Self-rechargeable cardiac pacemaker system with triboelectric nanogenerators

The development of self-powered implantable medical devices is a significant area of research, driven by the need to reduce the frequency of high-risk surgeries required for battery replacements. Current energy harvesting technologies have limitations in their ability to efficiently power implantable devices, particularly those requiring the power of titanium-packaged devices. The reliance on external power sources or short-lived internal batteries necessitates frequent surgical interventions, posing risks to patients. This research addresses these challenges by exploring the potential of triboelectric nanogenerators (TENGs) as a self-powered energy source for implantable medical devices. Specifically, the focus is on developing an inertia-driven TENG (I-TENG) that can harness the readily available mechanical energy from body movement and gravity to power a cardiac pacemaker. This approach aims to eliminate the need for battery replacements, offering a significant improvement in patient safety and the longevity of the device. The successful development of such a system would represent a substantial advancement in implantable medical technology, paving the way for a new generation of self-rechargeable and long-lasting implantable devices.

Previous research has explored various energy harvesting methods for implantable devices, including piezoelectric generators, electromagnetic induction, and other TENG designs. However, these approaches often face challenges related to low power output, complex device designs, or reliance on specific types of body movements. Piezoelectric generators, while capable of generating energy from mechanical stress, often exhibit limited power density and may not be suitable for all applications. Electromagnetic induction methods, while efficient in some scenarios, usually require complex circuitry and may be hindered by electromagnetic interference. Prior TENG designs have also faced limitations in their output power and scalability. The existing literature highlights the need for a more efficient, robust, and biocompatible energy harvesting solution for implantable medical devices, a need that this research aims to address. The development of this I-TENG system builds upon existing research on TENG technology, addressing the limitations of previous designs by focusing on maximizing energy output while ensuring biocompatibility and ease of integration with implantable medical devices. The use of inertia as the primary energy source also provides a more consistent and reliable method of power generation compared to some other methods that depend on specific types of body movements.

The researchers designed and fabricated a five-stacked I-TENG, aiming for a compact and highly efficient energy harvester. The device's core components include a polytetrafluoroethylene (PFA) film, a copper (Cu) electrode, and a polyvinyl alcohol (PVA-NH2) layer. The PFA film undergoes surface modification via reactive ion etching (RIE) and electrical polarization to enhance its triboelectric properties. The PFA film and Cu electrode form a triboelectric pair; relative motion between these materials generates electrostatic charge, which is then converted into electrical energy. The stacking of five I-TENG units in parallel was designed to increase the overall power output. The device's working mechanism involves the use of inertial forces generated by body motion and gravity. This indirect mechanical force synchronizes the operation of the five I-TENGs, allowing for efficient current amplification without the need for additional electronic components. The generated electrical energy is stored in capacitors and a lithium-ion battery through a power management system, which includes low-pass filters and a power management integrated circuit (PMIC). This system is designed to efficiently manage the harvested energy, regulate voltage levels, and charge the battery. The I-TENG's performance was characterized using a shaker to simulate body movements, measuring voltage and current output under various conditions, including varying frequencies, load resistances, and numbers of stacked I-TENGs. The internal energy conversion efficiency was calculated by comparing output electric energy to input kinetic energy. To assess the device's performance in a biological context, the researchers conducted preclinical studies in a large animal model. The encapsulated devices were implanted subcutaneously into a mongrel dog to evaluate real-time energy harvesting. Output voltage and capacitor charging data were collected wirelessly via a Bluetooth Low Energy (BLE) system. The biocompatibility of the encapsulated device was evaluated using Masson's trichrome stain to assess inflammatory response. Finally, the I-TENG was integrated with a cardiac pacemaker to create a self-rechargeable pacemaker system. The system's performance was evaluated in the animal model under both normal conditions and induced bradycardia. The system's capability of both sensing the heart rhythm and pacing when necessary was evaluated and recorded.

The five-stacked I-TENG demonstrated a root mean square (RMS) power density of 4.9 µW/cm³ under a 3 Hz shaking condition in laboratory experiments. This power output was significantly enhanced by the stacking and synchronization of multiple I-TENG units. The preclinical in vivo study demonstrated the ability of the I-TENG to effectively harvest energy from the animal's natural movements, including those during sleep. The device was able to charge a 60 µF capacitor even with minimal movement during sleep, generating around 144 mW of power over a 24-hour period. The power management system successfully charged a lithium-ion battery using the energy harvested by the I-TENG in the animal model. Biocompatibility studies indicated a mild inflammatory response and fibrotic capsule formation, comparable to a commercial medical device. This suggests acceptable biocompatibility with minimal adverse effects on the surrounding tissue. The integration of the I-TENG with a cardiac pacemaker resulted in a functional self-rechargeable system. The system successfully demonstrated ventricle pacing in both asynchronous (VOO) and synchronous (VVI) modes. The self-rechargeable pacemaker successfully sensed bradycardia induced by adenosine injection and/or vagus nerve stimulation, initiating ventricle pacing to maintain the heart rate above a pre-set threshold. The results also showed a nearly linear relationship between the vertical displacement of the I-TENG and the generated voltage.

The results of this study demonstrate the feasibility of creating a self-rechargeable cardiac pacemaker system using an I-TENG. The device effectively harvests energy from readily available body movements, negating the need for battery replacements. This technology offers significant advantages in terms of patient safety and improved device longevity. The in vivo preclinical testing showed that the I-TENG generates sufficient power to charge a battery and maintain the functioning of the pacemaker. The acceptable biocompatibility profile suggests minimal risk of adverse tissue reactions. The successful integration with the cardiac pacemaker and demonstration of both VOO and VVI pacing modes confirm the system's functionality and clinical relevance. The variation in power output between lab and in vivo experiments highlights the need for optimization of device placement and further investigation into the specific biomechanical inputs in different body locations. This work opens new opportunities for the development of self-powered implantable medical devices and health monitoring systems, improving patient care and reducing the burden of repeated surgical interventions. Future research might focus on further improving the energy harvesting efficiency of the I-TENG, optimizing the power management system, and conducting longer-term in vivo studies to fully evaluate the long-term reliability and biocompatibility of the device.

This study successfully demonstrated a self-rechargeable cardiac pacemaker system powered by an innovative inertia-driven triboelectric nanogenerator. The I-TENG efficiently harvests energy from body movements, successfully charging a lithium-ion battery and powering the pacemaker in a preclinical model. The system showed good biocompatibility and demonstrated both VOO and VVI pacing modes, offering a potential solution for eliminating the need for battery replacements in cardiac pacemakers. Future work should focus on enhancing the device's power output and conducting larger-scale, longer-term in vivo trials to further validate its clinical applicability and reliability.

The current study used a limited number of animal subjects, and longer-term studies are needed to assess the long-term reliability and biocompatibility of the device in vivo. The power output of the I-TENG may vary depending on the intensity and type of body movement, requiring further optimization for consistent performance. The study focused on a cardiac pacemaker application; the suitability of the I-TENG for powering other implantable medical devices requires further investigation.