Helical constructs are ubiquitous in nature at all size domains, from molecular to macroscopic. The helical topology confers unique mechanical functions that activate certain phenomena, such as ...twining vines and vital cellular functions like the folding and packing of DNA into chromosomes. The understanding of active mechanical processes in plants, certain musculature in animals, and some biochemical processes in cells provides insight into the versatility of the helix. Most of these natural systems consist of helically oriented filaments embedded in a compliant matrix. In some cases, the matrix can change volume and in others the filaments can contract and the matrix is passive. In both cases, the helically arranged fibers determine the overall shape change with a great variety of responses involving length contraction/elongation, twisting, bending, and coiling. Synthetic actuator materials and systems that employ helical topologies have been described recently and demonstrate many fascinating and complex shape changes. However, significant new opportunities exist to mimic some of the most remarkable actions in nature, including the Vorticella's coiling stalk and DNA's supercoils, in the quest for superior artificial muscles.
Mechanical actuation systems in plants and animals almost always involve helical structures and studies show that a helical arrangement of fibers in a compliant matrix generates a great diversity of movements and mechanical amplifications. Opportunities are identified to develop advanced artificial muscles since only a limited number of nature's mechanisms have been recreated in biomimetic systems to date.
A series of hydrogel‐based inks are developed to print 3D structures capable of reversible shape deformation in response to hydration and temperature. The inks are made of large polymer chains and UV ...curable monomers which form interpenetrating polymer networks after polymerization. By taking advantage of the long polymer chains in the ink formulations, it is possible to adjust the rheological properties of the inks to enable 3D printing. Hydrogels produced from the inks exhibit robust mechanical performance with their mechanical properties controlled by the nature of the long polymer chains within their networks. In this paper, hydrogel hinges are made from various ink formulations and a simple model is developed to predict their bending characteristics, including the bending curvature and bending angle. This model can be used as a guide to determine optimal parameters for a wide range of materials combination to create all‐hydrogel structures that undergo desired shape transitions.
4D printed hybrid hydrogels capable of reversible shape transition in response to hydration and temperature are prepared. The shape deformation of printed hydrogel sheets is determined by the print design and the constituting hydrogels properties. The latter is controlled by the development of tailored inks.
Large stroke torsional actuators are the newest class of artificial muscle technology that produces rotary motion or generate torque in response to various stimuli. A number of materials comprising ...twisted fibres or filaments have been shown to display high degrees of reversible untwist and retwist under various experimental conditions such as heating, electrochemical charging, chemical absorption or photonic excitation. Torsional actuators are of potential application in areas that include microfluidic mixing, microsensors, photonic displays, and energy-harvesting devices. Furthermore, the torsional actuation in fibres can be translated into a linear, or tensile, actuation when the fibres are formed into coils. These coil tensile artificial muscles are of potential use in soft and wearable robotics, medical devices and prosthetics. This review will provide a comprehensive overview of torsional actuators constructed from different functional materials, their actuating mechanism, potential applications, and their current limitations. The review will conclude with recent developments and future trends of torsional actuators as well as critical issues that need to be addressed and resolved.
Torsional actuators are of potential application in areas that include smart textiles, exoskeletons, microfluidic mixing, microsensors, photonic displays, and energy-harvesting devices.
New twist on artificial muscles Haines, Carter S.; Li, Na; Spinks, Geoffrey M. ...
Proceedings of the National Academy of Sciences - PNAS,
10/2016, Letnik:
113, Številka:
42
Journal Article
Recenzirano
Odprti dostop
Lightweight artificial muscle fibers that can match the large tensile stroke of natural muscles have been elusive. In particular, low stroke, limited cycle life, and inefficient energy conversion ...have combined with high cost and hysteretic performance to restrict practical use. In recent years, a new class of artificial muscles, based on highly twisted fibers, has emerged that can deliver more than 2,000 J/kg of specific work during muscle contraction, compared with just 40 J/kg for natural muscle. Thermally actuated muscles made from ordinary polymer fibers can deliver long-life, hysteresis-free tensile strokes of more than 30% and torsional actuation capable of spinning a paddle at speeds of more than 100,000 rpm. In this perspective, we explore the mechanisms and potential applications of present twisted fiber muscles and the future opportunities and challenges for developing twisted muscles having improved cycle rates, efficiencies, and functionality. We also demonstrate artificial muscle sewing threads and textiles and coiled structures that exhibit nearly unlimited actuation strokes. In addition to robotics and prosthetics, future applications include smart textiles that change breathability in response to temperature and moisture and window shutters that automatically open and close to conserve energy.
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 wearer’s 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.
Yarn-based supercapacitors having improved performance are needed for existing and emerging wearable applications. Here, we report weavable carbon nanotube yarn supercapacitors having high ...performance because of high loadings of rapidly accessible charge storage particles (above 90 wt% MnO
). The yarn electrodes are made by a biscrolling process that traps host MnO
nanoparticles within the galleries of helically scrolled carbon nanotube sheets, which provide strength and electrical conductivity. Despite the high loading of brittle metal oxide particles, the biscrolled solid-state yarn supercapacitors are flexible and can be made elastically stretchable (up to 30% strain) by over-twisting to produce yarn coiling. The maximum areal capacitance of the yarn electrodes were up to 100 times higher than for previously reported fibres or yarn supercapacitors. Similarly, the energy density of complete, solid-state supercapacitors made from biscrolled yarn electrodes with gel electrolyte coating were significantly higher than for previously reported fibre or yarn supercapacitors.
Here, we show that graphene oxide (GO) dispersions exhibit unique viscoelastic properties, making them a new class of soft materials. The fundamental insights accrued here provide the basis for the ...development of fabrication protocols for these two-dimensional soft materials, in a diverse array of processing techniques.
Graphene-based actuators are of practical interest because of their relatively low cost compared with other nanocarbon materials, such as carbon nanotubes. We demonstrate the simple fabrication of ...graphene oxide (GO)-based fibers with an infiltrated nylon-6,6 polymer by wet spinning. These fibers could be twisted to form torsional actuators and further coiled to form tensile actuators. By controlling the relative twisting and coiling direction of the GO/nylon fiber, we were able to realize reversible contraction or elongation actuation with strokes as high as −80 and 75%, respectively, when the samples were heated to 200 °C. The tensile actuation showed a remarkably little hysteresis. Moreover, this GO/nylon actuator could lift loads over 100 times heavier than itself and generate a stable actuation at high temperatures over the melting point of the polymer. This novel kind of GO-based actuator, which has a multidirectional actuation, has potential for a wide range of applications such as artificial muscles, robotics, and temperature sensing.
Artificial Muscles from Fishing Line and Sewing Thread Haines, Carter S.; Lima, Márcio D.; Li, Na ...
Science (American Association for the Advancement of Science),
02/2014, Letnik:
343, Številka:
6173
Journal Article
Recenzirano
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.
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