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Engineers at Northwestern University have introduced a groundbreaking pacemaker so diminutive that it can be injected through the tip of a syringe, allowing for non-invasive implantation inside the body.
This innovative device is compatible with hearts of various sizes but is particularly designed for the delicate hearts of newborns suffering from congenital heart defects.
Measuring less than a grain of rice, the pacemaker is combined with a compact, soft, flexible, wireless wearable device that adheres to a patient’s chest to manage the pacing. When the wearable detects an irregular heartbeat, it emits a light pulse that activates the pacemaker. These light pulses penetrate the skin, breastbone, and muscles to regulate heartbeats.
The pacemaker is intended for temporary use and dissolves after fulfilling its purpose. Its components are biocompatible, allowing them to dissolve naturally in the body’s fluids, thereby eliminating the need for surgical removal.
The forthcoming study is set to be published on April 2 in the journal Nature. The research demonstrates the effectiveness of the device through experiments on both large and small animal models, as well as on human hearts acquired from deceased organ donors.
“We believe we have created the world’s tiniest pacemaker,” stated John A. Rogers, a leader in bioelectronics at Northwestern, during the development of the device. “Temporary pacemakers are crucial, especially in pediatric heart surgeries, making size minimization essential. A smaller device means less burden on the body.”
Co-leader of the study, Igor Efimov, an experimental cardiologist at Northwestern, expressed, “Congenital heart defects affect about one percent of newborns worldwide, regardless of a country’s resources. The fortunate aspect is that these children typically only require temporary pacing post-surgery. Most hearts will heal themselves within around seven days, but that period is critical. With this miniature pacemaker, we can provide necessary support without further invasive surgeries for removal.”
Rogers serves as the Louis Simpson and Kimberly Querrey Professor of Materials Science and Engineering, Biomedical Engineering, and Neurological Surgery at Northwestern, and is the director of the Querrey Simpson Institute of Bioelectronics. Efimov holds professorships in biomedical engineering at McCormick and in medicine (cardiology) at the Feinberg School of Medicine. They co-led the study alongside Yonggang Huang and Wei Ouyang from Dartmouth College, and Rishi Arora from the University of Chicago.
Addressing a Significant Clinical Need
This innovation builds on previous work by Rogers and Efimov, who created the first dissolvable device for temporary cardiac pacing. Many patients require such pacemakers post-heart surgery, either while waiting for a permanent solution or to restore normal rhythm during recovery.
The conventional method involves surgeons affixing electrodes to the heart during surgery, with wires leading out of the chest to an external pacing device. When the temporary pacemaker is no longer required, the electrodes must be surgically removed, which carries risks of complications such as infections, displacement, or damage to heart tissues.
“Wires protruding from the body pose risks,” Efimov noted. “When the time comes for removal, pulling these wires can cause harm, as they may entangle in scar tissue.”
In response to these clinical challenges, Rogers, Efimov, and their teams crafted a dissolvable pacemaker, making its debut in Nature Biotechnology in 2021. This thin, lightweight device has eliminated bulky batteries and rigid hardware. Rogers’s research group pioneered the concept of bioresorbable electronics, which dissolve harmlessly in the body, similar to absorbable sutures. By adjusting the materials’ composition and thickness, they can control how long the device remains active before dissolving.
Novel Power Source
Initially, the quarter-sized dissolvable pacemaker performed well in trials, but surgeons expressed the need for a smaller format for easier implantation in young patients. The original design relied on near-field communication technology, akin to what is used in RFID tags and electronic payments, which necessitated a larger antenna.
“The original pacemaker was effective but limited in size due to the antenna,” Rogers explained. “To address this, we developed a light-based activation method, allowing for significant miniaturization.”
To further shrink the device, the team innovated its power source. Instead of relying on near-field communication, the new miniaturized pacemaker utilizes a galvanic cell, a simple battery system that converts chemical energy into electrical energy. It employs two metals as electrodes that function as a battery when in contact with bodily fluids, producing the electrical pulses needed to stimulate the heart.
“In the body, biofluids act as an electrolyte to connect the electrodes and generate electricity,” Rogers said. “A minuscule light-activated switch allows us to turn the device on using light delivered through skin from the wearable patch.”
Utilizing Light for Activation
The researchers implemented infrared light for activation, which can penetrate the skin safely. When the heart rate drops below a specified threshold, the wearable detects the change and activates a light-emitting diode, sending a series of flashes corresponding to the appropriate heart rate.
“Infrared light travels effectively through biological tissue,” Efimov remarked. “For instance, if a flashlight is pressed against your hand, the light can be seen glowing on the other side. Our bodies transmit light remarkably well.”
Despite its small dimensions—1.8 millimeters in width, 3.5 millimeters in length, and 1 millimeter in thickness—the pacemaker provides the same stimulation as traditional, larger devices.
“Only a minimal amount of electrical stimulation is needed for the heart,” stated Rogers. “By reducing size, we simplify procedures, lessen trauma to patients, and the pacemaker’s dissolvable nature negates the necessity for further surgical interventions.”
Enhanced Synchronization Capabilities
The small size of the devices allows for their distribution across the heart, with the ability to utilize different colors of light to control individual pacemakers. This capacity for multiple devices enhances synchronization beyond traditional methods. In certain scenarios, distinct regions of the heart can be paced at differing rhythms to manage arrhythmias effectively.
“Multiple small pacemakers can be applied to the heart’s exterior, each controlled independently,” Efimov stated. “This enables improved synchronized functioning. Additionally, we can embed these pacemakers into other medical devices, such as heart valves, to mitigate complications during recovery.”
Rogers added, “The tiny size allows for incorporation with nearly any implantable device. We have also showcased their use within frameworks for transcatheter aortic valve replacements, enabling activation as needed to resolve complications that may arise post-surgery.”
The adaptability of this technology opens vast potential for bioelectronic applications, including the promotion of nervous system and bone recovery, wound treatment, and pain management.
The research paper titled “Millimetre-scale, bioresorbable optoelectronic systems for electrotherapy” received support from the Querrey Simpson Institute for Bioelectronics, the Leducq Foundation, and the National Institutes of Health (award number R01 HL141470).
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