28 May 1999 Electrically stimulated bilayer hydrogels as muscles
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Abstract
Muscle-like actuators have been made from bilayers of crosslinked polyacrylamide and polyacrylic acid hydrogels sandwiched between electrodes. The polyacrylic acid responds to applied positive polarity field by contracting and expelling water which is taken up by the polyacrylamide layers. Previous studies have shown that the effective swelling modulus of polyacrylamide is much lower than polyacrylic acid. Hence the polyacrylamide acts as a sponge. As the polyacrylic acid layer contracts in the x, y and z directions the polyacrylamide is also pulled in on x and y, so that the whole stack becomes narrower and expands along the z- axis. Reversing the field reverses this effect with a time constant of about 1 minute for 1 mm thick layers with a thickness change of about 10%. Linear changes up to 50% have been obtained. Other gel actuators either transfer water across a sheet and so bend, or contract by expelling water. This new system shows a linear contraction and expansion without a volume change and so can be run (sealed) in a dry environment.
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Paul D. Calvert, Paul D. Calvert, Zengshe Liu, Zengshe Liu, } "Electrically stimulated bilayer hydrogels as muscles", Proc. SPIE 3669, Smart Structures and Materials 1999: Electroactive Polymer Actuators and Devices, (28 May 1999); doi: 10.1117/12.349682; https://doi.org/10.1117/12.349682
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