Implantable Cardiac Monitor Could Last Seven Decades In The Body
Northwestern scientists have developed a paper-thin patch that could adhere to the surface of the heart and monitor its activity. The researchers claim that innovations with the materials used in the patch could allow the implant to last up to seventy years without leaking.
The challenge of complex biosensors for cardiac implants is creating circuitry that is flexible enough to adhere to a beating heart without being prone to leaks, which would destroy the implant and endanger to the patient, explained John Rogers, professor of materials science and engineering at Northwestern. In November, Rogers and his team introduced a “tiny, wearable stethoscope” that could be worn on the outside of the body to monitor cardiac activity.
Now, Rogers team is moving inside the body with a paper-thin device that could adhere to the tissue of the heart and detect activity with 396 voltage sensors set in a 9.5 x 11.5-mm patch of silicone dioxide glass that insulates metal conductors. To ensure an even and leak-proof surface, researchers grew the device on a wafer of pure silicone, one layer at a time.
Rogers explained that the insulation is necessary to prevent dangerous electrical leaks caused by metal conductors corroding over time, but must be thin enough to allow strong electrical coupling.
“You want this layer to be as thin as possible to enable a strong electrical coupling to the surrounding tissue, but you need it to be thick enough to serve as a robust barrier to water penetration,” Rogers told IEEE Spectrum. “If water penetrates any location across the entire area of the device, it’s game over because you’ll get electrical leakage that destroys the entire device.”
Rogers further explained that short circuits could be life-threatening and would preclude the use of the device in humans. To reduce these risks, Northwestern’s sensor uses capacitive coupling that can be read through the layer of silicone dioxide.
In a study published in Nature Biomedical Engineering, researchers ran several tests with their devices to test its flexibility and long-term stability in conditions that mimic the body’s interior. First, they submerged the device in salt water at various temperatures and then attached the device to a rabbit’s heart. By analyzing leakage levels, researchers projected that the device could persist inside the body for seven decades.
“Individually, none of the concepts were entirely new — there’s been lots of innovation in this area — but taken together, it’s a very significant step,” said Polina Anikeeva, MIT professor of materials science and engineering, who was not involved in the research, to IEEE Spectrum. “People have done individual neurons and small groups of neurons, but not necessarily an entire heart.”
According to Rogers, the research is entirely scalable and could be applied to different organs in the body, even the brain. Researchers also plan to investigate whether the device could be used to transfer energy to an organ or muscle, similar to a pacemaker.
Related, recent research funded by JDRF has developed a longer-lasting continuous glucose monitor (CGM) by incorporating live cells into sensors that allow them regenerate over time.