Design of Self-Oscillating Gels and Application to Biomimetic Actuators

As a novel biomimetic polymer, we have developed polymer gels with an autonomous self-oscillating function. This was achieved by utilizing oscillating chemical reactions, called the Belousov-Zhabotinsky (BZ) reaction, which is recognized as a chemical model for understanding several autonomous phenomena in biological systems. Under the coexistence of the reactants, the polymer gel undergoes spontaneous swelling-deswelling changes without any on-off switching by external stimuli. In this review, our recent studies on the self-oscillating polymer gels and application to biomimetic actuators are summarized

Molecular Design and Functional Control of Novel Self-Oscillating Polymers

If we could realize an autonomous polymer system driven under biological conditions by a tailor-made molecular design, human beings could create unprecedented biomimetic functions and materials such as heartbeats, autonomous peristaltic pumps, etc. In order to achieve this objective, we have investigated the molecular design of such a polymer system. As a result, we were the first to demonstrate a self-oscillating polymer system driven in a solution where only malonic acid existed, which could convert the chemical energy of the Belousov-Zhabotinsky (BZ) reaction into a change in the conformation of the polymer chain. To cause the self-oscillation in solution, we have attempted to construct a built-in system where the required BZ system substrates other than the organic acid are incorporated into the polymer itself. That is, the novel polymer chain incorporated the metal catalyst of the BZ reaction, a pH-control site and an oxidant supply site at the same time. As a result of introducing the pH control and oxidant supply sites into the conventional-type self-oscillating polymer chain, the novel polymer chain caused aggregation-disaggregation self-oscillations in the solution. We clarified that the period of the self-oscillation of the novel self-oscillating polymer chain was proportional to the concentration of the malonic acid. Therefore, the concentration of the malonic acid can be determined by measuring the period of the novel self-oscillating polymer solution. In this review, we introduce the detailed molecular design of the novel self-oscillating polymer chain and its self-oscillating behavior. Moreover, we report an autonomous self-oscillating polymer gel actuator that causes a bending-stretching motion under the constant conditions

Active Polymer Gel Actuators

Many kinds of stimuli-responsive polymer and gels have been developed and applied to biomimetic actuators or artificial muscles. Electroactive polymers that change shape when stimulated electrically seem to be particularly promising. In all cases, however, the mechanical motion is driven by external stimuli, for example, reversing the direction of electric field. On the other hand, many living organisms can generate an autonomous motion without external driving stimuli like self-beating of heart muscles. Here we show a novel biomimetic gel actuator that can walk spontaneously with a worm-like motion without switching of external stimuli. The self-oscillating motion is produced by dissipating chemical energy of oscillating reaction. Although the gel is completely composed of synthetic polymer, it shows autonomous motion as if it were alive

Design of Autonomous Gel Actuators

In this paper, we introduce autonomous gel actuators driven by chemical energy. The polymer gels prepared here have cyclic chemical reaction networks. With a cyclic reaction, the polymer gels generate periodical motion. The periodic motion of the gel is produced by the chemical energy of the oscillatory Belouzov-Zhabotinsky (BZ) reaction. We have succeeded in making synthetic polymer gel move autonomously like a living organism. This experimental fact represents the great possibility of the chemical robot

DYNAMICS OF INTELLIGENT POLY(N-ISOPROPYLACRYLAMIDE) MICROGELS

This dissertation investigates the self assembly and automatic oscillation of intelligent poly (N-isopropylacrylamide) [PNIPAM] microgel particles. The equilibrium phase diagram as a function of temperature and concentration was constructed for the charged PNIPAM spheres. The PNIPAM microgel particles display rhythmic size oscillations when covalently coupled to a nonlinear chemical reaction, the Belousov-Zhabotinsky (BZ) reaction. The nonequilibrium dynamics of PNIPAM microgels in the presence of BZ reaction was studied by the systematic variation of substrate concentrations and temperature. In addition, the BZ chemical reaction was modeled to reveal the existence of upper temperature limits for nonlinear chemical systems. The experiments employ environment sensitive PNIPAM particles that are sensitive to temperature, pH, and ionic strength. The PNIPAM particles have been demonstrated here to behave as hard spheres at low pH values and soft spheres at high pH. This is done by measuring the freezing and melting boundary of fluid-crystal coexistence region with a new technique which is simpler and quicker compared to the traditional sedimentation method. A novel method was developed to achieve size uniformity of PNIPAM gel particles with covalently-bound tris(bipyridyl)ruthenium(II) via the coordination chemistry between a ruthenium complex and the monodispersed PNIPAM gel particles bearing bipyridine ligands. The correlation between the dynamic behavior of BZ reaction induced mechanical oscillations of PNIPAM particles and substrate concentrations was presented in a ternary phase diagram. In particular, the dependence of oscillation frequency and induction time on the substrate concentrations was studied. The temperature dependency of the induction time and oscillatory frequency of the BZ reaction in this polymerimmobilized catalyst system were compared to the bulk BZ reaction with the catalyst in the solution phase. Prolonged induction times were observed for the immobilized catalyst, compared with free catalyst, while little difference was observed on the oscillation frequency. A theoretical improvement has been achieved by incorporating the temperature dependence in the BZ Oregonator model. Bifurcation has been calculated in the phase space spanned by initial reagents concentration ratio, stoichiometric factor and temperature. The existence of upper temperature limits has been demonstrated

Iron-Catalyzed Belousov-Zhabotinsky Hydrogels and Liquid Crystals

Reducing stress is an important goal in poultry production. The Saccharomyces cerevisiae-derived yeast fermentation product Original XPC (XPC, Diamond V Mills, Cedar Rapids, IA, United States) has been shown to reduce the severity of enteric infection and reduce measures of stress in poultry exposed to acute or chronic stress. However, the effect of dietary supplementation of yeast fermentate on other physiological parameters and its mode of action in reducing stress remains unclear. This work aimed to investigate the effects of supplementing XPC or its liquid equivalent, AviCare (Diamond V Mills), on measures of stress susceptibility, health and well-being in poultry exposed to acute and chronic stressors. Three consecutive experiments were conducted to evaluate the effects of yeast fermentate supplementation on measures of stress, growth and feed efficiency in Cobb 500 male broilers exposed to acute and rearing stressors. Both XPC and AviCare consistently and equally reduced measures of short- and long-term stress across all 3 experiments, although trends in body weight gain and feed efficiency were inconsistent. A fourth experiment investigated the effects of XPC and AviCare on measures of stress, plasma biochemistry, cecal microbiome and expression of stress- and immune-related genes in Cobb 500 male broilers. Both XPC and AviCare reduced stress by reducing expression of the ACTH receptor, and modulated immune activity by reducing IL10 and CYP1A2 gene expression as well as plasma IL- The Belousov-Zhabotinsky (BZ) reaction is one of the most studied nonlinear dynamic chemical systems due to its autonomous periodic oscillations. It represents a suitable model for various oscillatory phenomena in Nature such as neuron synapsis, cardiac muscle beating and/or tachycardia, cellular formation cycle in molds, and other types of live-organism morphogenesis. The complexity of the BZ reaction chemical mechanism led to the creation of the Fields-Koros-Noyes model (FKN) that allows for studies via theoretical and mathematical models. Thus, experimental studies of this reaction are necessary to create 3D and life-like models. To bring these models into a more naturalistic setting, we researched the BZ reaction through hydrogels containing iron because of its natural occurrence and relevance. Chemically, the BZ reaction requires a catalyst based on iron (Fe), ruthenium (Ru) or cerium (Ce), and most of the current reports employ Ru. Alternatively, we employed Fe complexes as the catalyst due to their lower toxicity compared to Ru. The Fe-based catalyst was incorporated into polymer matrices (PNIPAM-co-PAAm, gelatin + kappa-carrageenan, and gelatin) to obtain hydrogels that exhibited pattern-rich, self-oscillatory response. Hence, the hydrogels served as models to investigate the effect of liquid crystalline structures on oscillations, the effect of geometry on the wave pattern of 3D-printed hydrogels, and the autonomous motion of hydrogels. Overall, these results open the door for future research on BZ reaction systems with low-toxicity. Furthermore, they contribute to the creation of new 3D locomotive hydrogels and to the development of realistic 3D models that could mimic Nature more efficiently.. However, cecal microbiome and antioxidative capacity were not affected after 42 d. Finally, 2 consecutive experiments were conducted to evaluate the effect of XPC and AviCare on measures of intestinal health in Cobb 500 male broilers and mixed-sex Pekin ducks exposed to cyclic heat stress during the last 14 d of growth. In both experiments yeast fermentate attenuated the negative effects of heat stress on villus length and villus/crypt ratio but not goblet cell density. Yeast fermentate also affected metabolism but did not improve electrolyte balance. In conclusion, adding yeast fermentate to the feed or drinking water reduced stress susceptibility by reducing glucocorticoid production, supported intestinal cell survival during cyclic heat stress, and modulated inflammatory processes in poultry exposed to rearing stress but not cyclic heat stress