Javad Foroughi

Artificial Muscles from Fishing Line and Sewing Thread

Toward an Artificial Muscle In designing materials for artificial muscles, the goals are to find those that will combine high strokes, high efficiency, long cycle life, low hysteresis, and low cost. Now, Haines et al. (p. 868; see the Perspective by Yuan and Poulin) show that this is possible. Twisting high-strength, readily available polymer fibers, such as those used for fishing lines or sewing thread, to the point where they coil up, allowed construction of highly efficient actuators that could be triggered by a number of stimuli. Polymer fibers can be transformed into highly efficient artificial muscles through the application of extreme twist. [Also see Perspective by Yuan and Poulin] The high cost of powerful, large-stroke, high-stress artificial muscles has combined with performance limitations such as low cycle life, hysteresis, and low efficiency to restrict applications. We demonstrated that inexpensive high-strength polymer fibers used for fishing line and sewing thread can be easily transformed by twist insertion to provide fast, scalable, nonhysteretic, long-life tensile and torsional muscles. Extreme twisting produces coiled muscles that can contract by 49%, lift loads over 100 times heavier than can human muscle of the same length and weight, and generate 5.3 kilowatts of mechanical work per kilogram of muscle weight, similar to that produced by a jet engine. Woven textiles that change porosity in response to temperature and actuating window shutters that could help conserve energy were also demonstrated. Large-stroke tensile actuation was theoretically and experimentally shown to result from torsional actuation.

Torsional Carbon Nanotube Artificial Muscles

Carbon nanotube yarns are used to make fast, multirotational torsional actuators. Rotary motors of conventional design can be rather complex and are therefore difficult to miniaturize; previous carbon nanotube artificial muscles provide contraction and bending, but not rotation. We show that an electrolyte-filled twist-spun carbon nanotube yarn, much thinner than a human hair, functions as a torsional artificial muscle in a simple three-electrode electrochemical system, providing a reversible 15,000° rotation and 590 revolutions per minute. A hydrostatic actuation mechanism, as seen in muscular hydrostats in nature, explains the simultaneous occurrence of lengthwise contraction and torsional rotation during the yarn volume increase caused by electrochemical double-layer charge injection. The use of a torsional yarn muscle as a mixer for a fluidic chip is demonstrated.

Electrically, Chemically, and Photonically Powered Torsional and Tensile Actuation of Hybrid Carbon Nanotube Yarn Muscles

Nanotube Yarn Actuators Actuators are used to convert heat, light, or electricity into a twisting or tensile motion, and are often described as artificial muscles. Most materials that show actuation either provide larger forces with small-amplitude motions, such as the alloy NiTi, or provide larger motions with much less force, such as polymeric materials. Other problems with such actuators can include slow response times and short lifetimes. Lima et al. (p. 928, see the Perspective by Schulz) show that a range of guest-filled, twist-spun carbon nanotube yarns can be used for linear or torsional actuation, can solve the problems of speed and lifetime, and do not require electrolytes for operation. Thermally driven actuators use a guest material within carbon nanotube yarns to generate fast torsional and tensile motions. Artificial muscles are of practical interest, but few types have been commercially exploited. Typical problems include slow response, low strain and force generation, short cycle life, use of electrolytes, and low energy efficiency. We have designed guest-filled, twist-spun carbon nanotube yarns as electrolyte-free muscles that provide fast, high-force, large-stroke torsional and tensile actuation. More than a million torsional and tensile actuation cycles are demonstrated, wherein a muscle spins a rotor at an average 11,500 revolutions/minute or delivers 3% tensile contraction at 1200 cycles/minute. Electrical, chemical, or photonic excitation of hybrid yarns changes guest dimensions and generates torsional rotation and contraction of the yarn host. Demonstrations include torsional motors, contractile muscles, and sensors that capture the energy of the sensing process to mechanically actuate.

Knitted Carbon-Nanotube-Sheath/Spandex-Core Elastomeric Yarns for Artificial Muscles and Strain Sensing

Highly stretchable, actuatable, electrically conductive knitted textiles based on Spandex (SPX)/CNT (carbon nanotube) composite yarns were prepared by an integrated knitting procedure. SPX filaments were continuously wrapped with CNT aerogel sheets and supplied directly to an interlocking circular knitting machine to form three-dimensional electrically conductive and stretchable textiles. By adjusting the SPX/CNT feed ratio, the fabric electrical conductivities could be tailored in the range of 870 to 7092 S/m. The electrical conductivity depended on tensile strain, with a linear and largely hysteresis-free resistance change occurring on loading and unloading between 0% and 80% strain. Electrothermal heating of the stretched fabric caused large tensile contractions of up to 33% and generated a gravimetric mechanical work capacity during contraction of up to 0.64 kJ/kg and a maximum specific power output of 1.28 kW/kg, which far exceeds that of mammalian skeletal muscle. The knitted textile provides the combination of strain sensing and the ability to control dimensions required for smart clothing that simultaneously monitors the wearers movements and adjusts the garment fit or exerts forces or pressures on the wearer, according to needs. The developed processing method is scalable for the fabrication of industrial quantities of strain sensing and actuating smart textiles.

Preparation and characterization of hybrid conducting polymer-carbon nanotube yarn

Hybrid polypyrrole (PPy)-multi walled carbon nanotube (MWNT) yarns were obtained by chemical and electrochemical polymerization of pyrrole on the surface and within the porous interior of twisted MWNT yarns. The material was characterized by scanning electron microscopy, electrochemical, mechanical and electrical measurements. It was found that the hybrid PPy-MWNT yarns possessed significantly higher mechanical strength (over 740 MPa) and Youngs modulus (over 54 GPa) than the pristine MWNT yarn. The hybrid yarns also exhibited substantially higher electrical conductivity (over 235 S cm(-1)) and their specific capacitance was found to be in excess of 60 F g(-1). Measurements of temperature dependence of electrical conductivity revealed semiconducting behaviour, with a large increase of band gap near 100 K. The collected low temperature data are in good agreement with a three-dimensional variable range hopping model (3D-VRH). The improved durability of the yarns is important for electrical applications. The composite yarns can be produced in commercial quantities and used for applications where the electrical conductivity and good mechanical properties are of primary importance.

The mechanical and the electrical properties of conducting polypyrrole fibers

The mechanical and the electrical properties of polypyrrole (PPy) fibers and electrochemically deposited PPy films were studied. It was found that the PPy fibers showed a significantly higher strength than the PPy films due to better orientation of the molecular structure. The electrochemically prepared PPy films had a higher electrical conductivity than that of the fibers at high temperature. At low temperature, the PPy fibers showed the higher conductivity. The conductivity results were analyzed in the frame of the three-dimensional variable range hopping model. The results showed that at room temperature the average hopping distance for the fibers was about 4 A while for the films it increases to about 5.7 A. This corresponds to about 1 and 2 monomer units in length for the fiber and film samples, respectively.

Developments in conducting polymer fibres: from established spinning methods toward advanced applications

Conducting polymers have received increasing attention in both fundamental research and various fields of application in recent decades, ranging in use from biomaterials to renewable energy storage devices. Processing of conducting polymers into fibrillar structures through spinning has provided some unique capabilities to their final applications. Compared with non fibrillar forms, conducting polymer fibres are expected to display improved properties arising mainly from their low dimensions, well-oriented polymer chains, light weight and large surface area to volume ratio. Spinning methods have been employed effectively to produce technological conducting fibres from nanoscale to hundreds of micrometre sizes with controlled properties. This review considers the history, categories, the latest research and development, pristine and composite conducting polymer fibres and current/future applications of them while focus on spinning methods related to conducting polymer fibres.

Fabrication of a graphene coated nonwoven textile for industrial applications

A cost effective electrically conductive textile for large scale applications would revolutionise numerous industries. Herein, we demonstrate a novel processing approach to produce conductive textiles for industrial applications. A conductive nonwoven textile was successfully fabricated using a simple dip coating method. The nonwoven polyester was coated with liquid crystallite graphene oxide with subsequent non-toxic chemical reduction. The process is readily scalable. The graphene coated fabric has been characterized by electron microscopy as well as by electrical, mechanical, thermal and abrasion resistance measurements. It was found that the electrical surface resistivity of the prepared polyester–graphene composite fabric was 330 Ω □−1. The electrical surface resistivity was 3 and 150 times lower than that of polypyrrole coated woven polyester fabric and graphene coated nonwoven fabrics, respectively, in previously published reports. The hybrid polyester–graphene textile prepared here should find applications in high-performance geotextiles or as heating elements.

Probe Sensor Using Nanostructured Multi-Walled Carbon Nanotube Yarn for Selective and Sensitive Detection of Dopamine

The demands for electrochemical sensor materials with high strength and durability in physiological conditions continue to grow and novel approaches are being enabled by the advent of new electromaterials and novel fabrication technologies. Herein, we demonstrate a probe-style electrochemical sensor using highly flexible and conductive multi-walled carbon nanotubes (MWNT) yarns. The MWNT yarn-based sensors can be fabricated onto micro Pt-wire with a controlled diameter varying from 100 to 300 µm, and then further modified with Nafion via a dip-coating approach. The fabricated micro-sized sensors were characterized by electron microscopy, Raman, FTIR, electrical, and electrochemical measurements. For the first time, the MWNT/Nafion yarn-based probe sensors have been assembled and assessed for high-performance dopamine sensing, showing a significant improvement in both sensitivity and selectivity in dopamine detection in presence of ascorbic acid and uric acid. It offers the potential to be further developed as implantable probe sensors.

Electrically contractile polymers augment right ventricular output in the heart

Research into the development of artificial heart muscle has been limited to assembly of stem cell-derived cardiomyocytes seeded around a matrix, while nonbiological approaches to tissue engineering have rarely been explored. The aim of the study was to apply electrically contractile polymer-based actuators as cardiomyoplasty for positive inotropic support of the right ventricle. Complex trilayer polypyrrole (PPy) bending polymers for high-speed applications were generated. Bending motion occurred directly as a result of electrochemically driven charging and discharging of the PPy layers. In a rat model (n = 5), strips of polymers (3 × 20 mm) were attached and wrapped around the right ventricle (RV). RV pressure was continuously monitored invasively by direct RV cannulation. Electrical activation occurred simultaneously with either diastole (in order to evaluate the polymers stand-alone contraction capacity; group 1) or systole (group 2). In group 1, the pressure generation capacity of the polymers was measured by determining the area under the pressure curve (area under curve, AUC). In group 2, the RV pressure AUC was measured in complexes directly preceding those with polymer contraction and compared to RV pressure complexes with simultaneous polymer contraction. In group 1, the AUC generated by polymer contraction was 2768 ± 875 U. In group 2, concomitant polymer contraction significantly increased AUC compared with complexes without polymer support (5987 ± 1334 U vs. 4318 ± 691 U, P ≤ 0.01). Electrically contractile polymers are able to significantly augment right ventricular contraction. This approach may open new perspectives for myocardial tissue engineering, possibly in combination with fetal or embryonic stem cell-derived cardiomyocytes.