**2. Experimental section**

312 Smart Actuation and Sensing Systems – Recent Advances and Future Challenges

thermoresponsive nature.

directly.

reaction, the metal catalyst undergoes spontaneous redox self-oscillation, and it changes the solubility from hydrophilic to hydrophobic at the same time. In order to cause the selfoscillation under temperature constant condition, the different solubility of the Ru catalyst in the reduced and oxidized state is utilized. In previous investigations, poly(Nisopropylacrylamide) (poly(NIPAAm)) was covalently bonded to (ruthenium (4 vinyl-4'-methyl-2,2-bipyridine) bis(2,2'-bipyridine)bis(hexafluorophosphate)) (Ru(bpy)3) and a negatively charged acrylamide-2-methylpropanesulfonic acid (AMPS) as a pH and solubility control site [47-50]. The AMPS-containing polymer systems caused self-oscillations originating from the different solubility of the Ru(bpy)3 moiety in the oxidized and reduced state. However, the conventional-type self-oscillating polymer system has the temperature limitation for causing the self-oscillation. That is because the conventional-type self-oscillating polymer system causes the aggregation or the contraction above the LCST. In this chapter, we introduce novel type self-oscillating polymers systems that are constituted the non-thermoresponsive and biocompatible poly-vinylpyrrolidone (PVP) as a polymer main-chain in order to expand the application fields. In our previous investigations, we first succeeded in causing the aggregation-disaggregation self-oscillation of the novel polymer chain and polymer gel under the constant condition induced by the BZ reaction. As for the VP-based self-oscillating polymer chain, the influence of the concentration of the three BZ substrates (sodium bromate, malonic acid and nitric acid) other than the metal catalyst on the waveform and period of the self-oscillation was investigated. As a result, it was demonstrated that the amplitude of the self-oscillation is hardly affected by the initial concentration of the BZ substrates. Furthermore, we firstly succeeded in causing the swelling-deswelling self-oscillation at high temperature condition by adapting the VP-main chain. We studied the influence of the initial concentration of the three BZ substrates other than the metal catalyst and the temperature on the period of the self-oscillation. As a result, it was clarified that the period of the self-oscillation for the VPbased polymer gel can be controllable by the selection of the initial concentration of the three BZ substrates (malonic acid (MA), sodium bromated (NaBrO3) and nitric acid) and the temperature. In addition, by optimizing the initial concentration of the BZ substrates and the temperature, it was demonstrated that the maximam frequency of the swellingdeswlling self-oscillation is 0.5 Hz. This value was 20 times as large as that of the conventional-type self-oscillating polymer gel (poly(NIPAAm-co-Ru(bpy)3 gel) with the

Next, in this chapter, we introduce the challenge of mimicking the peculiar locomotion of living organism, such as mollusks and apods, by utilizing polymer gel that cause the swelling-deswelling induced by the pH oscillating chemical reaction. Gastropods, like snails and slugs, can obtain the peristaltic movement by forming contraction waves, which is the propagation of the shrinking part of the body [61]. In this research, we focused on producing a functional gels obtaining peristaltic movements by the chemical energy

In addition, we introduce a novel-tpye nanofiber gel actuator that was manufactured by the electrospining method. The nanofiber gel actuator can cause bending-streching motion

#### *2.1.1. Synthesis of the poly(VP-co-Ru(bpy)3)*

The polymer chain was prepared as follows. 0.5g of ruthenium(4-vinyl-4'-methyl-2,2' bipylridine)bis(2,2'-bipyridine)bis(hexafluorophosphate) (Ru(bpy)3) as a metal catalyst for the BZ reaction, 9.5 g of vinylpyrrolidone (VP) and 0.35 g of 2,2'-azobis(isobutyronitrile) (AIBN) as an initiator were dissolved in the methanol solution (31 g) under total monomer concentration of 20 wt%. These polymerizations were carried out at 60 °C for 24 h *in vacuo*. These resulting reaction mixtures were dialyzed against graded series of water/methanol mixtures, for 1 day each in 0, 25, 50, 75, and 100 wt% of water, and then freeze-dried.

**Figure 1.** Chemical structure of poly(VP-*co*-Ru(bpy)3).
