April 12, 2013
Tiny, Injectable LEDs Shed Light On The Human Brain
[ Watch the Video: Tiny Injectable LEDs Help Neuroscientists Study the Brain ]
redOrbit Staff & Wire Reports - Your Universe Online
The ultrathin, flexible optoelectronic devices, which include LEDs the size of individual neurons, are an exciting advancement in the field of optogenetics, a new area of neuroscience that uses light to stimulate targeted neural pathways in the brain.
Optogenetics allow researchers to study precise brain functions in isolation in ways impossible through electrical stimulation, which affects neurons throughout a broad area, or with drugs, which saturate the whole brain.
“These materials and device structures open up new ways to integrate semiconductor components directly into the brain,” said study leader John Rogers, professor of materials science and engineering at the University of Illinois.
“More generally, the ideas establish a paradigm for delivering sophisticated forms of electronics into the body: ultra-miniaturized devices that are injected into and provide direct interaction with the depths of the tissue,” said Rogers, who directs the Frederick Seitz Materials Research Laboratory at the UI.
The researchers demonstrated the first application of their tiny devices by genetically programming specific neurons to respond to light.
Optogenetics experiments with mice illustrate the ability to train complex behaviors without physical reward, and to alleviate certain anxiety responses. The additional insights gained through optogenetics studies about the structure and function of the brain could also have implications for treatment of Alzheimer´s, Parkinson´s, depression, anxiety and other neurological disorders.
Although a number of important neural pathways can now be studied by optogenetics, researchers continue to struggle with the engineering challenge of delivering light to precise regions deep within the brain.
The most widely used methods tether the animals to lasers with fiber-optic cables embedded in the skull and brain. However, this is an invasive procedure that also limits movements, affects natural behaviors and prevents study of social interactions.
The new technologies developed in the current study bypass these limitations with specially designed powerful LEDs — among the world´s smallest, with sizes comparable to single cells — that are injected into the brain to provide direct illumination and precise control.
The devices are printed onto the tip end of a tiny, flexible plastic ribbon -- thinner than a human hair and narrower than the eye of a needle — that can be inserted deep into the brain with very little stress to tissue.
“One of the big issues with implanting something into the brain is the potential damage it can cause,” said fellow researchers Michael R. Bruchas.
“These devices are specifically designed to minimize those problems, and they are much more effective than traditional approaches.”
The active devices include not only LEDs but also various sensors and electrodes that are delivered into the brain with a thin, releasable microinjection needle. The ribbon connects the devices to a wireless antenna and a rectifier circuit that harvests radio frequency energy to power the devices.
This module then 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 complete device platform includes LEDs, temperature and light sensors, microscale heaters and electrodes that can both stimulate and record electrical activity. These components enable many other important functions, such as giving researchers the ability to measure the electrical activity that results from light stimulation, and providing new insight into complex neural circuits and interactions within the brain.
The range of device options suggests that this wireless, injectable platform could be used for other types of neuroscience studies as well, or even applied to other organs. For instance, Rogers´ team has already developed related devices for stimulating peripheral nerves in the leg as a potential route to pain management, and have developed devices with LEDs of multiple colors that allow several neural circuits to be studied with a single injected system.
“These cellular-scale, injectable devices represent frontier technologies with potentially broad implications,” said Rogers, whose group is known for its success in developing soft sheets of complex electronics that wrap the brain, the heart, or that adhere directly to the skin.
“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. Many cases, ranging from fundamental studies to clinical interventions, demand access directly into the depth. This is just the first of many examples of injectable semiconductor microdevices that will follow.”
The study is published online April 12 in the journal Science. An abstract can be viewed here.