Poly(3,4-ethylenedioxythiophene) (PEDOT), an inherently electrically conductive or conjugated polymer (CP), exhibits the potential to play a significant role in the development of innovative fiber materials for use in smart textiles, such as wearables. Furthermore, these fibers can function as artificial muscles in the emerging field of interactive fiber rubber composites. This study introduces a straightforward and efficient method for creating PEDOT-based, biomimetic, fiber-shaped, linearly contracting ionic electroactive polymer actuators. To achieve this, a wet-spinning technique is presented, which enables a continuous production of PEDOT:polystyrene sulfate (PSS) fibers at high production rates of 34 m h-1, an additional fiber washing step and a sulfuric acid posttreatment step to increase the fibers conductivity. The fibers provide a high conductivity of 1028 S cm-1, maximum tensile strength reaching 182 MPa, and a maximum elongation of 24%. When utilized as CP actuators in an aqueous sodium dodecylbenzenesulfonate electrolyte medium, the fibers demonstrate a repeatable maximum isometric contractile force of 1.64 mN and repeatable linear contractile strain up to 0.56%. Furthermore, a high level of cyclic long-term actuation stability can be demonstrated. Notably, these contractile strains are, to the best of knowledge, the highest reported values for pristine PEDOT:PSS fibers. This study introduces a wet-spinning method for high-volume production of poly(3,4-ethylenedioxythiophene):polystyrene sulfate-based conducting polymer fibers, spanning tens to hundreds of meters. Evaluating their physical properties, with emphasis on actuation, reveals robust and stable actuation capabilities, promising for integration into intelligent textiles for wearables or soft robotics with sensing or actuating functionalities.image (c) 2024 WILEY-VCH GmbH

This work presents a comparison of ionic coatings (ICs) developed specifically for electroactive yarn actuators, able to operate in open-air. Six ionically conducting materials, previously reported in different studies from our group, were used and compared. Two all-solid-state crosslinked materials based on polymeric ionic liquids and four ionogels are described. They are all soft but differ from (i) their nature, i.e. all-solid polymeric ionic liquid vs "wet" ionogel, and from (ii) their ionic charge carriers, i.e. conventional ionic liquid vs biofriendly ionic liquid. As a result, they have conductivities ranging over two orders of magnitude. In spite of the different electrical stimulations applied on the yarn actuators and their electrochemical charging behavior, i.e. bipolar or unipolar, we achieved a conceptual understanding of the key characteristics that ICs should exhibit to induce optimal CNT yarn actuation through the establishment of a relationship between stroke rate-to-potential of coiled CNT yarn actuators' operation in open air.

Conducting polymers (CP) have shown great features in building textile actuators. To date, most of the yarn-based or CP-yarn actuators have been operated in liquid electrolytes in a three-electrode-cell configuration, comprising an external counter and a reference electrode. For integration in textiles, a two-electrode system is needed, where both electrodes are in a yarn format. This can be achieved by having two CP-yarns, where one acts as the anode and the other as the cathode. For these two CP-yarns to operate synchronically, they both need to expand (or contract) during opposite reactions. This can be achieved by doping one CP-yarn with mobile anions that will expand during oxidation, while the other CP-yarn should be doped with immobile anions expanding during reduction. As a result, the same movement is created upon opposite redox reactions, both collaborating with the actuation in the same direction without the need for an external passive electrode to close the electrical circuit, which could oppose or hinder the movement. Most of the studies on textile actuators are based on cation-driven CP-yarn actuators, while little is known about anion-driven systems in CP-yarn actuators. Here, we first present a study of the effect of the dopants, solvents, and polymer layer combinations on the mechanism and strain of CP-yarns. The CP-yarns are coated with two layers: an inner poly(3,4-ethylenedioxythiophene) (PEDOT) layer and the outer and active polypyrrole (PPy) layer. According to our results, the dopant of the inner PEDOT layer seems to affect the actuation mechanism of the outer PPy layer and, thereby, of the whole CP-yarn actuator, influencing the direction of the movement and enhancing or hindering the total strain of the actuator. We show that a CP-yarn coated with PEDOT(Tos)/PPy(ClO4) and actuated in LiClO4 aqueous solution showed a pure anion-driven actuation. Next, based on the latter results, we demonstrate for the first time the dual actuation of two CP-yarns, doped with two different dopants, ClO4- and DBS-, actuating simultaneously driven by opposite redox reactions and exhibiting an average of 0.5% of strain, an important step toward in-air actuating yarns.

Electronic textiles (E-textiles) are made using various materials including carbon nanotubes, graphene, and graphene oxide. Among the materials here, e-textiles are fabricated with reduced graphene oxide (rGO) coating on commercial textiles. rGO-based yarns are prepared for e-textiles by a simple dip coating method with subsequent non-toxic reduction. To enhance the conductivity, the rGO yarns are coated with poly(3,4-ethylene dioxythiophene): poly(styrenesulfonic acid) (PEDOT) followed by electrochemical polymerization of polypyrrole (PPy) as the electromechanically active layer, resulting in textile actuators. The rGO-based yarn actuators are characterized in terms of both isotonic displacement and isometric developed forces, as well as electron microscopy and resistance measurements. Furthermore, it is demonstrated that both viscose rotor spun (VR) and viscose multifilament (VM) yarns can be used for yarn actuators. The resulting VM-based yarn actuators exhibit high strain (0.58%) in NaDBS electrolytes. These conducting yarns can also be integrated into textiles and fabrics of various forms to create smart e-textiles and wearable devices. A simple graphene oxide, PEDOT:PSS and PPy coated textile-based soft actuator is presented that shows good electrochemical strain and force. This opens a new perspective in the development of textile yarns with enhanced conductivity and/or actuation with possible applications in the field of smart textile materials.image

Like skeletal muscles having a fibrous structure, conducting polymers can actuate upon electrical stimulation and can be shaped into fibers. Through textile assembly strategies of such fibers, complex actuating architectures are possible. However, state-of-the-art strategies using short pieces of yarn, which compel manual integration, are not fully taking advantage of textiles. To manufacture actuating textiles that best exploit textile properties like softness and pliability, and to enable production upscaling, a production of continuous, actuating fibers is presented here. These fibers are produced from commercial polyamide 6/6 filaments by first continuously dip-coating in a modified commercial poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) dispersion before the electropolymerization of polypyrrole (PPy), where the fibers are withdrawn continuously through an electrolyte solution containing the pyrrole monomer. By employing a cyclic dip-coating with individual viscosity, drying temperature, and withdrawal speed for each layer, and by adjusting the tension, speed, and applied potential of the electropolymerization, their isotonic strain is enhanced threefold. Their specific tension, at 400 mu N tex-1, reaches slightly higher than human skeletal muscle fibers. Furthermore, these continuous actuating fibers produced on the meter are processable in an industrial knitting machine. This study anchors the development of textile muscle fibers for future textile muscles. Addressable textile muscles can only proliferate if the production of substantial lengths of textile muscle fibers is mature enough. To provide a firm foundation for the development of such production, textile muscle fibers are continuously produced via electropolymerized PPy (polypyrr) on top of a PEDOT (poly(3,4-ethylenedioxythiophene)) dip-coated commercial yarn. They are shown to meet their two objectives: actuation performance and textile processability. image

Smart textiles combine the features of conventional textiles with promising properties of smart materials such as electromechanically active polymers, resulting in textile actuators. Textile actuators comprise of individual yarn actuators, so understanding their electro-chemo-mechanical behavior is of great importance. Herein, this study investigates the effect of inherent structural and mechanical properties of commercial yarns, that form the core of the yarn actuators, on the linear actuation of the conducting-polymer-based yarn actuators. Commercial yarns were coated with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) to make them conductive. Then polypyrrole (PPy) that provides the electromechanical actuation is electropolymerized on the yarn surface under controlled conditions. The linear actuation of the yarn actuators is investigated in aqueous electrolyte under isotonic and isometric conditions. The yarn actuators generated an isotonic strain up to 0.99% and isometric force of 95 mN. The isometric strain achieved in this work is more than tenfold and threefold greater than the previously reported yarn actuators. The isometric actuation force shows an increase of nearly 11-fold over our previous results. Finally, a qualitative mechanical model is introduced to describe the actuation behavior of yarn actuators. The strain and force created by the yarn actuators make them promising candidates for wearable actuator technologies.

Electrochemical devices as conducting polymer-based actuators or textile actuators often use layers of different conducting polymers. Although research has been performed on such devices, it is still not very clear how the different layers affect each other. Here we attempt to clarify such influence on yarn actuators using electrochemical methods. Different electrochemical methods as cyclic voltammetry, chronoamperometry or chronopotentiometry were used to electropolymerize polypyrrole on top of a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) coated textile yarns by using different applied electrochemical conditions (potentials/currents). Thus, we found that selecting suitable conditions (as an applied potential of +0.8 V) for such electropolymerization is key to obtain a polypyrrole of high quality. Besides, we show that the underlying layer of PEDOT:PSS has an influence on such electropolymerization conditions and can be subjected to parallel redox reactions as oxidation or electrochemical degradation that influence the electropolymerized polypyrrole.

Controlling stem cell behavior at the material interface is crucial for the development of novel technologies in stem cell biology and regenerative medicine. The composition and presentation of bio-factors on a surface strongly influence the activity of stem cells. Herein, we designed an electroactive surface that mimics the initial process of trabecular bone formation, by immobilizing chondrocyte-derived plasma membrane nanofragments (PMNFs) on its surface for rapid mineralization within 2 days. Moreover, the electroactive surface was based on the conducting polymer polypyrrole (PPy), which enabled dynamic control of the presentation of PMNFs on the surface via electrochemical redox switching, further resulting in the formation of bone minerals with different morphologies. Furthermore, bone minerals with contrasting surface morphologies had differential effects on the differentiation of human bone marrow-derived stem cells (hBMSCs) cultured on the surface. Together, this electroactive surface showed multifunctional characteristics, not only allowing dynamic control of PMNF presentation but also promoting the formation of bone minerals with different morphologies within 2 days. This electroactive substrate could be valuable for more precise control of stem cell growth and differentiation, and further development of more suitable microenvironments containing bone apatite for housing a bone marrow stem cell niche, such as biochips/bone-on-chips.

Artificial muscles, or soft actuators, that could exhibit contractile stroke and operate in open-air, would be crucial for many applications, such as robotics, prosthetics, or powered exoskeletons. Amongst the different artificial muscle technologies, electrochemical carbon nanotube (CNT) yarn muscles, transducing capacitively ionic accumulation at the electrochemical double layer into linear contraction, are amongst the most promising candidates. However, their performances are either limited by an undesired bipolar behaviour or short lifetime due to the inevitable drying of water-based electrolytes. In this paper, we present here the fabrication of air -operating contractile linear artificial muscles from commercially available CNT yarns exhibiting outstanding performance. The synthesis and the junction of two ionogels based on cationic and anionic polyelectrolyte have been designed for the coating process on CNT yarns, and for selectively orienting the ionic flow allowing optimal electromechanical energy conversion. The dual-electrode CNT yarn actuators showed air-stable unipolar con-tractile stroke, reaching 9.7% without loss of performances after 2000 cycles.

Helical plants have the ability of tropisms to respond to natural stimuli, and biomimicry of such helical shapes into artificial muscles has been vastly popular. However, the shape-mimicked actuators only respond to artificially provided stimulus, they are not adaptive to variable natural conditions, thus being unsuitable for real-life applications where on-demand, autonomous operations are required. Novel artificial muscles made of hierarchically patterned helically wound yarns that are self-adaptive to environmental humidity and temperature changes are demonstrated here. Unlike shape-mimicked artificial muscles, a unique microstructural biomimicking approach is adopted, where the muscle yarns can effectively replicate the hydrotropism and thermotropism of helical plants to their microfibril level using plant-like microstructural memories. Large strokes, with rapid movement, are obtained when the individual microfilament of yarn is inlaid with hydrogel and further twisted into a coil-shaped hierarchical structure. The developed artificial muscle provides an average actuation speed of approximate to 5.2% s(-1) at expansion and approximate to 3.1% s(-1) at contraction cycles, being the fastest amongst previously demonstrated actuators of similar type. It is demonstrated that these muscle yarns can autonomously close a window in wet climates. The building block yarns are washable without any material degradation, making them suitable for smart, reusable textile and soft robotic devices.

A new radially expanding conducting polymer microactuator is presented. The radially expanding micro-actuators are used as electroactive gates in an electrically controlled microparticle sieve. A novel configuration to dynamically filter particles of different sizes in a microfluidic chip is conceptualized. Micropillars of SU-8 combined with conducting polymers to provide the radial actuation are positioned in a microfluidic chip with a specifically designed 3D printed housing to allow for selective filtration of microparticles with varied sizes. These pillar-shaped microactuators of polypyrrole actuate radially to function as dynamic gates for the fluidic channel, controlling the porosity of the filter allowing for the filtration of specific size of microparticles. This sieve design provides user defined channel width modulation with external stimuli. Photolithography and electrochemical polymerizations are combined with additive manufacturing to fabricate the individual func-tional parts of the microfluidic filter. To demonstrate the new conceptual filter design, we have shown filtration of microparticles of the sizes 60, 80, 90 and 100 mu m by electrically actuating micropillars of the dynamic gate. The flow and aggregation of the microparticles were analysed at the dynamic gates to characterize the perfor-mance of the filter.

Electro-stimulation is an effective way to manipulate the presentation of bio-factors at the materials interface. This study aimed to develop electrochemically-modified trabecular bone-like surfaces for manipulation of mesenchymal and hematopoietic cells. The electroactive surface was based on the conducting polymer polypyrrole for dynamic control of the presentation and mineralisation of chondrocyte-derived plasma membrane nanofragments (PMNFs) covalently immobilized on the surface. Electrochemical redox switching resulted in the PMNF-based formation of bone minerals with different morphologies, which further demonstrated to have distinct effects on the survival of mouse bone marrow-derived mesenchymal and hematopoietic cell populations cultured on the surface. This tunable electroactive surface could be a valuable tool for dynamically sensing and/or controlling stem cell functions in more suitable biomimetic microenvironments housing a stem cell niche.

Soft robotics has attracted great attention owing to their immense potential especially in human-robot interfaces. However, the compliant property of soft robotics alone, without stiff elements, restricts their applications under load-bearing conditions. Here, biohybrid soft actuators, that create their own bone-like rigid layer and thus alter their stiffness from soft to hard, are designed. Fabrication of the actuators is based on polydimethylsiloxane (PDMS) with an Au film to make a soft substrate onto which polypyrrole (PPy) doped with poly(4-styrenesulfonic-co-maleic acid) sodium salt (PSA) is electropolymerized. The PDMS/Au/PPy(PSA) actuator is then functionalized, chemically and physically, with plasma membrane nanofragments (PMNFs) that induce bone formation within 3 days, without using cells. The resulting stiffness change decreased the actuator displacement; yet a thin stiff layer couldnot completely stop the actuators movement, while a relatively thick segment could, but resulted in partial delamination the actuator. To overcome the delamination, an additional rough Au layer was electroplated to improve the adhesion of the PPy onto the substrate. Finally, an alginate gel functionalized with PMNFs was used to create a thicker mineral layer mimicking the collagen-apatite bone structure, which completely suppressed the actuator movement without causing any structural damage.

We herein describe the fabrication, optimisation and characterisation of a biohybrid variable stiffness actuator that creates its own bone. By combining the electroresponsive properties of polypyrrole (PPy) with the compliant response of alginate gels functionalised with cell-derived plasma membrane nanofragments (PMNFs) it was possible to obtain bio-induced variable stiffness actuators. When the PMNFs were incubated into MEM, i.e. exposure to Ca, this caused the formation of calcium-phosphate minerals (i.e. amorphous calcium phosphate and hydroxyapatite) in the alginate gel, resulting in a more rigid layer and thus reducing and finally impeding the movement of the actuator, locking it in a fixed position within only 2 days. These actuators could morph in various, pre-programmed shapes and change their properties from soft to rigid. Adding different patterns to the actuator allowed locking the device in a predetermined shape without energy consumption, facilitating its application as soft-to-hard robotics as a biohybrid variant of so-called 4D manufacturing. The devices could wrap around and integrate into bone by the induced mineralisation in and on the gel layer. This illustrates its use as a potential tool to repair bone or in bone tissue engineering. 

Inspired by the dynamic process of initial bone development, in which a soft tissue turns into a solid load-bearing structure, the fabrication, optimization, and characterization of bioinduced variable-stiffness actuators that can morph in various shapes and change their properties from soft to rigid are hereby presented. Bilayer devices are prepared by combining the electromechanically active properties of polypyrrole with the compliant behavior of alginate gels that are uniquely functionalized with cell-derived plasma membrane nanofragments (PMNFs), previously shown to mineralize within 2 days, which promotes the mineralization in the gel layer to achieve the soft to stiff change by growing their own bone. The mineralized actuator shows an evident frozen state compared to the movement before mineralization. Next, patterned devices show programmed directional and fixated morphing. These variable-stiffness devices can wrap around and, after the PMNF-induced mineralization in and on the gel layer, adhere and integrate onto bone tissue. The developed biohybrid variable-stiffness actuators can be used in soft (micro-)robotics and as potential tools for bone repair or bone tissue engineering.

Smart textile yarns have already shown their potential for fabrication of textile actuators. However, their actuation strain and force have been limited so far. Accordingly, twisting, and coiling techniques have attracted much attention to enhance the strain and force of yarn actuators. In this regard, coiled yarns that actuate under a liquid electrolyte have been studied well, but coiled yarn actuators that work in air are not explored as much. In this work, a double coiled yarn structure that works in air is designed, prepared, and investigated. Commercial textile yarns were coated with poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) solution. Thereafter, yarns were coiled using a motorized stage. Two coiled yarns, as cathode and anode, are then placed near each other and covered with an ionogel precursor mixture containing an ionic liquid as ion reservoir. The gel is cured and set using UV emission. The actuation properties of the prepared double coiled yarn actuator were investigated in air. A square wave potential of ±2 V was applied, and strain response of the actuator yarns was measured. The results showed that prepared double coiled yarn can potentially be a promising candidate as soft actuators in wearables and garments, e.g. for haptic applications.

The development of actuating wearable textiles is of great interest in fields as 30haptics or assistive devices. Electroactive conducting polymer-based actuatorsare being merged with yarns and fabrics to provide them with mechanicalactuation. One way to speed up the development of such mechanically activewearable textiles is the development of conducting polymer-based actuators thatcan be incorporated into textile processing. This imposes extra requirements tothe actuators such as the required size, improved mechanical andelectrochemical stability, actuation in air or the use of low/non-hazardousmaterials. Tape yarn actuators composed of conducting polymer/ionicallyconducting layer/conducting polymer are being developed and optimized to thataim. The latest developments on integrating such EAP tape yarns in wovenfabrics will be presented.

Enzymatic biofuel cells are presented as an untethered alternative energy source that could power small implantable or wearable medical devices. However, most of these catalytic processes do not provide with enough energy to power common small electronic-mechanical devices. On the other hand, conducting polymer-based actuators are of great interest for their biocompatibility, flexibility, processability, possibility to be miniaturized and low power consumption. So far, these artificial muscles have been driven by external power sources that prevent them for being completely autonomous. There is a need for a novel power source to elaborate actuators that could use physiological processes as a driving force. These soft actuators’ low power consumption matches the electrical power generated by the biocatalysis of some enzymes, such as glucose oxidase and laccase in presence of glucose and oxygen in aqueous media. Here, we present the latest results in the development of polypyrrole-based soft actuators powered by enzymatic biofuel cells. The actuator consists of a tri-layer conductive substrate on which the polypyrrole is electrodeposited in both sides. The polypyrrole layers act as the active part, expanding and contracting upon a redox reaction, resulting in a bending movement. Tetrathiofulvlene-7,7,8,8-tetracyanoquinodimethane (TTF-TCNQ) and 2,2′-azino-di-(3-ethylbenzthiazoline sulfonic acid) (ABTS) electron transfer mediators are cast on the surface of the polypyrrole to help the electron transmission. The glucose oxidase and laccase enzymes are immobilized in the modified-conducting polymer surface, integrating the electrode to the actuator. The bio-catalysis of enzymes in presence of glucose and oxygen in aqueous solution provides the actuator with the electrons needed for the redox reaction, converting the chemical energy into mechanical energy, i.e., movement. The glucose-self-powered soft actuator may contribute to the development of more complex implantable, ingestible, or wearable biomedical devices such as cardio-stimulators, insulin pumps, or muscle implants.

With the rise of ion-based devices using soft ionic conductors, ionotronics show the importance of matching electronic and biological interfaces. Since textiles are conformal, an essential property for matching interfaces, light-weight and comfortable, they present as an ideal candidate for a new generation of ionotronics, i-textiles. As fibers are the building blocks of textiles, ionically conductive fibers, named ionofibers, are needed. However, ionofibers are not yet demonstrated to fulfill the fabric manufacturing requirements such as mechanical robustness and upscaled production. Considering that ionogels are known to be conformal films with high ionic conductivity, ionofibers are produced from commercial core yarns with specifically designed ionogel precursor solution via a continuous dip-coating process. These ionofibers are to be regarded as composites, which keep the morphology and improve the mechanical properties from the core yarns while adding the (ionic) conductive function. They keep their conductivity also after their integration into conformal fabrics; thus, an upscaled production is a likely outlook. The findings offer promising perspectives for i-textiles with enhanced textile properties and in-air electrochemical applications.

Here we present a new class of variable stiffness actuators for soft robotics based on biohybrid materials that change their state from soft-to-hard by creating their own bones. The biohybrid variable stiffness soft actuators were fabricated by combining the electromechanically active polymer polypyrrole (PPy) with a soft substrate of polydimethylsiloxane or alginate gel. These actuators were functionalized with cell-derived plasma membrane nanofragments (PMNFs), which promote rapid mineralization within 2 days. These actuators were used in robotic devices, and PMNF mineralization resulted in the robotic devices to achieve a soft to stiff state change and thereby a decreased or stopped actuation. Moreover, perpendicularly and diagonally patterned actuators were prepared. The patterned actuators showed programmed directional actuation motion and could be fixated in this programmed state. Finally, patterned actuators that combined soft and rigid parts in one actuator showed more complex actuation motion. Together, these variable stiffness actuators could expand the range of applications of morphing robotics with more complex structures and functions. 

Recently, electrically driven conducting polymer (CP) coated yarns have shown great promise to develop soft wearable applications because of their electrical and mechanical behaviour. However, designing a suitable yarn actuator for textile-based wearables with high strain is challenging. One reason for the low strain is the voltage drop along the yarn, which results in only a part of the yarn being active. To understand the voltage drop mechanism and overcome this issue intrinsically conductive yarns were used to create a highly conductive path along the full length of the yarn actuator. Ag plated knit-de-knit (Ag-KDK) structured polyamide yarns were used as the intrinsically conductive core material of the CP yarn actuators and compared with CP yarn actuators made of a non-conductive core knit-de-knit (KDK) yarn. The CP yarn actuators were fabricated by coating the core yarns with poly(3,4-ethylene dioxythiophene): poly(styrene sulfonic acid) followed by electrochemical polymerization of polypyrrole. Furthermore, to elucidate the effect of the capillarity of the electrolyte through the yarn actuator, two different approaches to electrochemical actuation were applied. All actuating performance of the materials were investigated and quantified in terms of both isotonic displacement and isometric developed forces. The resultant electroactive yarn exhibits high strain (0.64 %) in NaDBS electrolytes as compared to previous CP yarn actuator. The actuation and the electroactivity of the yarn were retained up to 100 cycles. The new highly conductive yarns will shed light on the development of next-generation textile-based exoskeleton suits, assistive devices, wearables, and haptics garments.

Current additive manufacturing, including three-dimensional (3D) and so-called four-dimensional printing, of soft robotic devices is limited to millimeter sizes. In this study, we present additive manufacturing of soft microactuators and microrobots to fabricate even smaller structures in the micrometer domain. Using a custom-built extrusion 3D printer, microactuators are scaled down to a size of 300 x 1000 mu m(2), with minimum thickness of 20 mu m. Microactuators combined with printed body and electroactive polymers to drive the actuators are fabricated from computer-aided design model of the device structure. To demonstrate the ease and versatility of 3D printing process, microactuators with varying lengths ranging from 1000 to 5000 mu m are fabricated and operated. Likewise, microrobotic devices consisting of a rigid body and individually controlled free-moving arms or legs are 3D printed to explore the microfabrication of soft grippers, manipulators, or microrobots through simple additive manufacturing technique.

To control and manipulate fluids in lab‐on‐a‐chip (LOC) devices, active components such as pumps, valves, and injectors are necessary. However, such components are often complex and expensive to fabricate, limiting integration in disposable LOCs. A new type of flexible, all‐polymer diaphragm actuator system, called Double Diaphragm Active Polymer Actuator (DDAPA), is presented as a single modular unit that can be repurposed to diverse active microfluidic components. To demonstrate the versatility of the DDAPA concept, the DDAPA devices are investigated in three different configurations: as a single operation microinjector, as a flow regulating element, and as a pump in a hybrid configuration with unibody‐LOC unidirectional systems. The working principle, fabrication process, and the three examples of microfluidic components are presented. The trilayer diaphragm actuator is realized using the conductive polymer poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate as the actuating material and thiol‐acrylate‐based ionogels as solid‐state electrolyte and base material. The three demonstrators show the feasibility of using the DDAPA module to inject liquids, regulate flow, and unidirectionally pump fluids up to 112 µL min−1 when coupled with a 3D printed unibody check valve. Hence, the presented concept with a simple mechanism and easy manufacturability, broadens the choice of disposable actuators compatible with fully disposable autonomous LOC solutions.

Commercially available yarns are promising precursor for artificial muscles for smart fabric-based textile wearables. Electrochemically driven conductive polymer (CP) coated yarns have already shown their potential to be used in smart fabrics. Unfortunately, the practical application of these yarns is still hindered due to their slow ion exchange properties and low strain. Here, a method is demonstrated to morph poly-3,4-ethylenedioxythiophene:poly-styrenesulfonate (PEDOT:PSS) coated multifilament textile yarns in highly twisted and coiled structures, providing >1% linear actuation in <1 s at a potential of +0.6 V. A potential window of +0.6 V and -1.2 V triggers the fully reversible actuation of a coiled yarn providing >1.62% strain. Compared to the untwisted, regular yarns, the twisted and coiled yarns produce >9x and >20x higher strain, respectively. The strain and speed are significantly higher than the maximum reported results from other electrochemically operated CP yarns. The yarns actuation is explained by reversible oxidation/reduction reactions occurring at CPs. However, the helical opening/closing of the twisted or coiled yarns due to the torsional yarn untwisting/retwisting assists the rapid and large linear actuation. These PEDOT:PSS coated yarn actuators are of great interest to drive smart textile exoskeletons.

Textile assembly methods offer great possibilities to create complex, large-scale, multi-functional 2D materials (fabrics) by a continuous process of structuring yarns together, in an architected manner. By designing a specific pattern and using functionalized yarns the properties of such a fabric can enable a variety of roles for example actuation and mechanical stimuli. Moreover, actuation can be achieved in several directions as the textile assembly enables the construction of a network where yarns can be independently addressed in X and/or Y direction. These are advantages that can be utilized in the field of soft robotics in many ways. The requirements for human-robotic interactions call for soft and compliant materials that are safe for such collaborative interactions and involve several types of functionalities. Textiles are easily conformed to the body, whether that is a robotic or a human one. Here we report on the integration of novel functional actuating yarns in the purpose of creating pliable textile actuators that also exhibit versatile morphing  capabilities. The yarns consist of three layers; two of which are made of thin poly (3, 4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT: PSS) coatings that cover opposite sides of the third layer, an ionogel. This stretchable gel supplies the system with ions for the actuation mechanism and therefore enables in-air actuation. The yarns are transformed into fabrics by using woven assembly techniques. This is an additive method that structures one set of yarns in a parallel sequence that is perpendicular to another second set of yarns. By structuring a number of yarns together in parallel the performance in terms of force output including blocking force is shown to increase. The textile assembly process allows for two approaches, collective and individual addressing for the actuating yarns. For the former, arranging the yarns into different pre-determined segments enable collective actuation of each segment to change the overall shape of the textile structure. In regards to the latter, by individual addressing we show that a specific and targeted actuation can be achieved. Furthermore, the arrangement in which the yarns are interlaced in the fabric enables switching the modality of the actuation. This means that we can alter a motion specific to the yarns into another by their arrangement in the textile structure. With our developed textile assembly method, we are approaching low-cost, large-scale production of actuating systems for human-robotic applications

Commercial yarns can be functionalized with conducting polymers (CPs) todevelop yarn and textile actuators. Here we show a method of functionalizationof commercial polyamide yarns by poly-3,4-ethylenedioxythiophene:polystyrenesulfonate (PEDOT:PSS) coating. Aftercoating, while PEDOT:PSS is drying, it is possible to twist and coil the yarns,resulting in a major improvement of their linear strain and speed of movement.By using a potential window between +0.6 V and -1.2 V vs Ag/AgCl it waspossible to obtain a fully reversible actuation of a coiled yarn providing up to1.62% strain. A strain higher than 1% was achieved in less than 1 second.Compared to the untwisted, regular yarns, the twisted and coiled yarns produce>9× and >20× higher strain, respectively. These results are a step forward towardsthe development of soft, silent and compliant smart textile exoskeletons.

Electrochemically or electrothermally driven twisted/coiled carbon nanotube (CNT) yarn actuators are interesting artificial muscles for wearables as they can sustain high stress. However, due to high fabrication costs, these yarns have limited their application in smart textiles. An alternative approach is to use off-the-shelf yarns and coat them with conductive polymers that deliver high actuation properties. Here, novel hybrid textile yarns are demonstrated that combine CNT and an electroactive polypyrrole coating to provide both high strength and good actuation properties. CNT-coated polyester yarns are twisted and coiled and subjected to electrochemical coating of polypyrrole to obtain the hierarchical soft actuators. When twisted without coiling, the polypyrrole-coated yarns produce fully reversible 25 degrees mm(-1)rotation, 8.3x higher than the non-reversible rotation from twisted CNT-coated yarns in a three-electrode electrochemical system operated between +0.4 and -1.0 V (vs Ag/AgCl). The coiled yarns generate fully reversible 10 degrees mm(-1)rotation and 0.22% contraction strain, 2.75x higher than coiled CNT-coated yarns, when operated within the same potential window. The twisted and coiled yarns exhibit high tensile strength with excellent abrasion resistance in wet and dry shearing conditions that can match the requirements for using them as soft actuators in wearables and textile exoskeletons.

Nonconductive commercial viscose yarns have been coated with a commercial conducting poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) layer providing electrical conductivity which allowed a second coating of the electroactive conducting polymer polypyrrole through electropolymerization to develop textile yarns actuators. To simplify the PEDOT coating process and at the same time make this process more suitable for application in industry, a new coating method is developed and the properties of the PEDOT-PSS conducting layer is optimized, paying attention on its effect on the actuation performance. The effect of the concentration of an additive such as dimethylsulfoxide (DMSO) on actuation, and of PEDOT:PSS layers, is investigated. Results show that on improving this conducting layer, better performance than previously developed yarn-actuators is obtained, with strains up to 0.6%. This study provides a simple and efficient fabrication method toward soft, textile-based actuators for wearables and assistive devices with improved features.

The feasibility of additive manufacturing actuating microstructures and microdevices with small dimension is presented. Using a custom-built extrusion 3D printer and CAD model of the device structure, bilayer microactuators driven by hydrogels are fabricated down to a size of 300 x 1000 mu m(2,)with a minimum thickness of 30 mu m. To explore the limitations of the 3D printing process, microactuators with a width of 300 mu m and lengths ranging from 1000 to 5000 mu m are manufactured and thereafter operated to demonstrate the feasibility of the process. Similarly, microrobotic devices consisting of a passive rigid body and flexible moving parts are 3D printed to illustrate the ease and versatility of the additive manufacturing technique to fabricate soft microgrippers or micromanipulators.

Conducting polymer (CP) based soft actuators are good candidates for miniaturised manipulation systems and soft robotic applications. We present the fabrication, characterization, and modelling, of a novel ionically driven soft, flat, parallel manipulator with minimal footprint actuated by CP actuators. This three degrees of freedom (3Dof) manipulator consists of four trilayer actuators with poly (3, 4- ethylenedioxy-thiophene):poly(styrene sulfonate) (PEDOT:PSS) electrodes on both sides of PVDF separator membrane with 1-Ethyl-3-methylimidazoliummethyl imidazolium bis(trifluoromethylsulfonyl)imide ionic liquid used as the electrolyte. The complete manipulator is fabricated as a monolithic structure using commercially available off the shelf materials by additive manufacturing technique including a syringe type printer. Its workspace and dynamics are characterised and the results are compared with a multiphysics model based on the finite element method. The model uses two types of charge storage mechanism namely electrical double layer and redox reactions to describe the electrode kinetics. Through simulation the charge contributed by each of the processes is separated and presented providing new insights in the underlying kinetics in this type of actuators. It is found the double layer charge is the dominant phenomenon driving these actuators compared to the redox process. Finally, to demonstrate the versatile applications, the manipulator is explored for a four-way laser steering application. This work has demonstrated high levels of manipulability along three degrees of freedom from the printed CP actuators that are outstanding within the class of soft ionic actuators while using off the shelf commercially available materials keeping the fabrication method simple, scalable and cost-effective along with the electro-chemo-mechanical model providing an insightful view of the charge storage mechanism.

Untethered actuation is important for robotic devices to achieve autonomous motion, which is typically enabled by using batteries. Using enzymes to provide the required electrical charge is particularly interesting as it will enable direct harvesting of fuel components from a surrounding fluid. Here, a soft artificial muscle is presented, which uses the biofuel glucose in the presence of oxygen. Glucose oxidase and laccase enzymes integrated in the actuator catalytically convert glucose and oxygen into electrical power that in turn is converted into movement by the electroactive polymer polypyrrole causing the actuator to bend. The integrated bioelectrode pair shows a maximum open-circuit voltage of 0.70 +/- 0.04 V at room temperature and a maximum power density of 0.27 mu W cm(-2) at 0.50 V, sufficient to drive an external polypyrrole-based trilayer artificial muscle. Next, the enzymes are fully integrated into the artificial muscle, resulting in an autonomously powered actuator that can bend reversibly in both directions driven by glucose and O-2 only. This autonomously powered artificial muscle can be of great interest for soft (micro-)robotics and implantable or ingestible medical devices manoeuvring throughout the body, for devices in regenerative medicine, wearables, and environmental monitoring devices operating autonomously in aqueous environments.

Conjugated polymers (CPs), as exemplified by polypyrrole, are intrinsically conducting polymers with potential for development as soft actuators or artificial muscles for numerous applications. Significant progress has been made in the understanding of these materials and the actuation mechanisms, aided by the development of physical and electrochemical models. Current research is focused on developing applications utilizing the advantages that CP actuators have (e.g., low driving potential and easy to miniaturize) over other actuating materials and on developing ways of overcoming their inherent limitations. CP actuators are available as films, filaments/yarns, and textiles, operating in liquids as well as in air, ready for use by engineers. Here, the milestones made in understanding these unique materials and their development as actuators are highlighted. The primary focus is on the recent progress, developments, applications, and future opportunities for improvement and exploitation of these materials, which possess a wealth of multifunctional properties.

A simple and cost-effective method for the patterning and fabrication of soft polymer microactuators integrated with morphological computation is presented. The microactuators combine conducting polymers to provide the actuation, with spatially designed structures for a morphologically controlled, user-defined actuation. Soft lithography is employed to pattern and fabricate polydimethylsiloxane layers with geometrical pattern, for use as a construction element in the microactuators. These microactuators could obtain multiple bending motions from a single fabrication process depending on the morphological pattern defined in the final step. Instead of fabricating via conventional photolithography route, which involves multiple steps with different chromium photomasks, this new method uses only one single design template to produce geometrically patterned layers, which are then specifically cut to obtain multiple device designs. The desired design of the actuator is decided in the final step of fabrication. The resulting microactuators generate motions such as a spiral, screw, and tube, using a single design template.

The field of smart textile actuators has been progressing rapidly during the last years. Smart textiles are a class of textile products which exploit the determinant feature of responding to a stimulus, input, which can be chemical, mechanical, optical, magnetic or electrical. The building block for fabrication of such products is smart yarn. However, most smart textiles are focused on receiving an input stimulus (sensors) and only a few are dedicated to providing an output response (actuators). Yarn actuators show strain or apply force upon application of electrical stimulation in isotonic or isometric conditions, respectively. A small actuation in the yarn scale can be amplified by knitting or weaving the smart yarns into a fabric. In this work, we have investigated the effect of inherent properties of different commercial yarns on the linear actuation of the smart yarns in aqueous media. Since actuation significantly depends on the structure and mechanical properties of the yarns, elastic modules, and tenacity of the yarns were characterized. Investigating the actuation behavior, yarns were coated with PEDOT:PSS to make them conductive. Then polypyrrole which provides the electromechanical actuation was electropolymerized on the yarn surface under controlled conditions. Finally, linear actuation of the prepared smart yarns was investigated under aqueous electrolyte in both isotonic and isometric conditions.

A new family of ionogels for electrochemical devices was developed from a mixture of multifunctional thiols, diacrylate and triethylamine in the presence of ionic liquid using Michael addition chemistry. Polymerization kinetic studies show that the ionic liquid not only acts as an ion source but also a co-catalyst in the polymerization. Ionogels with tailorable surface and mechanical properties were prepared using three approaches: off-stoichiometry, methacrylate addition, and dithiol chain extender addition. 3-Dimensional ionogels were constructed by bonding the flexible ionogel film together using the ionogel solution as an ionic adhesive. A tube actuator with PEDOT-PSS patterned on inner and outer wall was prepared to illustrate the potential of these ionogels with reactive surfaces. In addition, micro-patterns of the ionogels were obtained by photolithography and soft imprinting lithography. All in all, this thiol acrylate Michael chemistry provides a platform to prepare various forms (films, micro-patterns, 3-dimensional structures, and adhesive) of ionogels for the next generation of flexible electrochemical devices.

With few exceptions (such as 1) textiles have not been considered as means for obtaining actuation. This is surprising as textiles have many advantageous characteristics such as the D=M property, which stands for Doing Devices while Making the Material. This means that functions are introduced simultaneously as the material, such as in a weave, is built up tread by tread. Traditionally a tread could have a certain colour so in total an aesthetical pattern is formed. Now we take a step beyond this working with threads having more advanced functions. Included are fiber formed structures showing actuation behavior. 

This we employ here. We make fiber formed actuating structures (FAS) following the McKibben principle (2) with braided mesh sleeves surrounding a prolonged inflatable tube. Here we worked with relatively large diameters in the relaxed state but show that there is prospect for obtaining relaxed diameters of less than 1 mm approaching the range of large scale weaving manufacturing.

We study the behavior of these fibre formed actuating structures individually. Length changes obtained are -20%. We then make textile constructions by integrating several of these FASes with textile processing. By this, we build simple models of fabrics showing actuating behavior.  

This study shows how textile constructions can support or hinder overall movement. It is a first logical step in order to get an understanding of actuating fabrics based also on other actuating mechanisms (3).

The feasibility of textile actuators and their advantages to develop soft actuators with synergetic actuation have been proven. They are composed of a passive fabric coated with an electroactive polymer that provides the mechanical motion. Until now, a two-step coating process was followed to make the textile actuators: a first coating that provided conductivity to the passive fabrics and, once conducting, a second coating by electropolymerization was used to get a highly electroactive (moving as much as possible) material. To simplify the fabrication process, we here used different commercially available conducting yarns (polyamide+carbon, silicon+carbon, polyamide+silver coated, cellulose+carbon, polyester+2 × INOX 50 μm, polyester+2 × Cu/Sn and polyester+gold coated) to develop such textile actuators.

Thus, it was possible to coat them through direct electrochemical synthesis, avoiding the first step, which should provide with an easier and more cost-effective fabrication process. The conductivity and the electrochemical properties of the yarns were sufficient to allow the electropolymerization of the conducting polymer polypyrrole on the yarns. The electropolymerization was carried out and both the linear and angular the actuation of the yarns was investigated. These yarns may be incorporated into textile actuators for assistive prosthetic devices.

Diseases of the nervous system, traumas, or natural causes can reduce human muscle capacity. Robotic exoskeletons are forthcoming to support the movement of body parts, e.g. assist walking or aid rehabilitation. Current available devices are rigid and driven by electric motors or pneumatic actuators, making them noisy, heavy, stiff and noncompliant. We are developing textile based assistive devices that can be worn like clothing being light, soft, compliant and comfortable. We have merged advanced textile technology with electroactive polymers. By knitting and weaving electroactive yarns, we are developing soft textile actuators ("Knitted Muscles") that can be used in wearable assistive devices. We will present the latest progress increase the performance and to rationalise the fabrication. In addition we will show some demonstrators of the textile exoskeletons.

Smart textiles have been around for some decades. Even if interactivity is central to most definitions, the emphasis so far has been on the stimuli/input side, comparatively little has been reported on the responsive/output part. This study discusses the actuating, mechanical, output side in what could be called a second generation of smart textiles-this in contrast to a first generation of smart textiles devoted to sensorics. This mini review looks at recent progress within the area of soft actuators and what from there that is of relevance for smart textiles. It is found that typically still forces exerted are small, so are strains for many of the actuators types (such as electroactive polymers) that could be considered for textile integration. On the other side, it is argued that for many classes of soft actuators-and, in the extension, soft robotics-textiles could play an important role. The potential of weaving for stress and knitting for strain amplification is shown. Textile processing enables effective production, as is analyzed. Textile systems are made showing automatic actuation asked for in stand-alone solutions. It is envisioned that soft exoskeletons could be an achievable goal for this second generation of smart textiles.

There is a need for soft microactuators, especially for biomedical applications. We have developed a microfabrication process to create such soft, on-chip polymer-based microactuators that can operate in air. The on-chip microactuators were fabricated using standard photolithographic techniques and wet etching, combined with special designed process to micropattern the electroactive polymer polypyrrole that drives the microactuators. By immobilizing a UV-patternable gel containing a liquid electrolyte on top of the electroactive polypyrrole layer, actuation in air was achieved although with reduced movement. Further optimization of the processing is currently on-going. The result shows the possibility to batch fabricate complex microsystems such as microrobotics and micromanipulators based on these solid state on-chip microactuators using microfabrication methods including standard photolithographic processes.