brain-recording device that melts into place

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A brain-recording device that melts into place (4/19/2010)

Neural

electrode array wrapped onto a model of the brain. The wrapping process

occurs spontaneously, driven by dissolution of a thin, supporting base

of silk. - Please credit C. Conway and J. , Beckman Institute

Scientists have developed a brain implant that essentially melts

into place, snugly fitting to the brain's surface. The technology could

pave the way for better devices to monitor and control seizures, and to

transmit signals from the brain past damaged parts of the spinal cord.

"These implants have the potential to maximize the contact between

electrodes and brain tissue, while minimizing damage to the brain. They

could provide a platform for a range of devices with applications in

epilepsy, spinal cord injuries and other neurological disorders," said

Walter Koroshetz, M.D., deputy director of the National Institute of

Neurological Disorders and Stroke (NINDS), part of the National

Institutes of Health.

The study, published in Nature Materials, shows that the

ultrathin flexible implants, made partly from silk, can record brain

activity more faithfully than thicker implants embedded with similar

electronics.

The simplest devices for recording from the brain are needle-like

electrodes that can penetrate deep into brain tissue. More

state-of-the-art devices, called micro-electrode arrays, consist of

dozens of semi-flexible wire electrodes, usually fixed to rigid silicon

grids that do not conform to the brain's shape.

In people with epilepsy, the arrays could be used to detect when

seizures first begin, and deliver pulses to shut the seizures down. In

people with spinal cord injuries, the technology has promise for

reading complex signals in the brain that direct movement, and routing

those signals to healthy muscles or prosthetic devices.

"The focus of our study was to make ultrathin arrays that conform to

the complex shape of the brain, and limit the amount of tissue damage

and inflammation," said Litt, M.D., an author on the study and an

associate professor of neurology at the University of Pennsylvania

School of Medicine in Philadelphia. The silk-based implants developed

by Dr. Litt and his colleagues can hug the brain like shrink wrap,

collapsing into its grooves and stretching over its rounded surfaces.

The implants contain metal electrodes that are 500 microns thick, or

about five times the thickness of a human hair. The absence of sharp

electrodes and rigid surfaces should improve safety, with less damage

to brain tissue. Also, the implants' ability to mold to the brain's

surface could provide better stability; the brain sometimes shifts in

the skull and the implant could move with it. Finally, by spreading

across the brain, the implants have the potential to capture the

activity of large networks of brain cells, Dr. Litt said. Besides its flexibility, silk was chosen as the base material

because it is durable enough to undergo patterning of thin metal traces

for electrodes and other electronics. It can also be engineered to

avoid inflammatory reactions, and to dissolve at controlled time

points, from almost immediately after implantation to years later. The

electrode arrays can be printed onto layers of polyimide (a type of

plastic) and silk, which can then be positioned on the brain.

To make and test the silk-based implants, Dr. Litt collaborated with

scientists at the University of Illinois in Urbana-Champaign and at

Tufts University outside Boston. , Ph.D., a professor of

materials science and engineering at the University of Illinois,

invented the flexible electronics. Kaplan, Ph.D., and Fiorenzo

Omenetto, Ph.D., professors of biomedical engineering at Tufts,

engineered the tissue-compatible silk. Dr. Litt used the electronics

and silk technology to design the implants, which were fabricated at

the University of Illinois.

Recently, the team described a flexible silicon device for recording from the heart and detecting an abnormal heartbeat.

In the current study, the researchers approached the design of a

brain implant by first optimizing the mechanics of silk films and their

ability to hug the brain. They tested electrode arrays of varying

thickness on complex objects, brain models and ultimately in the brains

of living, anesthetized animals.

The arrays consisted of 30 electrodes in a 5x6 pattern on an

ultrathin layer of polyimide - with or without a silk base. These

experiments led to the development of an array with a mesh base of

polyimide and silk that dissolves once it makes contact with the brain

- so that the array ends up tightly hugging the brain.

Next, they tested the ability of these implants to record the

animals' brain activity. By recording signals from the brain's visual

center in response to visual stimulation, they found that the ultrathin

polyimide-silk arrays captured more robust signals compared to thicker

implants.

In the future, the researchers hope to design implants that are more

densely packed with electrodes to achieve higher resolution recordings.

"It may also be possible to compress the silk-based implants and

deliver them to the brain, through a catheter, in forms that are

instrumented with a range of high performance, active electronic

components," Dr. said.

Note: This story has been adapted from a news release issued by the NIH/National Institute of Neurological Disorders and Strokehttp://www.brainmysteries.com/research/A_brain-recording_device_that_melts_into_place.asp