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Flexible implant maps heart’s electrical activity

U. PENN (US)—Researchers have created and tested a new type of implantable device for measuring the heart’s electrical output. The device represents the first use of flexible silicon technology for a medical application.

“We believe that this technology may herald a new generation of active, flexible, implantable devices for applications in many areas of the body,” says Brian Litt, co-senior author of a paper published in Science Translational Medicine and an associate professor of neurology at the University of Pennsylvania School of Medicine. “Initially, we plan to apply our findings to the design of devices for localizing and treating abnormal heart rhythms.

Litt says the device could allow doctors “to more quickly, safely, and accurately target and destroy abnormal areas of the heart that are responsible for life-threatening cardiac arrhythmias,” says Litt.

The team tested the new devices—made of nanoscale, flexible ribbons of silicon embedded with 288 electrodes, forming a lattice-like array of hundreds of connections—on the heart of a porcine animal model. The tissue-hugging shape allows for measuring electrical activity with greater resolution in time and space. The new device can also operate when immersed in the body’s salty fluids.

Story Landis, director of the National Institute of Neurological Disorders and Stroke, which provided support for the study, says implantable silicon-based devices could potentially serve as a tool “for mapping and treating epileptic seizures, providing more precise control over deep brain stimulation, as well as other neurological applications.”

“The new devices bring electronic circuits right to the tissue, rather than having them located remotely, inside a sealed can that is placed elsewhere in the body, such as under the collar bone or in the abdomen,” explains Litt. “This enables the devices to process signals right at the tissues, which allows them to have a much higher number of electrodes for sensing or stimulation than is currently possible in medical devices.”

For example, devices for mapping and eliminating life-threatening heart rhythms allow for up to 10 wires in a catheter that is moved in and around the heart, and is connected to rigid silicon circuits distant from the target tissue. This design limits the complexity and resolution of devices since the electronics cannot get wet or touch the target tissue.

The devices can collect large amounts of data from the body, at high speed. This allowed the researchers to map electrical activity on the heart of the large animal.

“Our hope is to use this technology for many other kinds of medical applications, for example to treat brain diseases like epilepsy and movement disorders,” adds Litt and co-senior author John Rogers, from the University of Illinois.

For the experiment, researchers built a device to map waves of electrical activity in the heart of a large animal. The device uses the 288 contacts and more than 2,000 transistors spaced closely together, while standard clinical systems usually use about five to 10 contacts and no active transistors.

“We demonstrated high-density maps of electrical activity on the heart recorded from the device, during both natural and paced beats,” says coauthor David Callans, professor of medicine at Penn.

“We also plan to design advanced, ‘intelligent’ pacemakers that can improve the pumping function of hearts weakened by heart attacks and other diseases.” For each of these applications, the team is conducting experiments to test flexible devices in animals before starting human trials.

Another focus of ongoing work is to develop similar types of devices that are not only flexible, like a sheet of plastic, but fully stretchable, like a rubber band. The ability to fully conform and wrap around large areas of curved tissues will require stretchability, as well as flexibility.

“The next big step in this new generation of implantable devices will be to find a way to move the power source onto them,” says Rogers. “We’re still working on a solution to that problem.”

Researchers from Penn, Illinois, and Northwestern University contributed to the work, which was funded by National Institute of Neurological Disorders and Stroke, the Klingenstein Foundation, the Epilepsy Therapy Project, and the University of Pennsylvania Schools of Engineering and Medicine.

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