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An Additive Manufacturing Technique for the Facile and Rapid Fabrication of Hydrogel-based Micromachines with Magnetically Responsive Components

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Oxygen reduction reaction induced pH-responsive chemo-mechanical hydrogel actuators.

Cunjiang Yu¹, Peixi Yuan, Evan M Erickson

¹Department of Materials Science and Engineering, University of Illinois-Urbana Champaign, Urbana, Illinois 61801, USA. jrogers@illinois.edu.

|September 2, 2015

Summary

Researchers developed novel electrochemical hydrogel actuators using polyacrylic acid (PAA) that respond to pH changes driven by the oxygen reduction reaction (ORR). These PAA hydrogel actuators offer stable, reversible actuation for micro- and macro-scale applications.

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Area of Science:

Materials Science
Electrochemistry
Soft Robotics

Background:

Hydrogel actuators offer potential for soft robotics and biomedical devices.
Controlling hydrogel actuation typically requires external stimuli, which can be complex to implement at micro- and macro-scales.
Electrochemical methods provide a precise way to control localized chemical environments.

Purpose of the Study:

To design and characterize micro- and macro-scale chemomechanical hydrogel actuators.
To investigate the use of the oxygen reduction reaction (ORR) to drive hydrogel actuation via pH gradients.
To explore fabrication methods and understand design-dependent mass transfer effects for optimized actuator performance.

Main Methods:

Fabrication of polyacrylic acid (PAA) hydrogel actuators integrated with gold mesh micro-electrochemical arrays.
Utilizing the oxygen reduction reaction (ORR) at the cathode to create localized pH gradients within the PAA hydrogel.
Characterization of actuator response (strain, speed, reversibility) under varying electrochemical conditions and designs (micro- and macro-scale).

Main Results:

Demonstrated stable and reversible actuation of PAA hydrogel actuators driven by electrochemically induced pH gradients.
Observed that proton consumption during ORR leads to localized pH changes, causing osmotic pressure and volumetric expansion via water imbibition.
Investigated two fabrication approaches: molded actuators on fixed electrodes and embedded micro-electrode arrays within larger actuators, highlighting mass transfer impacts.

Conclusions:

Electrochemical control of pH gradients is an effective mechanism for driving chemomechanical hydrogel actuation.
The developed hydrogel actuators exhibit fast, large-amplitude, and reversible responses suitable for various applications.
Understanding mass transfer phenomena is crucial for optimizing mesoscopic design rules for these electrochemical actuators.