1. Introduction

El

1. History

Thectroact five polymers (EAPs) are a versatile class of electrically deformable polymers. These polymers have the ability to deform when excited byeld of EAPs emerged back in 1880, when Wilhelm Röntgen designed an experiment in which he tested the effect of an electrical potentials ^[1] ostatic fieldue to their inherent electro-on the mechanical properties ^[2].of Thea piezoelectric couplings instripe of natural rubber.^[4] EAPsThe provide them with unique capabilities that are of significant interest in actuators and soft robotics ^[3]. Additirubber stripe was fixed at one end and was attached to a mass at the other. Electric charges were then sprayed ontonally, their ability to transform an electrical stimulus into a mechanical response has the potential to develop biocompatible artificial muscles. Furthermore, EAPs have become an attractive material for wearable sensors and biomimetics. Due to their versatile applications, EAPs are of significant interest for research innovation in the mechano- rubber, and it was observed that the length changed. It was in 1925 that the first piezoelectric polymer was discovered (Electret). Electret was formed by combining carnauba wax, rosin and beeswax, and then cooling the solution while it is subject to an applied DC electrical bias. The mixture would then solidify into a polymeric material that exhibited a piezoelectrical sect effect. Polymer of lates that respond to ^[4][5].

Electnviroactive polymers could be split between two major types depending on how they are produced: elnmental conditions, other than an applied electric current, have also been a large part of this area of study. In 1949 Katchalsky et al. dectrmonic EAPs and ionic EAPs. Electronic EAPs, such as dielectric elastomers, mechanicallystrated that when collagen filaments are dipped in acid or alkali solutions, they would respond to thewith a changes in el in volume.^[5] The ctrical charge, typically byollagen filaments were found to expansion. Similarly, ionic EAPs can be activated by an electric field that causes deformationd in an acidic solution and contract in an alkali solution. Although other stimuli (such as pH) have been investigated, due to ion movement. Comparatively, ionic EAPs require a lower voltage than ts ease and practicality most research has been devoted to developing polymers that respond to electronic EAPs for activation and tical stimuli in order to mimic biological systems. Ther nefore have received repeated attentionxt major breakthrough in EAPs took place in the literaturate ^[6]1960s. OIn the other hand, electronic EAPs have progressed significantly, and there are different types of 1969 Kawai demonstrated that polyvinylidene fluoride (PVDF) exhibits a large piezoelectric EAPeffect.^[5] This spalready present in the market. Statistically, the overall market of the rked research interest in developing other polymers systems that would show a similar effect. In 1977 the first electroactiveically conducting polymer was approximately $3.51 billion ins were discovered by Hideki Shirakawa 2017,et al.^[6] wShich is projected to be 5.12 billion by 2022 ^[7].

Orakawa along with Alane major advantage of EAP is that the amount of strain these materials may experience is much higher than what many conventional mechanical actuators would allowMacDiarmid and Alan Heeger demonstrated that polyacetylene was electrically conductive, and that by doping it with iodine vapor, they could enhance its conductivity by ^[8].8 Theorefore, EAPs have significant usage in the development of organic actuators, which are highly desirable in prosthetics. Due to their biocompatible makeup, flexibility, and light weight, EAPs are a potentialders of magnitude. Thus the conductance was close to that of a metal. By the late 1980s a number of other polymers had been shown to exhibit a piezoelectric effect or were demonstrated to be conductive. caIndidate for artificial muscle the early 1990s, ionic polymer-metal composites ^[9].(IPMCs) were Adevelso, EAPs stand to benefit the field of soft roboticoped and shown to exhibit electroactive properties far superior to previous EAPs. The use of soft actuators eliminates some safety concerns that are present when traditional robots interact with humans or delicate toolmajor advantage of IPMCs was that they were able to show activation (deformation) at voltages as low as 1 or 2 volts.^[5] SThince soft robots tend to be lighter and more compliant, they ars is orders of magnitude less likely to apply crushing forcethan any previous ^[10]EAP. BeyNond being able to control the movement of EAPs, their adaptability allows for novel robotic motions, such as a snake-shaped robot travelling in a serpentine patht only was the activation energy for these materials much lower, but they could also undergo much larger deformations. IPMCs were shown to exhibit anywhere up to ^[11].380% Dielecstric elastomers, known for their high deformabilityain, orders of magnitude larger than previously developed EAPs.^[1] aInd ease of production, could be useful in these types of r 1999, Yoseph Bar-Cohen proposed the Armwrestling Match of EAP Robotic applications. OtherArm Against Human Challenge.^[5] typeThis of applications, such as underwater or in corrosive environments,was a challenge in which research groups around the world competed to design a robotic arm consisting of EAP muscles that could benefit from the use of EAPsdefeat a human in an arm wrestling match. The first ^[12]. EAPs chan be designed as a noiseless propulsion devise, which is beneficialllenge was held at the Electroactive Polymer Actuators and Devices Conference in 2005.^[5] Anoto marine organisms that may be damaged by loud noises. Additionally, a soft robot made withher major milestone of the field is that the first commercially developed device including EAPs would be less likely to cause catastrophic failure or corrosion inas an artificial muscle was produced in 2002 by Eamex in Japan.^[1] tThe event of a collision. Lastly, wearable electronics may have a variety of uses for EAPs. Wearable devices often require small electronics foris device was a fish that was able to swim on its own, moving its tail using an EAP muscle. But the progress in practical development has not been satisfactory.^[7] nDARPA-fuanced applications, such as implanted or surface-mounted sensorsnded research in the 1990s at SRI International and ^[12]. EAPS couled be used in such applications.

2. Different Types of EAPs

Ey Ron Pelrine developed an electroactive polymer us are typically divided into two categories. One is ionic EAPs, and the other one is electronic EAPs. Each of these divisions can be further sub-divided into multiple branches, as shown ining silicone and acrylic polymers; the technology was spun off into the company Artificial Muscle in 2003, with industrial production beginning Figure 1in 2008.^[8] In 2010, Arthis review, four types of popular subdivisions of each category are going to be discussedificial Muscle became a subsidiary of Bayer MaterialScience.^[9] Moreover, some

2. Types

EAPs can have also been developed incorporating both ionseveral configurations, but are generally divided in two principal classes: Dielectric and Ionic.

Dielectric

Dielectronic EAPs to obtain specific advantages. This review will present a brief overview of various EAPs, and discuss their properties, applications, and challenges. In the follare materials in which actuation is caused by electrostatic forces between two electrodes which squeeze the polymer. Dielectric elastomers are capable of very high strains and are fundamentally a capacitor that changes its capacitance when a voltage is applied by allowing subsections, the synthesis routes of different ionic EAPs are depicted with schematic illustrations.

Figure 1. Different types of electroactive polymers.

Ththe polymer to compress in thickness and expand in area due to the electric field. This type of EAP typically require are multiple routess a large actuation voltage to produce ionic EAPs using different materials. Based on these routes, ionichigh electric fields (hundreds to thousands of volts), but very low electrical power consumption. Dielectric EAPs could be subdivided into several categories, such as ionic polymer-metal composites (IPMCs), condurequire no power to keep the actuator at a given position. Examples are electrostrictive polymers (CPs), ionic polymerand dielectric elastomers. g

Ferroelectric polymers

Fels (IPGs), and rroelectrorheological fluids (ERFs)ic polymers are a group of crystalline polar ^[13]. It is impolymertant to notes that are also ferroelectric, meaning that these categories are not rigid. Instead, they are often combinedy maintain a permanent electric polarization that can be reversed, or switched, in an external electric field.^[10][11] intFerro new ionic EAPs as their properties are explored and understood. The following sections detail the synthesis steps of several ionic EAPs that fit into one or morelectric polymers, such as polyvinylidene fluoride (PVDF), are used in acoustic transducers and electromechanical actuators because of their inherent piezoelectric response, and as heat sensors because of the above-mentioned categories.

Cir inherent pyroelectric respondse.^[12] right|thuctmb|Fing Polymers are often associated with ionic polymer gels sincegure 1: Structure of Poly(vinylidene fluoride)

Electrostrictive graft polymers

the saume polymers used in CPs can be made into an ionic b|300px|left|Figure 2: Cartoon of an electrostrictive graft polymer. geEl. These gelectrostrictive graft polymers consist of an ionic liquid in a solid matrix. They have gained attention since they do not include water, allowing them to function in the air better than other kinds of CPs. They are also similar in texture to biological muscles, making tflexible backbone chains with branching side chains. The side chains on neighboring backbone polymers cross link and form crystal units. The backbone and side chain crystal units can then form polarized monomers, which contain atoms with partial charges and generate dipole moments, shown in Figure 2.^[13] Whemn an potentially useful for biomedical purposes. Ionic polymer gel EAPs tend to follow a trilayer structure, with the gel forming the ion-exchange membrane; and a conductive materelectrical field is applied, a force is applied to each partial charge and causes rotation of the whole polymer unit. This rotation causes electrostrictive strain and deformation of the polymer.

Liquid crystalline polymers

Main-chal, such as metals or conductingin liquid crystalline polymers, as the electrodes. Also, some gel actuators include a layer of activated carbon between have mesogenic groups linked to each other by a flexible spacer. The mesogens within a backbone form the membrane and the electrode, forming a 5-layersophase structure causing the polymer itself to adopt a conformation compatible with the structure, as shown below ine of the mesophase. The direct coupling Figure 2of the ^[14].

Figure 2. IPMC with a five-layer structure. Redrawn from ^[14].

Eleiquid ctronic electroactivrystalline order with the polymers have received significant research attention in the last few decades. In contrastr conformation has given main-chain liquid crystalline elastomers a large amount of interest.^[14] witTh ionic EAPs, Electronic EAPs do not require any electrolyte medium or ion migre synthesis of highly oriented elastomers leads to have a large strain thermal actuation ^[15]. Therefalore,ng the field of electronic EAPs is rapidly developingpolymer chain direction with the increased interest in lightweight materials that are biocompatible and simple to manufacture ^[16]. Semperature variation resulting in unique mechanical properties and potential applications as mechanical actuato far, different kindss. of e

Ionic

• Ionic EAPs, in which actuation is caused by the displacement of ions inside the polymer. Only a few volts are needed for actuation, but the ionic flow implies a higher electrical power needed for actuation, and energy is needed to keep the actuator at a given position. Examples of ionic EAPS are conductive polymers, ionic polymer-metal composites (IPMCs), and responsive gels. Yet another example is a Bucky gel actuator, which is a polymer-supported layer of polyelectrolyte material consisting of an ionic liquid sandwiched between two electrode layers consisting of a gel of ionic liquid containing single-wall carbon nanotubes.^[15] The name comes from the similarity of the gel to the paper that can be made by filtering carbon nanotubes, the so-called buckypaper.^[16]

Electrorheological fluid

Figure 3: The cations in the ionic polymer-metal composite are randomly oriented in the absence of an electric field. Once a field is applied the cations gather to the side of the polymer in contact with the anode causing the polymer to bend.

Electronrheologic EAPs have been developed for numerousal fluids change the viscosity of a solution with the applications. Di of an electric, electrostrictive graft, electrostrictive paper, field. The fluid is a suspension of polymers in a low dielectro-viscoelastic, ferroelectric, andic-constant liquid.^[17] crysWith tal are some notablhe application of a large electric EAPs, widely discussed in the literaturfield the viscosity of the suspension increases. Potential applications of these fluids include ^[16][17][18].

3. Properties of EAPs

EAPshock are a robust fambsorbers, engine mounts and acoustic dampers.^[17]

Ionic polymer-metal composite

Ionic poly of materials with versatile mechanical, electrical,mer-metal composites consist of a thin ionomeric membrane with noble metal electro-mechanical, and tribological properties. Eachdes plated on its surface. It also has cations to balance the charge of these properties plays a significant role in serving anions fixed to the polymer backbone.^[18] tThe intended purpose iny are very active actuator, coating, or soft electronics. By combining general polymer attributes and electro-mechanical properties, EAPs have become a material thats that show very high deformation at low applied voltage and show low impedance. Ionic polymer-metal composites work through electrostatic attracts the attention of scientists and engineersion between the cationic counter ions and the ^[19]. In cathode following subsections, the mechanical,of the applied electroactive, and tribological properties of ionic EAPs will be covered.

Mic field, a schematic representation is shown in Figure 3. These typechanicals of properties are important physical properties that a material exhibits against an applied force. Modulus of elasticity, fatigue limit, tensile strength,olymers show the greatest promise for bio-mimetic uses as collagen fibers are essentially composed of natural charged ionic polymers.^[19] Naflexibility, and hardness are some of the mechanical properion and Flemion are commonly used ionic polymer metal composites.^[20]

Stimuli-responsive gels

Stimuli-res of EAPs. These properties modulate the bending capability when the EAP is used in actuators.

Inponsive gels (hydrogels, when the swelling agent is an aqueous solution) are thea performance of EAPs, electric properties play a significant rolespecial kind of swellable polymer networks with volume phase transition behaviour. These properties include, but are not limited to, electrostriction, dielectric constant, capacitance, impedance, and electrical conductivitymaterials change reversibly their volume, optical, mechanical and ^[20]. Each of theser properties has impact on the EAP’s mechanical andby very small alterations of certain physical (e.g. electric field, light, temperature) or chemical properties(concentrations) stimuli. ^[21]The ivolumpacts may vary across each respective EAP, but since EAPs are a family of polymers, there are a lot of similarities within the familye change of these materials occurs by swelling/shrinking and is diffusion-based. Gels provide the biggest change in volume of solid-state materials.

^[22] Comparbined to ionic EAPs (<10 V), electronic EAPs are driven by larger electric fields (>100 MV/m) to achieve linear deformwith an excellent compatibility with micro-fabrication between the 4 to 360% rangetechnologies, ^[21]. Poespeciallyv stinylidene fluoride (PVDF) is one of the most common EAPs with ferroelectric behavior ^[22]. PVDF hamuli-responsive hydrogels are of strong increasing interest for microsystems hwigh stiffness, mechanical strength, toughness and creepth sensors and actuators. Current fields of research and abrasion resistance, goodpplication are chemical resistance, high dielectric strength, chemical inertness, low flammability, and low moisture absorption capabilities ^[23]sensor systems, microfluidics and multimodal imaging systems.

3. Comparison of Dielectric and Ionic EAPs

Dielectric epolastomers (DEs) are capable of large strains and change their capacitance when a ymers are able to hold their induced displacement while activated under a DC voltage.^[23] This applied by compressing the thickness of the llows dielectric polymer and expanding its cross-section ^[24]s to be considered for robotic applications. Thies type of EAPs typically requires a large voltage to generate a high electric field, but it consumes very little powere types of materials also have high mechanical energy density and can be operated in air without a major decrease in performance. However, dielectric ^[24]. PVDF, PVDF’s copolymers of trifluoroethylene (PVDF-TrFE), nylon-11 and polyuriarequire very high activation fields (>10 V/µm) that are considered piezoellose to the breakdown level. The actrivation of ionic polymers, on ^[25].the PVDFother and its copolymers constitute mosthand, requires only 1-2 volts. They however need to maintain wetness, though some polymer-based piezoelectric geners have been developed as self-contained encapsulated activators ^[26].which allows their use Piezoelectrn dry environments.^[19] Ionic polymers also have a lower piezoelectric strain constant than ceramic materials electromechanical coupling. They are however ideal for bio-mimetic devices. ^[27].

4. Characterization

While Howthever, piezore are many different ways electricoactive polymers could help to develop much better sensors than ceramics due to higher piezoean be characterized, only three will be addressed here: stress–strain curve, dynamic mechanical thermal analysis, and dielectric stressthermal analysis. cons

Stress–strain curve

Main page: Physics:Stress–strain curve

tanhumb|250px|right|Figure ^[27].4: PiThezoelectric unstressed polymeric sensors and actuators have the advantage of processing flexibility being lightweight, tough, and amenable to be easily cut and formed into complex shape spontaneously forms a folded structure, upon application of a stress the polymer regains its original length. Stress strain curves provide information about the polymer's mechanical properties such as the brittleness, elasticity and yield strength of the polymer. This ^[27].

4. Recent Advancements in the Applications of Electroactive Polymers

EAPis done by providing are notable for their ability to tur force to the polymer at a uniform rate and measuring the deformation that results.^[24] An examplectrical energy into mechanical energy. In particular, EAPs are widely investigated for actuators. EAPs can be beneficial in circumstances of this deformation is shown in Figure 4. This technique is useful for determining the type of material (brittle, tough, etc.), but it is a destructive technique as the stress is increased until the polymer fractures. w

Dynamic mechanical thermal analysis (DMTA)

Main page: Dynamic mechanical analysis

Bothere harddynamic mechanical parts may be undesirable. Additionally, EAP actuators are a single component rather than a series of parts that may rub and produce wear. EAPs can operate with minimal noise, and their use could dramatically reduce wear and friction compared to traditional actuatoranalysis is a non destructive technique that is useful in understanding the mechanism of deformation at a molecular level. In DMTA a sinusoidal stress is applied to the polymer, and based on the polymer's deformation the elastic modulus and damping characteristics are obtained (assuming the polymer is ^[28][29].a damped Furthermore, theirarmonic oscillator).^[24] fElexible nature helps them to alter their properties according to the situation forastic materials take the mechanical energy of the stress and convert it into potential energy which they are neededcan later be recovered. ^[30].An Thidese properties make EAP actuators useful for multiple applications where traditional actuators are not optimal. Also, in recent years, EAPs-based coating has become a viable option for improving product performance. There are a variety of advantages that becomeal spring will use all the potential energy to regain its original shape (no damping), while a liquid will use all the potential energy to flow, never returning to its original position or shape (high damping). A viscoeleastic polymer will exhibit a combination of both types of behavior.^[24]

Dielectric thermal analysis (DETA)

Main page: Dielectric thermal analysis

DETA is avasimilable by coating a substrate material with EAPs. Those advantages include: increasr to DMTA, but instead of an alternating mechanical force an alternating electrochemical capacitance, reducing friction, wear, corrosion protection, reducing electric resistance, biomedical applications, and stabilization of oxide surfaces ^[31]ic field is applied. The applied field can lead to polarization of the sample, and if the polymer contains groups that have permanent dipoles (as in Figure 2), they will align with the electrical field.^[24] Ther pefore, EAPs have been successfully used in fields such as engineering and medicine to make numerous devices. Some of the interesting applications of EAPs are highlighted herermittivity can be measured from the change in amplitude and resolved into dielectric storage and loss components. The electric displacement field can also be measured by following the current.

I^[24] Once the field of robotics, soft robots usingis removed, the dipoles will relax back into a random orientation.

5. Applications

Figure 5: Cartoon drawing of an arm controlled by EAPs. When a voltage is applied (blue muscles) the polymer expands. When the voltage is removed (red muscles) the polymer returns to its original state.

EAPs have significant potential. Soft actuators are able to deform while still being functionalmaterials can be easily manufactured into various shapes due to the ease in processing many polymeric materials, making them safe for interaction with humans. Furthermore, their flexibility and adaptability allow for novel robotic motion, such as avery versatile materials. One potential application for EAPs is that they can potentially be integrated into microelectromechanical systems (MEMS) to produce smart actuators.

Artificial muscles

Asnak the-shaped robot capable of serpentine motion most prospective practical research direction, EAPs have been used in artificial ^[32]muscles.^[25] Their flexiability also allows for the development of nuanced structures, such as a simulated human fingertip. The potential for most EAPs to beto emulate the operation of biological muscles with high fracture toughness, large actuation strain and inherent vibration damping draw the attention of scientists in this field.^[5] mad

Tactile displays

In rece into actuation devices allow years, "electro active polymers for refreshable Braille displays"^[26] has emerged for virtto aid the visually all EAPs to be used in robotics according to specific requirements. However, a few types stand out as the most widely applicable. Dielectric elastomers (DEAs) could be particularly useful in some robotic applications due to their large deformations, light weight, easy proimpaired in fast reading and computer assisted communication. This concept is based on using an EAP actuator configured in an array form. Rows of electrodes on one side of an EAP film and columns on the other activate individual elements in the array. Each element is mounted with a Braille dot and is lowered by applying a voltage across the thickness of the selected element, causing local thickness reduction, and adaptability. Under computer control, dots ^[33].would CPbe actuators can also be useful, particularly in biomedical applications, because they are typically bio-compatible andivated to create tactile patterns of highs and lows representing the information to be read. c

Figure 6: High resolution tactile display consisting of 4,320 (60x72) actuator pixels based on stimuli-responsive hydrogels. The integration density of the device is 297 components per cm². This display gives visual (monochromic) and physical (contours, relief, textures, softness) impressions of a virtual surface.

Visuan bel manufactured at the micro and nano scales ^[34].and tactile impressions of a virtual surface Various other types of EAPs are useful depending on the exact circumstances that the actuator is intended toe displayed by a high resolution tactile display, a so-called "artificial skin" (Fig.6) .^[27] bThe used.

Syse monolithetic muscles, either for use as prosthetics or robotic components, represent another potential application for EAP actuators. The characteristics of EAPs, such aic devices consist of an array of thousands of multimodal modulators (actuator pixels) based on stimuli-responsive hydrogels. Each modulator is able to change individually their transmission, height and softness. Besides their large bending strain and similarity to natural muscles, would make them useful as synthetic musclepossible use as graphic displays for visually impaired such displays are interesting as ^[35]. Fufrtheermore, EAPs generally have inaudible actuation programmable keys of touchpads and consoles. This

Microfluidics

EAP maktes them viable for prosthetics since they would not audibly disrupt the user or others. Dielectric EAPs, in particular, have been investigated for their potential as synthetic muscles due to their quick rials have huge potential for microfluidics e.g. as drug delivery systems, microfluidic devices and lab-on-a-chip. A first microfluidic platform technology reported in literature is based on stimuli-responsive gels. To avoid the electrolysis of water hydrogel-based microfluidic devices are mainly based on temperature-response time, durability, and noiselessnessive polymers with lower critical solution temperature ^[36]. (LCSomeT) EAP actuators have even proven useful in the field of acoustic engineering for sound dampeningcharacteristics, which are controlled by an electrothermic interface. Two types of micropumps are known, a diffusion micropump and a displacement micropump.^[28] EAP aMictuators have been used for devices,rovalves based on stimuli-responsive hydrogels show some advantageous properties such as noise-cancelling headphones, transducers, an particle tolerance, no leakage and outstanding pressure resistance.^[29][30][31] Besides resonatorsthese microfluidic standard ^[37][38][39]. Hcompownever,nts the high activation voltage of electrical EAP actuatydrogel platform provides also chemical sensors^[32] and may be dangerous for users. Another challenge is handling novel class of microfluidic components, the chemical transistors (also referred as chemostat valves).^[33] tThe dielectric breakdown, which is not desirable in a synthetic musclese devices regulate a liquid flow if a threshold concentration of certain chemical is reached. Chemical transistors ^[40][41]. Sforme types of ionic EAPs may also be used to create synthetic muscles, as their bending de the basis of microchemomechanical fluidic integrated circuits. "Chemical ICs" process exclusively chemical information can be used to obtain linear motion, are energy-self-powered, operate automatically and are able for large-scale integration.^[34] with Anothe appropriate techniquesr microfluidic platform is based on ionomeric ^[42]. Rmategriardless of the type of EAPls. Pumps made from that is used as synthetic muscles, tribological considmaterial could offer low voltage (battery) operations are significant due to the damage and pain that friction can cause, extremely low noise signature, high system efficiency, and highly accurate control of flow rate.^[35] iAn the human bodother technology ^[43].that Also,can electroactive polymer coating was found useful for developing flexible artificial muscles. Ebadi et al.benefit from the unique properties of EAP actuators is optical membranes. Due to their low modulus, the mechanical impedance of the actuators, ^[44]they appre wellied EAP coating to polyurethane nanofibers, and achieved an angular-matched to common optical membrane materials. Also, a single EAP actuator is capable of generating displacement between 48°–225°. This illustrates a clear benefit, especially when considering flexible bodies as muscless that range from micrometers to centimeters. For this reason, these materials can be used for static shape correction and jitter suppression.

W Thearablse electronics is another sector in which EAP actuators are widely usedactuators could also be used to correct for optical aberrations due to atmospheric interference.^[36] Since theyse are flexible, they can adapt to the shapes of human body parts. Additionally, they can be fabricated as very small devices, so that they can bematerials exhibit excellent electroactive character, EAP materials show potential in biomimetic-robot research, stress sensors and acoustics field, which will make EAPs become a more attractive study topic in the near future. They have been used for nuanced applications. For instance, Ig Mo Koo et alvarious actuators such as face muscles and arm muscles in humanoid robots.^[37] d

6. Future Directions

Thev fieloped a tactile display for a human fingertipd of EAPs is far from mature, which leaves several issues that consists ostill need to be worked on.^[5] The performance a series of tactile simulators made with dielectric elastomers ^[45]nd long-term stability of the EAP should be improved by designing a water impermeable surface. ItThis is even possible to create a fabric with EAPs that has will prevent the evaporation of water contained in the EAP, and also reduce the potential to change its density based oloss of the positive counter ions when the activity for which it is neededEAP is operating submerged in an aqueous environment. Improved ^[46]. Weasurfable EAPs could also be harnessed to harvest mechanical energy because they generate an electric charge when they are deformed. Electronic EAPs are the most common type of EAPs for these applications since they are easier to ce conductivity should be explored using methods to produce a defect-free conductive surface. This could possibly be done using metal vapor deposition or other doping methods. It may also be possible to utilize conductive polymers to form a thick conductive layer. Heat resistant EAP would be desirable to allow operate in the open air compared to ionic EAPs. However, ionic EAPs have the potential to be safer for human use because of their lower activation voltage. Polyvinylidene fluoride (PVDF) is a type of electrical EAPs that has gained attention for wearable technology due to its superior propertiesion at higher voltages without damaging the internal structure of the EAP due to the generation of heat in the EAP composite. Development of EAPs in different configurations (e.g., fibers and fiber bundles), would also be beneficial, in order to increase the range of possible modes of motion. ^[12].