More than Flexible—Soft Electronics for Seamless Integration with the Human Body

Soft electronics is an exciting research field that aims to seamlessly integrate electronic components and devices onto non-rigid, non-planar, complex 3D surfaces and objects. The research on soft electronics has been mainly driven by the increasing request for a new category of portable and ubiquitous electronic systems capable of bridging the gap between biology and electronics, and of being integrated with the human body, with non-conventional features such as conformability. One of the most interesting field of applications of epidermal electronics is undoubtedly the engineering of bioelectrodes for monitoring biopotentials, such as electrocardiography (ECG), electromyography (EMG), electrooculography (EOG) and electroencefalography (EEG) signals from the surface of the skin.<br/>The main challenge today lies in the methods of connecting such imperceptible films to external electronics, a problem that effectively voids some of the main advantages of having an ultra-thin and conformable device. On the other hand, another important issue to be solved is related to the improvement of the conformability of such electrodes in order to maximize their signal recording capabilities.<br/><br/>We here present our recent results on the engineering of soft bioelectrodes, utilizing cost-effective conductive polymers functionalized with a new category of ionic liquids and ferromagnetic nanoparticles.<br/>We propose a simple, cost-effective approach using low-resolution, large-area manufacturing techniques for the fabrication of tattoo bioelectrodes based on biocompatible materials such as PEDOT:PSS and ionic liquids. Thanks to the ionic liquids, we demonstrate an impressive level of conformability and mechanical stability of the electrodes, enabling them to record biopotentials (ECG, EMG, EOG, and EEG) for several hours with performance (i.e., signal-to-noise ratio) comparable to that of commercial wet electrodes.<br/>Moreover, thanks to the functionalization of the proposed ultra-thin tattoos inexpensive ferromagnetic nanoparticles, they can be directly interfaced with the read-out electronics using magnetic connectors without compromising their conformability.<br/>This approach, at the intersection of epidermal and organic electronics, offers high-performing and conformable soft bioelectrodes, while overcoming important issues related to interfacing electronics and the human body.