Biology presents us with answers to design problems that we suspect would be very useful if only we could implement them successfully. We use the Russian theory of problem solving - TRIZ - in a novel way to provide a system for analysis and technology transfer. The analysis shows that whereas technology uses energy as the main means of solving technical problems, biology uses information and structure. Biology is also strongly hierarchical. The suggestion is that smart technology in hierarchical structures can help us to design much more efficient technology. TRIZ also suggests that biological design is autonomous and can be defined by the prefix "self-" with any function. This autonomy extends to the control system, so that the sensor is commonly also the actuator, resulting in simpler systems and greater reliability.

While some researchers see developments on the nanotechnology scale as the major or exclusive biomimetic trend in the 21st century, others insist that the exploration of the biomimetic potentialities of macroscopic systems has hardly been started. On either scale exploration of biological systems and development of engineering materials proceed in parallel and this provides the opportunity to actively search for similar, convergent solutions and designs in both directions. Recent studies of plant motors ranging from rapid calcium-dependent shape changes in plant proteins (forisomes) to the rapid closure of Venus flytraps and the ultra- rapid opening of dogwood flowers attracted the attention of both biologists and engineers. Here we summarize the principal differences of the nanomotors and macromotors that drive plant and animal movements. Then we describe three types of hydration motors that are common in plants: osmotic, colloid, and fibrous. In engineering electroactive polymers (EAPs) have emerged as new actuation materials with large, electrically induced strain and bending capacity. It remains to be seen whether hydrated EAPs with low voltage-actuation have bioconvergent relevance and proximity to biological situations; in particular plant movements. So far we only know that (i) pH-sensitive poly-ionic polymers like pectins are a common occurrence in the primary walls and occasionally some vacuoles of plant cells, (ii), that strong electric field changes also occur in living tissues, and (iii) that some aspects of their action are not understood and remain a matter of further investigation.

Evolution allowed nature to introduce highly effective biological mechanisms that are incredible inspiration for innovation. Humans have always made efforts to imitate nature's inventions and we are increasingly making advances that it becomes significantly easier to imitate, copy, and adapt biological methods, processes and systems. This brought us to the ability to create technology that is far beyond the simple mimicking of nature. Having better tools to understand and to implement nature's principles we are now equipped like never before to be inspired by nature and to employ our tools in far superior ways. Effectively, by bio-inspiration we can have a better view and value of nature capability while studying its models to learn what can be extracted, copied or adapted. Using electroactive polymers (EAP) as artificial muscles is adding an important element to the development of biologically inspired technologies. This paper reviews the various aspects of the field of biomimetics and the role that EAP plays and the field outlook.

Wearable dielectric elastomer actuators have the potential to enable new technologies, such as tactile feedback gloves for virtual reality, and to improve existing devices, such as automatic blood pressure cuffs. They are potentially lighter, quieter, thinner, simpler, and cheaper than pneumatic and hydraulic systems now used to make compliant, actuated interfaces with the human body. Achieving good performance without using a rigid frame to prestrain the actuator is a fundamental challenge in using these actuators on body. To answer this challenge, a new type of fiber-prestrained composite actuator was developed. Equations that facilitate design of the actuator are presented, along with FE analysis, material tests, and experimental results from prototypes. Bending stiffness of the actuator material was found to be comparable to textiles used in clothing, confirming wearability. Two roll-to-roll machines are also presented that permit manufacture of this material in bulk as a modular, compact, prestressed composite that can be cut, stacked, and staggered, in order to build up actuators for a range of desired forces and displacements. The electromechanical properties of single- layered actuators manufactured by this method were measured (N=5). At non-damaging voltages, blocking force ranged from 3,7-5,0 gram per centimeter of actuator width, with linear strains of 20,0-30%. Driving the actuators to breakdown produced maximum force of 8,3-10 gram/cm, and actuation strain in excess 30%. Using this actuator, a prototype tactile display was constructed and demonstrated.

Electroactive Polymer Artificial Muscle (EPAM[R]) technology is becoming a robust, high performance, cost effective solution for commercial applications in many sectors. Since its inception in 2004, Artificial Muscle, Inc. (AMI), a spinout company from SRI International, has rigorously pursued the commercialization of this form of artificial muscle technology through innovative designs and fabrication processes, dramatically increasing performance, reliability and manufacturability across a wide variety of applications. Scaleable solutions developed by AMI include air and liquid pumps, valves, linear and angular positioners, rotary motors, sensors and generators. Innovative device designs demonstrating the ability to meet the specifications of demanding applications across broad operating environments and combining practical levels of power densities and actuation lifetimes will be discussed. Integrated electronics control modules allow the freedom to design artificial muscles directly into new or existing product lines while effectively managing the transition from conventional technologies. Simple modular, versatile designs, coupled with low cost industrial materials and flexible automated manufacturing processes, provide a cost effective solution for products serving such diverse industries as consumer electronics, medical devices, and automobiles. Several case examples are presented to illustrate the commercial viability of EPAM[R]-based devices.

In this paper, the authors explore various ways that designed chambering of elastomers can enhance electroactive polymer (EAP) actuation. Such enhancements include structuring of chambers for various mechanical functions and advantages, boosting of surface area of a polymer for enhanced ionic migration, construction of advanced electret foams for sensing and for tunable hydrophobicity for micro/pumping action, and distribution of composite EAP devices throughout the chambered elastomer to achieve discrete controllability of electroactive polymer actuators. The authors also discuss the chambering of EAP materials themselves for enhanced actuation effects. With varied design of the chambers of the elastomer, the mechanical and structural properties of the elastomer can be tuned to greatly enhance EAP actuation. The chambers can be designed in accordion-like bellows to achieve extreme elongation with low forces, in spiral geometries to effect negative or neutral poisson's ratio under actuation, and with embedded fluidic bellows for fluidic actuation or sensing. These are but a few examples of the advantages that can be achieved via designed chambering of elastomers. The authors also discuss various application uses of the described chambering technologies. Such chambered elastomers, combined with advanced muscle-like actuators, can substantially benefit facelike robots (useful for entertainment and education etc), prosthetics, and numerous modalities of bio-inspired locomotion. In the efforts of the authors to generate facial expression robots with low-power lightweight actuators is described.

On March 7, 2005, the first arm wrestling match of an EAP robotic arm against a human was held during the EAP-inaction session of the EAPAD conference in San Diego. The primary object was to demonstrate the potential of the EAP technology for applications in the field of robotics and bioengineering. The Swiss Federal Laboratories for Materials Testing and Research (Empa), Switzerland, was one of the three participating organizations in this competition. The presented Empa robot was driven by a system of dielectric elastomer actuators. More than 250 rolled actuators were arranged in two groups according to the human agonist-antagonist operating principle in order to achieve an arm-like rotation movement in both directions. The robot was powered by a computer-controlled high voltage amplifier. The rotary motion of the arm was performed by electrical activation respectively deactivation of the corresponding actuator group.

This paper describes new electroelastomer films that exhibit high actuation performance at zero to minimal mechanical prestrain. Prestrain is generally required for electroelastomers, also known as dielectric elastomers, such as the VHB 4910 acrylic elastomer, to obtain high electromechanical strain and high elastic energy density. However, the prestrain can cause several serious problems, including the use of a prestrain-supporting structure, a large performance gap between the active materials and packaged actuators, instability at interfaces between the elastomer and prestrain-supporting structure, and stress relaxation. We have introduced a polymerizable and closslinkable liquid additive into highly prestrained acrylic films and subsequently cured the additive to form the second elastomeric network. In the as-obtained Interpenetrating Polymer Networks (IPN), the additive network can effectively support the prestrain of the acrylic films and consequently eliminate the external prestrain- supporting structure. The IPN composite films without external prestrain exhibit electrically-induced strains up to 233% in area, comparable to the VHB 4910 films under high prestrain.

We compression molded 50 micron thick silicone films between hot platens (150°C) and room temperature platens (23°C), under high shear flow. After molding and post-curing, a voltage ramp was used to measure dielectric strength in 72 samples, each 1 cm in diameter. Breakdown strengths ranged from 16 to 183 V/μm. Overall, the two methods yielded dielectric films with comparable breakdown strengths.

Novel actuator configurations for various applications can be obtained using cylindrical dielectric elastomer actuators. A new configuration for a contractile electro-elastomer is presented here for the first time. A cylindrical or tubular configuration is used to realize simultaneous axial shortening and radial expansion when a voltage is applied across the thickness of the hollow cylinder. In this configuration, the inner and outer surfaces of a cylindrical dielectric elastomer are coated with compliant electrodes. The outer cylindrical surface is then enclosed by a network of helical fibers that are very thin, very flexible and inextensible. Fiber networks or cord families are commonly used in many different materials and for a variety of applications. The primary purpose of these networks is structural, that is to say, for reinforcement. The composite active structure proposed here is reminiscent of the McKibben actuator, a pneumatically actuated cylindrical construct consisting of a flexible rubber bladder sheathed in a fiber network, which garners its impressive contracting force from the inextensible fibers that prevent axial extension when an inflation pressure is applied to the internal bladder [1]. The system is modeled using an electro- elastic formulation derived from the large deformation theory of reinforced cylinders [2]. The model combines Maxwell-Faraday electrostatics and nonlinear elasticity theory [3]. Illustratively, solutions are obtained assuming a Mooney-Rivlin material model for a silicone actuator. The results indicate that the relationship between the axial contraction force and the axial shortening is linear for the voltage range considered. The importance of other system parameters such as the fiber angle and the applied constant pressure is also reported.

Linear dielectric elastomer actuators with contractile ability are demanded for several types of applications. In order to achieve such a goal, two basic actuating configurations are today available: the multilayer stack and the helical structure. The first consists of several layers of elementary planar actuators stacked in mechanical series and electrical parallel. The second relies on a couple of helical compliant electrodes alternated to a couple of helical dielectrics. The fabrication of both these configurations presents today some specific difficulties, arising from the peculiarity of each structure. Even though successful implementations have been reported and further improvements are currently in progress, the availability of simpler solutions would boost the short-term use of contractile actuators in practical applications. In order to propose a viable alternative to the present configurations, a new structure is here described. It is designed to obtain a contractile monolithic actuator, starting from a planar electroded sheet, which is then folded up. The resulting compact structure is equivalent to a multilayer stack with interdigited electrodes. With respect to the conventional multilayer stack, the new configuration is advantageously not discontinuous and can be manufactured in one single phase, avoiding layer-by-layer multistep procedures. The current developmental stage of this new actuator with a silicone elastomer is here presented.

In this work the electromechanical performance of planar, single- layered dielectric elastomer (DE) actuators was investigated. The mechanical power density and the overall electromechanical efficiency of DE stripe actuators under continuous activation cycles were examined. The viscoelastic behavior of the dielectric film was modeled with a three-dimensionally coupled spring-damper framework. This film model was fitted to the mechanical behavior of the acrylic film VHB 4910 (3M) evaluated in a combination of a uniaxial loading test with holding time and subsequent unloading. In addition the quasielastic film model was derived in order to evaluate the quasistatic behavior of DE actuators under activation. For the simulation of DE actuators the boundary conditions of the film model were accordingly adapted. By embedding the actuator into an appropriate electrical circuit electrodynamic effects were incorporated as well. The quasielastic model of a planar DE actuator with free boundary conditions predicted a stable deformation state for activation with constant charge. For activation with constant electrical voltage, however, the model showed a stable and an instable equilibrium state. For activation voltages beyond a critical voltage the film collapses in thickness direction due to the electrostatic forces (Maxwell stresses). A biaxially prestrained stripe actuator was described with the viscoelastic film model. The stripe actuator was cyclically activated and cyclically elongated with a phase shift (displacement-controlled). A qualitative parameter study showed that the overall electromechanical efficiency as well as the specific power density of such DE actuators strongly depends on the electrical activation and the external mechanical loading.

Molecular Dynamics (MD) techniques have been used to study the structure and dynamics of hydrated Li- and Na-Nafion membranes. The membranes were generated using a Monte Carlo-approach for Nafion 117 oligomers of Mw = 1100 and with water contents of 7.5 and 20 % by weight, equivalent to 5 and 15 water molecules per sulfonate group, respectively. After equilibration, local structural properties and dynamical features such as coordination, cluster stability, solvation and ion conductivity were studied. In a comparison between the two cationic systems, it is shown that the Na-Nafion system is more sensitive than Li-Nafion to the level of hydration, and also show higher ion conductivity. The ionic conductivity is shown to increase with higher level of hydration.

In this paper the general-purpose finite element (FE) software ABAQUS is used to develop models to simulate large nonlinear viscoelastic response of non-axisymmetric dielectric elastomer actuators. The FE models assume the material to be a simple homogenous, isotropic, and incompressible material. The hyperelastic and viscoelastic material constants are determined using results from constant load uniaxial tensile tests and a constant load uniaxial creep test, respectively. Actuator with elliptical and rectangular cavities fabricated and tested at 5.5, 6.0, and 6.5 kV. The FE models are validated using experimental results obtained after 90 seconds.

Multifield theories are powerful frameworks able to manage complexities arising in the modelling of physical phenomena. In the mechanics of active materials a multifield theory, consisting in balance and constitutive equations, may be constructed by assigning to each point of the solid an additional parameter (the morphological descriptor) which accounts for the activation mechanisms at the level of microstructure. The main elements of multifield theory applied to continuum mechanics are given. The relevant equations of the problem of a cantilever beam of conductive polymer subject to flux of ions are reported to show the coupling between chemical (ion concentration) and mechanical behaviour (end deflection).

With technological interests in renewable raw materials and more environmentally friendly and sustainable resources, much attention has been focused on cellulose research and application. This paper presents a recent discovery of cellulose papers as smart materials that can be used for bio-mimetic sensor/actuator devices and microelectro-mechanical systems (MEMS). This cellulose paper is termed as Electro-Active paper (EAPap). First, the story of EAPap as an actuation material is addressed along with fabrication and recent improvement of EAPap materials. The actuation mechanism is also explained by gathering all information on physical, chemical, electrical and mechanical observations. Also the functional capability of sensor/actuator is discussed with experimental testimony. The cellulose EAPap materials have merits in terms of ultra-lightweight, dryness, low cost, low actuation voltage, low power consumption and biodegradability. To demonstrate these advantages, applications such as micro insect robots, micro flying objects, MEMS, biosensors and flexible electrical displays are discussed with some examples. In summary, the possibility of cellulose papers as smart materials is addressed with the future direction and challenges in this research.

Electro-Active Paper (EAPap) is attractive for EAP actuator due to its merits in terms of lightweight, dry condition, large displacement output, low actuation voltage and low power consumption. EAPap actuator has been made with cellulose material. Cellulose fibers are dissolved into a solution and cast in a sheet form, and a thin gold electrode is made on it. The cellulose solution has been made according to the viscous process that uses aqueous solvent NaOH/Urea. The use of strong alkali aqueous solvent results in decreasing hydrogen-bond of cellulose molecules. It makes EAPap material possessing ionic behavior. This paper presents the fabrication process and the performance evaluation of EAPap in terms of free displacement with respect to frequency and activation voltage.

A new material, called synthetic rubber in this paper, is proposed as a material for artificial muscle actuator based on dielectric elastomer. The presented material displays enhanced electrical as well as mechanical characteristics in terms of higher dielectric constant, elastic strength and lower stress relaxation. Several experiments are performed to evaluate actuation performance of the material. Also, its advantages are proved by conducting comparative studies with the other existing materials.

This paper focuses on actuating mode shapes of cellulose-based electro-active paper (EAPap) in order to investigate its suitability as actuators. Firstly, actuating mechanism of EAPap is addressed based on intrinsic characteristics of cellulose structures under electric fields. EAPap actuator is then fabricated by embedding gold as electrodes into both sides of cellophane sheets. Actuating mode shapes under electric fields are phenomenological measured via laser scanning vibrometer at different exciting frequencies as well as relative humidity. Various actuating performances with large deformations are obtained by applying low electric fields, which can produce a suitable deformation capability with light weight, low power consumption and simple fabrication. Experimental results provide that EAPap can be used as a potential actuating candidate for shape control of smart structures, along with bio-inspired actuator materials.

Ionomeric polymer transducers have received considerable attention in the past several years. These actuators, sometimes referred to as artificial muscles, have the ability to generate large bending strain and moderate stress at low applied voltages. Typically, ionic polymer actuators are composed of Nafion-117 membranes with platinum electrodes and are saturated with water diluents. Recently the authors have developed a novel fabrication technique named the Direct Assembly Process (DAP), which allowed good control on electrode morphology and composition. The DAP consists of spraying two high surface area metal-ionomer electrodes on a Nafion membrane. A single- walled carbon nanotubes (SWNT) and ruthenium dioxide (RuO₂) hybrid electrode was sprayed on a Formamide hydrated Nafion-117 membrane using the DAP method. This transducer was shown to generate 9.4% peak-peak strain under the application of ±2V at a strain rate of 1%/sec. Furthermore using the DAP one is capable of incorporating several types of diluents in ionomeric polymer transducers. Transducers with ionic liquid diluents are demonstrated to operate in air for long periods of time. In this work we will present a reliability study of transducers fabricated using the DAP. Each transducer is tested under a frequency range of 0.2Hz to 1Hz, and a potential of ±1V to ±3V. Water hydrated transducers dehydrates and stop moving within 5 minutes while operating in air under ±2V. Transducers with Formamide diluents operate for 20,000 cycles under ±1.5V and 0.5Hz (around 11hrs), while they degrade in less than 3000 cycles under ±2V and 0.5Hz. Ionic liquid based transducers are demonstrated to operate in air for over 400,000 with little loss in performance, and over 1 million cycle with a loss of only 43%. Actuators with several electrode compositions are fabricated and a correlation between the reliability of ionic liquid-ionic polymer transducers and maximum strain will be presented. This correlation will be used to assess the adhesion between the high surface area electrodes and the Nafion membrane. SEM images of tested transducers will be presented.

Crystalline nanomesa and nanowell formation has recently been discovered in polyvinylidene fluoride trifluoroethylene [P(VDF TrFE)] copolymer film, developed by Langmuir-Blodgett (LB) deposition. In this paper, a continuum field model is proposed to analyze this remarkable phenomenon, which is implemented in numerical simulations using finite difference method. Good agreement with experimental observations is observed.

A perfluorinated carboxylic acid membrane, i.e. Flemion, shows improved performance as actuator material compared with Nafion (perfluorinated sulfonic acide). Flemion has a higher ion exchange capacity and good mechanical strength. Especially, Flemion will deform with no back relaxation when applied electrical stimulus. However, with water as solvent, the operation of Flemion in air has serious problems. Since water would evaporate quickly in air. Moreover, the electrochemical stability for use in water is around 1V at room temperature. In previous work, investigations on Nafion with ionic liquid as solvents have been carried out and good results have been obtained. In this work, we explore the use of highly stable ionic liquid instead of water as solvent in Flemion. Experimental results indicate that Flemion based actuators with ionic liquid as solvent have improved stability as compared to the water samples. Although the forces exhibited by Flemion based actuators with the use of ionic liquid decreased dramatically as compared to water, these preliminary results suggest a good potential for use of Flemion with ionic liquid in some applications.

Electrochemomechanical deformation (ECMD) of a conducting polymer, polypyrrole (PPy) has been studied to attain better performance as soft actuators. The PPy films were electrochemically prepared from methyl benzoate solution of tetra butyl ammonium (TBA) trifluoromethansulfonate, TBACF₃SO₃ and TBA bis(perfluoroalkylsufonil)imid, TBA (C_nF_2n+1SO₂)₂ N) (n = 1- 4). The PPy films prepared from TBACF₃SO₃ are tough and flexible with the conductivity of more than 100 S/cm, and characterized as large force muscle with maximum stress of 49MPa. On the other hand, the PPy films obtained from TBA (C_nF_2n+1SO₂)₂ N were porous and gel in wet, and characterized as large contraction ratio muscle with the strain of 39% at the maximum. The maximum contraction ratio and force are more than those of natural muscles. The energy conversion efficiency of the electrical input to mechanical output has been estimated under the application of load. It has been found that during contraction of the film 0.2-0.25 % of input electrical energy was utilized for the mechanical work as the output.

The ions present in the electrolyte in which a conjugated polymer actuator is cycled are known to affect performance. Understanding how force, response time, and strain are affected by ion size and other ion characteristics is critical to applications, but is not yet well understood. In this paper, we present the effect of alkali cation size on transport velocity and volume change in polypyrrole doped with dodecylbenzenesulfonate, PPy(DBS), which is a cation- transporting material. Volume change measured by mechanical profilometry is greatest for Li⁺ and decreases in order of atomic mass: Li⁺ > Na⁺ > K⁺ > Rb⁺ > Cs⁺. Ion transport, measured by phase front propagation experiments, is also fastest for Li⁺, contradicting the expectation that larger species would move more slowly.

Previously, we presented a model for ion transport in conjugated polymers during electrochemical reduction. In this paper, we will present a more advanced model that includes hole transport, which was neglected in the first-cut model. This addition takes into account the interactions between holes and cations during transport. The result is that the front between oxidized and reduced material now propagates with constant velocity, instead of slowing down over time. Also, an electrolyte layer has been added to the model, and as a result the ion concentration behind the phase front is more accurately predicted.

Bilayer microactuators of gold and polypyrrole doped with dodecylbenzene sulfonate, PPy(DBS), are characterized with respect to their response times and the influence of operation temperature. These parameters are needed for biomedical applications such as microvalves. To fully open and close the valves, the bilayer hinges must be able to rotate within a few seconds at body temperature. Bilayers were subjected to potential steps to switch the PPy between the oxidized and reduced states. Actuation was viewed through an optical microscope and recorded by a digital camera. The velocity profiles during reduction and oxidation follow the same trends. Two different phases of actuation can be identified. In the first phase there is rapid movement, and in the second phase the velocities slowly decrease until the position reaches steady-state. In order to investigate the effects of elevated temperature on the actuators, the operation temperature was varied stepwise from 25 °C to 55 °C. The curvature increased irreversibly by up to 45% at elevated temperatures, and the output force dropped.

It is important to increase the switching speed of conjugated polymers between oxidized and reduced states for a wide range of devices, including capacitors, electrochromic displays, and actuators. In this paper, we compare the in-plane and the out-of- plane ion transport speed during electrochemical reduction of a conjugated polymer, polypyrrole doped with dodecylbenzenesulfonate. Results show that the in-plane ion transport is approximately 50 times faster than out-of-plane transport. The anisotropy is likely induced by the dodecylbenzenesulfonate, which has been shown previously to form layers parallel to the surface. An engineering method is presented to enhance the in-plane ion transport by etching pores into the polymer.

Electrorheological characteristics of poly (dimethyl siloxane)(PDMS) networks containing camphorsulfonic acid (CSA) doped-polyaniline (PANI) particles were investigated. Samples were prepared by dispersing fine polyaniline particles into cross-linked PDMS. Rheological properties of the PANI/PDMS blends were studied in the oscillatory shear mode in order to study the effects of electric field strength, particle concentration, and operating temperature on their electromechanical responses. The electrostriction of the blends were observed as a result of an attractive force among polarized particles embedded in the network. The sensitivity values of blends are defined as the storage moduli at any applied electric field subtracted by those values at zero electric field, and divided by theb moduli at zero field. They were found to increase about 10-50% when electric field strength was increased from 0 to 2 kV/mm. The storage and loss moduli increased with particle concentration and temperature but they decreased with crosslink density of the matrices.

The focus of this paper is on our experimental observation that addition of single wall carbon nanotubes (SWNTs) to a non-polar polyimide induces an electromechanical behavior, where bending strains are observed in response to applied electric fields. Percolation studies are carried on the nanocomposites. The samples used for studying actuation are above the percolation threshold. The electromechanical mechanism is identified as electrostriction, and the coefficients of electrostriction are calculated under different conditions of SWNT loading and applied electric fields. The electrostriction is believed to be a result of induced polarization in these materials, which shows an increase with the SWNT content. Furthermore, the polarizability of SWNTs modifies the local electric field in the surrounding polymer matrix, resulting in a low actuation voltage.

The numerous possible applications of the Ionic Polymer-Metal Composite (IPMC) as an underwater propulsor have lead to the investigation of the IPMC behavior in an aqueous environment. This study compares the performance of the IPMC when subjected to fluid drag forces to its performance without such forces. Both the form (i.e. pressure) drag and the viscous (i.e. skin friction) drag forces experienced by the IPMC due to the surrounding liquid are modeled. These forces are incorporated into an existing analytical model of a segmented IPMC¹, which adequately models the relaxation behavior of the IPMC. It is important to note that it is assumed that the IPMC exhibits planar motion, i.e. the center of mass does not move in the direction normal to the plane of the bending motion, therefore the hydrodynamic model developed is 2-dimensional. The maximum IPMC deflection and amount of relaxation predicted for aqueous and non-aqueous environments are compared. Results from this model are used to assess the suitability of the IPMC for underwater use.

Until now there have been few studies on the electrochemical behaviors of the electrode surface of Ionic Polymer- Metal Composites (IPMCs). In general, the electrochemical reactions under imposed electric fields cause the variations of overall resistance and capacitance of IPMCs and, therefore, lead to changes in the actuation behavior of IPMCs. The electro-chemo-mechanical interpretation of the electrodes made with Pt and Au are described in this paper. The standard electrochemical analyses, including voltammetry and electrochemical impedance spectroscopy on the electrode surface, were carried out in aqueous (water) and non-aqueous (ionic liquid) environments. The redox behaviors over a wide range of operation were analyzed using the cyclic voltammetry method. A load cell was used in measuring blocking forces. The experimental results suggest that the selection of appropriate electrode materials and solvents, and operating conditions are key parameters to predict the performance of IPMC actuators. It should be pointed out that unwanted reactions caused by the electrocatalyst under certain conditions can be avoided or minimized when an effective electrode-material is selected. IPMC samples having highly conductive electrodes or being solvated with ionic liquids generate improved and repeatable actuation with nearly no relaxation. Also, a thicker IPMC sample than conventional 50-300 micron thick IPMCs did not show any relaxation behaviors.

The multi-fields responsive ionic polymer-metal composites, which have wide applications such as actuators, sensors and dampers in one body, are synthesized through an in-situ standard ion-exchange method using Ni particles doped on a Nafion^TM film. SEM, EDS, and XRD were utilized for revealing their crystal shape and type. Also dynamic mechanical analysis, vibrating sample magnetometry, and cyclic voltammetry were used to investigate the mechanical, magnetic, and electrical properties of the Ni doped ionic polymer-metal composites. The nano-sized Ni particles (ca. 300 nm) were synthesized on the Nafion^TM film with 2.5 μm layer. The Ni doped ionic polymer-metal composites demonstrated good magnetic, electric and electro-mechanical responses.

Incorporation of small amounts (3-7 wt%) of nanoparticles such as layered silicate (MMT), silica, and carbon nanotube (CNT) may greatly alter important mechanical and electrical properties of Nafion^TM matrix. These fillers can be easily modified and functionalized to implement unique properties of IPMC. Our recent study indicates that Nafion/MMT, Nafion/silicates composites can be prepared with nano-scale dispersion. Most of IPMCs based on Nafion nanocomposite exhibit improved displacements and blocking forces compared to pure Nafion^TM based IPMC. Due to the barrier property and hygroscopic nature of silicates, water loss of IPMC under dc voltage is greatly reduced, which prolong the service life of IPMC. In the case of Nafion / layered silicate nanocomposite, however, response is slow due to the barrier effect of the clay platelet; while in Nafion / silica and Nafion / CNT systems, response rate is comparable with that of conventional IPMC. Improvement in mechanical properties and relaxation was achieved without any significant loss of important properties.

It is found from the locomotion of snake-like underwater robot using Ionic Polymer-Metal Composite (IPMC) as its actuator that, although we specify the same amplitude of driven voltages to each segmented IPMC unit, the resultant bending amplitudes along the body's progressive waves change from small to large toward the robot's tail. To analyze this phenomenon, which is also observed in locomotions of slender fishes, we discuss the modeling and analysis of bending motions of IPMC actuators using the Euler-Bernoulli beam theory. Eigenfunction expansion technique is used to solve the model of a partial differential equation. The envelope curve can be drawn by the obtained solution, and simulation results reappear the same phenomenon. Deflection of the real robot is measured by video camera and laser beam. Experimental results verifies the validity of the proposed model. Parameter identification is also performed with measured data.

This paper deals with the characterization and dynamic modeling of the behavior of two types of the Ionic Polymer Metal Composite (IPMC) "artificial muscle" materials. Environmental Robots, Inc. (ERI) was the initial vendor and its IPMC products required hydration for optimal performance. Virginia Polytechnic Institute and State University (Virginia Tech, VT) subsequently developed their innovative ionic solvent filled IPMCs that obviated hydration. Static tests were conducted to characterize force, displacement and current as a function of applied voltage. Dynamic tests were conducted to observe the frequency response of the material. Fatigue tests were performed on the ERI IPMCs to observe the change in behavior over time. It was found that the VT IPMCs had a bandwidth that was almost half that of the ERI product. However, the obviation of hydration of the VT's IPMC ensured the repeatability of performance and generated increased force densities. A feasibility study is presented to estimate the amount of IPMC materials and power consumption for a biceps exo-muscular assistance device based on the characteristics of the current IPMC materials and a primitive exo-muscular fiber bundle structure.

The degradation mechanism of ionic polymer metal composites (IPMCs) containing hydrophobic ionic liquids has been investigated. The ionic liquid was mixed with ethylene glycol in order to obtain high solvent uptake. The actuation response of the IPMCs with the mixed solvent was faster than that with only ethylene glycol. During the actuation durability tests under an AC square wave input, the IPMCs suffered from liquid squeezing-out problem, resulting in lower solvent concentration inside the IPMCs and hence poor actuation response. The degradation development of the IPMCs was influenced by the applied AC frequency. The tip displacement and the electric current were used to study the degradation development under AC electric field. Tin layer of polyurethane was applied on the IPMC surface to minimize the squeezing problems. The degradation was not significant observed after being subjected to 3V square wave input for more than 20 hours. However, the conductivity of the coated IPMCs was lower than that of the uncoated ones.

This paper presents a new way to design and fabricate ionic polymer actuators showing a linear movement in air. This is done by use of an original shaping during the polymerization step. The possible solutions for linear actuation were tested with a simulation technique that has been designed on purpose, which helped us to choose the best. By means of very unusual fabrication techniques that were required for that, actuators were made following this principle and their performances were measured.

In response to a clear need, the research community on EAP (Electroactive Polymer) has just started to work on a standard test methodology to characterize EAP actuators. A very general test methodology for EAPs, covering the characterization procedures for extensional and bending actuators was recently presented. In the present work, well known IPMC samples are characterized following such test methodology. Also, additional tests, not covered by the preliminary standard are included. These tests are conducted using the EAP Unit Tester, a test bench specifically designed for the characterization of EAP actuators. Rather than presenting new material's results, the paper focuses on the instrumentation, procedures and form of presenting results. Although the paper is focused on IPMC the method can be extrapolated to other bending actuators.

A research project called FACE (Facial Automaton for Conveying Emotions) in course at the Research Centre "E. Piaggio" of the University of Pisa is aimed at developing an android face endowed with dynamic expressiveness and artificial vision. The bioinspired approach behind the development of this system foresees the adoption of electroactive polymers as pseudo-muscular actuators to provide motion to the silicone skin of FACE, as well as to its eyeballs. The eyes of such a human-like automaton, and in particular the achievable movements of them, play a relevant role for the "believability" of the overall system, and thus of its effectiveness, as well as for the performance of the embedded artificial vision. This work presents preliminary results related the actuation of the FACE eyeballs by means of a new type (buckling) of dielectric elastomer actuator. This kind of actuator operates with out-of-plane unidirectional displacements. It is similar to the diaphragm-type one, with the difference that the necessary pre-deformation is enabled by an underlying hemispheric support, instead of pressurised air. One silicone-based buckling actuator was connected to a plastic eyeball of FACE via a tendon-like wire, in order to enable unidirectional rotations. Relative out-of-plane displacements of the actuator larger than 50% were achieved and used to provide rotations up to 13 degrees.

The assessed high electromechanical performances of dielectric elastomer actuators are encouraging the study of possible future applications of such devices for active prosthetic or orthotic systems for humans. Although the high electric fields currently needed for their driving prevent today a short-term use in endo- prostheses, their adoption for eso-prostheses or orthoses can be considered more realistic. Exoskeletons for improving muscular performance in specific tasks or for rehabilitation are examples of possible fields of investigation. Beyond a necessary technological development towards materials and devices capable of improved performances at reduced fields, the study of such applications requires even the identification of suitable strategies of activation and control. In particular, actuators to be used for such applications may take advantage from the possibility of being activated by electrophysiological signals. This would permit advantageous body's controls of the artificial system. In this context, this work presents activities carried on towards such a goal. In particular, activations of silicone-made dielectric elastomer actuators by means of different types of electrophysiological signals, opportunely elaborated, are presented and discussed.

This paper discusses the design and the realization of a prototype magnetic resonance imaging (MRI)-compatible tactile display device based on interpenetrated networks of conductive polymer actuators shaped into a pastille form. The electro-active polymers are investigated as an alternative solution to conceive tactile displays dedicated to fMRI studies. The tactile display is a 3×3 matrix- arranged pin; each pin is actuated independently and linked with the pastille-shaped IPN-CP actuator through a unilateral contact without intermediary motion or force amplification mechanism. All the technical aspects are discussed and presented.

In this paper, a dynamic model of simply supported ionic polymer- metal composite (IPMC) beam resting on human tissues is developed. The IPMC beam is actuated by an alternative electric potential. The bending moment due to electric potential is obtained by Nemat- Nasser's hybrid actuation model. Analytical solution of transverse vibration is obtained to describe the vibration response of IPMC beam to a command of electric potential. Pressure generated by IPMC beam on human tissue is estimated by numerical integration. Comparison shows that the generated pressure is comparable with experimental data from literature. The developed model is useful not only for the biomedical devices that employ IPMC materials but also for any other applications that utilize the vibration of IPMC materials.

The most common methods for the drug delivery are swallowing pills or receiving injections. However, formulations that control the rate and period of medicine (i.e., time-release medications) are still problematic. The proposed implantable devices which include batteries, sensors, telemetry, valves, and drug storage reservoirs provide an alternative method for the responsive drug delivery system [1]. Using this device, drug concentration can be precisely controlled which enhances drug efficiency and decreases the side effects. In order to achieve responsive drug delivery, a reliable release valve has to be developed. Biocompatibility, low energy consumption, and minimized leakage are the main requirements for such release method. A bilayer structure composed of Au/PPy film is fabricated as a flap to control the release valve. Optimized potentiostatic control to synthesize polypyrrole (PPy) is presented. The release of miniaturize valve is tested and showed in this paper. A novel idea to simultaneously fabricate the device reservoirs as well as protective packaging is proposed in this paper. The solution of PDMS permeability problem is also mentioned in this article.

Electro-Active Polymer (EAP) actuators inherently involve energy flow in multiple energy domains: mechanical, electrical, and at times, chemical and thermal. However, a complete predictive model explaining the behavior of EAPs has not yet been reported because of their complexity, particularly regarding the coupling phenomena between several energy domains. In this paper, we develop a model of EAPs suitable for dynamic simulations. The model uses bond graph methods as bond graphs are particularly appropriate for systems with multiple energy domains. Specifically, we develop a bond graph model for a conjugated polymer that behaves as an extensional electrolyte storage actuator using one cation- and one anion-exchanging polymer. The aims of this modeling are the following: to permit identification of known and as yet, unknown material properties of the elements in the system as a guide for future research by chemists and material scientists, to permit analytical evaluation of important questions such as what behavior determines the time constants and efficiency of the system, to allow design simulations which can provide guidance for best parameter choices for new devices, and to provide a modeling template for application to other sorts of EAP actuators such as IPMCs and gel-type.

Electrolyte polymer gels are a very attractive class of actuation materials with remarkable electronic and mechanical properties having a great similarity to biological contractile tissues. They consist of a polymer network with ionizable groups and a liquid phase with mobile ions. Absorption and delivery of solvent lead to a considerably large change of volume. Due to this capability, they can be used as actuators for technical applications, where large swelling and shrinkage is desired. In the present work chemically and electrically stimulated polymer gels in a solution bath are investigated. To describe the different complicated phenomena occurring in these gels adequately, the modeling can be conducted on different scales. Therefore, models based on the statistical theory and porous media theory, as well as a multi-field model and a discrete element formulation are derived. A refinement of the different theories from global macroscopic to microscopic are presented in this paper: The statistical theory is a macroscopic theory capable to describe the global swelling or bending e.g. of a gel film, while the general theory of porous media (TPM) is a macroscopic continuum theory which is based on the theory of mixtures extended by the concept of volume fractions. The TPM is a homogenized model, i.e. all geometrical and physical quantities can be seen as statistical averages of the real quantities. The presented chemo-electro-mechanical multi-field formulation is a mesoscopic theory. It is capable of giving the concentrations and the electric potential in the whole domain. Finally the (micromechanical) discrete element (DE) theory is employed. In this case, the continuum is represented by distributed particles with local interaction relations combined with balance equations for the chemical field. This method is predestined for problems involving large displacements, strains and discontinuities. The presented formulations are compared and conclusions on their applicability in engineering practice are finally drawn.

In this paper we present experimental measurements and analytical predictions for the electro-mechanical behaviour of Carbon Nanotube (CNT) actuators. Carbon nanotube actuators are chemo-electro- mechanical converters and exhibit very promising material parameters. To describe the electro-mechanical behavior, in the experimental part, some fundamental tests have been realized varying the voltage pattern while keeping the CNT materials, electrolyte, test configuration and other parameters unchanged. For out-of-plane deformation of the sheet material under applied voltage within a chemical environment, this analytical prediction is capable to show the voltage vs. active displacement behaviour for that material. Based on the experimental results from the different types of rectangular voltage pulses, we could successfully predict the material behaviour for triangular pulses. Finally based on these fundamental effects we are able to confirm the analytic prediction and to develop more sophisticated actuators.

Dielectric Elastomer (DE) actuators have been studied extensively under laboratory conditions where they have shown promising performance. However, in practical applications, they have not achieved their full potential. Here, the results of detailed analytical and experimental studies of the failure modes and performance boundaries of DE actuators are presented. The objective is to establish fundamental design principles for DE actuators. Analytical models suggest that DE actuators made with highly viscoelastic films are capable of reliably achieving large extensions when used at high speeds (high stretch rates). Experiments show that DE actuators used in low speed applications, such as slow continuous actuation, are subject to failure at substantially lower extensions and also have lower efficiencies. This creates an important reliability/performance trade-off because, due to their viscoelastic nature, highest DE actuators forces are obtained at low speeds. Hence, DE actuator design requires careful reliability/performance trade-offs because actuator speeds and extensions for optimal performance can significantly reduce actuator life.

Compact sensing methods are desirable for ionic polymer-metal composite (IPMC) actuators in microrobotic and biomedical applications. In this paper a novel sensing scheme for IPMC actuators is proposed by integrating an IPMC with a PVDF (polyvinylidene fluoride) thin film. The problem of feedthrough coupling from the actuation signal to the sensing signal, arising from the proximity of IPMC and PVDF, presents a significant challenge in real-time implementation. To reduce the coupling while minimizing the stiffening effect, the thickness of the insulating layer is properly chosen based on the Young's modulus measurement of the IPMC/PVDF structures. Furthermore, a nonlinear circuit model is proposed to capture the dynamics of the still significant coupling effect, and its parameters are identified through a nonlinear fitting process. A compensation scheme based on this model is then implemented to extract the correct sensing signal. Experimental results show that the developed IPMC/PVDF structure, together with the compensation algorithm, can perform effective, simultaneous actuation and sensing. As a first application, the sensori-actuator has been successfully used for the open-loop micro-injection of living Drosophila embryos.

Dielectric elastomer electroactive polymer (EAP) loudspeakers have been built and demonstrated at SRI International. Dielectric elastomer loudspeakers have the advantages of being very lightweight and able to conform to any shape or surface, making them attractive as low-profile, surface-mounted speakers in rooms or vehicle interiors, and for applications in active noise control. Loudspeaker performance depends on a number of mechanical factors, such as speaker shape and mechanical bias, as well as on electrical driving characteristics. This paper discusses important aspects of loudspeaker performance, including sound pressure level and directivity.

Five-layer-structured electrochromic glass (window), containing a transparent conductive layer, an electrochromic layer, an ionic conductive layer, an ionic storage layer and a second conductive transparent layer, was fabricated. The electrochromic glass adopts the conjugated polymer, poly[3,3-dimethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine] (PProDOT-Me2), as a blue electrochromic active layer, vanadium pentaoxide film as an ion storage layer and polymer gel electrolyte as the ionic transport layer. Dimension of smart glass up to 12 x 20 inch was developed. UV curable sealant was applied for the sealing devices. Color changing or switching speed of 12 x 20 inch smart glass from dark state to the transparent state (or vise versa) is less than 15 seconds under applied 1.5 voltages. Besides the long open circuit memory (the colored state or transparent state remains the same state after the power is off), the smart window can be adjusted easily into the intermediate state between the dark state and the transparent state by just simply turn the power on or off. No space consuming or dirt collecting shades, curtains or blinds are needed. The applications of the smart window, e.g. in the aircrafts, automobiles and architectures were discussed as well.

This paper describes the use of free-standing electrically conductive ultra-low modulus materials that withstand elongations up to 1000% as sensors for the measurement of large strains. NanoSonic has developed novel, high performance, multifunctional polymers for use in self-assembly processing that result in durable free-standing conductive films - with both controlled nominal conductivity and Young's modulus. Such films exhibit a change in electrical conductivity as a function of tensile strain; whereby the magnitude of the change is controlled via chemical processing.

We prepare a thin (~100 μm) silicone-based elastomer membrane and sputter ultra-thin copper electrodes (16-192 nm) onto each side of the film. Voltages of varying magnitude (1-8 kV) are applied to the electrodes causing an electrostatic pressure to develop which then compresses the elastomer in the through thickness direction. The edges of the membrane are constrained against in-plane expansion, forcing the membrane to deform out of plane. The in-plane strains developed by applying an electric field are characterized by measuring the stiffness of the membrane via indentation at different applied voltages. Closed-form solutions for membrane deflection are used with the experimental measurements to determine the relationship between the modulus of the cracked electrode/elastomer multi-layer and the electrically induced in-plane strain. Analytical models predicting the relationship between electrode crack spacing, layer properties, and effective modulus of the multi-layer are presented. Building on the knowledge gained from the membrane experiments, uni- axial tension specimens of an electrode/elastomer multi-layer are tested and preliminary results discussed.

A compliant electrode material is presented that was inspired by the electroding process used to manufacture ionic polymer-metal composites (IPMCs). However, instead of an ion-exchange membrane, a UV-curable acrylated urethane elastomer is employed. The electrode material consists of the UV-curable elastomer (Loctite 3108) loaded with tetraammineplatinum(II) chloride salt particles through physical mixing and homogenization. The composite material is made conductive by immersion in a reducing agent, sodium borohydride, which reduces the salt to platinum metal on the surface of the elastomer film. Because the noble metal is mixed into the elastomer precursor as a salt, the amount of UV light absorbed by the precursor is not significantly reduced, and the composite loses little photopatternability. As a result meso-scale electrodes of varying geometries can be formed by exposing the precursor/salt mixture through a mask. The materials are mechanically and electrically characterized. The percolation threshold of the composite is estimated to be 9 vol. % platinum salt, above which the compliant electrode material exhibits a maximum conductivity of 1 S/cm. The composite maintains its electrical conductivity under axial tensile strains of up to 40%.

This paper investigates a method for actively controlling the stiffness and damping provided by piezoelectric films such as may be used to construct biomimetic skins on small aerial vehicles. The method being investigated is based on the idea of elasticity control via piezoelectric coupling, and uses a tunable electronic circuit in parallel with a polyvinilidene fluoride (PVDF) film. The focus of the current work is on a fundamental-level understanding of the elasticity control method, and in particular, on theoretically and experimentally characterizing the degree of dissipation control possible with this method. The paper discusses the theoretical and experimental work so far which shows encouraging improvements in the dissipation in response to structural loads. Particular emphasis here is on modeling of the impulse response of a PVDF membrane. Work so far shows reasonable agreement between analytical and experimental results. Finally, a control circuit based on a low-power operational amplifier is seen to be effective in significantly improving the dissipation rate available with the PVDF membrane.

Plants have the ability to develop large mechanical force from chemical energy available with bio-fuels. The energy released by the cleavage of a terminal phosphate ion during the hydrolysis of a bio- fuel assists the transport of ions and fluids in cellular homeostasis. Materials that develop pressure and hence strain similar to the response of plants to an external stimuli are classified as nastic materials. Calculations for controlled actuation of an active material inspired by biological transport mechanism demonstrated the feasibility of developing such a material with actuation energy densities on the order of 100 kJ/m³. The mathematical model for a simplified proof of concept actuator referred to as micro hydraulic actuator uses ion transporters extracted from plants reconstituted on a synthetic bilayer lipid membrane (BLM). Thermodynamic model of the concept actuator predicted the ability to develop 5 percent normalized deformation in thickness of the micro- hydraulic actuator. Controlled fluid transport through AtSUT4 (Proton-sucrose co-transporter from Arabidopsis thaliana) reconstituted on a 1-Palmitoyl-2-Oleoyl-sn-Glycero-3-[Phospho-L- Serine] (Sodium Salt) (POPS), 1-Palmitoyl-2-Oleoyl-sn-Glycero-3- Phosphoethanolamine (POPE) BLM on a porous lead silicate glass plate (50μm with 61μm pitch) was driven by proton gradient. Bulk fluid flux of 1.2 μl/min was observed for each microliter of AtSUT4 transporter suspension (16.6 mg/ml in pH7.0 medium) reconstituted on the BLM. The flux rate is observed to be dependent on the concentration of sucrose present in pH4 buffer. Flux rate of 10 μl/min is observed for 5 mM sucrose in the first 10 minutes. The observed flux scales linearly with BLM area and the amount of proteins reconstituted on the lipid membrane. This article details the next step in the development of the micro hydraulic actuator - fluid transport driven by exergonic Adenosine triphosphate (ATP) hydrolysis reaction in the presence of ATP-phosphohydrolase (red beet ATP-ase) enzyme in the reconstituted bilayer.

Miniature spring roll dielectric elastomer actuators for a novel kinematic-free force feedback concept were manufactured and experimentally characterized. The actuators exhibited a maximum blocking force of 7.2 N and a displacement of 5 mm. The theoretical considerations based on the material's incompressibility were discussed in order to estimate the actuator behavior under blocked-strain activation and free-strain activation. One prototype was built for the demonstration of the proposed force feedback concept.

We study ionomeric polymer-metal composite (IPMC) actuators in situations where the strip of actuator acts either on maximum mechanical power or maximum amplitude of actuation. We apply a modified equivalent circuit of IPMC muscle which takes into account the surface resistance change while material bends. In case of series of bending acts, the first actuation of IPMC actuator is performed by a relaxed actuator, it bends over it's full length. During the next movements the most of the energy is caught by fore-part of actuator. The explanation of that effect is given.