I'm All Ears

Location:

Concepts Shown:

Hearing, prosthesis, electrode

Equipment:

Petri dish containing cochlear prosthetic electrodes, transparencies of diagrams and charts, includes diagrams for MSE 400 class.

Procedure:

Use diagrams and charts to help students visualize the mechanism of cochlea prosthetic. Let students see electrodes.

Science:

Cochlear prosthesis electrodes are devices which are implanted in the inner ear to improve the hearing of those whom hearing aids do not help. Even those who are profoundly deaf can hear low frequencies when electrode is implanted in the inner ear (telephone ring, automobiles, loudness and rhythm of speech).

Materials: Materials are an integral part of developing a prosthetic. Knowing the properties of a material is necessary in developing something that is placed into the body. Many materials fit the function of the implant, yet without biocompatibility it will never work.

The cochlea is one of the most sensitive cellular areas in the body. Metal is an excellent conductor, but it has a problem of corrosion in highly acidic solutions. The body is highly caustic.

Two problems result from using improper materials for wires in electrode:

1. Corrosion giving off highly toxic heavy metal ions into the immediate vicinity of neurons.
2. Electrolysis of water which produces mechanically disruptive bubbles of hydrogen and oxygen. This leaves behind local concentrations of hydroxyl and hydronium ions that can reach toxic levels of alkalinity and acidity.

Solution: Wires made from platinum and iridium do not have problems of corrosion and electrolysis. These elements produce reversible, non toxic electrochemical reactions that safely induce ionic currents in body fluids.

Other materials used:

Gold/brass: This combination provides good electrical contact. Gold/brass is biocompatible (dental applications).
Teflon: Inert material. Will not react. Good insulator.
Silastic: Used as insulator and "glue". Silicone product.
Methyl methacrylate: Acrylic used in many biological applications. Insulator.

Purpose:

Ball and wire: Cause electronic stimulation.
Teflon: Hold and insulate wires.
Silastic: Hold and insulate wires.
Methyl methacrylate: Isolate bone and issue from external voltage. Keep connector in place.

Comments: Have students look at the electrodes. The petri dish contains a three socket and a two socket connector. The three socket connector is the one that is illustrated. Keep dish sealed to prevent damage or loss of electrodes.

References:

Author:
Marcia Muller
Credits:


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