Biocatalytic reactions controlling the chemical actuator. Inset: Equivalent logic circuit corresponding to the input-processing biocatalytic cascade.
Artificial Muscle Reversibly Controlled by Enzyme Reactions
Chemically induced actuation of a polypyrrole (Ppy) artificial muscle was controlled by biocatalytic reactions resulting in the changes of the redox state of the polymer film mediated by soluble redox species. The biocatalytic process triggered by diaphorase in the presence of NADH resulting in the reduction of the Ppy film was reflected by the potential shift in the negative direction generated in the film. Conversely, the biocatalytic process driven by laccase in the presence of O2 resulted in the oxidation of the Ppy film, thus yielding the positive potential shift. Both reactions produced opposite bending of the Ppy flexible strip allowing reversible actuation controlled by the biocatalytic processes. The biocatalytic reactions governing the chemical actuator can be extended to multi-step cascades processing various patterns of biochemical signals and mimicking logic networks. The present chemical actuator exemplifies the first mechano-chemical device controlled by biochemical means with the possibility to scale up the complexity of the biochemical signal–processing system.
|Images of the Ppy-functionalized strip
upon application of various biochemical signals: (A) Initial state of
the strip before the signal application in the presence of 10 mM K4[Fe(CN)6]
(note the initial reduced state of the redox mediator); (B) After the
application of laccase (Input A; 0.25 mg mL-1); (C) After
application of diaphorase (Input B; 0.25 mg mL-1). The
reacting solution also included 12 mM NADH and O2 (in
equilibrium with air) in 0.5 M NaClO4 aqueous solution, pH
6.0. Images of the Ppy-functionalized strip upon application of
external electrical potentials: (D) -12 mV; (E) +200 mV; (F) -60 mV.
The solution included only 0.5 M NaClO4. The digital images
and the open circuit potential were obtained 180 s after the signal
See also movie showing bending of the modified strip upon electrochemical signals.
The bar chart showing the open circuit potential changes generated on the Ppy-strip upon different combinations of the enzyme-input signals (A,B,C) corresponding to the three-enzyme biocatalytic system.