Self-powered hydrogel wearable bioelectronics

The current wearable devices are largely rigid and bulky, which calls for the development of next-generation soft biocompatible technologies. Another limitation is that conventional wearable devices are generally powered by thick and non-compliant batteries, hindering the miniaturization and improvement of wearable electronics. Hydrogels have attracted tremendous attention in the field of wearable bioelectronics due to their tissue-like properties, which can minimize the mechanical mismatch between flexible devices and biological tissues. Moreover, to take advantage of physical and chemical energy from the human body or ambient environment, such as mechanical energy of human motions, body heat energy, biofuel, water or wind power from nature, more and more novel technology for portable power supply has been carried out, facilitating the improvement of wearable bioelectronics. In this review, recent advances in self-powered wearable bioelectronics based on hydrogels are summarized. Firstly, the excellent properties of hydrogels are introduced, including the prominent mechanical properties, self-healing nature, high conductivity due to the incorporation of conductive polymers or additives, interfacial adhesion functionality, biocompatibility, and antibacterial properties. Then, several novel strategies of energy harvesting are discussed, such as triboelectric nanogenerators (TENGs), piezoelectric nanogenerators (PENGs), thermoelectric nanogenerators (TEGs), biofuel cells (BFCs), hydrovoltaics, antennas, and hydrogel-based batteries. Next, some representative applications of self-powered bioelectronics are illustrated (i.e., human motion monitoring, healthcare monitoring and therapies, neural stimulation and human-machine interaction). Finally, a brief summary and outlook for self-powered hydrogel bioelectronics is presented.