Helically shaped hollow polypyrrole for efficient molecular pumping

This work reports the design, fabrication, and characterization of a novel wireless electro-chemo-mechanical (ECMD) pump based on a helically shaped, hollow polypyrrole (PPy). The device is fabricated via galvanostatic electropolymerization on a metallic wire template. When employed as a bipolar electrode under an external electric field, the helical pump exhibits a highly efficient, orientation-dependent fluid transport capability. A systematic investigation reveals that aligning the helix's major axis parallel to the electric field maximizes the bipolar polarization, resulting in a pumping rate of 2.3 µL/min. This represents a performance enhancement of over 64 % compared to a rigorously defined linear PPy tube containing an equivalent volume of material, isolating geometry as the key performance driver. The underlying mechanism is elucidated through a combination of local resistance mapping and fluorescence staining, which confirm that the optimal orientation establishes well-defined anodic and cathodic poles at the helix extremities, driving an asymmetric ECMD response. A quantitative model based on the Hagen-Poiseuille equation is presented to correlate the pumping rate with the actuator's geometry and field alignment. The consistent and repeatable actuators’ performance, over initial operational cycles, confirms the robustness of the pumping mechanism. These findings demonstrate that introducing geometric complexity is a powerful strategy for enhancing the performance of wireless electrochemical systems, with significant implications for soft robotics, microfluidics, and controlled drug delivery.