IEEE Spectrum September, 2009 - 28

heSe viSionS (if I may) might seem
far-fetched, but a contact lens with
simple built-in electronics is already
within reach; in fact, my students and
I are already producing such devices in
small numbers in my laboratory at the
University of Washington, in Seattle.
These lenses don't give us the vision
of an eagle or the benefit of running subtitles on
our surroundings yet. But we have built a lens with
one LED, which we've powered wirelessly with RF.
What we've done so far barely hints at what will
soon be possible with this technology.
Conventional contact lenses are poly mers
formed in specific shapes to correct faulty vision.
To turn such a lens into a functional system, we
integrate control circuits, communication circuits,
and miniature antennas into the lens using custombuilt optoelectronic components. Those components will eventually include hundreds of LEDs,
which will form images in front of the eye, such as
words, charts, and photographs. Much of the hardware is semitransparent so that wearers can navigate their surroundings without crashing into them
or becoming disoriented. In all likelihood, a separate, portable device will relay displayable information to the lens's control circuit, which will operate
the optoelectronics in the lens.
These lenses don't need to be very complex to be
useful. Even a lens with a single pixel could aid people with impaired hearing or be incorporated as an
indicator into computer games. With more colors
and resolution, the repertoire could be expanded to
include displaying text, translating speech into captions in real time, or offering visual cues from a navigation system. With basic image processing and
Internet access, a contact-lens display could unlock
whole new worlds of visual information, unfettered
by the constraints of a physical display.
Besides visual enhancement, noninvasive monitoring of the wearer's biomarkers and health indicators could be a huge future market. We've built
several simple sensors that can detect the concentration of a molecule, such as glucose. Sensors built
onto lenses would let diabetic wearers keep
tabs on blood-sugar levels without needing to prick a finger. The glucose detectors
we're evaluating now are a mere glimmer
of what will be possible in the next 5 to 10
years. Contact lenses are worn daily by
more than a hundred million people, and
they are one of the only disposable, massmarket products that remain in contact, through
fluids, with the interior of the body for an extended
period of time. When you get a blood test, your
doctor is probably measuring many of the same
biomarkers that are found in the live cells on the
surface of your eye-and in concentrations that correlate closely with the levels in your bloodstream.
An appropriately configured contact lens could
monitor cholesterol, sodium, and potassium levels, to name a few potential targets. Coupled with

a wireless data transmitter, the lens could relay
information to medics or nurses instantly, without
needles or laboratory chemistry, and with a much
lower chance of mix-ups.
Three fundamental challenges stand in the way
of building a multipurpose contact lens. First, the
processes for making many of the lens's parts and
subsystems are incompatible with one another and
with the fragile polymer of the lens. To get around
this problem, my colleagues and I make all our
devices from scratch. To fabricate the components
for silicon circuits and LEDs, we use high temperatures and corrosive chemicals, which means we
can't manufacture them directly onto a lens. That
leads to the second challenge, which is that all the
key components of the lens need to be miniaturized
and integrated onto about 1.5 square centimeters of
a f lexible, transparent polymer. We haven't fully
solved that problem yet, but we have so far developed our own specialized assembly process, which
enables us to integrate several different kinds
of components onto a lens. Last but not least, the
whole contraption needs to be completely safe for
the eye. Take an LED, for example. Most red LEDs
are made of aluminum gallium arsenide, which is
toxic. So before an LED can go into the eye, it must
be enveloped in a biocompatible substance.
So far, besides our glucose monitor, we've been
able to batch-fabricate a few other nanoscale biosensors that respond to a target molecule with an
electrical signal; we've also made several microscale
components, including single-crystal silicon transistors, radio chips, antennas, diffusion resistors,
LEDs, and silicon photodetectors. We've constructed
all the micrometer-scale metal interconnects necessary to form a circuit on a contact lens. We've also
shown that these microcomponents can be integrated through a self-assembly process onto other
unconventional substrates, such as thin, f lexible
transparent plastics or glass. We've fabricated prototype lenses with an LED, a small radio chip, and an
antenna, and we've transmitted energy to the lens
wirelessly, lighting the LED. To demonstrate that
the lenses can be safe, we encapsulated them in a
biocompatible polymer and successfully
tested them in trials with live rabbits.

NA * iEEE SpEctrum * SEptEmbEr 2009

eeing The lighT-LED light-is a reasonable accomplishment. But seeing something useful through the lens is clearly the
ultimate goal. Fortunately, the human eye
is an extremely sensitive photodetector. At
high noon on a cloudless day, lots of light streams
through your pupil, and the world appears bright
indeed. But the eye doesn't need all that optical power-
it can perceive images with only a few microwatts of
optical power passing through its lens. An LCD computer screen is similarly wasteful. It sends out a lot of
photons, but only a small fraction of them enter your
eye and hit the retina to form an image. But when the
display is directly over your cornea, every photon generated by the display helps form the image.
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Table of Contents for the Digital Edition of IEEE Spectrum September, 2009