The electrical interface in standard implantable medical devices hasn't changed much in decades. There's an electrode contact, a wire soldered to that and it goes back to a can that contains a battery and the active electronics. Researchers at the University of Pennsylvania (Philadelphia) have developed a flexible silicon technology half the diameter of a human hair that brings electronic circuits directly to the tissue rather than having them located remotely that, if validated, could herald a new generation of implantable medical devices.
"We hope this will revolutionize the interface between devices and tissues in many different medical applications," Brian Litt, MD, an associate professor of neurology at the University of Pennsylvania School of Medicine and an associate professor of bioengineering in Penn's School of Engineering and Applied Science, told Medical Device Daily. "Nowadays people use the term 'disruptive technology' to describe a breakthrough like this. That's what we hope it will be."
In the first reported application, a team of cardiologists, materials scientists and bioengineers have created and tested a new type of implantable device to measure the heart's electrical output to be used as part of cardiac ablation procedures to correct heart rhythm irregularities.
Today's devices for mapping and eliminating irregular heart rhythms allow for up to 10 wires in a catheter that is moved in and around the heart, and are connected to rigid silicon circuits distant from the target tissue. The design limits the complexity and resolution of devices since the electronics cannot get wet or touch the target tissue.
Litt and his team report in Science Translational Medicine that they built a device to map waves of electrical activity in the heart of a large animal. It uses the 288 contacts and more than 2,000 transistors spaced closely together, compared with the standard of just 10 contacts. They demonstrated high-density maps of electrical activity on the heart recorded from the device, during both natural and paced beats.
"We've eliminated the restraints," Litt said. "Rather than stimulating with a single lead in a pacemaker, you can do a wave of stimulation. You could theoretically wrap it around damaged heart regions and synchronize pacing."
The device is flexible and the physical properties are tuned to adhere to the heart, bending and flexing with it as well as obtaining recordings. Ease of use is a huge advantage: It can be curled up and introduced via a catheter.
"The devices sample with simultaneous submillimeter and submillisecond resolution through 288 amplified and multiplexed channels," Litt and colleagues wrote in their report. "We use this system to map the spread of spontaneous and paced ventricular depolarization in real time, at high resolution, on the epicardial surface in a porcine animal model."
The results are impressive enough that a start-up company, MC10 (Waltham, Massachusetts) was formed last year to commercialize the flexible silicon technology for a variety of medical applications. North Bridge Venture Partners committed to participating in a $5 million Series A round of financing, which closed in December. That was in addition to an earlier seed round led by Osage Partners. Litt said the new company is "well funded" at this point.
MC10 licensed the silicon technology from the University of Illinois at Urbana-Champaign, where material scientist and MC10 co-founder John Rogers, PhD, invented it.
Litt said one of his students at U-Penn heard Rogers speak about the technology a couple of years ago. A telephone call and 1.5 years later, a cadre of scientists have now taken the technology from concept to practical application. The research is funded by National Institute of Neurological Disorders and Stroke (Bethesda, Maryland), the Klingenstein Foundation (New York), the Epilepsy Therapy Project (Middleburg, Virginia) and the University of Pennsylvania Schools of Medicine and Engineering.
Although the cardiac application was the first to emerge, Litt's specialty is neurology. A paper still under embargo and due out next month will reveal experiments for a neurological application.
"The cardiac application is the first of what will be a flurry of activity in this area," Litt said.
Litt said the technology was in fact designed originally for brain applications, "But in early forms of the device, we wanted to test a big signal and the heart's signals are bigger than the brain. We think this is a platform to be used for a whole variety of applications such as peripheral nerve stimulation, bladder stimulation . . . since it's silicon-based electronics we can put all kinds of devices on it."
Rogers told MDD that he has been working on the flexible silicon technology for about seven years. He was originally focused on developing it for consumer electronics applications.
"Going from flexible displays like that to an application like this — intimate integration with the human body — has a lot of challenges, but we're intrinsically excited about it. For electronics to work well in the body, they need to be extremely flexible and capable of conforming to tissue. It also needs to be compatible when immersed in biofluids."
Rogers said his team is focussed on applying the technology to advanced surgical devices, with a vision toward long-term implantables.
"In cardiac ablation therapy for arrhythmias, we use a sheet like this to map out electrical activities to locate aberrant tissues, then to selectively activate ablation electrodes to eliminate the tissue. This type of electronics technology would enable a much more rapid and effective therapy based on what's available today."
Rogers said most of the materials science world is developing flexible electronics for displays and are using organic or plastic-based materials, moving away from silicon.
"That kind of approach is valuable, but requires reinvention of an entire set of electronic material s that can be used to build circuits," he said, adding that he turned back to silicon because it enables a higher level of performance.
The silicon sheets, 100 nm thick, are floppy and bendable. Creating an encapsulating barrier so that it can be used in the salty human body, one that didn't reduce the flexibility, was a challenge. His team found the right combination: a multilayer stack of polymers separated by silicon nitride.
"Alternating stacks make for a very effective moisture barrier," Rogers said. "The encapsulating thickness is a couple of microns thick, so it's still very thin."
Litt said the basic designs are so well advanced now that he anticipates human testing of the cardiac mapping/ablation device within a year.
In addition to work through MC10, he envisions multiple partnerships with medical device firms to explore the vast potential applications.
The next big step in this new generation of implantable devices will be to find a way to move the power source onto them. "We're still working on a solution to that problem," Rogers said.
Lynn Yoffee; 770-361-4789