Overwhelming increase of adult and chronic diseases on account of population aging motivates the development of health and activity trackers, which can offer an all-day activity, sleep patterns, weight profiles, medical diagnosis and more. While the portable electronics serve as the state-of-the-art activity monitoring technology, they are unable to meet the stringent and ever-increasing demands for the patients with adult and chronic diseases, such as diabetes, asthma, anemia and etc. The wearable and implantable electronics are attracting increased interest for applications in health and activity trackers due, in part, to their ability to dramatically improve the convenience, comfortability, and sensibility. The market for wearable and implantable devices has indeed grown exponentially over the past decades, and demand for the devices is expected to reach up to 51 billion US dollars by 2022 [1]. While those devices are emerging as the health and activity trackers, they face many potential challenges, such as potential toxicity to the human being, inaccuracy sensing, and flexible and stretchable power supplier. Especially, the power supplier for future technology requires sustainability, maintenance-free, flexibility and stretchability. The development in electronics has been miniaturization and portability so that it leads to requiring the tiny-scale energy for powering the small electronics, making it possible to utilize the energy harvesting from our environment to power them. This is a newly emerging field of Nano Energy [2], which is the application of nanomaterials and nanotechnology for harvesting and storing energy.

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Herein, we have devoted to developing the self-powered wearable and implantable nanoelectronics, with an emphasis on important components such as energy harvesting/storage devices and bioinspired sensors. The proposed research has focused on: (1) the development of flexible and stretchable energy harvesting devices in which piezoelectric and triboelectric materials facilitate the energy harvesting from renewable sources, and (2) the development of flexible and stretchable energy storage devices to integrate into wearable and implantable electronics. Lastly, (3) the development of the bio-inspired biosensors which are operational in the range of micro-milli Watt.

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[1] "Wearable Devices Market By Product Analysis (Wrist-wear, Foot-wear, Eye-wear, Body-wear, Neck-wear); By Application Analysis (Fitness and sports, Infotainment, Healthcare, Defense, Enterprise and industrial) and By Regional Analysis - Global Forecast by 2016 – 2022", Heraldkeeper, April 2018.
[2] Z. L. Wang, G. Zhu, Y. Yang, S. Wang, C. Pan, Materials Today (2012) 15, 532-543.

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Acknowledgments
We acknowledge the supports from the Department of Mechanical Engineering, Faculty of Engineering, the University Research Committee @ HKU, Environment and Conservation Fund, and Research Grants Council.

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Ongoing projects