The development of engineered devices that can harvest and convert the mechanical motion of the human body into electricity is essential for powering bioelectronic devices. This mechanoelectrical energy conversion is vital for devices like cardiac pacemakers, brain stimulators, and wearable drug delivery systems. While there have been numerous attempts to create miniaturized mechanoelectrical converters over the last decade, the challenge to achieve high electrical output along with designs that conform to the body's structure continues to be a significant challenge. Now, researchers have achieved a breakthrough with the development of a high-performance mechanoelectrical energy converter based on hydrogels—water-rich soft polymeric materials—for powering bioelectronic devices.

At The University of Hong Kong (HKU, Pokfulam, Hong Kong), researchers have built an electric generator using an ion-loaded hydrogel placed between two electrodes. When mechanical pressure is applied to this setup, the positively charged ions and negatively charged ions in the hydrogel move at varying rates. This movement results in the separation of electric charges, generating voltage and current that can be harnessed by an external circuit. The team has innovatively used asymmetric designs in the device, significantly boosting the electrical output to levels much higher than previously achieved, specifically 5.5mA/m2 and 916 mC/m2 per cycle. This output surpasses that of triboelectric nanogenerators and other flexible generators by approximately ten times. In their study, the researchers demonstrated a soft patch capable of controlled drug release, highlighting the potential applications of this technology in other biomedical devices such as cardiac pacemakers, wearable health monitors, and interfaces for virtual and augmented reality.

“The key is to use structural and chemical asymmetry to amplify the separation of charges in the ion-loaded hydrogel.” said HKU’s Professor Lizhi Xu, adding, “with these asymmetric designs, the electrical output of the hydrogel generators was enhanced by orders of magnitudes, which is important for the powering of miniaturized biomedical devices.”

“Hydrogels are good body-conformal device structures because they are soft, flexible, and can be designed to mimic the properties of biological tissues. They are highly biocompatible and able to conform to the shape of various tissues in the body.” Professor Xu said. 

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