Biomimetic Artificial Muscles Research Articles

Effects of Air Gaps on the Output Force Density in COMSOL Simulations of Biomimetic Artificial Muscles

Effects of Air Gaps on the Output Force Density in COMSOL Simulations of Biomimetic Artificial Muscles

Investigation of the influence of nano ZnO particle doping in electrode membrane on the output characteristics of biomimetic artificial muscles

AbstractBiomimetic artificial muscles (BMAMs) aim to imitate the movement and capabilities of natural muscles, drawing inspiration from their structure and function. This research utilized multiwalled carbon nanotubes to increase the conductivity of the electrode membrane and replaced traditional electroactive polymers with sodium alginate to improve the output performance of BMAMs. To further strengthen the output force of the electrode membrane, nanoscale ZnO was chosen as the doping material. Various composite electrode membranes were created during the experiments, each containing varying amounts of ZnO nanoparticles. The membranes' surface morphology was extensively examined with scanning electron microscopy, and the composite electrode membranes were fully assessed on an electrochemical workstation. Electrochemical testing showed that adding nanoscale ZnO particles greatly boosted the specific capacitance of the electrode membrane, which was directly linked to the performance of BMAMs. Impedance spectroscopy test results indicated a minimal impact of nanoscale ZnO particle doping on the internal resistance of the electrode membrane.Highlights Sodium alginate replaces electroactive polymers, easing environmental impact. Nano ZnO doping boosts electrode membrane's capacitance for stronger muscles. ZnO doping shows minimal effect on electrode membrane's resistance.

Investigation into the high electroactuation performance of a gelatinous biomimetic artificial muscle constructed using glycyrrhiza polysaccharide cross-linking modification

The Gelatinous Biomimetic Artificial Muscle (GBAM) is a novel actuator composed of intelligent polymer material capable of undergoing stretching, bending, tightening, or expansion by altering its internal structure in response to an applied electric field. This study employed sodium alginate (SA) and glycyrrhiza polysaccharides (GP) as the cross-linking agent to construct an electric-actuating membrane of the GBAM. Its electroactuation performance was assessed through the utilization of evaluation indicators including peak output force density (Dp), response speed (Vr), working life (TL), and duty cycle (Cd). By altering the electric-actuating membrane, the electroactuation performance of GBAM was enhanced. The findings indicated that following the GP cross-linking modification, the Dp value reached 22.69 mN/g, and the Vr value reached 0.093 mN/g·s. The TL value of 1262 s, the tremor frequency at only 53.4%, and the tremor amplitude at 8.3% of the control group were observed when the GP-SA cross-linking ratio was 4:5, leading to a much pronounced enhancement in the electroactuation performance of GBAM. When the GP-SA cross-linking ratio was 5:5, the elastic modulus exhibited a minimum value of 11.48 MPa, the Cd value demonstrated a minimum value of 13.5%, the specific capacitance attained a maximum value of 126.68 mF/g, the resistance value was measured at 2.22 Ω, the galvanostatic charge/discharge time was recorded as 5.3 s, and the energy value was quantified as 2.3 J. Furthermore, the GBAM displayed the most comprehensive internal structure, optimal cross-linking density, and superior performance in terms of output force, tensile strength, electrochemical behavior, and deflection displacement.

Analysis of the Impact of Electrochemical Properties of Copper-Doped Electrode Membranes on the Output Force of Biomimetic Artificial Muscles.

In this study, a biomimetic artificial muscle electroactive actuator was fabricated using environmentally friendly sodium alginate extract. Ultrasonic agitation was employed to embed ultrafine copper powder within a mesh-like structure formed by multi-walled carbon nanotubes (MWCNTs), aimed at reducing the internal resistance of the composite electrode membrane and enhancing its output force performance. Focused gallium ion beam-scanning electron microscopy observations, energy-dispersive X-ray spectroscopy (EDS) analysis, and surface morphology imaging confirmed the successful incorporation of the ultrafine copper powder into the MWCNT network. Additionally, we designed and constructed an output force measurement apparatus to assess the output performance of biomimetic artificial muscles (BMAMs) doped with varying quantities of ultrafine copper powder. Electrochemical testing results demonstrated that the artificial muscles exhibited optimal performance when doped with a mass of 1.5 g, yielding a maximum output force of 6.96 mN, an output force density of 30.64 mN/g, and a peak average rate of 0.059 mN/s. These values represented improvements of 224%, 189%, and 222% compared to the electrode membrane without the addition of ultrafine copper powder, respectively.

Bioinspired Artificial Muscles Based on Sodium Alginate-Wrapped Multi-Walled Carbon Nanotubes and Molybdenum Disulfide Composite Electrode Membrane.

Using a naturally extracted polymer sodium alginate extracted from natural seaweed as the primary raw material, we have successfully developed an electroactive actuator known as biomimetic artificial muscle (BMAM). In comparison to conventional synthetic materials, this BMAM aligns more coherently with the prevailing principles of environmentally friendly development. During the preparation of the BMAM electrode membrane, we employed ultrasonic oscillation to adsorb varying quantities of MoS2 onto a reticulated structure formed by multi-walled carbon nanotubes (MWCNTs), thus enhancing the mechanical and electrochemical performance of the BMAM. Scanning electron microscopy and energy-dispersive X-ray spectroscopy (EDS) confirmed the successful encapsulation of MoS2 by the MWCNTs network in the composite. To measure the output force of the BMAM fabricated with different masses of MoS2 doping, we established a self-built experimental platform and conducted tests on the electrode membranes doped with varying quantities of MoS2 using an electrochemical workstation. The results revealed that the BMAM exhibited optimal mechanical performance when doped with 1.5 g of MoS2, with a maximum output force of 7.81 mN, an output force density of 34.36 mN/g, and a response rate of 0.09 mN/s. These performances were improved by 309%, 276%, and 175%, respectively, compared to the samples without MoS2 doping, with a mass-specific capacitance enhancement of 151%.

Output Force Density Saturation in COMSOL Simulations of Biomimetic Artificial Muscles

Many modern applications, such as undersea drones, exoskeletal suits, all-terrain walker drones, prosthetics, and medical augments, would greatly benefit from artificial muscles. Such may be built through 3D-printed microfluidic devices that mimic biological muscles and actuate electrostatically. Our preliminary results from COMSOL simulations of individual devices and small arrays (2 × 2 × 1) established the basic feasibility of this approach. Herein, we report on the extension of this work to N × N × 10 arrays where Nmax = 13. For each N, parameter sweeps were performed to determine the maximal output force density, which, when plotted vs. N, exhibited saturation behavior for N ≥ 10. This indicates that COMSOL simulations of a 10 × 10 × 10 array of this type are sufficient to predict the behavior of far larger arrays. Also, the saturation force density was ~9 kPa for the 100 μm scale. Both results are very important for the development of 3D-printable artificial muscles and their applications, as they indicate that computationally accessible simulation sizes would provide sufficiently accurate quantitative predictions of the force density output and overall performance of macro-scale arrays of artificial muscle fibers. Hence, simulations of new geometries can be done rapidly and with quantitative results that are directly extendable to full-scale prototypes, thereby accelerating the pace of research and development in the field of actuators.

Electrically actuated characteristics and electrochemical mechanism of a flexible biomimetic artificial muscle regulated by the responsive polymer of the calcium alginate gelation

In comparison to conventional actuated techniques, the utilization of a Flexible Biomimetic Artificial Muscle (FBAM) incorporating calcium alginate hydrogel, a type of responsive polymer, offers numerous benefits including reduced weight, lower actuated voltage requirements, enhanced specific energy density, and minimal acoustic disturbances, among others. This paper presents the fabrication of the FBAM through calcium alginate gelation utilizing six calcium salts with identical Ca2+ molar mass. Subsequently, the electrically actuated characteristics and electrochemical mechanism of the FBAM were investigated, employing four evaluation indexes: peak force density (D, mN/g), operating life (Tt, s), response speed (Vr, mN/g·s), and rise time (Ts, s). The findings of this study hold significant implications for the advancement of novel responsive polymers for artificial muscles. The findings of the study indicate that the electrically actuated characteristics of FBAM were most optimal when calcium alginate gelation with CaH8I2O4 was employed. This was evidenced by the D value of 22.807 mN/g, Tt value of 1066 s, Vr value of 98 s, and Ts value of 0.1046 mN/g·s. The sufficient degree of calcium alginate gelation between sodium alginate molecule and Ca2+ cations resulted in the formation of intermolecular bridges within the calcium alginate hydrogel, which consisted of polymer β-D-mannuronic and α-L-guluronic. Notably, this gelation process was found to be inversely related to the pH level in the aqueous solution of the electrically actuated membrane.

Fuel-Driven Redox Reactions in Electrolyte-Free Polymer Actuators for Soft Robotics.

Polymers that undergo shape changes in response to external stimuli can serve as actuators and offer significant potential in a variety of technologies, including biomimetic artificial muscles and soft robotics. Current polymer artificial muscles possess major challenges for various applications as they often require extreme and non-practical actuation conditions. Thus, exploring actuators with new or underutilized stimuli may broaden the application of polymer-based artificial muscles. Here, we introduce an all-solid fuel-powered actuator that contracts and expands when exposed to H2 and O2 via redox reactions. This actuator demonstrates a fully reversible actuation magnitude of up to 3.8% and achieves a work capacity of 120 J/kg. Unlike traditional chemical actuators, our actuator eliminates the need for electrolytes, electrodes, and the application of external voltage. Moreover, it offers athermal actuation by avoiding the drawbacks of thermal actuators. Remarkably, the actuator maintains its actuated position under load when not stimulated, without consuming energy (i.e., catch state). These fuel-powered fiber actuators were embedded in a soft humanoid hand to demonstrate finger-bending motions. In terms of two main actuation metrics, stress-free contraction strain and blocking stress, the presented artificial muscle outperforms reported polymer redox actuators. The fuel-powered actuator developed in this work creates new avenues for the application of redox polymers in soft robotics and artificial muscles.

3D-printed biomimetic artificial muscles using soft actuators that contract and elongate.

Biomimetic machines able to integrate with natural and social environments will find ubiquitous applications, from biodiversity conservation to elderly daily care. Although artificial actuators have reached the contraction performances of muscles, the versatility and grace of the movements realized by the complex arrangements of muscles remain largely unmatched. Here, we present a class of pneumatic artificial muscles, named GeometRy-based Actuators that Contract and Elongate (GRACE). The GRACEs consist of a single-material pleated membrane and do not need any strain-limiting elements. They can contract and extend by design, as described by a mathematical model, and can be realized at different dimensional scales and with different materials and mechanical performances, enabling a wide range of lifelike movements. The GRACEs can be fabricated through low-cost additive manufacturing and even built directly within functional devices, such as a pneumatic artificial hand that is fully three-dimensionally printed in one step. This makes the prototyping and fabrication of pneumatic artificial muscle-based devices faster and more straightforward.

Scalable microfluidic double-helix weave architecture for wiring of microcapacitor arrays in 3D-printable biomimetic artificial muscles

Practical artificial muscles are highly desirable in a wide range of applications: acoustically quiet underwater propulsion, exoskeletons, walker robots, prosthetics, and medical augments. 3D-printable microfluidic electrostatic biomimetic artificial muscles in particular hold high promise for low-cost, energy-efficient, high-strength-to-weight-ratio, manufacturable actuator solutions. Their basic design and operational principles have been established. However, there remains a major problem to solve as to how to wire them fluidically and electrically in a scalable, efficient, and practicable fashion. This short communication offers an innovative solution to this very problem. Herein, each muscle fiber is a double helix of microfluidic channels connecting longitudinal arrays of microcapacitor plates of alternating polarity. The fibers are arrayed in the two lateral dimensions to produce muscle fiber bundles that are connected by binary-tree architectures that taper off to only two inputs and two outputs for the entire muscle. This solution ensures full scalability, efficient fluidic loading, simple electrical interface, and resilience to single-point failures. Hence, the offered solution is a major step towards the practical implementation of 3D-printable artificial muscles and their applications.

Recent advances of dynamic molecular crystals with light-triggered macro-movements

Dynamic molecular crystals showing light-triggered macro-movements have attracted great attention due to their unique ability for light–force conversion. These molecular crystals are driven remotely without any intermediary devices like wires and motors, which can transform light energy into mechanical work directly. However, the limited space restricts molecular rotation and motion in the crystalline state; thus, realizing macro-movements in molecular crystal systems is still a formidable challenge. In this review, we aim to focus on the underlying working mechanism of the photo-controllable macroscopic motion of molecular crystals with special focus on their practical applications. In detail, we discuss the basic principles and macroscopic photomechanical effects of these dynamic molecular crystals, including their deformation (i.e., bending, twisting, curling); complex motion (i.e., crawling, rotating, rolling); and disintegration (i.e., photosalient effect). Then, we introduce the most promising applications of photomechanical molecular crystals in the fields of all-optical devices, crystal actuators, and biomimetic artificial muscles. Therefore, this review will provide inspiration to develop state-of-the-art dynamic molecular crystals by bridging the disciplines of physics, chemistry, and engineering science.

On the computational modelling of nonlinear electro-elasticity in heterogeneous bodies at finite deformations

Dielectric elastomer actuators (DEA) have been demonstrated to exhibit a quasi-immediate electro-mechanical actuation response with relatively large deformation capability. The properties of DEA make them suitable to be used in the form of major active components within soft robotics and biomimetic artificial muscles. However, some of the electro-active material properties impose limitations on its applications. Therefore, researchers attempt to modify the structure of the homogeneous DEA material by the incorporation of fillers that possess distinct electro-mechanical properties. This modification of the material’s structure leads to a fabricated inhomogeneous composite. From the point of mathematical material modelling and numerical simulation, we propose a material model and a computational framework using the finite element method, which is capable of emulating nonlinear electro-elastic interactions. We consider a coupled electro-mechanical description with the electric and the electro-mechanical properties of the material assumed to be nonlinearly dependent on the deformation. Furthermore, we demonstrate a coupled ansatz that expresses the electric response as dielectrically quasi-linear with only density-dependent electric permittivity. We couple the electro-mechanical models to the extended tube model, which is a suitable approach for the realistic emulation of the hyperelastic response of rubber-like materials. Thereafter, we demonstrate analytical and numerical solutions of a homogeneous electro-elastic body with the Neo-Hookean material model and the extended tube model to express the hyperelastic response. Finally, we use the finite element method to investigate several heterogeneous configurations consisting of soft DEA matrix filled with spherical stiff inclusions with changing volume fraction and ellipsoidal inclusions with varying aspect ratio.

Simulations of 3D-Printable biomimetic artificial muscles based on microfluidic microcapacitors for exoskeletal actuation and stealthy underwater propulsion

Practical artificial muscles are highly desirable in a wide range of applications, including strength augmentation in military exoskeletons, medical prosthetics for amputees, locomotion boosters for geriatric and handicapped patients, walker robots, and acoustically quiet underwater propulsion systems. So, artificial muscles have been a subject of active research through a variety of approaches, e.g. electromagnetics, pneumatics, hydraulics, thermal expansion/contraction, piezoelectrics, shape memory alloys, and electrically active polymers. Herein we propose a new approach based on a combination of microfluidics, 3D printing/additive manufacturing (AM), and electrostatic actuation. Back-of-the-envelope calculations promise 33 MPa generated stress under feasible conditions. Respective integral architectures are described. Individual devices and 2 × 2 arrays are analyzed through COMSOL simulations. Simulations predict 10–20 % strain, which is ample for most applications. Parameter sweeps in the simulations offer quantitative insights into optimal values for maximizing the output force density. The simulations demonstrate that alternative wiring schemes produce muscle or counter-muscle behavior of the same arrays, offering novel capabilities. The proposed technology promises a major impact on a range of important applications, e.g. exoskeletons, prosthetics, walker vehicles, and stealthy undersea propulsion.

Linear Artificial Muscle Based on Ionic Electroactive Polymer: A Rational Design for Open‐Air and Vacuum Actuation

AbstractThe development of linear muscle‐like actuators remains a key objective in the field of electroactive polymers (EAPs). While ionic EAPs are promising technologies to develop biomimetic artificial muscles, their reliance on liquid electrolytes for operation typically restricts them to use in bending devices. Seldom have ionic linear actuators been demonstrated in air, and never in vacuum. Here both are demonstrated. A rational approach supported by a theoretical model is described to identify the general conditions allowing the design of ionic actuators with intrinsically linear deformations. The model highlights that linear deformation can occur by combining two electroactive electrodes with different mechanical and/or electromechanical properties. Where previous work on laminated actuators resulted in bending only, here it is shown that by combining one soft and one stiff electrode, or one highly expanding electrode, and the other minimally deforming electrode, 0.55% linear strain is achieved when activated with 2 V. Best combination of electrodes is selected based on electromechanical model predictions. Single actuator fibers are fabricated for experimental validation. Graded force up to 0.18 N has been achieved by bundling together five linear actuators. The resulting artificial muscles operate in open‐air, and also under high vacuum conditions, opening possibilities for space applications.

Hierarchical Graphene‐Based Films with Dynamic Self‐Stiffening for Biomimetic Artificial Muscle

Biological tissues such as muscle cells can adapt their structural and mechanical response upon external mechanical stimuli. Conversely, artificial muscles, intended to reproduce the salient functional features of biological muscles, usually undergo mechanical fatigue when subjected to dynamic stress. Besides passively improving the resilience to dynamic loads, here, it is reported that macroscopic films based on graphene and its chemical derivate exhibit an increase in modulus by up to 84% after subjected to a low‐amplitude (0.1%) dynamic tension. Through a combination of experimental testing and molecular dynamics simulations, the unique self‐stiffening behavior is attributed to the straightening and reorientation of graphene sheets and is further tuned through tailoring interlayer adhesion. Meanwhile, artificial muscles based on graphene films are designed and interestingly improved stiffness of our muscle materials after “training” are demonstrated. These results help to harness the stiffening mechanism and can be useful for the development of adaptable structural materials for biomechanical applications.

An Electrolyte-Free Conducting Polymer Actuator that Displays Electrothermal Bending and Flapping Wing Motions under a Magnetic Field.

Electroactive materials that change shape in response to electrical stimulation can serve as actuators. Electroactive actuators of this type have great utility in a variety of technologies, including biomimetic artificial muscles, robotics, and sensors. Electroactive actuators developed to date often suffer from problems associated with the need to use electrolytes, slow response times, high driving voltages, and short cycle lifetimes. Herein, we report an electrolyte-free, single component, polymer electroactive actuator, which has a fast response time, high durability, and requires a low driving voltage (<5 V). The process employed for production of this material involves wet-spinning of a preorganized camphorsulfonic acid (CSA)-doped polyaniline (PANI) gel, which generates long, flexible, and conductive (∼270 S/cm) microfibers. Reversible bending motions take place upon application of an alternating current (AC) to the PANI polymer. This motion, promoted by a significantly low driving voltage (<0.5 V) in the presence of an external magnetic field, has a very large swinging speed (9000 swings/min) that lies in the range of those of flies and bees (1000-15000 swings/min) and is fatigue-resistant (>1000000 cycles).

Actuation Properties Investigation: A Muscle like Linear Actuator Based on Biopolymer Material: Ionic Polymer Metal Composites

In this manuscript, a muscle-like linear actuator based on the combination of Bi-IPMC linear actuator unit was developed focusing on the applied requirements in the biomimetic artificial muscles using as the actuators. Subsequently, the muscle-like linear actuator was mainly fabricated by two segmented IPMC film, which is obtained through a special process and the actuation performance of the muscle-like linear actuator was further experimented by the testing platform. The results found our actuator behaved a high displacement performance, and this kind of muscle-like linear actuator has a potential value in the engineering practice.

Fabrication and applied investigation of a muscle‐like linear actuator using lonic polymer metal composites

Focusing on the existing issues of ionic polymer metal composites (IPMC), for example, little force output and swing motion, and the applied requirements in the biomimetic artificial muscles using as the actuators, under the current framework, a muscle‐like linear actuator based on the combination of Bi‐IPMC linear actuator unit, whose experimental characteristics have been discussed in our previous work, was fabricated. The performance investigation showed that it can generate a linear movement type like artificial muscle, and there is an prominent improvement of force output capabilities compared with Bi‐IPMC linear actuator unit. Also, based on the 3D printing technique, a bionic jumping robot was experimented using the fabricating muscle‐like linear actuator, and the experimental result was validated against the feasibility of muscle‐like linear actuator. POLYM. COMPOS., 38:147–156, 2017. © 2015 Society of Plastics Engineers

Electroactive artificial muscle based on crosslinked PVA/SPTES

Based on a crosslinked ionic networking membrane of sulfonated poly(arylenethioethersulfone) copolymer (SPTES) and poly(vinyl alcohol) (PVA), a novel biomimetic artificial muscle with electrically driven bending deformation was developed. Sulfonated endcapped poly(arylenethioethersulfone) copolymer (SPTES) was synthesized through direct copolymerization of sulfonated monomers and poly(vinyl alcohol) (PVA) was crosslinked with SPTES by the dehydration method. The crosslinking reaction and molecular interactions between PVA and SPTES were observed in the FT-IR spectra of the PVA/SPTES ionic networking membrane. In comparison with the Nafion membrane, the crosslinked PVA/SPTES membrane shows much higher proton conductivity and ionic exchangeable capacity that are main factors influencing the actuation performance. Electroactive PVA/SPTES actuators show much larger bending deformation under step inputs without straightening-back relaxation and harmonic responses under sinusoidal excitations in a wide frequency band.

A membrane actuator based on an ionic polymer network and carbon nanotubes: thesynergy of ionic transport and mechanical properties

There is a growing interest in the development of ionic polymer–metal composites(IPMC) as sensors and actuators for biomedical applications due to their largedeformation under low driving voltage. In this study, we employed poly(vinylalcohol)/poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PVA/PAMPS)blend membranes as semi-interpenetrating polymer networks for ion exchange inIPMC construction. To improve the mechanical and electrical properties of theIPMC, multi-walled carbon nanotubes (MWNT) were added into PVA/PAMPSmembranes. The actuator performance of the membranes was measured as a function oftheir water uptake, ion exchange capacity, ionic conductivity and the amount ofMWNT in the membrane. The dispersion quality of the modified MWNT in thePVA/PAMPS membrane was measured using transmission electron microscopy. Thecantilever-type IPMC actuator bends under applied voltage and its bending angle andthe generative tip force were measured. Under an applied voltage, IPMC with∼1 wt% MWNT showed the largest deflection and generated the largest blocking tip forcecompared with those of IPMC with other various amounts of MWNT. These results showthat a small addition of MWNT can optimize the actuation performance of IPMC. Theresult indicates that IPMC with MWNT shows potential for use as biomimetic artificialmuscle.