Injectable microLEDs Turn Light On in Brain

Microscopic LEDs injected deep inside the brain are the latest probe for triggering targeted neurons, providing insight into the brain’s structure, function and complex connections.

Researchers at the University of Illinois at Urbana-Champaign and at Washington University in St. Louis have developed ultrathin, flexible optoelectronic devices — including neuron-size LEDs — that are illuminating the mysteries of the brain for neuroscientists in optogenetics and beyond.

“These materials and device structures open up new ways to integrate semiconductor components directly into the brain,” said John A. Rogers, the Swanlund professor of materials science and engineering and director of the Frederick Seitz Materials Research Laboratory at the University of Illinois. “More generally, the ideas establish a paradigm for delivering sophisticated forms of electronics into the body: ultraminiaturized devices that are injected into and provide direct interaction with the depths of the tissue.”

A thin plastic ribbon printed with advanced electronics is threaded through the eye of an ordinary sewing needle. The device, containing LEDs, electrodes and sensors, was developed by researchers at the University of Illinois at Urbana-Champaign and Washington University in St. Louis and can be injected into the brain or other organs. Courtesy of John A. Rogers.

The technique was first demonstrated in optogenetics, enabling researchers to study precise brain functions in isolation in ways not possible with electrical stimulation, which affects neurons throughout a broad area, or with drugs, which saturate the whole brain. Optogenetic experiments with mice have illustrated the ability to train complex behaviors without physical reward and have alleviated certain anxiety responses. Fundamental insights that have emerged from these studies could have implications for treatment of Alzheimer’s, Parkinson’s, depression, anxiety and other neurological disorders.

Although many important neural pathways can be studied using optogenetic methods, researchers continue to struggle with the engineering challenge of delivering light to precise regions deep within the brain. Most of these methods tether the animals to lasers with fiber optic cables embedded in the skull and brain — an invasive procedure that also limits movements, affects natural behaviors and prevents study of social interactions.

The specially designed injectable microLEDs bypass these limitations to provide direct illumination and precise control. The devices are printed onto the tip of a thin, flexible plastic ribbon — thinner than a human hair and narrower than the eye of a needle — that is inserted deep into the brain with very little stress to tissue.

The microLED device next to a human finger. Courtesy of University of Illinois-Urbana Champaign and Washington University-St. Louis.

“One of the big issues with implanting something into the brain is the potential damage it can cause,” said Michael R. Bruchas, a professor of anesthesiology at Washington University. “These devices are specifically designed to minimize those problems, and they are much more effective than traditional approaches.”

The device also includes temperature and light sensors, microscale heaters and electrodes that can both stimulate and record electrical activity. The plastic ribbon connects the devices to a wireless antenna and to a rectifier circuit that harvests radio frequency energy to power the device. This module mounts on top of the head and can be unplugged from the ribbon when not in use.

“Study of complex behaviors, social interactions and natural responses demands technologies that impose minimal constraints,” Rogers said. “The systems we have developed allow the animals to move freely and to interact with one another in a natural way, but at the same time, provide full, precise control over the delivery of light into the depth of the brain.”

The components could provide many other important functions; e.g., researchers can measure the electrical activity that results from light stimulation, giving additional insight into complex neural circuits and interactions within the brain. It could even be applied to other organs, the investigators say. Rogers’ team has developed related devices for stimulating peripheral nerves in the leg as a potential route to pain management.

The microLED device implanted in a rodent’s brain to demonstrate the optical properties of devices in intact tissue. Courtesy of University of Illinois-Urbana Champaign and Washington University-St. Louis.

Instruments with multiple-colored LEDs also were built to study several neural circuits with a single injected system.

“These cellular-scale, injectable devices represent frontier technologies with potentially broad implications,” Rogers said. His group has developed soft sheets of sophisticated electronics that wrap around the brain or the heart, or that adhere directly to the skin. (See: Stretchable Electronics — Good for the Heart and Stretchable Electronics).

“But none of those devices penetrates into the depth of tissue,” he said. “That’s the challenge that we’re trying to address with this new approach. This is just the first of many examples of injectable semiconductor microdevices that will follow.”

Earlier this month, Rogers received the 2013 Mid-Career Researcher Award for his contributions to developing flexible electronic systems. (See: Rogers Honored by MRS for Flexible Electronics Work)

The work, supported by the National Institutes of Health and the Department of Energy, appeared in Science (doi: 10.1126/science.1232437).

For more information, visit: www.illinois.edu