Glaucoma is the second-leading cause of blindness in the world, according to the World Health Organization. It’s characterized by damage to the optic nerve. One of the major risk factors is abnormally high eye pressure, called intraocular pressure (IOP). It can occur when nourishing fluids called aqueous humor fail to drain from the anterior chamber, located between the iris and the cornea. The resulting fluid buildup presses on the optic nerve, injuring it. While there are treatments, there is no cure.
Traditionally, ophthalmologists spotcheck eye pressure by blowing a puff of air into a patient’s eye and measuring the resulting pressure with a tonometer. “It’s really annoying, and it only gives an instantaneous measurement,” says Michael Armstrong, a senior mechanical engineering student at Stevens Institute of Technology. That’s a problem because IOP fluctuates throughout the day.
A tiny high-tech solution
That’s why Armstrong and fellow Stevens mechanical engineering seniors Aaron Henry, Justin Koch and Nicholas Pollio are working on a prototype for a smart contact lens with an embedded pressure sensor made from carbon nanotubes (CNT).
Called Ocularity, the device is designed to continuously monitor intraocular pressure in glaucoma patients, charting the peaks and valleys of IOP fluctuations throughout the day. It would then wirelessly transmit the readings to a doctor who could then “see patterns and set a design treatment schedule,” says Armstrong.
Unlike some surgical implants that measure eye pressure, it’s noninvasive.
A small team changes gears
Originally they’d planned to work on an IOP-relieving microvalve, but their advisors, Professor E.H. Yang and Assistant Professor Xian Zhang, encouraged them to switch gears. “They thought people would flock to the sensor more,” Armstrong explains.
Because the team was supposed to have five people, they tried to enlist an electrical engineering or biomedical engineering student “to help fill in some of our knowledge gaps,” says Henry, “but it didn’t happen.”
Plowing ahead anyway, he and Pollio specialized in the lens design, while Armstrong and Koch focused on the electrical components.
“We used small committees of two to make decisions, and we had overlap for each part,” Pollio says. “That way, if someone was out, we’d have good knowledge of what’s going on.”
Interlocking carbon nanotubes
The first step was to create the lens. For this, they needed a mold, which Pollio and Henry designed using SolidWorks CAD. “We talked to a lot of experts on campus,” says Pollio. “Jennifer Field and Biruk Gebre were very helpful.” The PROOF lab printed the mold in VeroClear on the 3D Objet Connex 350 printer.
Into the mold they poured nontoxic silicone called polydimethylsiloxane (PDMS). It’s typically cured on hot plate in about 15 minutes, but the curved shape of the mold made that approach difficult, so Armstrong took it home to cure in the open air. It took a few days, and the result wasn’t perfect—small bubbles developed—but it retained its lens-like shape.
Then it was time to sandwich two plates of CNT between layers of PDMS. Pointed at each other, these plates function as a variable resistor. When there’s a force on the resistor—such as fluid buildup—the nanotubes interlock like the bristles of two hairbrushes. The more they touch, the better the connection, which lowers resistance and increases the current. By reading the change in voltage, Ocularity could determine the pressure exerted on the CNT.
A pair of glasses holds a battery and the electronics. It wirelessly transmits power to the smart lens using magnetic induction. “We are using copper magnet wire, which is wound into coils—one for the glasses and one for the lens,” Armstrong says. “The exterior coil is connected to a battery and a transistor, and the lens coil will be connected to the carbon nanotubes.”
They’re now attempting to transmit data using radio frequency via Arduino microcontrollers, “but a fully realized product—which we will probably be unable to develop—would be a significantly smaller device or even use Bluetooth technology,” he explains.
The prototype was built at Stevens’ MicroDevice Laboratory (MDL).
When machines fail
The biggest challenge was posed by something entirely out of their control: the MDL’s nanoimprintor, which produces the carbon nanotubes, broke down over winter break. “We had to maneuver,” Armstrong says. “What else could we test? What other aspects could we move forward with?”
Luckily, the machine was soon back online. They scrambled to find time to work together—both Pollio and Armstrong are commuters—and sometimes collaborated via FaceTime.
The team isn’t alone in attempting to create a smart contact lens. The closest to Ocularity is the Triggerfish sensor, a hydrogel lens that measures pressure peaks and valleys throughout the day. The data is transmitted via Bluetooth to a small adhesive antenna worn near the eye.
Getting comfortable with nanotech
“Working at the microscale has been a new challenge for all of us,” Pollio says. “When I first learned about nano and micro tech, I thought it was daunting—a completely different world you can’t even see. While there are differences, it’s not as scary as you’d think.”
“I know people at other schools who only do semester-long projects,” Armstrong says. “I have a friend at University of Maryland whose senior project only took him a semester, and he didn’t get to do nearly as much as we did.”
At the Innovation Expo on May 3, “We are hoping to have a model of the lens that is macro-scale and be able to show that it can read pressure changes and output those values,” says Henry.
“The best part [of the project] for me is solving a problem,” says Armstrong. “With some projects, it’s hard to see the use for it. But with an issue like glaucoma—1.5 million people are diagnosed in U.S alone every year. We’re doing something in long run that we can take to the healthcare community and that can provide better treatment and better quality of life.”
“Most if not all of us have personal stake in this project,” says Pollio. “We’ve had a family member or friend suffering from this. I think that’s kept us motivated and on track to make a difference.”