In-Phase Synchronization of Chemical and Mechanical Oscillations in Self-Oscillating Gels

Abstract

A novel gel which undergoes an autonomic and periodical swelling−deswelling oscillation has been prepared by the copolymerization of N-isopropylacrylamide (NIPAAm) with ruthenium tris(2,2‘-bipyridine) (Ru(bpy)3) as a catalyst for the Belousov−Zhabotinsky (BZ) reaction, which is known as an oscillating reaction accompanying a rhythmical change in the redox potential. The swelling−deswelling cycle of a miniature cubic poly(NIPAAm-co-Ru(bpy)3) gel was found to be synchronized with the chemical oscillation without a phase difference. The oscillating profiles of the swelling−deswelling changes as well as the redox changes were studied as a function of the substrate concentrations by using an image-processing method. Both period and amplitude of chemical oscillation varied depending on the substrate concentration. This variation led to a change in the swelling−deswelling oscillation: i.e., the swelling−deswelling amplitude increased with an increase in the period and amplitude of the redox changes. In the synchronization process, a feedback mechanism from mechanical to chemical oscillation was also suggested. The change in gel size with ca. 20% to the initial size was obtained as the maximum value. The swelling−deswelling amplitude of the gel is controllable by changing the initial concentration of substrates or the content of immobilized Ru(bpy)3 catalyst within the gel.

Chemo-responsive, self-oscillating gels that undergo biomimetic communication

“…51,52 The gLSM yielded qualitative agreement between the findings from computational studies and various experimental results. For example, in agreement with experiments, the results from this model revealed the in-phase synchronization of the chemical and mechanical oscillations for relatively small-sized samples 38,49 and a decrease of the oscillation period with an increase in the concentration of malonic acid. 5,49 Additionally, the shape-and size-dependent pattern formation observed in these gLSM simulations showed qualitative agreement with experimental studies.…”

“…4,5,8,[37][38][39][40] This polymer network is swollen in an aqueous solution of sodium bromate (NaBrO 3 ), nitric acid (HNO 3 ), and malonic acid (MA); MA acts as an organic substrate for the BZ reaction. The kinetics of the BZ reaction involves two dozen reactive species and tens of chemical reactions.…”

Development of self-oscillating polymers and gels with autonomous function

“…In miniature gels that are sufficiently smaller than the wavelength of the chemical wave (typically several mm), the redox change of the ruthenium catalyst can be regarded to occur homogeneously without pattern formation. 12 Because of the redox oscillation of the immobilized Ru(bpy) 3 2+ , the mechanical swellingdeswelling oscillation of the gel autonomously occurs with the same period found for the redox oscillation. The volume change is isotropic, and the gel beats as a whole, similar to a heart muscle cell.…”

Self-oscillating gel as novel biomimetic materials

“…Self-oscillating behavior of the gel 2.1 Self-oscillation of gel with smaller size than chemical wavelength and control of oscillating behavior Figure 3 shows the observed oscillating behavior under a microscope for the small cubic poly(NIPAAm-co-Ru(bpy) 3 2+ ) gel (each length of about 0.5mm). In miniature gels sufficiently smaller than the wavelength of the chemical wave (typically several mm), the redox change of ruthenium catalyst can be regarded to occur homogeneously without pattern formation (Yoshida et al, 2000). Due to the redox oscillation of the immobilized Ru(bpy) 3 2+ , mechanical swelling-deswelling oscillation of the gel autonomously occurs with the same period as for the redox oscillation.…”

“…The chemical and mechanical oscillations are synchronized without a phase difference (i.e., the gel exhibits swelling during the oxidized state and deswelling during the reduced state). (Yoshida et al, 2000) Typically, the oscillation period increases with a decrease in the initial concentration of substrates. Further, in general, the oscillation frequency (the reciprocal of the period) of the BZ reaction tends to increase as the temperature increases, in accordance with the Arrhenius equation.…”