Direct-Write Printing of Multifunctional Iontronic Composites That Sense, Rectify, and Actuate

The development of advanced materials capable of performing multiple functions is a key step toward adaptive, autonomous systems for emerging technologies. However, multifunctional material systems designed to integrate sensory, computational, and actuation capabilities are challenging to realize due to manufacturing and materials limitations. Here, we present electrically controllable, multifunctional iontronic composites (MICs) that demonstrate ionic sensing, current regulation, and ionomotive bending actuation capabilities within a single architecture. Our MICs are fabricated using a multimaterial direct-write printing process, in which a poly(ionic liquid) (pIL) structural electrolyte is sandwiched between two Ti₃C₂T_x MXene-based electrodes. The printing process enables seamless integration of concentrated MXene electrode inks with pIL electrolytes with printable layer thicknesses down to 25 and 200 μm, respectively. When used as a sensor, MICs exhibit capacitance changes up to 4% under compressive loads of 45 N. When printed with electrodes of asymmetric thickness, MICs can also function as ionic diodes, achieving rectification ratios up to 14. Finally, the composites demonstrate ionomotive actuation with a maximum bending strain of 0.21%. Our key innovation lies in achieving all three functionalities through additive manufacturing, which reduces the number of fabrication steps required to integrate all MIC materials together. Our MICs represent a significant advance in electrically controlled, multifunctional composites and motivate new directions toward next-generation autonomous and responsive material systems for soft robotics, electronics, and adaptive structures.