Atoms to Systems Lab 

Skin-conformal and stretchable sensors are currently at the centre stage of wearable electronics and human-machine interfaces. Despite tremendous progress in recent years, the design of pressure, strain, and tactile sensors with high performance, high stability, and mechanical robustness is still a challenge.

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Our group have developed several generations of flexible and self-healable pressure sensors. Some designs are bio-inspired, such as by the bean pod structure. Our sensors obtain unprecedented sensitivity, improved linearity, and a wide sensing range. We have fabricated devices based on a novel structures and chemical compositions, including one consisting a microspacer core layer of polystyrene (PS) microspheres, sandwiched by two laser-induced graphene/polyurethane (LIG/PU) films. We have realized the technique in the form of a patch attachable to the human wrist,. The sensor enables continuous human arterial pulse monitoring, successfully demonstrating the differentiation of percussion (P), tidal (T) and diastolic (D) peaks. Our flexible pressure sensors are highly suitable for human physiological diagnostics and other advanced wearable applications.

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Since the last couple of years, we have been exploring piezoionic skins. The human somatosensory network relies on ionic currents to sense, transmit, and process tactile information. We synthesize hydrogels that transduce pressure into ionic currents. As in fast- and slow-adapting mechanoreceptors, piezoionic currents can vary widely in duration, from milliseconds to hundreds of seconds. These currents can be used for neuromodulation and muscle excitation, suggesting a path toward bionic sensory interfaces. Signal magnitude and duration depend on cationic and anionic mobility differences. Patterned hydrogel films with gradients of fixed charge provide voltage offsets akin to cell potentials. The piezoionic sensing mechanism provides a charge density 4-6 orders of magnitude higher than those of triboelectric and piezoelectric devices, holding promise as a revolutionary approach to mechanosensing. Other promising avenues include mixed ionic and electronic transport, further expanding the reach of possible performance and applications.

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