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GBM8320 Dispositifs Médicaux Intelligents
Electrodes – Part II
Mohamad Sawan et al. Laboratoire de neurotechnologies Polystim !
!!
http://www.cours.polymtl.ca/gbm8320/!mohamad.sawan@polymtl.ca!
M5418!
April 2013
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Integrated Microelectrodes : Course outline • Introduction
− Electrogenic cell
• Electrode/electrolyte interface − Electrical double layer − Half-cell potential − Polarization − Electrode equivalent circuits
• Biopotential electrodes − Body surface electrodes − Internal electrodes − Implantable electrodes − Electrode arrays − Microfabricated electrodes − Microelectrodes.
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Metal-plate electrodes Large surface: Ancient, therefore
still used, ECG • Metal disk with stainless
steel; platinum or gold coated • EMG, EEG • Smaller diameters • Motion artifacts • Disposable foam-pad: Cheap!
(a) Metal-plate electrode used for application to limbs. (b) Metal-disk electrode applied with surgical tape. (c) Disposable foam-pad electrodes, often used with ECG
Commonly used biopotential electrodes Body-surface electrodes • Metal-plate ; • Suction ; • Floating ; • Flexible.
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Double-sided Adhesive-tape ring
Insulating package Metal disk
Electrolyte gel in recess
(a) (b)
Reusable
(c)
Snap coated with Ag-AgCl External snap
Plastic cup
Tack
Plastic disk
Foam pad Capillary loops
Dead cellular material
Germinating layer
Gel-coated sponge Disposable
Commonly used biopotential electrodes Metal plate electrodes (Floating electrodes)
(a) Recessed electrode with hot structure;
(b) Cross-sectional view of electrode (a)
(c) Cross-sectional view of another disposable electrode.
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• Body contours are often irregular
• Regularly shaped rigid electrodes may not always work
• Special case : infants
• Used materials - Polymer or nylon with silver - Carbon filled silicon rubber
(Mylar film).
(a) Carbon-filled silicone rubber electrode. (b) Flexible thin-film neonatal electrode. (c) Cross-sectional view of the thin-film electrode in (b)
Commonly used biopotential electrodes Flexible electrodes
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• Needle and wire electrodes for percutaneous measurement of biopotentials:
• Insulated needle electrode
• Coaxial needle electrode.
• Bipolar coaxial electrode.
• Fine-wire electrode connected to hypodermic needle, before being inserted.
• Cross-sectional view of skin and muscle, showing coiled fine-wire electrode in place.
Internal Electrodes
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Integrated Microelectrodes : Course outline • Introduction
− Electrogenic cell
• Electrode/electrolyte interface − Electrical double layer − Half-cell potential − Polarization − Electrode equivalent circuits
• Biopotential electrodes − Body surface electrodes − Internal electrodes − Implantable electrodes − Electrode arrays − Microfabricated electrodes − Microelectrodes.
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Implantable electrodes
• Electrodes for detecting fetal ECG (Use of intracutaneous needles)
• Suction electrode
• Helical electrode
• Electrodes for Cardiac stimulation.
• Electrodes for detecting biopotentials
• Wire-loop electrode
• Platinum-sphere cortical surface potential electrode
• Multielement depth electrode.
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Implantable neural electrodes
• ENG measurement (three contacts) • Stimulation (2 contacts)
• Cuff electrodes
• Helical electrodes • Pins electrodes
• Multicontacts electrodes • etc
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Integrated Microelectrodes : Course outline • Introduction
− Electrogenic cell
• Electrode/electrolyte interface − Electrical double layer − Half-cell potential − Polarization − Electrode equivalent circuits
• Biopotential electrodes − Body surface electrodes − Internal electrodes − Implantable electrodes − Electrode arrays − Microfabricated electrodes − Microelectrodes.
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Microfabricated Electrode Arrays
• Examples of microfabricated electrode arrays:
(a) One-dimensional plunge electrode array (b) Two-dimensional array, and (c) Three-dimensional array.
(c)
Tines
Base
Exposed tip
Contacts Insulated leads
(b)
Base
Ag/AgCl electrodes
Ag/AgCl electrodes
Base Insulated leads
(a)
Contacts
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Microelectrodes based on microelectronics
• Beam-lead multiple electrodes : Wise, et al.
• Multielectrode silicon probe : Drake et al.
• Multiple-chamber
electrode : Prohaska et al.
• Peripheral-nerve electrode : Edell.
(b)
(d)
(a)
(c)
Bonding pads
Silicon probe
Exposed electrodes
Insulated lead vias
Lead via
Electrode
Silicon probe
Miniature insulating chamber Hole
Channels Silicon chip
Contact metal film
Si substrate Exposed tips
SiO2 insulated Au probes
Various applications
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Microelectrodes based on microelectronics
An 8-probe array of 64 contacts each
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Microelectrodes Micromachining
Robofil 2030
Metalic arrays of electrodes
• Wire-EDM cut • Surface electropolish • Oxalic acid attack • Platinum deposition • Epoxy base • Support Grinding • Assembly.
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• Surface electropolish • Oxalic acid attack • Platinum deposition • Epoxy base • Support Grinding • Assembly.
Microelectrodes Micromachining
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Integrated Microelectrodes : Course outline • Introduction
− Electrogenic cell
• Electrode/electrolyte interface − Electrical double layer − Half-cell potential − Polarization − Electrode equivalent circuits
• Biopotential electrodes − Body surface electrodes − Internal electrodes − Implantable electrodes − Electrode arrays − Microfabricated electrodes − Microelectrodes.
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Structure of a metal microelectrode for intracellular recordings.
Structures of two supported metal microelectrodes: (a) Metal-filled glass micropipet (b) Glass micropipet or probe, coated with metal film.
Microelectrodes Intracellular recordings : The glass micropipet
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• The electrical activity of cells can be recorded without disrupting the cell membrane using extracellular recording techniques
• For extracellular recordings, the cells are located directly on top of a transducing element, which is, in most cases, either a metallic electrode or an open-gate transistor
• When electrical activity or a so-called action potential in a cell occurs, ions flow across the cell membrane within msec.
• Ions sensitive transistors can be used to transduce the cells activity.
Microelectrodes Extracellular recordings (in vivo)
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Extracellular Recording (in vivo)
• When a cell is close to a transducer, the moving ions generate an electric field or voltage, which can be recorded by the metallic microelectrode or field-effect transistor
• Extracellular recordings are non-invasive (no puncturing of the cell membrane)
• Models: - Metal electrode - Open field-effect transistor.
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Why use IC and CMOS technology
• Two main advantages in using integrated-circuit (IC) or CMOS technology: – Connectivity: larger numbers of transducers or electrodes can be
addressed by on-chip multiplexing architectures
– Signal quality; the signal is conditioned right at the electrode by means of dedicated circuitry units (filters, amplifiers)
• The use of CMOS technology allows to realize a large number of electrodes on a small system chip
• On-chip microelectronics, as provided by the use of IC or CMOS technology, translate into system capability: signal conditioning can be performed on-chip, ensuring that weak neural signals are faithfully recorded;
Summary
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Why use IC and CMOS technology
• A CMOS system also enables a bidirectional communication via the electrodes (stimulation and recording);
• Smart switching schemes allow for stimulating the cell ensemble via an arbitrarily selectable set of electrodes, all while recording from other electrodes uninterruptedly during stimulation
• On-chip analog-to-digital conversion means that such chip produces a robust signal that may be easily manipulated and transferred without compromising its information content
• Moreover, the use of on-chip electronics allows for the monolithic integration of the complete system on a single chip, which leads to small system dimensions and low power consumption, a key requirement for implantable devices
Summary (Cont’d)
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Why use IC and CMOS technology
• The use of multiplexers enables the integration of a large number of electrodes or transducers so that measurements at high spatiotemporal resolution become feasible
• Traditional Microelectrode arrays (MEAs) without multiplexers usually offer 64 electrodes with each electrode needing a connection to external circuitry, which adds parasitic capacitance and attenuates the weak signals
• CMOS-based MEAs comprise up to 16,384 electrodes and the needed addressing circuitry on the same chip
• A disadvantage of CMOS ICs is that silicon is not transparent to visible light in contrast to standard cell culture substrates used in biology
Summary (Cont’d)
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IC and CMOS technology: The drawbacks
• The IC or its components can corrode upon operation and long-term exposure to liquids (salt water)
• A good packaging solution is needed: – To protect the IC against metabolism products
– To prevent the cells from being poisoned or disturbed by toxic materials released by the IC, such as the CMOS metal aluminum that dissolves in saline solution.
Notes : • Make a better electrode • Research different electrode technologies
– Ion selective, immunosensors, ISFET, electrochemical – MEMS microelectrode technologies – Polymer based electrodes..
Summary (Cont’d)
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