Engineering self-assembled bilayer hyper-elastic electronic skin with a disrupted toughness-hysteresis trade-off: Fabrication, characterization, and applications

Abstract

Electronic skin (e-skin) designed for human activity and health monitoring often faces a trade-off between toughness and hysteresis, where increased toughness typically results in significant hysteresis, compromising sensing reliability. Here, we report a tough yet low-hysteresis e-skin, achieved through a self-assembled bilayer architecture consisting of a porous hyper-elastic Ecoflex layer embedded with multi-walled carbon nanotube (MWCNT) based conductive ink and a non-porous hyper-elastic matrix. The porous layer provides low Young’s modulus and reduced toughness, while the non-porous layer enhances Young’s modulus and overall toughness, effectively disrupting the conventional toughness-hysteresis correlation. The toughness of the bilayer was ∼9 times higher and the hysteresis was ∼2 times lower compared to its constituents. The physics behind the disruption observed from the experiments was studied by finite element simulations where strain softening effect could be observed as a cause of this disruption. Structural characterization confirms a uniform bilayer configuration with well-dispersed MWCNTs, ensuring superior mechanical resilience, minimal hysteresis, and optimal electrical conductivity. The sensor demonstrates a strain sensitivity of 2.4 up to 600 % strain, rapid response time of 81 ms, minimal dynamic drift, 0.1 % of strain resolution, and an outstanding repeatability and durability. Applications demonstrated include wearable sensing for mechanical impedance-based muscle fatigue assessment and assessment of elongation in air-burst testing of male condoms, highlighting its potential for both biomedical and industrial applications.