
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Transcatheter Aortic Valve Implantation
ThinFilms 2016, Singapore, July 13th, 2016
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
ThinFilms 2016, Singapore, July 13th, 2016
Leaflet Forming & Annealing
Forming Annealing
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Patterned Leaflets
ThinFilms 2016, Singapore, July 13th, 2016
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
ThinFilms 2016, Singapore, July 13th, 2016
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
- Superelastic TiNi Thin Films for Medical Devices
- Magnetoelectric Composites for Biomagnetic Field Sensors
- Principle- General Features- Exchange-biased Sensors- Tuning Fork Sensors
- Conclusions and Outlook
Outline
ThinFilms 2016, Singapore, July 13th, 2016
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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
ThinFilms 2016, Singapore, July 13th, 2016
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Magnetic Fields in Medicine
ThinFilms 2016, Singapore, July 13th, 2016
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
ThinFilms 2016, Singapore, July 13th, 2016
Composite magnetoelectric effectcan be described as a product property:
magnetostrictive property * coupling* piezoelectric property
Composite Magnetoelectric Effect in Thin Films
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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
ThinFilms 2016, Singapore, July 13th, 2016
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
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Mag
neto
stric
tionλ
(a.u
.)
λ
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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
ThinFilms 2016, Singapore, July 13th, 2016
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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
ThinFilms 2016, Singapore, July 13th, 2016
Nature Materials 11 (2012), 523-529.
no bias field needed
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Tuning Fork Magnetoelectric Sensor
ThinFilms 2016, Singapore, July 13th, 2016
• 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
- 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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- 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
ThinFilms 2016, Singapore, July 13th, 2016
Team in Kiel, especially:
Dr. Rodrigo Lima de Miranda(CEO Acquandas)- SMA Technology -
Dr. Dirk Meyners- ME Composites -
Prof. Manfred Wuttig, University of Maryland