Northwestern University controls pacemaker with wearable light source

08 Apr 2025

Design of world's smallest pacemaker will suit fragile hearts of newborn babies.

A team at Northwestern University (NU) has developed a pacemaker small enough to fit inside the tip of a syringe and be non-invasively injected into the body.

Although it can work with hearts of all sizes, the small dimensions of the pacemaker make it particularly well-suited to the tiny, fragile hearts of newborn babies with congenital heart defects.

Described in Nature, the breakthrough design incorporates a wearable patch for the patient containing an infra-red light source, with the emissions triggering the pacemaker when required.

"We have developed what is, to our knowledge, the world's smallest pacemaker," said Northwestern bioelectronics pioneer John A. 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."

The new platform builds on previous research at NU into improved pacemaker designs, including the 2021 creation of dissolvable devices for patients requiring temporary pacemakers after heart surgery. Varying the composition and thickness of the biocompatible materials in these devices controlled the precise number of days they remain functional before dissolving.

Those pacemakers still relied on a radio frequency scheme for wireless control of heart stimulation, however, one factor limiting the extent to which the device could be miniaturized. The NU team has now redesigned its device around optical stimulation via a wearable patch worn on the patient's chest, along with a novel power source for the implant.

Multiple synchronized pacemakers driven by light

Once the pacemaker is in place, the wearable device monitors the patient's heart rate. It that drops below a certain rate, a light-emitting diode in the patch is triggered, flashing on and off at a rate that corresponds to the normal heart rate. The light penetrates through the body to the pacemaker's bioresorbable photodetector and triggers the device.

Rather than requiring a battery, the implanted part of the device is powered by galvanic action, via two electrodes made of dissimilar metals both in contact with the biofluids surrounding the pacemaker. The resulting chemical reactions cause electrical current to flow to stimulate the heart.

Between them these redesigns have allowed the NU pacemaker to be shrunk in size to just 1.8 by 3.5 by 1 millimeters while still delivering as much stimulation as a full-sized pacemaker, according to the project.

Such a small size could mean that a number of devices can be distributed across the heart. The NU team envisages different colors of light being able to independently control specific pacemakers, bringing about more sophisticated synchronization than traditional pacing can provide. Pacing different areas of the heart at different rhythms can, for example, terminate arrhythmias.

The optically-driven pacemakers could also be incorporated into other medical devices. NU has investigated integrating them across the frameworks that serve as transcatheter aortic valve replacements, activating the pacemakers as necessary to address complications that can occur during a patient's recovery process.

"Because it's so small, this pacemaker can be integrated with almost any kind of implantable device," commented Rogers. "That's just one example of how we can enhance traditional implants by providing more functional stimulation."