AAWSAP DIRD, Biosensors and BioMEMS: A Survey of the Present Field, March 2010

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Figure 27. Power Transfer by Magnetic Induction to an Implanted BioMEMS Retinal Prosthesis. This is
the Boston Retinal Implant Project.
(http://www. bostonretinaIim plant. org/retina I approach. php ?fontsize= normal&hicontrast)
MICROSCALE IN THERAPEUTIC NEUROSTIMULATION
Some of the biggest excitement in medical neuroprosthetics has been in the notion that
we can use micro-implantable devices rather than drugs to reduce or better control the
effects of stroke, heart disease, epilepsy, and other disorders of the human condition.
Bioelectrical stimulation has effects which are very specific on local tissues rather than
indiscriminately affecting all tissues and so may offer fewer side effects of drugs. Such
devices can be finely controlled in their effects and provide a greater flexibility in terms
of treatment.
Any implanted device has to be small in order to be minimally invasive, especially in the
brain. Powering of implanted devices by batteries is only practical in a few biomedical
situations. Also implants may need to communicate with the outside world wirelessly.
Having wires penetrating the skin is uncomfortable and could lead to infection in the
tissue.
The notion of placing bioelectronic stimulation devices inside of the body for therapeutic
reasons goes back to the early invention of the pacemaker. These kind of devices have
internal batteries to support an electrical pulse generator that paces the rhythm of the
heart.
Because the amount of energy in each pulse is relatively small the power drain is low
and the pacemaker batteries can last years. The difficulty is that they are bulky, must
be eventually replaced on the order of seven years, and their placement is invasive.
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