Bio Materials Tutorial

Biomaterials Tutorial

Bioelectrodes

Floyd Karp
University of Washington Engineered Biomaterials

Bioelectrodes function as an interface between biological structures and electronic systems.  Electrical activity within the biological structure is either sensed or stimulated.  The electrical systems are either passively sensing (measuring) or actively stimulating (inducing) electrical potentials within the biological structure or unit.

Electrical currents are generated by many biological structures.  Currents give rise to potential differences that can be measured using electrodes and can be interpreted to gain insight in the functioning of the source structure. Conversely, current can be applied to the biological structure through electrodes to affect the target.

The same electrode may function either passively or actively, depending on the purpose and the electronic system controls.  An example seen on TV is the large defibrillation paddles used by paramedics to resuscitate people in cardiac distress.  When the paddles are applied to a patient, the electrical system is programmed to first passively sense the electrical activity (or lack of) within the heart. Then the electrical system uses algorithms to determine if a stimulation (shock) is required, and finally to provide the appropriate electrical stimulation.

The size of bioelectrodes ranges from microscopic intra-cellular research electrodes to large (3 x 5-inch) defibrillation paddles.

Most bioelectrodes are made of metal, but the microscopic intra-cellular research electrodes are glass capillary tubes filled with a conductive saline solution.

The following table gives some examples of applications, characteristics, and materials.

Common Bioelectrode Application

Key characteristics determining selection of material

Material

Surface Finish

External defibrillation of heart – Paddles

safety, convenience of cleaning

stainless steel

passivated*

External defibrillation of heart – Disposable patch

safety, reliability during patient transport

tin

oxide*

Internal cardiac defibrillation and/or pacemaking

minimal long-term foreign body reaction

stainless steel

tip is platinum plated and may have thin iridium oxide coating

 Electroencephalography (brain-wave sensing)

safety, comfort, ease of application and removal

stainless steel

passivated*

Intra-cellular recording

small size, cellular biocompatability

buffered solutions in glass capillary tube

ultra-clean

Neurological implantation

stability and minimal long-term foreign body reaction

gold, platinum

iridium oxide

Capital punishment with the “electric chair”

reliability, convenience of cleaning

stainless steel

passivated

Bone remodeling (healing following fracture)

safety, comfort, ease of application and removal

stainless steel

passivated*

* has a conductive gel applied

Perhaps one of the most infamous applications of bioelectrodes is the “Electric Chair,” used for executing criminals in certain localities.  A voltage is applied with so much power that the nervous system, including the pacing of the heart, are overwhelmed and cease to function, causing death.

Neurophysiology techniques are used to measure variations in electrical potentials for understanding the pathways and functions of the nervous system. Bioelectrodes provide the interface.

Bioelectrode Method 

Neurological Situation

Patch Clamp Technique

Recording current flow from single ion channels of a neuron.

Glass capillary tube containing electrolytic solution.  Tiny glass tip pierces the cell wall and seals to the lipid bilayer.

Intracellular Recording

Electrical recording from INSIDE of a single neuron.

Extracellular Recording

Electrical recording from outside of a single (or a few) neuron.

Mass Unit Recording

Electrical recording from outside of a group of neurons.

Evoked Potentials

Electrical activity of the brain synchronized to an event.

Electroencephalography (EEG)

Electrical activity of the brain recorded with scalp or brain electrodes.

References

  1. Venugopalan R, Ideker R. Bioelectrodes. In Ratner BD, Hoffman AS, Schoen FJ, Lemons JE, editors. Biomaterials Science, 2nd edition.  San Diego, CA: Elsevier Academic Press; 2004.  p 649-657.
    Please note that this chapter includes an excellent bibliography.
  2. Geddes L, Baker LE. editors. Electrodes. Principles of applied biomedical instrumentation, 3rd edition. New York: Wiley-Interscience; 1989.
  3. http://www.medtronic.com/  Medtronic Corporation, Minneapolis, MN  company Web site. A search engine for many products incorporating bioelectrodes, including extensive background information.
  4. http://www.guidant.com/  Guidant Corporation, Indianapolis, IN  company Web site. A search engine for many products incorporating bioelectrodes, including extensive background information.

Content courtesy of University Of Washington at http://www.uweb.engr.washington.edu/research/tutorials/bioelectrodes.html