Engineering design for soft biomedical devices : from sensor to power

Abstract

Soft and robust biomedical electronics attract more and more attentions. Soft electronics has undergone significant advancements over the last twenty years. Emerging soft biomaterial electronics have broad applications in health monitoring, medical treatment, kinematics, and more, as they can seamlessly integrate with skin or internal tissues and function without affecting the wearer's daily activities. Despite significant progress in material and structural improvements, challenges still remain in the development of soft biomaterial electronics. This thesis aims to improve the sensors and power components of soft biomaterial electronic devices through appropriate engineering design.

Kirigami structure is able to improve the stretchability of devices by introducing incisions and has advantages such as low modulus, low stiffness, high stretchability, with the ability to be integrated into complex 3D surfaces. However, stress concentration at the incision significantly reduces the overall fracture toughness of the device when stretched. Therefore, we developed a tough multifunctional framework for cut-paper electronics and demonstrated experimentally and theoretically that this hyperbranched fiber network framework can effectively suppress crack propagation and improve the overall toughness of the device. On this basis, we integrated relevant circuits into this framework, and the resulting devices exhibited superior mechanical and electrical performance as human-machine interaction interfaces, paving the way for the practical application of kirigami electronics.

One potential solution for powering soft electronic devices is by harvesting low-frequency mechanical energy from the human body and converting it into electrical energy. This approach offers several advantages, including the elimination of the need for charging, a negligible impact on normal physiological activity, and no reliance on external environmental factors. Existing energy conversion technologies have their own advantages and disadvantages. Electromagnetic induction generators can output high current at high frequencies but are bulky and have a high density. Triboelectric and piezoelectric generators are known for their high output voltage and low frequency requirements. However, due to their high internal resistance, they suffer from low output current. Currently, there is no device that can output high current and high transfer charge under low-frequency mechanical stimulation. Using this concept as a foundation, we have created a groundbreaking ion-motion-based converter capable of efficiently harvesting and converting low-frequency mechanical energy into high-current output. In comparison to other devices, our converter possesses a significantly higher transfer charge, making it a highly promising solution for powering soft electronic devices. We demonstrated the working principle of this type of device through experimental and theoretical analysis, and applied it to an intelligent drug release system. The ion-based converter we have developed is inherently compatible with biological systems and has the potential to serve as a reliable power source for a variety of applications, including wearable and implantable electronics, as well as bone repair, drug delivery, wound healing, and more.