Biosafety, anti-swelling and anti-freezing amino acid-based ionogels for flexible strain sensors

Abstract

Conductive hydrogels have attracted considerable attention in flexible sensor applications due to their flexibility, conductivity, and sensitivity. However, conventional hydrogels suffer from swelling-induced deformation, low-temperature freezing susceptibility, and inadequate safety, which severely restrict their practical use. In this work, a green and biocompatible choline-amino acid ionic liquid was synthesized, effectively resolving the poor dispersibility of sugarcane cellulose. Subsequently, a polyvinyl alcohol-cellulose-choline amino acid exchanged (PCCE) ionogel was successfully fabricated through a simple freeze-thaw and solvent exchange approach, which was endowed with exceptional anti-swelling capability, environmental stability, and biosafety. The PCCE hydrogel exhibits remarkable mechanical properties, achieving a tensile strength of 2.4 MPa and toughness of 3705 kJ/m³. No crystallization peak was observed in PCCE even at −90 °C, and its mechanical properties and conductivity at −20 °C remained nearly identical to those at room temperature, demonstrating excellent anti-freezing performance. After storage in a 37 °C oven for 7 days, PCCE retained over 85 % of its weight, indicating superior environmental stability. Immersion in water and physiological saline for 28 days resulted in swelling ratios of only 25 % and 15 %, respectively, significantly outperforming other hydrogels in anti-swelling performance. PCCE was assembled into a strain sensor, successfully achieving flexible sensing functions under room temperature, low-temperature, and underwater conditions. The excellent recyclability of PCCE ionogel significantly extends its lifespan and reduces production costs. In vitro antibacterial and cell proliferation experiments confirmed PCCE's outstanding antimicrobial properties and biosafety. These unique properties provide a solid theoretical foundation and data support for the broad application of PCCE in the field of smart medicine.