Wearable and Implantable Triboelectric Nanogenerators for Sensing and Energy Harvesting in Healthcare Applications

Abstract

Healthcare management has been a topic of interest for researcher since ages due to its vital importance in our lives. With the miniaturization of electronic devices, a need of a technology is arisen that can provide all major solutions i.e., sensing, self-powered, and can treat the diseases. The nanogenerator (NG) technology provides a new pathway by using nanostructured and eco-friendly materials toward biomedical systems by harvesting biomechanical energy. Among these technologies, triboelectric NGs (TENGs) are well-developed to meet all these demands, giving self-powered, sustainable, environment-friendly, biodegradable, flexible, and low footprint devices. Based on these technologies, various healthcare solutions are suggested to make human lives better. TENG is an energy harvesting technology that converts repetitive mechanical energy into electrical energy using the concept of contact electrification and electrostatic induction. In this thesis, novel materials and TENG structures are developed to sense the changes in the human body, harvest energy from those changes, and provide treatment solutions for any abnormality. Certain limitations such as device durability, low electrical performance, non-biodegradability in human tissues, and energy harvesting from non-traditional sources are discussed and minimized by proposing the highly improved TENG devices. Firstly, we demonstrated a new rolling type triboelectric nanogenerator (RL-TENG), that produced lower crest factor (the ratio of the peak to the RMS value of output voltage) than the contact-separation mode TENGs, using a metal layer and graphene nanoplatelets-doped PDMS. These additions improved the dielectric constant and the charge storage capacity of the TENG, leading to a high electrical output while minimizing surface damage. As compared to a pristine TENG, our device, the RL-TENG, generated a high open-circuit peak voltage of 75.2 V, which was almost 15-fold of the pristine device, and a short-circuit peak current of 7.36 μA, which was 12 times higher. A dual-side double-belt TENG (DB-TENG) was also designed to improve these values to 164 V and 10 μA. Lastly, our device was used in a real-life application, to harvest mechanical energy from the movement of the human elbow while walking, and produced a very high voltage output of up to 821 V. This wearable device was used to monitor walking patterns such as walking, jogging, and running to evaluate human walking behaviors. These results show that the DB-TENG can be used for high-efficiency harvesting of energy from human motion. Secondly, a solution for faster bone healing is proposed using the TENG technology. We presented a flexible, biodegradable, and implantable triboelectric nanogenerator (TENG) powered by 20 kHz ultrasound. The TENG device is fabricated using a new material blend that increases flexibility and degradation rate along with twice the energy harvesting efficiency as compared to pristine material. Ultrasound-driven degradation of the device is also achieved to fasten the degradation process. Moreover, an FEM simulation resulted that serrated electrode (SE) used in the device increased the maximum output electric field intensity by 27% compared to a flat interdigitated electrode. Direct electrical stimulation of the bone cells without intermediate circuits successfully increased cell proliferation by 93% and cell differentiation by 15%. This absence of any circuitry in the device can also help in the full degradation of it without any harmful consequences. Lastly, an integrated ultrasound TENG device (iUS-TENG) was implanted subcutaneously under in a Sprague-Dawley (SD) rat to demonstrate its in-vivo power generation capability. We believe this broad-spectrum study of TENG devices to facilitate healthcare is a milestone in realizing a comprehensive detection, self-sustainable, and treatment system. Artificial intelligence (AI) coupled with such devices can make it a completely independent healthcare solution making any external intervention unnecessary.