Engineers at Northwestern University have developed what they believe is the world’s smallest pacemaker—a device so miniaturized it can be noninvasively injected into the body through a syringe. Smaller than a grain of rice, this biocompatible pacemaker significantly advances temporary cardiac pacing technology.

The pacemaker measures just 1.8 millimetres in width, 3.5 millimetres in length, and 1 millimetre in thickness. Despite its diminutive size, the device delivers electrical stimulation equivalent to a full-sized pacemaker.

To achieve this level of miniaturization, the engineering team had to redesign the entire power system. “Our original pacemaker worked well,” explains Northwestern bioelectronics engineer John A. Rogers, who led the device development. “It was thin, flexible and fully resorbable. But the size of its receiver antenna limited our ability to miniaturize it.”

The solution involved a shift from radio frequency-based control to a light-activated mechanism, eliminating the need for a built-in antenna and allowing for a substantial size reduction.

Unlike conventional pacemakers that rely on batteries, this device operates through a galvanic cell that utilizes the body’s fluids as an electrolyte.

“When the pacemaker is implanted into the body, the surrounding biofluids act as the conducting electrolyte that electrically joins two metal pads to form the battery,” Rogers explains.

The pacemaker uses two metals as electrodes to deliver electrical pulses to the heart. When these electrodes come into contact with surrounding biofluids, they form a simple battery. The resulting chemical reactions generate an electrical current that flows to stimulate cardiac tissue.

The pacemaker pairs with a small, flexible, wireless wearable device mounted on the patient’s chest. This external component monitors the heart’s rhythm and automatically emits infrared light pulses that penetrate the patient’s skin, breastbone, and muscles when detecting an irregular heartbeat.

These light pulses activate a tiny switch on the pacemaker, turning it from an “off” state to an “on” state. The light then flashes at a rate corresponding to the normal heart rhythm, controlling the pacing.

“Infrared light penetrates very well through the body,” notes Igor Efimov, Northwestern experimental cardiologist and study co-lead. “If you put a flashlight against your palm, you will see the light glow through the other side of your hand. It turns out that our bodies are great conductors of light.”

While the pacemaker works with hearts of all sizes, it’s particularly well-suited for newborns with congenital heart defects, representing about 1% of births worldwide.

“Our major motivation was children,” Efimov explains. “The good news is that these children only need temporary pacing after surgery. In about seven days or so, most patients’ hearts will self-repair. But those seven days are absolutely critical.”

The device addresses specific limitations in treating pediatric patients whose tiny, fragile hearts require minimal and gentle interventions. Traditional temporary pacing methods can be especially problematic for these little patients.

Designed for patients requiring only temporary pacing, the pacemaker dissolves naturally after it’s no longer needed. All components are biocompatible and naturally dissolve into the body’s biofluids, eliminating the need for surgical extraction.

This addresses a significant limitation of current temporary pacemakers, which require surgical removal that can potentially damage heart tissue.

“The heart requires a tiny amount of electrical stimulation,” Rogers notes. “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.”

The current standard of care for temporary pacing involves surgeons sewing electrodes onto the heart muscle during surgery. Wires from these electrodes exit through the patient’s chest and connect to an external pacing box that delivers current to control heart rhythm.

When no longer needed, physicians must remove these pacemaker electrodes—a procedure that can lead to complications including infection, dislodgement, tissue damage, bleeding, and blood clots.

“Wires literally protrude from the body, attached to a pacemaker outside the body,” Efimov explains. “When the pacemaker is no longer needed, a physician pulls it out. The wires can become enveloped in scar tissue. So, when the wires are pulled out, that can potentially damage the heart muscle.”

The small size of these devices enables new therapeutic approaches that weren’t previously possible. Physicians could potentially deploy multiple pacemakers across different areas of the heart and control each independently using different coloured light.

“We can deploy a number of such small pacemakers onto the outside of the heart and control each one,” says Efimov. “Then we can achieve improved synchronized functional care.”

This approach enables more sophisticated synchronization compared to traditional pacing. In exceptional cases, different areas of the heart can be paced at different rhythms to terminate arrhythmias.

The technology’s versatility extends beyond cardiac applications. The tiny injectable pacemaker could be integrated with various implantable medical devices, including heart valve replacements.

“Because it’s so small, this pacemaker can be integrated with almost any kind of implantable device,” Rogers notes. “We also demonstrated integration of collections of these devices across the frameworks that serve as transcatheter aortic valve replacements.”

The fundamental technology might eventually support other bioelectronic medicine applications, including nerve and bone healing, wound treatment, and pain blocking.

The study, published in Nature, demonstrates the device’s efficacy across large and small animal models and human hearts from deceased organ donors, validating its potential for clinical applications.

This work builds on previous research by Rogers and Efimov, who developed the first dissolvable device for temporary pacing several years ago. The current innovation represents a significant advancement in size reduction and functionality.

If these trials continue to demonstrate success, this ultra-miniature pacemaker could offer a less invasive, lower-risk alternative for patients requiring temporary cardiac pacing, mainly benefiting the most minor and most vulnerable patients.