BME 552 - Class 2 2009

BME 552 - Class 2 2009 - 1/22/2009 1 BME 552 Device-Tissue...

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Unformatted text preview: 1/22/2009 1 BME 552 Device-Tissue Interface I Electrochemistry of Bioelectrodes January 23, 2008 Todays Lecture HW related to this lecture posted on line Overview of next 5 lectures Overview of next 5 lectures Summary of this class Two student paper reviews Newman (Alex) Franks (Nick) 1/22/2009 2 Overview of next 5 classes We will examine the signal path from current generator to neurons (not in that order) neurons (not in that order) Class 2-3 Electrodes/Packaging Class 4-5 Stimulating neural activity: short, medium, long-term effects Class 5 Circuits for neural stimulation Class 6 applications of neural stim: retina, deep brain stimulation, peripheral nerve For now, assume circuit has power and data source Overview of Class 2 Electrode Basics Half- cell potential Double Laye Double Layer Capacitive vs. Faradaic current Pertubation from resting potential Instrumentation (three electrode method, ref electrode) Impedance Impedance circuit modeling Impedance vs. size behavior Cyclic Voltammetry Electrode Surface Area Electrode characterization Electrode Materials Pseudo capacity of platinum Valence Change Oxides Capacitive electrodes Conducitng polymers 1/22/2009 3 Todays Reading Material Merrill Paper, section 1 Newman Franks Electrodes Electrodes are pieces of metal on which an electrochemical reaction is occurring* an electrochemical reaction is occurring An anode is an electrode on which an anodic or oxidation reaction is occurring* A cathode is an electrode on which a cathodic or reduction reaction is occurring* Bioelectrodes contact the body to sense biopotentials or stimulate nerve and/or muscle *Kinetics of Corrosion, Bob Cottis, 1997 1/22/2009 4 Big Picture Electrodes are important because they will have a significant impact on system power Reducing electrode impedance saves on power Control the chemical reactions at the interface allow safe stimulation The interaction between metal or metal-oxides and aqueous solutions is complex. You could spend a whole semester (career?) on this topic, but it can be simplified for the purposes of neural implant design We will look at the complex general situation of metal- solution interface, then focus on the specific problem of electrodes for neural stimulation and recording Nice description of half-cell potential When a metal contacts electrolyte, chemical reactions proceed at the interface These result in the exchange of charge and the development of an electrical potential When electrical and chemical forces are chemical forces are equal, this is the half-cell potential, often called equilibrium, resting, or open circuit potential 1/22/2009 5 Nernst Equation Governs Half-Cell Potential E = E o + (RT/nF)*ln(C o /C r ) Each reaction (O + ne- <-> R) will have its own equilibrium potential Multiple reactions will result in the...
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BME 552 - Class 2 2009 - 1/22/2009 1 BME 552 Device-Tissue...

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