Medical implants edge toward 'bionic man'
From: EE Times - 09/12/2005 - page 1
By: Chappell Brown

Cell phones have been a big hit because they untether communications
technology from the desk, giving anyone that capability anywhere. The logic
of this trend would suggest that the next step might be to implant a tiny
cell phone-on-a-chip directly into the cerebral cortex. With dense electrode
connections to the speech center of the brain and RF communications to the
nearest Wi-Fi hotspot, it would be the next best thing to being psychic. 

Sound extreme? Maybe. But this is a pivotal moment in the history of
electronics, when technology is morphing from something that extends the body
to something that merges with it. Electronic components can shore up
faltering human capabilities, in the form of artificial limbs that use
real-time embedded control, implantable defibrillators that correct the
heart's rhythms, and artificial ear and eye systems that help the deaf and
the blind.  

"There are a variety of people in the investment community, and I share their
view, who believe that this century is clearly the century of the 'bionic
man' - the human being whose life style has been improved substantially
through the use of these electronic enhancements," said 

Nicholas Colella, senior vice president in the Product Miniaturization
Division at Tessera Inc. (San Jose, CA). Tessera has been developing
miniaturized chip-scale packaging over the past 10 years, a critical
technology in this area. 

Yet, for all their promise, the developments in implant electronics also
carry profound implications for medicine and ethics. On a more mundane level,
they present major design challenges. Connecting inorganic silicon circuits
to the delicate nerve nets of the body poses a host of problems in itself.
And then comes the hurdle of building safe, highly compact, extremely
low-power components that can exist independently in the body for decades.  

The market, meanwhile, has barely begun. Cochlear implants - hearing aids
that link directly to the auditory nerves in the ear, while the rest of the
system is worn externally - are now being marketed as products, but vision
research, which is inherently more difficult, is still in the R&D stage.
Compact vision systems that can be worn on glasses and connect directly to
the optic nerve have been demonstrated. Elsewhere, implantable control
systems that monitor and correct heart function have become common. Further
down the road are electrode implants that would cure paralysis resulting from
nerve damage.  

The quest to heal such ills has the blessing of large institutions like the
National Institutes of Health, hospital research centers and charities. It
also has a feel-good component that makes it possible to accept - or at least
contemplate - the idea of rather bizarre intrusions into the body. But when
the usual dynamic of commercialization takes hold, ethics and conventional
morality tend to work against the notion of the bionic man.  

Consider, for example, a small step toward such futuristic visions of
im-plantable electronics: A couple of years ago, a number of individuals
volunteered to have radio frequency ID tags implanted under their skin. This
is a medically benign operation, but the social implications are a little
scary. The demo project touched off a heated debate over issues such as
personal privacy and whether the body should be declared off-limits to
invasive technology.  

If a device is surgically implanted, it needs to be highly reliable and
ultralow in power consumption in order to remain viable for periods lasting
decades. "Medical devices have to have very good reliability, requiring
long-term tests on your material," said Mike Warner, chief engineer at
Tessera. Then, too, "everything has to be sterilized, and you sometimes have
to use specialized materials that are compatible with the body." 

Indeed, a major problem for the field of implantable electronics is the lack
of long-term studies on circuits and materials. That data is crucial for the
product design stage of development, and explains why the market will be very
slow to take off.  

Another need is ultrasmall packages. "If you think about the traditional
electronic system such as a radio or television, if you used [Tessera's]
miniaturized 3-D packaging approach that is now available to the medical
market, you could reduce that to a 10th of the volume and weight," Warner
said. "This technology is being used in commercial products in very
high-volume PDAs, cell phones, things like that, so it is a technology that
is mature from the manufacturing and cost standpoint." 

As for what will be going into the chip-scale packages that Tessera has
developed, it most likely will not be state-of-the art digital processors.
The power of Pentium-class CPUs would certainly be welcomed for the demanding
information-processing algorithms needed in medical implants - but not the
power consumption and waste heat.  

It is here that a new design frontier using CMOS as a low-power analog
technology is emerging. Analog systems can attain the computational levels
required for interfacing with the nervous system at very low power, said
Rahul Sharpeshkar, director of MIT's Analog VLSI and Biological Systems
Group. Sharpeshkar is developing a fully implantable replacement for the
cochlea, the sound-processing system that resides in the inner ear.  

"The constraints with a fully implanted system are that it has to operate on
a battery without [additional] surgery for about 30 years. If that is the
case, the electronics have to be very, very low power," he said. "I have just
designed a processor that can run on a 100-milliampere battery for 30 years.
There is a company that hopefully will commercialize it soon."  

Sharpeshkar and his colleagues had to come up with a bandpass filter that
could operate in the 100- to 200-Hz range with a dynamic range of 66 dB while
consuming only a few tenths of a microwatt. To achieve those kinds of
figures, they used a 1.5-micron BiCMOS technology and ran it at very low
voltages. 

"Our low power is achieved by running the transistor where everyone thinks
it's off, and it has very low leakage currents," Sharpeshkar said. "We
exploit its action in that region."  

The implantable cochlea makes a good test system for this new design
frontier. The circuit has to do signal processing on 16 channels with a
sampling rate between 500 Hz and 2 kHz. Even at those specs, the actual
sound-processing capability is fairly crude. A basic constraint has been the
inability to make very many connections to the auditory-nerve network in the
ear. The cochlea has hundreds of millions of tiny hairs that respond to sound
vibrations and stimulate nerves. The result is a rich experience of detailed
sound.  

Artificial cochleas must reduce the design objective to something achievable
and vital, such as speech recognition. That requires only a rather crude
reception of a series of amplitudes, whereas the full experience of a
symphony orchestra, say, would need both amplitude and phase information.
With the scaled-down requirement, it is possible to get by with only 16
connections to the auditory nerves.  

Such constraints are common in implantable designs. "Whether they are
pacemakers or defibrillators - and now people are working on almost fully
implanted systems for paralysis - they have to be small, they have to be low
power and they have to be wireless," Sharpeshkar said.  

While the field is only in its infancy, the prospect of merging information
technology intimately with the brain has some startling implications. For
example, work on implanting control systems in the brain at Miguel Nicolelis'
lab at Duke University Medical Center has led to the speculation that it
would be possible to not only control remote robotic systems mentally, but
actually perceive them as part of the body. The same type of technology would
make it possible to implant databases in the brain that would allow someone
to recognize people and know their detailed history, without ever having met
them.  

And then there is the implantable cell phone - an RF device that could link
minds directly. Enhanced vision systems, meanwhile, could detect infrared,
ultraviolet light or RF radiation.  

It can be done. The technological hurdles are large, but not impossible.
Social, ethical and personal issues are, of course, exceedingly complex. When
the technology moves beyond therapy into the realm of creating a superior
being - a bionic man - there will be much more discussion. Indeed, merging
electronics with the body may ultimately change not only how we conceive of
ourselves, but what we are. 

Link to article:
http://www.eetimes.com/issue/fp/showArticle.jhtml?articleID=170701960&pgno=1

Links:
Tessera Inc.
http://www.tessera.com/

Miguel A. L. Nicolelis, MD, PhD
http://neuro.duke.edu/Faculty/Nicolelis.htm

Duke Neurobiology in the News
http://neuro.duke.edu/new.htm