Implanted Pump May Assist Hearing Loss Treatment

July 2009

Editor: Some of the proposed hearing loss treatments involve delivering precise quantities of chemicals to a very tiny region of the cochlea. I don't know if this new device is the answer, but it sure sounds like at least a step in the right direction.

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An implanted electronic ion pump in organic material can be used to carry signals to specific cells in the nervous system and in this way treat various illnesses. In a unique study, researchers at Linköping University (LiU) and Karolinska Institutet (KI) have used the pumps to successfully manipulate the hearing in laboratory animals.

The technique which is described in an article in the journal Nature Materials represents a breakthrough for the machine-to-brain interface, with opportunities for greater symbiosis between electronics and biological systems.

"In the future we envisage a wirelessly controlled and permanent implant", says Magnus Berggren, Professor of Organic Electronics at LiU and one of the authors of the article.

The small electrically charged organic molecules that transmit signals between nerve cells are known as neurotransmitters. The most important substance in the cochlea is glutamate, which regulates signals from the inner hair cells to the auditory nerve. But excessive quantities of glutamate can be toxic and lead to cell depletion.

To test their idea of selectively transporting neurotransmitters electronically the researchers used the hearing organ in guinea pigs as a model system. The tip of an ion pump, with similar design to a small syringe, was inserted in animals under anaesthesia near the membrane in the inner ear called the round window. When the power was switched on exact doses of glutamate were delivered via an electrically charged plastic film and diffused through the round window to the intended target, the hair cells.

By measuring the auditory response of the brainstem the researchers were able to study what was happening as the transport of glutamate was taking place. After one hour the glutamate concentration reached levels where the result was loss of hearing.

The tests show how the ion pump can be used to control the supply of neurotransmitters and to direct them to specific cell types.

Osmotic pumps are today used to transport the substances in a liquid, risking over-dosage, leaking and excessive pressure in small spaces, for example in the cochlea