Surface Modification of Neural Electrode with Electrodeposited - - PowerPoint PPT Presentation

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2019 US-Korea Nanoforum

Surface Modification of Neural Electrode with Electrodeposited Nanoparticles for Stimulation Performance Enhancement

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Application Potentials

• Applications for neurological disorders

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Multi-electrode Array (MEA)

• Definition

– MEAs or microelectrode arrays are devices that contain multiple micro plates – Extracellular recording & stimulation

– 1st MEA by Thomas Jr. (1972) & commercialized by Multi-Channel Systems (1996)

• Application potential

Disease model Drug screening Cell-based sensors Network modelling Learning

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Specifications

• Requirements for neural-computer bi-directional interface

Recording

• High SNR: » 5
• Low noise
• Long-term viability
• Temporal resolution
• Electrode size: <30 μm

– Single unit recording

• High # of channel: ~256 CH
• Intimate contact
• Spike sorting

Stimulation

• Charge injection capacitance: »
• Charge injection limit: » 1 mC/cm2
• Charge injection efficiency: ~1
• Damage threshold: 1 mC/cm2
• Long-term durability
• Field focality

Decoding Encoding

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Extracellular Recording & Stimulation

• Recording issue

– Impedance control for reduction of interfacial noise

• Stimulation

– Charge storage capacitance – Charge injection limit

• Electrochemical window: -0.64 ~ 0.75 V (vs. SCE)*
• Safety limit: ~ 1 mC cm-2 **

– Material dependence

• Common requirement

– Increase in surface area

• Long-term reliability issues

Ne.e = √4 k T Re(Ze

) Δf

Ze

  1 / As 2

𝑟𝑑 = 𝐷𝑒𝑚 ∆𝑊

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Pt black 1980 Pine

Nanomaterials for surface modification

TiN 1998 Egert IrOx 2002 Weiland PEDOT 2004 Xiao Au NW 2007 Yoon CNT 2009 Shein CP 2010 Abidian NPG 2010 Seker Au nanoflake 2010 Kim NP Pt 2010 Park Layered Au NPs 2012 Zhang CNT + Au NP 2014 Zhang PEDOT + CNT 2014 Castagnola Ir-NiO 2014 Stilling

from Chapman & Seker (2017)

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Primary neuronal cell culture

• SD rat

Incubator

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Electrode Materials for Neural Interface

• Five criteria*

– Tissue response – Allergic response – Electrode-tissue impedance – Charge injection capability – Radiographic visibility

• Metals

– List of biocompatible metals

• Au, Pt, Pt-Ir, stainless steel, Pd, W, Pt-Rh, Cr-Mo, Au-Ni-Cr, Au-W, Ti, IrOx,

– List of improper metals

• Fe, Cu, Ag, Co, Zn, Mg, Mn, Al, Bi, Cd, Ni

– Hierarchy of allergenic metals

• Be > Hg > Cu > Au > Ag

– Best candidates as implants

• Au, Pt, W, Rh, Pd, Ti

– Choice for stimulating electrodes

• Pt, Pt-Ir, Au, W, Rh
• Non-metals

– Organic materials

• CNT, conducting polymers

– Inorganic materials

• ITO, IrOx,

Nanostructures

• Nanostructures

– Nanoparticles – Nanorods – Nanowires – Nanoflakes – Nanoporous structures

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Fabrication of MEA

• Bi-layer lift-off resist technique

– Lift-off resist + Negative photoresist + Sputter deposition of SiO2

Y.H. Kim et al., Optimization of bi-layer structure formation and SiO2 sputter-deposition process for fabrication of gold multi-electrode array, RSC Advances 5, 6675 (2015) Y.H. Kim et al., Fabrication of multi-electrode array platforms for neuronal interfacing with bi-layer lift-off resist sputter deposition, J. Micromech.

• Microeng. 23, 097001 (2013)

Excellent uniformity in impedance

ITO Au Lift-off resist Negative PR ф~30 μm

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Electrodeposition of metallic nanoparticles

• Typical 3-electrode configuration

– MEA electrode (working), Pt foil (counter), AgAgCl (reference)

• Electrochemical characterization

– Electrodeposition – Electrochemical impedance spectroscopy (EIS) – C-V – voltage transient

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• List of electrodeposited metallic nanostructures

Au NPs Pt NPs Au-Pt NPs Pt black NPG

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20 40 60 20 40

• 50
• 40
• 30
• 20
• 10

10 20 30 40 50

Time(s) Amplitude(V)

10 20 30 40 50 60

• 50
• 30
• 10

10 30 50

Time(s) Amplitude(V)

10 20 30 40 50 60

• 50
• 30
• 10

10 30 50

Time(s) Amplitude(V)

44.180 44.185 44.190 44.195

• 200
• 100

100 200

Amplitude (V) Time (sec)

30 40 50 60

• 200
• 100

100 200

Amplitude (V)

10 20 30

• 200
• 100

100 200

Amplitude (V)

* *

3.000 3.005 3.010 3.015

• 200
• 100

100 200

Amplitude (V) Time (sec)

* *

10

• 1

10 10

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lZl (Ohm) Frequency (Hz)

Bare gold Au NPs Au-Pt Nps

Au Au NP Au-Pt NP Pt NP

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Modification with nanoporous Au (NPG)

Au MEA Electro-co-deposition

• f Ag:Au on Au

Chemical leaching

• f Ag in conc.

Nitric acid @ 70 ℃ Electrodeposition of IrOx on NPG NPG

Y.H. Kim et al., In vitro extracellular recording and stimulation performance of nanoporous gold-modified multi- electrode arrays, J. Neural Eng. 12, 066029 (2015) Y.H. Kim et al., Iridium oxide-electrodeposited nanoporous gold multielectrode array with enhanced stimulus efficacy, Nano Lett. 12, 066029 (2016)

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10

• 1

10 10

1

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lZl () Frequency (Hz)

bare Au electrode Au NP-modified electrode nanoporous Au-modified electrode

Au Au NP NPG Au NPG IrOx/Au IrOx/NPG

• 0.9
• 0.6
• 0.3

0.0 0.3 0.6 0.9

• 0.020
• 0.015
• 0.010
• 0.005

0.000 0.005 0.010 0.015 0.020 Current (A/cm2) V vs. Ag/AgCl, sat'd KCl

100-cycled IrOx/Au 50-cycled IrOx/NPG 70-cycled IrOx/NPG 100-cycled IrOx/NPG NPG

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• Cont’d

– Cathodic charge storage capacitance (cCSC) vs. charge injection limit – Derived from voltage transient measurement – Water window, -0.6 V

– The charge injection limit is defined as the maximum quantity of charge that an electrode can inject before reaching the water electrolysis potential

0.0 0.1 0.2 0.3 0.4 0.5

• 9
• 6
• 3

3 6 9

V vs. Ag/AgCl, Sat'd KCl Time (ms)

Time duration 100s 50 A 100 A 300 A 500 A 1000 A Material cCSC (mC/cm2) Charge injection limit (mC/cm2) Efficiency ( CIL/cCSC) Pt 0.1-0.35, 0.05- 0.15 Au 0.27 Pt black 16 TiN 0.87 PEDOT 2.30.6 Roughed Pt >8.9 1.0 CNT 1.6 1-1.6 EIROF 23.54, 16, 25 1.27 0.054 SIROF 36.15, 54, 31.56.6 2-3, 4.61 0.13

NPG 1.0 0.98 ~1 IrOx/NPG 8.8 2.3 0.26

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• Stimulation performance

NPG IrOx/NPG

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• Durability test
• Excellent mechanical durability
• Some MEA manufacturers recommend

‘Do not apply sonication’

• 8 hours a day, 25th day of use
• Excellent anti-corrosion ability ?

200 400 600 800 1000 1200 0.1 0.5 1 2 3 4 5 6 7 1st DAY 25th DAY

fEPSPs peak amplitude (µV)

Stimulation intensity (V)

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• Flexibility of LOR passivation technique

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NEXT

• Mushroom-type MEA for slice tissue interfacing
• LOR passivation + electro-co-deposition of Ag:Au alloy

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64 & 128 CH MEA System

• FPGA-based 128 CH bi-directional MEA system

MEA

• 128 channel recording (4.16 MSamples/s)
• Real-time online spike sorting (feature

learning & extraction capability)

• 8 channel arbitrary voltage and current

stimulation

• J. Park et al., A 128 channel FPGA-based Real Time Spike Sorting Bidirectional

Closed-loop Neural Interface System, IEEE Transactions on Neural Systems & Rehabilitation Engineering, Vol. 25, 2227-2238 (2017). Analog front-end

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All metal-oxide-based MEAs

A ITO cleaning B ITO etching C PR stripping D Bi-layer coating E Overhang formation F SiO2 deposition G Lift-off ITO Positive PR Lift-off resist Negative PR SiO2 H ITO NW growth I ITO etching J PR stripping K IrOx electrodeposition IrOx

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Fabrication of flexible electrode

• Fluoropolymer-based flexible electrode

– Fluorinated ethylene propylene (FEP): m. p. ; Tg – FEP plasma treatment and thermal pressing beyond the meting temperature – Solely composed of FEP and Au without adhesion metal

FEP FEP FEP FEP

RF plasma pretreatment Cr & Au patterning RF plasma treatment Thermal pressing RF plasma etching Cr etching Impedance control Al patterning

Ar plasma O2 plasma

Y.H. Kim et al., Fluoropolymer-based flexible neural prosthetic electrodes for reliable neural interfacing, ACS Appl. Mater Interfaces, Vol. 9,43420-43428 (2017).

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16-CH ECoG electrode array

• Excellent chemical stability

– Longer than an hour in conc. Nitric acid @ 70 ℃

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Co-work Program

• Reliability test with primate platform

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