Tiny pacemaker is powered by light
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Engineers in the US have developed a pacemaker small enough to be injected into the body.
The pacemaker developed at Northwestern University is aimed at the tiny, fragile hearts of newborn babies with congenital heart defects.
At 3.5 x 1.8mm and 1mm thick, the device is smaller than a single grain of rice but the battery structure still delivers as much stimulation as a full-sized pacemaker.
It is paired with a small, soft, flexible, wireless, wearable device that mounts onto a patient’s chest to control the pacing of the heart. When the wearable device detects an irregular heartbeat, it automatically shines an infrared pulse to activate the pacemaker. These short pulses— which penetrate through the patient’s skin, breastbone and muscles — control the pacing.
This is designed for patients who only need temporary pacing and dissolves after it’s no longer needed. All the pacemaker’s components are biocompatible, so they naturally dissolve into the body’s biofluids, bypassing the need for surgical extraction. By varying the composition and thickness of the materials in these devices, the team can control the precise number of days they remain functional before dissolving.
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However an array of these pacemakers could also be used across a larger heart.
“We have developed what is, to our knowledge, the world’s smallest pacemaker,” said Prof John Rogers, who led the device development. “There’s a crucial need for temporary pacemakers in the context of pediatric heart surgeries, and that’s a use case where size miniaturization is incredibly important. In terms of the device load on the body — the smaller, the better.”
“Our major motivation was children,” said Northwestern experimental cardiologist Igor Efimov, who co-led the study. “About 1% of children are born with congenital heart defects — regardless of whether they live in a low-resource or high-resource country. The good news is that these children only need temporary pacing after a surgery. In about seven days or so, most patients’ hearts will self-repair. But those seven days are absolutely critical. Now, we can place this tiny pacemaker on a child’s heart and stimulate it with a soft, gentle, wearable device. And no additional surgery is necessary to remove it.”
This builds on a dissolvable pacemaker that Rogers, Efimov and their teams developed in 2021 that was the size of a coin and powered by near field communications (NFC) with a built-in antenna.
“Our original pacemaker worked well,” Rogers said. “It was thin, flexible and fully resorbable. But the size of its receiver antenna limited our ability to miniaturize it. Instead of using the radio frequency scheme for wireless control, we developed a light-based scheme for turning the pacemaker on and delivering stimulation pulses to the surface of the heart. This is one feature that allowed us to dramatically reduce the size.”
The pacemaker uses two different metals in a galvanic cell as electrodes to deliver electrical pulses to the heart. When in contact with surrounding biofluids, the electrodes form a battery. The resulting chemical reactions cause the electrical current to flow to stimulate the heart.
“When the pacemaker is implanted into the body, the surrounding biofluids act as the conducting electrolyte that electrically joins those two metal pads to form the battery,” Rogers said. “A very tiny light-activated switch on the opposite side from the battery allows us to turn the device from its ‘off’ state to an ‘on’ state upon delivery of light that passes through the patient’s body from the skin-mounted patch.”
The team used an infrared wavelength of light that penetrates deeply and safely into the body. If the patient’s heart rate drops below a certain rate, the wearable device detects the event and automatically activates a light-emitting diode. The light then flashes on and off at a rate that corresponds to the normal heart rate.
“The heart requires a tiny amount of electrical stimulation,” said Rogers. “By minimizing the size, we dramatically simplify the implantation procedures, we reduce trauma and risk to the patient, and, with the dissolvable nature of the device, we eliminate any need for secondary surgical extraction procedures.”
Because the devices are so small, and array could be used across a larger heart, each sensitive to a different wavelength of infrared light. This could enable more sophisticated synchronization compared to traditional pacing. In special cases, different areas of the heart can be paced at different rhythms, for example, to terminate arrhythmias.
“We can deploy a number of such small pacemakers onto the outside of the heart and control each one,” Efimov said. “Then we can achieve improved synchronized functional care. We also could incorporate our pacemakers into other medical devices like heart valve replacements, which can cause heart block.”
“Because it’s so small, this pacemaker can be integrated with almost any kind of implantable device,” Rogers said. “We also demonstrated integration of collections of these devices across the frameworks that serve as transcatheter aortic valve replacements. Here, the tiny pacemakers can be activated as necessary to address complications that can occur during a patient’s recovery process. So that’s just one example of how we can enhance traditional implants by providing more functional stimulation.”
The paper is at 10.1038/s41586-025-08726-4
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