Solar-Powered Eye Sensor

A cornea-implanted computer can monitor the eyeball's pressure

3 min read

In the future, that twinkle in your loved one's eye might be an implanted solar-powered pressure monitor. At the 2011 IEEE International Solid-State Circuits Conference in February, engineers from the University of Michigan, in Ann Arbor, described their work on a cubic-millimeter-size sensor meant to monitor pressure inside the eye. The researchers have yet to test the device in human eyes or animal ones, but they hope their system will one day thwart optic nerve damage brought on by glaucoma.

To determine a glaucoma patient's treatment, doctors must monitor pressure inside the eye, says Gregory Chen, a graduate student of electrical engineering at Michigan. Today's methods gauge that pressure by pushing on the cornea, the eye's clear outer coating. The results may be inaccurate: "If you just happen to have a really thick cornea, your eye is going to be harder, no matter what the pressure is," Chen says. The engineers' prototype device would allow a microelectromechanical systems (MEMS) capacitive sensor to record pressure from inside the eye about every 15 minutes and store it to static RAM. Once a day, the system would wirelessly transmit the day's data, via two on-chip inductors, to a wand. The inductors would send the data at both 400- and 900-megahertz carrier frequencies, as a means of mitigating the signal's noise and increasing its range.

Powering this daily transmission was one of the team's biggest challenges, says Mohammad Hassan Ghaed, the Michigan grad student who designed the radio system. "The common way of transmitting data is to use an external antenna," he says, "but in this millimeter-cubed space, we don't have that luxury." The team designed the diminutive device for easy implantation, but the small size comes at a cost: The device's inductors require more power to send data than a bigger antenna would, a peak of 47 milliwatts. That was a problem, given that the peak power supplied by their device's thin-film lithium battery is only about 40 microwatts.

To make up for this shortfall, the system stores enough energy to transmit one bit in a capacitor. The device then sends that bit and refills the capacitor from the battery for another go. The bit-by-bit method provides a transmission rate of around 10 kilobits per second, but with a day's data totaling around 1.5 Kb, it's still "near instantaneous," says Dennis Sylvester, a professor of electrical engineering, who led the team with colleague David Blaauw. The battery itself lasts around 28 days before it's drained, but the device also includes a miniature solar panel. The team expects that about 10 hours of indoor lighting or 1.5 hours of sunlight daily could recharge it.

"As far as I know, nobody does solar power at this size," says Pedro Irazoqui, director of the Center for Implantable Devices at Purdue University, who is also developing an implantable glaucoma sensor. Irazoqui praises the Michigan team for its energy-harvesting system and on-chip radios. His own team's tadpole-shaped device, which is now being tested in rat eyes, uses radio waves from an external source to power a 2.7-mm antenna "tail" for transmission and to charge an onboard supercapacitor.

Irazoqui's commendation of the Michigan device comes with some caution. "There are a lot of impressive innovations here," he says, "but until they've actually implanted it in a live eye and measured the pressure, they haven't shown that the device works." Of particular concern, he says, is that surgeons would need to implant the device in the "very delicate" iris tissue.

The Michigan team notes that human testing is still several years away. "Now that we have a system that is working, we can start to expand into long-term effects," Blaauw says, noting grad student Razi Haque's work to optimize the device's packaging in collaboration with Michigan professor and IEEE Fellow Kensall Wise.

What doesn't seem to be a concern is that staring into the wearer's eyes might reveal a speck of cyborg. "We're expecting to make different colors," Chen jests. "It's going to be a fashion statement."

This article originally appeared in print as "The Sun’s in Your Eyes"

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This CAD Program Can Design New Organisms

Genetic engineers have a powerful new tool to write and edit DNA code

11 min read
A photo showing machinery in a lab

Foundries such as the Edinburgh Genome Foundry assemble fragments of synthetic DNA and send them to labs for testing in cells.

Edinburgh Genome Foundry, University of Edinburgh

In the next decade, medical science may finally advance cures for some of the most complex diseases that plague humanity. Many diseases are caused by mutations in the human genome, which can either be inherited from our parents (such as in cystic fibrosis), or acquired during life, such as most types of cancer. For some of these conditions, medical researchers have identified the exact mutations that lead to disease; but in many more, they're still seeking answers. And without understanding the cause of a problem, it's pretty tough to find a cure.

We believe that a key enabling technology in this quest is a computer-aided design (CAD) program for genome editing, which our organization is launching this week at the Genome Project-write (GP-write) conference.

With this CAD program, medical researchers will be able to quickly design hundreds of different genomes with any combination of mutations and send the genetic code to a company that manufactures strings of DNA. Those fragments of synthesized DNA can then be sent to a foundry for assembly, and finally to a lab where the designed genomes can be tested in cells. Based on how the cells grow, researchers can use the CAD program to iterate with a new batch of redesigned genomes, sharing data for collaborative efforts. Enabling fast redesign of thousands of variants can only be achieved through automation; at that scale, researchers just might identify the combinations of mutations that are causing genetic diseases. This is the first critical R&D step toward finding cures.

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