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Mohammadjavad Eslamian1 Fereshtehsadat Mirab1 Vijay Raghunathan1 Sheereen Majd1 Mohammad Reza Abidian1

1, University of Houston, Houston, Texas, United States

Conducting polymer actuators are promising materials for biomedical applications ranging from artificial muscles to drug delivery devices. These devices rely on bulk volume changes of conducting polymers (CPs) which arise from electrochemical redox processes. The changes in polymer chains conformation combined with the transportation of ions and solvent in and out of the polymer matrix are responsible for the micro and macro-scale expansion/contraction of the CPs. Construction of bilayer/trilayer bending devices is a very common strategy to convert the reaction-driven volume changes into macroscopic motions, where electrical energy is transduced into mechanical energy via electrochemical redox reactions in the active CP layer. In such devices, the CP layer is adhered to a passive thin layer to convert the in-plane actuation strain generated in the CP layer into macroscopic bending movements. Prior works have focused on the actuation of bilayer/trilayer actuators based on polypyrrole (PPy) films. We have previously proposed a novel structure for PPy:polystyrene sulfonate (PSS) in the form of randomly-oriented nanotubes and studied their ion transport behavior during cyclic voltammetry (CV) via electrochemical quartz crystal microbalance. Here, we report a bilayer actuator based on PPy nanofibers doped with PSS and constructed on a passive layer of Au-coated polypropylene (PP) film (length= 20 mm, width= 1 mm, PP thickness= 30 µm, Au thickness= 180 nm, PPy thickness= 12 µm). The PPy nanofibers were fabricated using electrochemical deposition of PPy (charge density 3.6 C/cm2) around electrospun poly-L-lactide nanofibers with the average diameter of 140±4 nm. The average diameter of the resultant PPy nanofibers was 626±16 nm. The bending behavior of the PPy nanofibers was investigated by measuring the tip deflection of actuator in both liquid and agarose gel (0.2%) electrolytes containing 0.1 M NaPSS. The PPy nanofibers were subjected to CV in the potential range of –0.8 V to +0.4 V at various scan rates of 10, 50, 100, and 200 mV/s for 20 cycles. The actuator showed a reversible bending movement during each potential cycle. The maximum deflection of actuator decreased in both liquid and gel electrolytes by increasing the scan rate. The maximum tip deflection in liquid was 7.89±0.08 mm, 5.38±0.04 mm, 3.81±0.01 mm, and 2.52±0.01 mm, respectively at the scan rates of 10, 50, 100, and 200 mV/s. The maximum tip deflection in gel was 432±11 µm, 301±2 µm, 222±1 µm, and 148±1 µm, respectively at the scan rates of 10, 50, 100, and 200 mV/s. Ultimately, the actuation moment generated during cycling at various scan rates was calculated using linear bending beam theory and Bernoulli's equation for fluid drag force. The findings in this study may have a great impact on the utilization of CP nanofibers for development of bioactuators.

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