Self-oscillating Polymer Gels Research Articles

Creation of softmaterials based on self-oscillating polymer gels

Creation of softmaterials based on self-oscillating polymer gels

Self-oscillating chemoelectrical interface of solution-gated ion-sensitive field-effect transistor based on Belousov\u2013Zhabotinsky reaction

The Belousov–Zhabotinsky (BZ) self-oscillation reaction is an important chemical model to elucidate nonequilibrium chemistry in an open system. However, there are only a few studies on the electrical behavior of pH oscillation induced by the BZ reaction, although numerous studies have been carried out to investigate the mechanisms by which the BZ reaction interacts with redox reactions, which results in potential changes. Needless to say, the electrical characteristic of a self-oscillating polymer gel driven by the BZ reaction has not been clarified. On the other hand, a solution-gated ion-sensitive field-effect transistor (ISFET) has a superior ability to detect ionic charges and includes capacitive membranes on the gate electrode. In this study, we carried out the electrical monitoring of self-oscillation behaviors at the chemoelectrical interface based on the BZ reaction using ISFET sensors, focusing on the pH oscillation and the electrical dynamics of the self-oscillating polymer brush. The pH oscillation induced by the BZ reaction is not only electrically observed using the ISFET sensor, the electrical signals of which results from the interfacial potential between the solution and the gate insulator, but also visualized using a large-scale and high-density ISFET sensor. Moreover, the N-isopropylacrylamide (NIPAAm)-based self-oscillating polymer brush with Ru(bpy)3 as a catalyst clearly shows a periodic electrical response based on the swelling–deswelling behavior caused by the BZ reaction on the gate insulator of the ISFET sensor. Thus, the elucidation of the electrical self-oscillation behaviors induced by the BZ reaction using the ISFET sensor provides a solution to the problems of nonequilibrium chemistry.

A chemical micropump actuated by self-oscillating polymer gel

Abstract We demonstrated a self-driven chemical micropump powered by self-oscillating motions of synthetic polymer gel converting chemical energy into displacements of a thin polydimethylsiloxane (PDMS) sheet to produce a directional flow via micro check valves. The gel oscillations induced by the oscillatory Belousov-Zhabotinsky (BZ) reaction generate large volume change. To effectively exploit this volume change, gel bars were used as drivers. They were sandwiched by a fixed cover glass and a push-bar to communicate the expanding (pushing) force of the gel bars to the pumping chamber. At 25 °C, this gel micropump generated a 0.07 mN stroke force and a 0.28 μL/min positive net flow in the microchannel. Additionally, the flow rate of this gel micropump was increased as the temperature was raised from 20 to 30 °C. Compared to existing chemical micropumps, this gel-based micropump provides advantages of self-oscillating property, easy refueling and thermal controllability. This gel-based soft micropump would be used as wearable or medical devices exploiting the flexibility and quietness.

Autonomous oil flow generated by self-oscillating polymer gels

The previously reported gel and polymer actuators require external inputs, such as batteries, circuits, electronic circuits, etc., compared with autonomous motions produced by the living organisms. To realize the spontaneous motions, here, we propose to integrate a power supply, actuators, and control into a single-component self-oscillating hydrogel. We demonstrate self-actuating gel pumps driven by the oscillatory Belousov–Zhabotinsky (BZ) reaction without electronic components. We have developed the volume oscillation of gels synchronized with the BZ reaction (BZ gel). Since the self-actuating gel pumps are driven by chemo-mechanical energy from BZ gels, the self-actuating gel pumps don’t require complex wiring designs, energy supply, and assembling. The mechanical work generated by BZ gels is extremely small. We formulated the thermodynamic cycle of BZ gels and maximized mechanical work. We found that pre-stretched BZ gel shows larger mechanical works. We physically separated the BZ gels and working fluid to create practical pumps. By using optimizing mechanical generated by BZ gels, we demonstrated the self-actuating gel pumps that transfer mechanical work through a stretchable elastomer membrane.

Contraction waves in self-oscillating polymer gels

As one type of active soft matter, polymer gels coupled mechanical and chemical oscillations, such as Belousov–Zhabotinsky (BZ) gels are widely researched and developed into biomimetic actuators. In the previous literature, the self-oscillating BZ cylindrical gels can generate swelling waves along their longitudinal direction when they are operated without external stimuli. Here, we explore the contraction waves of BZ gels by the means of changing the external mechanical boundary. We firstly synthesize the self-oscillating gel, which is composed of N-isopropyl acrylamide (NIPAAm) gel and a covalently bound metal catalyst of the ruthenium complex. Then, the stress-curve of the gels is investigated to evaluate the elastic modulus of each state of the BZ gel and verified our method. Finally, we investigate the effects of several factors including initial diameters of the gel, various strain, and measuring process on the generation of contraction waves in gels undergoing the BZ reaction by experiments.

Designing multifunctional gels with electrical conductivity, mechanical toughness and self-oscillating performance

Self-oscillating polymer gels driven by the Belousov–Zhabotinsky (BZ) oscillating chemical reaction are a new class of functional gels that have potential applications in autonomously functioning membranes and as artificial muscle actuators.

Design of Self-oscillating Polymer Gels and the Development as Biomimetic Materials

Design of Self-oscillating Polymer Gels and the Development as Biomimetic Materials

Sustained larger-amplitude self-oscillations induced by the BZ reaction involving Fe(phen)3 catalyst

The poly(VP-co-AA-co-CD-co-Fe(phen)3) self-oscillating polymer gels composed of 5-acrylamide-1,10-phenanthroline bis(1,10-phenanthroline) iron(II) (Fe(phen)3), vinyl-pyrrolidone (VP), beta-cyclodextrin (β-CD) and acrylic acid (AA) were synthesized by radical polymerization. The volume, color and the redox potential self-oscillations were observed synchronizing with chemical wave propagation in acid-free conditions. The amplitude of diameter oscillation was about 40 µm to approximately 10% of its initial diameter and that of the redox potential about 125 mV at the optimal conditions. Moreover, the oscillation could sustain several hours. The long-lasting oscillation gels with large amplitude under mild conditions will be useful for the development of biomimetic materials that can undergo self-oscillation without external stimuli in mild conditions.

Three-dimensional displacement measurement of self-oscillating gel using digital holographic microscopy.

To measure the 3D microdisplacement of a self-oscillating polymer gel driven by the Belousov-Zhabotinsky reaction, we propose, to the best of our knowledge, a new particle detection and tracking method based on a phase image/volume template matching using digital holographic microscopy. We demonstrate the precision of the proposed method and compare it with conventional approaches. The method is applied to 3D measurement of the motions of particles attached to the surface of an oscillating gel. Measurement results show that the local area of the gel oscillates periodically, and the motion propagates throughout the gel. Our method can measure rapid and complex 3D microdisplacement change.

Self-oscillating polymer gels as biomimetic and smart softmaterials

In living systems, there are many autonomous and oscillatory phenomena to sustain life such as heart beating. We developed “self-oscillating” polymer gels that undergo spontaneous cyclic swelling–deswelling changes without any on–off switching of external stimuli, as with heart muscle.The self-oscillating gels were designed by utilizing the Belousov-Zhabotinsky (BZ) reaction, an oscillating reaction, as a chemical model of the TCA cycle. We have systematically studied these self-oscillating polymer gels since they were first reported in 1996. Potential applications of the self-oscillating polymers and gels include several kinds of functional material systems such as biomimetic actuators, mass transport systems and functional fluids. In this review, our recent progress on the self-oscillating polymer gels is summarized.

Tuning the synchronization of a network of weakly coupled self-oscillating gels via capacitors.

We consider a network of coupled oscillating units, where each unit comprises a self-oscillating polymer gel undergoing the Belousov-Zhabotinsky (BZ) reaction and an overlaying piezoelectric (PZ) cantilever. Through chemo-mechano-electrical coupling, the oscillations of the networked BZ-PZ units achieve in-phase or anti-phase synchronization, enabling, for example, the storage of information within the system. Herein, we develop numerical and computational models to show that the introduction of capacitors into the BZ-PZ system enhances the dynamical behavior of the oscillating network by yielding additional stable synchronization modes. We specifically show that the capacitors lead to a redistribution of charge in the system and alteration of the force that the PZ cantilevers apply to the underlying gel. Hence, the capacitors modify the strength of the coupling between the oscillators in the network. We utilize a linear stability analysis to determine the phase behavior of BZ-PZ networks encompassing different capacitances, force polarities, and number of units and then verify our findings with numerical simulations. Thus, through analytical calculations and numerical simulations, we determine the impact of the capacitors on the existence of the synchronization modes, their stability, and the rate of synchronization within these complex dynamical systems. The findings from our study can be used to design robotic materials that harness the materials' intrinsic, responsive properties to perform such functions as sensing, actuation, and information storage.

Recent Advances in Self-Oscillating Polymer Material Systems.

In 1996, we first reported self-oscillating polymer gels exhibiting autonomous swelling-deswelling oscillations driven by the Belousov-Zhabotinsky reaction. In contrast to conventional stimuli-responsive gels, the self-oscillating gel can autonomously and periodically change its volume in a closed solution without any external stimuli. Since the first report, the novel concept of self-oscillating gels has been expanded into various polymer and gel systems. Herein, we summarize recent advances in self-oscillating polymers and gels.

Large deformation of self-oscillating polymer gel.

A self-oscillating gel is a system that generates an autonomous volume oscillation. This oscillation is powered by the chemical energy of the Belousov-Zhabotinsky (BZ) reaction, which demonstrates metal ion redox oscillation. A self-oscillating gel is composed of Poly-N-isopropylacrylamide (PNIPAAm) with a metal ion. In this study, we found that the displacement of the volume oscillation in a self-oscillating gel could be controlled by its being subjected to a prestraining process. We also revealed the driving mechanism of the self-oscillating gel from the point of view of thermodynamics. We observed that the polymer-solvent interaction parameter χ is altered by the redox changes to the metal ion incorporated in the self-oscillating gel. The prestraining process leads to changes in χ and changes in enthalpy and entropy when the self-oscillating gel is in a reduced and oxidized state. We found that nonprestrained gel samples oscillate in a poor solution (χ>0.5) and prestrained gel samples oscillate in a good solution (χ<0.5).

Creation of Self-Oscillating Polymer Gels and New Development as Molecular Assembly Forming Network

<b>Creation of Self-Oscillating Polymer Gels and New Development as </b><b>Molecular Assembly Forming Network </b>

Achieving synchronization with active hybrid materials: Coupling self-oscillating gels and piezoelectric films.

Lightweight, deformable materials that can sense and respond to human touch and motion can be the basis of future wearable computers, where the material itself will be capable of performing computations. To facilitate the creation of “materials that compute”, we draw from two emerging modalities for computation: chemical computing, which relies on reaction-diffusion mechanisms to perform operations, and oscillatory computing, which performs pattern recognition through synchronization of coupled oscillators. Chemical computing systems, however, suffer from the fact that the reacting species are coupled only locally; the coupling is limited by diffusion as the chemical waves propagate throughout the system. Additionally, oscillatory computing systems have not utilized a potentially wearable material. To address both these limitations, we develop the first model for coupling self-oscillating polymer gels to a piezoelectric (PZ) micro-electro-mechanical system (MEMS). The resulting transduction between chemo-mechanical and electrical energy creates signals that can be propagated quickly over long distances and thus, permits remote, non-diffusively coupled oscillators to communicate and synchronize. Moreover, the oscillators can be organized into arbitrary topologies because the electrical connections lift the limitations of diffusive coupling. Using our model, we predict the synchronization behavior that can be used for computational tasks, ultimately enabling “materials that compute”.

Evolution of self-oscillating polymer gels as autonomous polymer systems

We have developed ‘self-oscillating’ gels that undergo spontaneous cyclic swelling–deswelling changes without any on–off switching of external stimuli, as with heart muscle. The self-oscillating gels were designed by utilizing the Belousov–Zhabotinsky (BZ) reaction, an oscillating reaction, as a chemical model of the tricarboxylic acid cycle. We have systematically studied these polymer gels since they were first reported in 1996. Our studies represent innovative research, creating new concepts of functional gels and expanding their potential, and they have attracted attention in many research fields and have inspired related studies. Here, our recent progress on self-oscillating polymer gels is summarized. We developed ‘self-oscillating’ polymer gels that undergo spontaneous cyclic swelling–deswelling changes without any on–off switching of external stimuli like a heart muscle. Here, our recent progress on the self-oscillating polymer gels was summarized. Muscles and other soft tissues in the body experience spontaneous rhythmic changes, such as a heartbeat, hormonal secretion and the cell cycle, without requiring external stimulation. Ryo Yoshida and Takeshi Ueki from the University of Tokyo, Japan, review their team's progress to develop polymer gels that freely undergo cyclic swelling and shrinking. Although tremendous efforts to mimic biological systems have generated numerous synthetic responsive materials for smart tissue engineering and therapeutic applications, these existing systems lack autonomy and depend on induced pH, temperature and other environmental fluctuations to operate. In contrast, the team's gels rely on the oscillating Belousov–Zhabotinsky reaction — a metal-catalyzed oxidation reaction that exhibits spontaneous periodic temporal and spatial patterns. The self-oscillating gels have applications that include biomimetic actuators and tubular intestine-like mass transport systems, providing new perspectives for materials science, robotics and biophysics.

Generative Force of Self-Oscillating Gel

We succeeded in measuring the generative force of a self-oscillating polymer gel in an aqueous solution comprising the three substrates of the Belousov-Zhabotinsky (BZ) reaction (malonic acid, sodium bromate, and nitric acid) under constant temperature. In this study, we developed an apparatus with a microforce sensor for measuring the generative force of small-sized gels (1 mm(3)). The self-oscillating polymer gel directly converts the chemical energy of the BZ reaction into mechanical work. It was determined that the generative force of the self-oscillating gel was 972 Pa, and the period of self-oscillation was 480 s at 18 °C. We demonstrated that the generative force of the gel was about a hundredth the generative force of a muscle in the body. We analyzed the time dependence of the color change in the self-oscillating polymer gel. The color of the gel changed periodically owing to the cyclic change in the redox state of the Ru moiety, induced by the BZ reaction. The peaks of the waveforms of the generative force and color change were almost identical. This result showed that the generative force was synchronized with the periodical change in the oxidation number of the Ru catalytic moiety in the gel. To understand a theoretical basis for the generative force of a self-oscillating gel, we considered a general theory that is based on the volume phase transition of gel and the two-parameter Oregonator model of the BZ reaction.

時空間機能をもつバイオミメティックな自励振動ゲルの創製とその展開

As a novel biomimetic gel with spatiotemporal function, we developed “self-oscillating” gel that undergoes spontaneous cyclic swelling-deswelling changes without any on-off switching of external stimuli like a heart muscle. The self-oscillating gel was designed by utilizing the Belousov-Zhabotinsky (BZ) reaction which is a oscillating reaction as a chemical model of the TCA cycle. Since the first report in 1996, we have systematically studied the novel polymer gels. As an innovative study to create a new concept of functional gels and expand the potential of gels, our studies have attracted much attention in many research fields and have inspired other related studies. Here our recent progress on the self-oscillating polymer gels was summarized.

Self-Oscillating Structural Polymer Gels

self-oscillating polymer gel has become a distinguished class of smart soft materials. Here we fabricated and demonstrated a self-oscillating structural gel network with the incorporation of the Belousov-Zhabotinsky (BZ) reaction. The structural polymer gel oscillates at a macroscopic level with remarkably faster kinetics compared to a normal gel of similar chemical compositions. The structural polymer gel also displays larger oscillating amplitude compared to the normal gel because of the increased diffusion of fluids surrounding the gel particles. This type of structural polymer gels can be harnessed to provide novel and feasible applications in a wide variety of fields, such as drug delivery, nanopatterning, chemical and biosensing, and photonic crystals.

Dynamical hysteresis in a self-oscillating polymer gel

An ionic polymer gel may undergo rhythmical swelling-deswelling kinetics induced by chemical oscillation. We demonstrate that the gel admits of dynamical hysteresis, which is manifested in the non-vanishing area of the response function--concentration (of reaction substrate) hysteresis loop, the response function being the integrated probability of residence of the polymer in any one of the swelled or deswelled states. The loop area depends on temperature and exhibits a turnover as a function of the strength of thermal noise--a phenomenon reminiscent of stochastic resonance. The numerical simulations agree well with our proposed analytical scheme.