Lignin-reinforced eutectogel with environmentally stability for high-performance human multi-functional sensor.

Intrinsic environmental instability of hydrogels has limited their practical applications as durable flexible sensors in human life. In this study, a bio-based eutectogel (BEG) with environmental tolerance was designed via deep eutectic solvent (DES), thioctic acid (TA) and lignin. Benefit from self-ring-opening polymerization of TA monomer in the ethanol and the lignin acting as free radicals, the BEG was fabricated through efficient cast-drying method. The dynamic interaction formation between DES and TA polymer network was revealed by using in-situ infrared spectroscopy during the ethanol evaporation process. The introduction of lignin not only improve the mechanical properties of the eutectogels, but also endow the BEG with moisture tolerance by activating self-aggregated dense hydrophobic layer on the surface while in high humidity environment. This bio-based eutectogels with non-volatility, board range operating temperature and proper self-adhesion could serve as long-term stable temperature-strain dual sensor with high sensitivity (GF = 1.17, TCR = 4.26 %/K) and rapid response behavior (373 ms). Furthermore, the biocompatible BEG was validated for recording human physiological signals over extended period with performance comparable to commercial hydrogel electrodes. This strategy could broaden the range of making durable stretchable eutectogels in human healthcare monitoring.