Northwestern University scientists have developed a pacemaker so small that it can fit inside the tip of a syringe — and be non-invasively injected into the body.
While still years away from being tested in humans, the wireless pacemaker was hailed as a "transformative breakthrough" that could spur advances in other areas of medicine.
The pacemaker, which is smaller than a grain of rice, is controlled by light shone through the skin. The device generates power and squeezes the heart’s muscles after injection through a stint.
In a recently published study, the pacemaker demonstrated its ability to consistently coordinate healthy heart beats in the hearts of rats, dogs, and humans. Additionally, it is biocompatible and, after brief use, is eventually broken down by the body. The device, which is more than 23 times smaller than earlier bioabsorbable pacemakers, paves the way for minimally invasive implants that wirelessly check on heart health following major surgery or other cardiac issues.
“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.”
“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.”
Instead of using near-field communication to supply power, the new, tiny pacemaker operates through the action of a galvanic cell, a type of simple battery that transforms chemical energy into electrical energy. Specifically, the pacemaker uses two different metals 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, reports Northwestern.
“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.”
Pulsing with light
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.
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“Infrared light penetrates very well through the body,” Efimov said. “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.”
Even though the pacemaker is so tiny — measuring just 1.8 millimeters in width, 3.5 millimeters in length and 1 millimeter in thickness — it still delivers as much stimulation as a full-sized pacemaker.
“The heart requires a tiny amount of electrical stimulation,” Rogers said. “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.”
More sophisticated synchronization
Because the devices are so tiny, physicians could distribute collections of them across the heart. A difficult color of light could illuminate to independently control a specific pacemaker. Use of multiple pacemakers in this manner enables 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 technology’s versatility opens a broad range of other possibilities for use in bioelectronic medicines, including helping nerves and bones heal, treating wounds and blocking pain.
