Smart Thin Films for Medical Applications

Transcription

1 Christian-Albrechts-Universität zukiel Smart Thin Films for Medical Applications Eckhard Quandt Institute for Materials Science Faculty of Engineering University of Kiel Germany Outline - Introduction - Superelastic TiNi Thin Films for Medical Devices - Magnetoelectric Composites for Biomagnetic Field Sensors - Conclusions and Outlook 2 1

2 Outline - Introduction - Superelastic TiNi Thin Films for Medical Devices - Magnetoelectric Composites for Biomagnetic Field Sensors - Conclusions and Outlook 3 Smart Materials Magnetic Field or Stress Electric Field or Stress Temperature or Stress Ferroic Properties 4 2

3 Smart Material Thin Films Inherent effects can be down-scaled to micrometer or nanometer dimensions Transduceelectromagnetic and mechanical energies mechanisms for actuators and sensors Combination of different effects natural or composite multiferroics Cost-effective batch fabrication compatible to MEMS/NEMS 5 Cleanroom: 350 m 2 Kieler Nanolabor Thin Film Technology Magnetron Sputtering, Evaporation, PLD, PECVD Lithography Mask Aligner, E-Beam, FIB Etching Ion Beam Etching, Reactive Ion Etching, Bosch Process Wet Etching 6 3

4 Outline - 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 7 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 8 4

5 Stent Technology D. Stöckel, NDC 9 Stent Fabrication: Traditional Process Flow NiTi-Tube Laser-Beam Cutting Deburring Honing Heat Treatment Blasting Electropolishing Limits: Minimum tube thickness (approx. 50 µm) Minimum feature size (approx. 20 µm) 10 5

6 Strokes (#4 Killer in the U.S.) Ischemic Stroke ~ 300 of people (i.e. ~ 725,000 strokes / year (US)) ~ 15% mortality rate ~ 15 30% permanent handycapped Intercerebral Hemorrhage: ~ 30 of people in the developed world are affected Subarachnoid Hemorrhage (Cerebral Aneurysms): ~ 15 von people (i.e. ~ / year (US)) high mortality rate è Development of new technology essential 11 Planar Thin Film Process (1) TiNi Thin Film (2) Photo Resist / (3) Cu Sacrificial Layer UV Lithography TiNi Etching Process (4) Cu Etching (5) Removal of 700 (6) µmtini Deposition Photo Resist (4) (7) Sacrificial Layer Wet Etch Advanced Engineering Materials 15 (2013), Photo Resist TiNi Cu Substrate 20 µm (7) 12 6

7 Workflow for Thin Film Acquandas CAD Design UV- Lithography Sputtering Process Heat Treatment / Shape setting Sample Release by wet-chemical Etching Wafer after Sputtering Process 13 Improved Mechanical Properties Fracture strains of up to ~40% Alternating strains of up to ±1.5% σ / MPa T= 35 C Acquandas thick film (laser cut & surface finished) Conventional sheet metal (laser cut & surface finished) ε / % Alternating Strain / % NiTi Film Fracture NiTi Film Run out (10 Mio. cycles) NiTi Standard Fracture NiTi Standard Run out (10 Mio. cycles) Mean strain / % è Improvement of mechanical properties by a factor of 2.5 Advanced Engineering Materials 15 (2013), Journal of Materials Engineering and Performance 23, (2014) 14 7

8 Fatigue in Superelastic TiNiCu Films stress / MPa a) 400 near- aquiatomic b) Ti- rich Ti 51 Ni 36 Cu 13 Ti 54 Ni 34 Cu T Test = 78 C T Test = 70 C A f = 72 C A f = 65 C strain cycle 1 cycle 10 cycle 50 cycle 100 cycle strain Aquiatomic TiNi similar (even worse) compared to aquiatomic TiNiCu Functional and structural fatigue behavior is strongly influenced by the Ti content Science 348 (2015) Ultra-low Fatigue in Superelastic Ti-rich TiNiCu Films Fatigue test of the full superelastic transformation at 10 Hz stress / MPa Ti 54 Ni 34 Cu 12 T Test = 70 C A f = 65 C 0 0,000 0,005 0,010 0,015 0,020 strain cycle 1 cycle 200 cycle 10 7 No functional fatigue for 10 7 full superelastic cycles Science 348 (2015)

9 Crystallographic Compatibility middle eigenvalue (λ 2) Cofactors (CCI and CCII) tru det U 2 a a Ucof{ U I} n = 0 J. Cui et al., Nature Materials 5, (2006) Y. Song et al., Nature 502, (2013) The low fatigue Ti-rich sample satisfies the cofactor conditions better than the near equiatomic sample Science 348 (2015) Epitaxy in Phase Transformation Occurrence of Ti 2 Cu precipitates only in the Ti-rich TiNiCu thin film Science 348 (2015)

10 Ti 54 Ni 34 Cu 12 Advantages of Thin Film Technology T Test = 70 C stress / MPa A f = 65 C cycle 1 cycle 200 cycle ,000 0,005 0,010 0,015 0,020 strain Miniaturization Complex Design Options Fatigue Life Material Combination Cost effective (Batch process) Integration of Functions Rapid Prototyping Micropatterned Surfaces Excellent Biocompatibility Simple Alloy Optimization 19 Mechanical Thromboembolectomy Deepak S Nair, MD (Vascular Neurology INI Stroke Center, OSF Saint Francis Medical Center)

11 Thin Film Stent Retriever strut thickness: 30 µm internal structure hight: 10 µm 21 Transcatheter Aortic Valve Implantation Minimal invasive implantation Biological valve Developed to treat high risk patients 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 µm NiTi thin film leaflets Long durability High crimpability (superelasticity) Leaflet thickness µm Edwards Lifescience 22 11

12 Fabrication of NiTi Thin Film Leaflets Leaflet Forming & Annealing Forming Annealing 23 Patterned Leaflets µm 24.6 µm 84.9 µm 10 mm Fabrication of structured heart valve leaflets Diameter: 20 mm Height: 18 mm Film thickness: 10 and 15 µm Cell seeding of smooth muscle cells for 7 days 24 12

13 Performance in Comparison to Biological Valve TiNi Full 10 µm TiNi Mesh 10 µm Opening Phase Closing Phase Opening cycle of heart valves at a heart rate of 70 bpm Porcine 25 Outline - 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 26 13

14 Focus of the Collaborative Research Centre 1261 Development of a biomagnetic interface to measure the magnetic fields of heart and brain currents magnetoelectric composites (magnetostrictive, piezoelectric components) as magnetic field sensors magnetoelectric sensor (array) systems medical applications of the biomagnetic interfaces 27 Magnetic Fields in Medicine earth magnetic field urban noise Challenges: small signals large noise level no cooling magnetocardiography(mcg) magnetoencophalography(meg) SQUID noise Frequency 28 14

15 Natural and Composite Magnetoelectric Effects Composite magnetoelectric effect can be described as a product property: magnetostrictive property * coupling * piezoelectric property 29 Composite Magnetoelectric Effect in Thin Films 30 15

16 General Features of Magnetoelectric Thin Film Sensors frequency dependent noise sources amplification by mechanical resonance current noise ~ 1/f voltage noise LOD mechanical resonance linear response over orders of magnitude Appl. Phys. Lett (in press) 31 Plate Capacitor vs. Interdigital Electrodes: α ME α / mv/oe α / mv/oe B bias / mt B bias / mt approximately factor 10 in effect size Appl. Phys. Lett., 103, (2013)

17 Magnetoelectric Effect vs. Magnetic Bias Field Magnetostriction b (MPa) λ (a.u.) λb dλ/dh α ME µ 0 H (mt) dλ/dh (a.u.) Magnetoelectric effect directly related to magnetostrictive susceptibility (piezomagnetic coefficient) Magnetic bias field needed: at H=0 ME effect almost vanishes 0 α ME (V/cmOe) 33 Biased ME Sensors External bias: limits miniaturization crosstalk in sensor arrays adds additional noise source X Y M sensor array Intrinsic bias via exchange bias: FM AFM 3d sensor T Néel < T < T Curie H EB H FM AFM T < T Néel Exchange Coupling 34 17

18 Exchange Biased Magnetoelectric Sensor magnetostrictive Fe 50 Co 50 or Fe 70.2 Co 7.8 Si 12 B 10 t FM MnIr Cu Ta x times Mn 70 Ir 30 7 nm Cu 3 nm Ta 7 nm (111) textured seed magnetostrictive MnIr Cu Ta AlN Si total thickness of magnetostrictive layer approx. 1 µm AlN 2 µm 650 µm x 3 mm x 25 mm Si cantilever with trench 35 Exchange Biased Magnetoelectric Sensor Fe 70.2 Co 7.8 Si 12 B 10 8 x (t FM = 130nm) <-> 1040nm FeCoSiB f = 1.2kHz α ΜΕ / V / cmoe µ 0 H / mt) no bias field needed Nature Materials 11 (2012),

19 Tuning Fork Magnetoelectric Sensor single sensor vibrations cancel out magnetic field induced strains add up high LoD in less shielded environments Sensors and Actuators A: 237 (2016), tuning fork 37 Outline - Introduction - Superelastic TiNi Thin Films for Medical Devices - Magnetoelectric Composites for Biomagnetic Field Sensors - Conclusions and Outlook 38 19

20 Summary - Superelastic TiNi thin films show unique properties - Fabrication methode allows realization of thin film medical implants 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 field for operation - Tuning fork sensors are less sensitive to vibrations and acoustic noise 39 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 40 20