Biologically chargeable ear implants- A major breakthrough

The chip is small enough to fit in the cavity of the middle ear. (Credit: Patrick P. Mercier)

  In a recent issue of the journal Nature Biotechnology, a team of researchers from MIT, the Massachusetts Eye and Ear Infirmary (MEEI) and the Harvard-MIT Division of Health Sciences and Technology (HST) demonstrated for the first time that cochlear potentials could power implantable electronic devices without impairing hearing. This has far reaching potential in the areas of diagnostics, and other implantable devices like cochlear implants and fully implantable hearing aids.  Today the cochlear  implants is powered by an external power source.  

Konstantina Stankovic, an otologic surgeon at MEEI, and HST graduate student Andrew Lysaght implanted electrodes into the cochlea of guinea pigs' ears. Attached to the electrodes were low-power electronic devices developed by MIT's Microsystems Technology Laboratories (MTL). After the implantation, the guinea pigs responded normally to hearing tests, and the devices were able to wirelessly transmit data about the chemical conditions of the ear to an external receiver.  .  

The cochlea is the auditory portion of the inner ear. The cochlea is a spiralled, hollow, conical chamber of bone.It houses three chambers or scalae within,  which are as follows: 

• the scala vestibuli (containing perilymph), which lies superior to the cochlear duct and abuts the oval window
• the scala tympani (containing perilymph), which lies inferior to the scala media and terminates at the round window
• the scala media (containing endolymph), or cochlear duct, a region of high potassium ion concentration that the cilia of the hair cells project into.

    This ionic gradient generates  the endocochlear potentials.  Endocochlear potential (EP) is a battery-like electrochemical gradient found in and actively maintained by the inner ear. The scala vestibuli and scala tympani has a high concentration of Na+ ions, while the scala media higher concentration of K+ ions,  The difference in gradients generate  this EP.    Anantha P Chandrakasan and fellow scientists demonstrated that the mammalian EP can be used as a power source for electronic devices. They achieved this by designing an anatomically sized, ultra-low quiescent-power energy harvester chip integrated with a wireless sensor capable of monitoring the EP itself.  The  voltage generated by these EP is very low.  A device powered by this biological battery can harvest only a small fraction of its power. Low-power chips, however, are precisely the area of expertise of Anantha Chandrakasan's group at MTL.  Saurav Bandyopadhyay, a graduate student in Chandrakasan's group, equipped their chip with an ultralow-power radio transmitter: After all,  an implantable medical monitor wouldn't be much use if there were no way to retrieve its measurements. The MTL chip also includes power-conversion circuitry in order to amass enough charge to power the radio.   In the experiments, the chip itself remained outside the guinea pig's body, but it's small enough to nestle in the cavity of the middle ear.

What does it mean for the speciality? This means that we will be able to monitor voltage changes in the endolymph and perilymph on real time basis in patients.   This could shed more  light in understanding the different stages of Meniere's disease.    Imagine being able to know what happens when we perfuse gentamycin or dexamethasone in those patients with Meniere's disease or with Sudden hearing loss.  Newer inner ear drugs could be developed in the future using this technology.  You could have a fully implantable cochlear implant and a totally implantable hearing aid of a different design in the near future.  This technology has tremendous potential for not only otology but even for other branches of modern medicine.

Source:

1)Patrick P Mercier, Andrew C Lysaght, Saurav Bandyopadhyay, Anantha P Chandrakasan, Konstantina M Stankovic. Energy extraction from the biologic battery in the inner ear. Nature Biotechnology, 2012; DOI:10.1038/nbt.2394.

2)Massachusetts Institute of Technology (2012, November 8). Medical devices powered by the ear itself. ScienceDaily.