Researchers from Northwestern University, the University of Illinois at Urbana-Champaign and the University of Pennsylvania are the first to demonstrate a flexible silicon electronics device used for a medical application. The thin device produced high-density maps of a beating heart's electrical activity, providing potential means to localize and treat abnormal heart rhythms. The results are published as the cover story in the March 24 issue of the journal Science Translational Medicine.
The emerging technology holds promise for a new generation of flexible, implantable medical devices, for the treatment of abnormal heart rhythms or epilepsy, as well as new flexible sensors, transmitters, and photovoltaic and microfluidic devices. These biocompatible silicon devices could mark the beginning of a new wave of surgical electronics.
"We believe that this technology may herald a new generation of active, flexible, implantable devices for applications in many areas of the body", stated co-senior author Brian Litt, MD, an associate professor of Neurology at the University of Pennsylvania School of Medicine and also an associate professor of Bio-engineering in Penn's School of Engineering and Applied Science. "Initially, we plan to apply our findings to the design of devices for localizing and treating abnormal heart rhythms. We believe these new devices will allow doctors to more quickly, safely, and accurately target and destroy abnormal areas of the heart that are responsible for life-threatening cardiac arrhythmias."
Several treatments are available for hearts that dance to their own tempo, ranging from pacemaker implants to cardiac ablation therapy, a process that selectively targets and destroys clusters of arrhythmic cells. Current techniques require multiple electrodes placed on the tissue in a time-consuming, point-by-point process to construct a patchwork cardiac map. In addition, the difficulty of connecting rigid, flat sensors to soft, curved tissue impedes the electrodes' ability to monitor and stimulate the heart.
"Implantable silicon-based devices have the potential to serve as tools for mapping and treating epileptic seizures, providing more precise control over deep brain stimulation, as well as other neurological applications", stated Story Landis, PhD, director of the National Institute of Neurological Disorders and Stroke, which provided support for the study. "We are excited by the proof of concept evident in the investigators' ability to map cardiac activity in a large animal model."
The patchwork grid of cardiac sensors adheres to the moist surfaces of the heart on its own, with no need for probes or adhesives, and lifts off easily. The array of hundreds of sensors gives cardiac surgeons a more complete picture of the heart's electrical activity so they can quickly find and fix any short circuits. In fact, the cardiac device boasts the highest transistor resolution of any class of flexible electronics for non-display 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", explained Brian 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."
Now, 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 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. 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", added Brian Litt and co-senior author John Rogers, PhD, from the University of Illinois.
In this experiment, the 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 2000 transistors spaced closely together, while standard clinical systems usually use about five to 10 contacts and no active transistors. The new device is 14,4 millimeters by 12,8 millimeters, roughly the size of a nickel. "We demonstrated high-density maps of electrical activity on the heart recorded from the device, during both natural and paced beats", stated co-author David Callans, MD, 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", stated John Rogers. "We're still working on a solution to that problem." One solution could be to have the heart power the device.
Any significant bending or stretching to circuits renders an electronic device useless, which is what limits current electronics for use on the body. Younggang Huang and John Rogers jumped this sizeable hurdle by creating an array of tiny circuit elements connected by metal wire "pop-up bridges". When the array is bent or stretched, the wires - not the circuits - pop up. This approach allows circuits to be placed on a curved surface.
This research is a result of a collaboration between the John Rogers laboratory, where the flexible electronics technology in the devices was developed and fabricated, and Brain Litt's bio-engineering laboratory at Penn, where the medical applications were designed and tested. Heart rhythm experiments were designed and performed in David Callans' cardiology laboratory. Mechanical engineers Younggang Huang, PhD, and Jianliang Xiao at Northwestern University and University of Illinois performed the mechanical modelling and design that enables the devices to wrap around the heart and other irregular, curved organs.
The title of the paper is "A Conformal, Bio-Interfaced Class of Silicon Electronics for Mapping Cardiac Electrophysiology". In addition to Younggang Huang, John Rogers and Brian Litt, other authors of the paper are Jianliang Xiao, of Northwestern; Dae-Hyeong Kim and Yun-Soung Kim, of the University of Illinois; and Jonathan Viventi, Justin A. Blanco, Nicholas Annetta, Andrew Hicks, Joshua D. Moss and David J. Callans, of the University of Pennsylvania.
Brian Litt and John Rogers noted that the core of their collaboration is Penn Bioengineering PhD student Jonathan Viventi and University of Illinois post-doctoral fellow Dae-Hyeong Kim, PhD, who are co-first authors on the publication. The work was also supported by Joshua Moss, MD, a cardiology fellow at Penn, and several undergraduates and master's students. The research was funded by National Institute of Neurological Disorders and Stroke, the Klingenstein Foundation, the Epilepsy Therapy Project, and the University of Pennsylvania Schools of Medicine and Engineering.
Penn Medicine is one of the world's leading academic medical centres, dedicated to the related missions of medical education, biomedical research, and excellence in patient care. Penn Medicine consists of the University of Pennsylvania School of Medicine - founded in 1765 as the United States' first medical school - and the University of Pennsylvania Health System, which together form a $3,6 billion enterprise. Penn's School of Medicine is currently ranked no. 3 in U.S. News & World Report's survey of research-oriented medical schools, and is consistently among the nation's top recipients of funding from the National Institutes of Health, with $367,2 million awarded in the 2008 fiscal year.