Engineering the interface of cellulose nanocrystals for transient and bioactive iontronics based on protein eutectogels

Abstract

Incorporating cellulose nanocrystals (CNCs) into eutectogels has emerged as a promising strategy to impart enhanced functional properties, such as improved ionic conductivity, optical responses to stimuli, and mechanical strength, to give rise to next-generation sustainable and biobased iontronics. These enhancements rely on interfacial engineering approaches, including the physical adsorption of hydrogen-bonding molecules (e.g., tannic acid, TA) onto CNC surfaces and their surface chemical modification (e.g., carboxylation) to optimize compatibility with both protein-based gelling agents and deep eutectic solvents (DESs). In this study, we integrate both strategies, i.e., CNC physical and chemical modifications, by first introducing carboxylic functional groups onto the CNC surface, followed by the improved adsorption of TA. This dual modification promotes favorable interactions among CNCs, the gelatin protein network (via triple-helix formation), and the nonaqueous choline chloride: ethylene glycol (ChCl-EG) DES. The resulting eutectogels demonstrate outstanding mechanical properties (elongation at break of 425% and compressive strain at break of 90%), enhanced thermal stability (Tm above 50 °C), and high ionic conductivity (1.73 mS cm⁻¹) compared with those prepared using either physical or chemical modification alone, while retaining the transient and reversible nature of gelatin-based eutectogels for strain-sensing applications.Moreover, the dynamic assembly of the eutectogel components allows the system to act as a reservoir of antibacterial agents, including the DES and TA-coated CNC, thereby imparting additional bioactivity in vitro against clinically relevant bacterial strains. This feature is particularly advantageous for iontronic applications such as multifunctional strain sensors, where gelatin-based eutectogels reinforced with TA-coated CNC complexes can combine mechanical and thermal resilience with antimicrobial functionalities.