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Cite this:DOI: 10.1039/c8mh01647j

Handedness-controlled and solvent-drivenactuators with twisted fibers†

Bo Fang,a Youhua Xiao,a Zhen Xu,*ab Dan Chang,a Bo Wang,a Weiwei Gao a andChao Gao *a

Plenty of biological materials are constructed from repeated unit cells

with handed configurations, wherein the hierarchical self-assembly of

handed units confers optimized mechanical properties and environ-

mental adaptability to bulk biological materials. Inspired by biological

handed architectures, we propose handedness-controlled and solvent-

driven actuators by programming twisted fibers, such as twisted

graphene oxide fibers (TGFs), with mirrored handedness, mechanical

robustness and superb flexibility. The large twists (beyond 4800 turns per

meter), hair-like diameter (down to 63 lm), large tensile strain (29%) and

light weight (1.49 g cm�3) of TGFs enable them to provide a large start-

up torque of 2.7� 10�7 N m, and to deliver a record rotor kinetic power

of 89.3 W kg�1 when stimulated by polar solvents such as acetone and

water. By assembling handed TGF units, we achieve precise outputting of

rotor kinetic energy (from 0.78 W kg�1 to 12.5 W kg�1), controllable

harvesting of electrical energy (from 2.37 W kg�1 to 11.5 W kg�1), and

free handling of a heavy object. The activeness, inertness and operation

of all the actuating systems are well controlled by the handedness of TGF

units. They are highly stable and reversible, and maintain a high energy

output efficiency over multiple operation cycles. These handedness-

controlled systems are also extended to hybrid twisted fibers containing

nanocomposites and polymers, indicating their general practicability.

Handedness-controlled actuators open an alternative avenue for

fabricating energy harvesters, responsive textiles, electronic skins

and soft robots.

Introduction

A variety of biological materials, such as DNA, actin, collagen,and keratin, are composed of repeated unit cells with handed-ness. The hierarchical self-assembly of handed units enables

bulk materials to exhibit optimized mechanical properties andenvironmental adaptability.1 For example, fibrous actin (F-actin)composed of right-handed and double-helical globular actin(G-actin) makes muscles to maintain rigidity under tensionand flexible under torsion.2 Right-handed triple-helical super-coils assembled from left-handed procollagen helices conferreliable damage tolerance and toughness of tropocollagen, dueto the opposite twisting directions of supercoils and procollagenunder tension.3 The prospects of artificially evolving biologicalhanded architectures for application are encouraging.4 However,creating this ability in practical engineered systems poseschallenges in the design of both reliable unit cells and properconstruction at the micron scale.

Inspired by biological handed architectures, we proposed ahandedness-controlled rule to design solvent-driven actuators byprogramming handed twisted fibers, with mirrored helix configura-tions and hair-like diameter. Some previously reported actuating

a MOE Key Laboratory of Macromolecular Synthesis and Functionalization,

Department of Polymer Science and Engineering, Zhejiang University,

No. 38 Zheda Road, Hangzhou 310027, China. E-mail: chaogao@zju.edu.cnb National Key Laboratory of Science and Technology on Advanced Composites in

Special Environments, Harbin Institute of Technology, Harbin 150080, China.

E-mail: zhenxu@zju.edu.cn

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c8mh01647j

Received 24th December 2018,Accepted 5th March 2019

DOI: 10.1039/c8mh01647j

rsc.li/materials-horizons

Conceptual insightsHandedness-controlled conception has been widely found in nature. Beingconstructed with repeated unit cells with handed configurations, manybiological materials such as actin, collagen, and keratin exhibit optimizedmechanical properties and environmental adaptability. The prospects ofartificially evolving biological handed architectures for application arepromising. But creating this ability in practical engineered systems poseschallenges in the design of both reliable unit cells and proper construction.We propose a handedness-controlled rule to construct actuating systems withcontinuous twisted fibers as the unit cells, with handed helix configurations,mechanical robustness and hair-like diameter. We demonstrate that twistedfibers afford impressive start-up torques driven by polar solvating species,exceeding those of previously reported artificial muscles. The handedness-controlled actuating system controllably outputs rotor kinetic energy in thetwo-unit system, harvests electrical energy in the three-unit system andhandles heavy objects in the four-unit system. The handedness-controlledactuating system delivers power to the load with high precision and efficiency.This handedness-controlled conception is extensively observed for twistedfibers containing graphene oxide, nanocomposites and polymers. Thisapproach is conducive to the design of energy harvesters, responsivetextiles, electronic skins and agile soft robots.

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systems also exhibited helix microstructures, being actuated totransform when exposed to a chemical or physical stimulus.5–14

However, they are limited in several ways. Firstly, practical actuatorsrequire diverse actuating models to work in complex operatingenvironments and to deliver the precise amount of energy to meetthe actual demand of the receiver, which has rarely beenaddressed.15 Secondly, the processing of previous helix actuatorssuffers from some experimental challenges such as tight processcontrol, legacy cost of purification and low yields due to low-efficiency manufacturing facilities.16–18 Thirdly, the energy conversa-tion efficiency and energy output of polymer-19–22 and carbon-basedactuators23–27 are still quite low. For example, a polymer/CNT hybridcloth actuator only afforded a start-up torque of 1.26 � 10�7 N m�1

in response to water,21 and twisted carbon nanotube (CNT) fiberswith a rotary stroke of 2050 revolutions per meter yielded a low rotorkinetic power output of 29.7 W kg�1 in the presence of ethanol.24

Here, we report handedness-controlled actuating systemsresponding to polar solvating species. Starting from low-costgraphene oxide (GO) suspensions, continuous handed TGFswith mechanical robustness and superb flexibility were fabricatedby a liquid crystalline wet spinning protocol and an industrialtwisting–drawing technique. The prepared TGFs are driven tooutput rotor kinetic energy by polar solvents selectively, andamong them, 0.05 mL acetone drives TGFs to reach a high rotaryspeed of 6050 rpm, a large start-up torque of 2.7 � 10�7 N m, anda high peak power output of 89.3 W kg�1. These three figures-of-merit reach record high in graphene-based actuators. We pro-grammed multiple TGF units to actuate in a controlled manner.By modulating the handedness of individual TGFs, we preciselyachieved rotor kinetic energy from 0.78 W kg�1 to 12.5 W kg�1 inthe two-unit system, and electrical energy from 2.37 W kg�1 to11.5 W kg�1 in the three-unit system and handled a heavy objectbeyond 60 times its own weight in the four-unit system. Thishandedness-controlled approach can meet the actual demand ofpractical applications and is also conducive to the design ofresponsive textiles, electronic skins and agile soft robots. Thegeneral practicability of this handedness-controlled conception isdemonstrated by our investigation of hybrid twisted fibers con-taining nanocomposites and polymers, such as carbon nanotubes(CNTs), polyvinyl alcohol (PVA), and titania nanoparticles.

Results and discussion

Derived from traditional wet-spinning protocols,28–32 continuousGO belts were first obtained by a liquid crystalline wet spinningmethod and the continuous extrusion of dopes was controlledusing a micro-fluidic system (Fig. 1a). In particular, GO liquidcrystalline dispersions in dimethyl formamide (DMF, 10 mg mL�1)were used as spinning dopes, then extruded into ethyl acetate (EA)through a micro-fluidic channel at a rate of 20 m min�1. Themicrofluidic system was a hollow gallery with a width of 2 mmand a height of 200 mm. Solvent exchange and hydrogen-bondinteractions facilitated the formation of gel belts in EA, and thebirefringence shown in Fig. 1b indicated the oriented alignment ofGO sheets in the gel belts aided by shear flowing. With the rapid

removal of DMF and EA in air, gel belts evolved into neat GO beltswith a width of 200 mm and favorable stretchability (Fig. 1c andFig. S1, ESI†).

Flexible GO belts were processed into continuous TGFsusing a twisting–drawing apparatus (Fig. 1d). The out-of-planerevolution of the roller generated a normal torque (Fig. 1e),managing to twist axially oriented GO belts (Fig. S2a and b,ESI†) into spirally oriented TGFs (Fig. S2e and f, ESI†), andfurther storing strain energy into TGFs. Simultaneously, thein-plane rotation of the roller functioned to collect TGFs at arate of 7 cm min�1. A right-handed TGF (RTGF, Fig. 1f and g)and a left-handed TGF (LTGF, Fig. 1h and i) with a smoothsurface and uniform circular cross section (Fig. 1j) wereacquired by adjusting the rotation direction. Fig. 1k displaysthe diameter (D) dependence of the helical angle (y, degrees)with respect to the twisting direction and the twist number inturns per meter (T = tan y/(pD), turns per m).33,34 Both y and Tincrease with decreasing D, and T reaches 4880 turns per mwhen D decreases to 63 mm (Fig. S3, ESI†). It is noteworthythat our method provides a new type of protocol to achievecontinuous TGFs,9–11 saving the trouble of batch-to-batchdisparity and low productivity. Continuous TGFs exhibit favorableflexibility and mechanical robustness, as the large inserted twistevokes a great capability to deform without tearing. A typical tensilestress–strain curve for a 63 mm-thick TGF shows a large tensilestrength of 130 MPa. The extreme elongation prior to failure is 29%(Fig. S4, ESI†), which is around 10 fold that (o3%) of highlystretched GO fibers.35–39

Benefitting from their superb mechanical durability (see thediscussion in Fig. S4, ESI†), TGFs output rich rotor kineticenergy from solvating stimulators. We investigated the actuatingbehavior of a suspended LTGF (B40 mg) with a length of 20 cm,which was loaded with a copper paddle weighing 50 mg (Fig. 2aand Movie S1, ESI†). After feeding 0.05 mL acetone, the copperpaddle was accelerated to an angular speed (o) of 633 rad s�1

in a short period of 0.7 s, with an average acceleration of904 rad s�2. Since the moment of inertia ( J) is measured as3 � 10�10 kg m�2, the maximum start-up torque (t) is calculatedas 2.7 � 10�7 N m, which is 18 times that of a moisture-drivengraphene fiber motor,25 3.6 times that of a CNT fiber actuator,24

and 2.1 times that of a polymer-based fiber actuator.21 Such alarge start-up torque provides a high peak power output( p = Jo2/2t) of 89.3 W kg�1 to the copper paddle, superior toCNT artificial muscles40 (61 W kg�1) and a graphene oxide fibermotor (71.9 W kg�1). The revolutions per minute (rpm) are 6050,which is the highest value ever achieved by graphene-basedkinetic energy actuators,25,41 and much higher than those ofpolymer-based actuating systems.19–21

In particular, the actuating properties of a TGF rotor are wellcontrolled by adjusting the polarity of solvating species. Wetested some solvents with an individual volume of 0.05 mL andincreasing polarity (Fig. 2b and c). In general, high peak outputpowers of 39.7, 33.9, 29.7 and 27 W kg�1 were achieved uponexposing TGFs to highly polar stimulators, e.g., methanol,water, ethanol and DMSO, and the start-up torques exceededthose of previously reported CNT fiber-based artificial muscles

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(ref. 15, 16, and 35 in Fig. 2c). Inefficient energy output valueswere recorded for other polar solvents (IPA, EA, TCM, DCM andDMF), which yielded peak powers between 0.1 and 20 W kg�1.By contrast, stimulation by non-polar solvents was fairly weak.The rotary speeds for hexane, cyclohexane and methylbenzeneare 88, 79 and 49 rpm, respectively, and the system reachedinertness in the case of 1-octanol.

The strong actuating ability of TGFs driven by polar solventscan be explained in two aspects. In one case, the oxygen-richfunctional groups on the surfaces of TGFs induce good affinityand rapid infiltration of polar molecules,42–44 thus resulting infast radial expansion and untwisting of TGFs. This explanationis verified by the diffusion speed difference of solvents on TGFsobserved by confocal laser scanning microscopy (CLSM, Fig. S6,ESI†). Uniform diffusion of acetone along the axial directionwas clearly observed for 4 seconds, where the diffusion speed of

acetone was faster than those of other solvating species. In theother case, during the infiltration of polar solvents, a strongsurface tension (g, the inset in Fig. 2b) and a contact angle (a)would increase along the liquid–solid interface.45 Therefore, anelastocapillary force (Fe = g sin a) vertical to the interface wastriggered, initiating the rapid untwisting. While pure nonpolarsolvents were inert, they can be applied to adjust their apparentactuating properties. In a case study of mixing 1-octanol (inert)and acetone (active, Fig. S7a, ESI†), the measured rotary speedincreased gradually upon addition of acetone, leading to a peakoutput power beyond 70 W kg�1 as the volume fraction ofacetone was beyond 70%.

The torsional rotation of TGFs was demonstrated to berepeatable at least 100 times when triggered by some polarsolvents, such as acetone, methanol and ethanol (Fig. 2d). Asdiscussed above, the infiltration of polar solvents induced the

Fig. 1 The fabrication of continuous and robust TGFs with mirrored handedness. (a) Optical image of continuous GO belts passing through a micro-fluidic channel. (b) POM image of the as-prepared GO belts. (c) SEM image of knotted GO belts. The picture (d) and scheme (e) of a drawing–twistingprocess to obtain continuous TGFs. SEM images of a RTGF (f and g) and a LTGF (h and i), and the cross-sectional observation (j). (k) The relationshipbetween the helical angle, inserted twist and diameters.

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untwisting of TGFs. To guarantee the reversibility of torsionalrotation, we tethered the TGF at both ends to prohibit theexcessive release of strain energy. Highly volatile fluids, i.e.acetone, methanol and ethanol, departed from TGFs soon afterthe untwisting finished, causing negligible harm to helicalmicrostructures. The rapid release of strain energy in theuntwisting process produced a reverse internal stress, whichdrove untwisted TGFs to rotate reversely to rebuild the initialarchitectures. The reverse rotation was slower than the forwardrotation. For example, the recovery speed of TGFs decreased to4830 rpm from a forward speed of 6050 rpm when actuated byacetone, to 3510 rpm from 4200 rpm when driven by methanoland to 1800 rpm from 3300 rpm when stimulated by methanoland ethanol. The reversibility and repeatability of liquid waterwere poor, since liquid water swelled GO laminates, destroying

the helical structures of TGFs in the first cycle. Due to theirnon-volatile properties, high viscosity fluids, such as DMSO,also suppressed the reversibility and repeatability of actuatingsystems.

Uniting a couple of units into a handedness-controlledactuating system can precisely control the rotary speed andkinetic energy output. The configuration of the two TGF systemis either homochiral (RR or LL) or heterochiral (RL or theequivalent LR) depending on the relative handedness. For theRR configuration, the system remained silent when one unitwas wetted with acetone, but the RR system coiled rapidly (seeMovie S2, ESI†) after the other unit was wetted (Fig. 2e). Thiscoiled configuration is highly similar to the architecture ofF-actin.2 The LL system showed similar behavior to the RRsystem but rotated toward the reverse direction. The SEM images

Fig. 2 Handedness-controlled rotor kinetic energy harvesters constructed with solvent-driven TGFs. (a) The optical images of the reversible rotation ofa TGF in the presence of 0.05 mL acetone. The relationship of rotary speed (b), start-up torque and peak power output (c) with the polarity of exposedsolvents. (d) The measured speeds of the forward rotation and reverse rotation of TGFs driven by polar solvating species for 100-cycle tests. The schemerecording the responses of two united TGFs suffering the successive wetting of acetone, with the alternating handedness of RR (e) and RL (f). (g) Thescheme showing that the actuation of a two-TGF system is realized by their resultant torque. (h) The relationship between the peak power output, rotaryspeed and spacing width between two RR or LL units. (i) The monolayer fabric woven with cotton fibers and a LL configuration. The composite fabricformed a helical morphology when wetted in an acetone bath.

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in Fig. S7b (ESI†) indicated that the screw pitch of a coiled helixswitched between the millimeter level (1.7 mm) and the micronlevel (320 mm). When we replaced a L unit with a R unit, the builtRL/LR configuration was immune to the consecutive doping withstimulating solvents (Fig. 2f). The two torques generated in RR/LL configurations (t1 and t2, respectively, Fig. 2g) had the samemagnitude and direction, contributing equally to the torsionalrotation. While t1 and t2 completely cancelled each other in theRL/LR configurations due to the opposite direction, the rotaryspeed of the RR/LL configurations was modulated by tailoringthe spacing width (W) between the two fibers (Fig. 2h). Byincreasing the value of W from 2 mm to 10 mm, we demonstratedthat the rotary speed decreased from 3190 rpm to 800 rpm in theRR system, accompanied by a decrease of power output from12.5 W kg�1 to 0.78 W kg�1, while the corresponding power outputin the LL system decreased from 12.3 W kg�1 to 0.77 W kg�1. Theabove tests further inspire us to create a ring-like actuator (Fig. S8a,ESI†) and a smart textile (Fig. 2i and Fig. S8b–e, ESI†), whichexhibited repeatable actuating motion upon repeated exposures toacetone.

Based on the optimization studies, we adapted handedness-controlled actuating systems to collect electrical energy fromthe rotor kinetic energy by modulating the handedness of threeunits. Uniting three units can activate a high moment-of-inertiamagnet rotor, thus improving the energy harvesting efficiency.More units are not suitable due to the lower rotary speed(o5 rpm, as discussed later). The electrical power outputfrequency changed from 10 Hz to 5 Hz in three-TGF-basedelectromagnetic induction systems, i.e., RRR, LLL, RRL, RLLand RLR (Fig. 3a). For the RRR configuration, the rotationgenerated a peak gravimetric electrical power of 9.8 W kg�1,

corresponding to an output electrical energy of 0.86 J kg�1 percycle (Fig. 3b). Because the rotary speed was 600 rpm, the peakpower output was calculated to be 18.15 W kg�1. Thus, thekinetic-to-electrical energy conversion coefficient was 54%,superior to those of artificial polymer muscles.46 Similarly,the LLL configuration achieved a gravimetric electrical powerof 11.5 W kg�1, an output electrical energy of 0.88 J kg�1 percycle and an energy conversion coefficient of 57%. For the RRLconfiguration, the reverse torque produced by the L unit in theend partially counteracted the middle R unit, providing agravimetric output electrical power of 5.9 W kg�1 and anelectrical energy per cycle of 0.51 J kg�1, around 60% and58% of those of the RRR configuration, respectively. Thegravimetric output electrical power and energy per cycle bythe RLR configuration decreased to 2.37 W kg�1 (23% of theRRR configuration) and 0.21 J kg�1 (24% of the RRR configu-ration), since the torque of the middle LTGF cancelled those ofthe remaining RTGFs. All the configurations maintained highand stable energy conversion efficiencies from 50% to 60%during our cycle tests (Fig. 3c). The above tests demonstrate thefeasibility of three-TGF systems to precisely control the elec-trical energy harvesting by programming the handedness ofunit cells, while maintaining high efficiency and stability.

We modified a handedness-controlled actuating system tooperate as a soft actuator, which handled a heavy object in acontrolled mode. This is an ability indispensable for softrobotics. The soft actuator was constructed by tethering fourTGF units with a pendant weighing 2.5 mg (m0), around 61 foldthat of a single unit (41.7 mg). For the RRRR system, the unitedaxial extension of the four TGFs caused the pendant to experi-ence a helical swing when actuated by in-plane torques.

Fig. 3 Handedness-controlled electrical energy harvesters constructed with RRR, LLL, RRL, RLL and RLR configurations, respectively. The dependencesof gravimetric output electrical power (a) and electrical energy (b) on the handedness and arrangement of TGF units. (c) The kinetic-to-electrical energyconversion coefficients of all the configuration during 10 cycle tests.

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The pendant rose from the horizontal position to a nearlyvertical position for 15 seconds (t0) (Fig. 4a) with the increaseof the tilting angle from 01 to 881 and a constant swing speed of5.871 s�1 (Fig. S9, ESI†). The mass center was raised by 1.2 cm(h). Thus, the output gravitational potential energy (G = m0gh)and gravitational potential power (Pg = G/t0) were calculated tobe 17.66 J kg�1 and 1.17 W kg�1, respectively. Due to theclockwise synergistic torque produced by the four RTGFs, theRRRR-TGF system swung in a clockwise direction. As a compar-ison, the pendant in the LLLL system swung to the anticlockwisedirection and a height of 1.2 cm at a speed of 5.901 s�1 (Fig. S10,ESI†). The nearly same swing speed and rising height of theRRRR configuration as those of the LLLL configuration suggeststhe reliable symmetry of the handedness-controlled actuatingsystem (Fig. S9, ESI†). For LRRR, the system swung in theunaltered direction, but the rising height and G values decreasedto 0.76 cm and 11.2 J kg�1 (Fig. 4b and Movie S3, ESI†). This isbecause the new added LTGF produced an anticlockwise torquecounteractive to those of the remaining three RTGFs, weakeningthe synergistic torsion action. The rising height and G weredecreased to 0.48 cm and 7.04 J kg�1 in the RLRR configuration

(Fig. 4c), due to the bilateral influence of the middle torque ofthe LTGF, as discussed in the RLR configuration (Fig. 3a).

By adjusting the arrangement of units in four-TGF config-urations, we conclude that the working direction is controlledby the quantitative proportion of two kinds of units, which isnothing to do with the spatial arrangement. As displayed in thered zone of Fig. 4d, RRRR, RRRL, RRLR, RLRR, and LRRRconfigurations occurred in the clockwise swing since the pro-duced torques of the RTGF overmatched those of the LTGF.And the blue zone represented the anticlockwise swing whereLTGF units predominated. The system remained silent whenRTGF units and LTGF units were numerically equal (e.g. RLLR,RLRL and RRLL configurations), because they counteractedeach other. Different from the working directions, the gravita-tional energies and power outputs are closely related to thespatial arrangement of units. We summarized the time depen-dences of the rising height and average gravitational energyoutput of the RTGF-dominated configurations (Fig. 4e), findingthat the movement of the suspended object maintained aconstant speed in all the systems. In the whole working process,the G remained at 17.66 J kg�1 in the RRRR configuration, and

Fig. 4 Handling a heavy object using a four-TGF actuating system. The pictures in (a), (b) and (c) recording the movement of the heavy object in RRRR,LRRR, and RLRR configurations driven by acetone, which exhibits controllable swing and lifting. The relationship of the swing direction (d), lifting heightsand output gravitational energy (e) of the actuating system with the helical chirality of the components.

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decreased by 40% in the LRRR configuration, and by 35% in theRLRR configuration.

All the handedness-controlled systems discussed aboveexhibit superb controllability and high efficiency. More impor-tantly, this phenomenon can also be extended to other unitcells by hybridizing different materials with TGFs. We haveshown different examples of hybrid TGFs with CNTs, PVA, andtitania nanoparticles, individually. Nanomaterials with weightfractions beyond 50% dispersed uniformly in the hybrid fibers(Fig. 5a and Fig. S11, ESI†). The operation capacities of twistedfibers fabricated using different materials (i.e. graphene oxide,CNTs, PVA and titania) were mainly decided by four factors.They are the hydrophily of materials, the affinity betweenmaterials and fluid stimuli, the torsion moduli and the twistnumbers in turns per meter (T). Carboxylated CNTs and PVAare more hydrophilic than titania nanoparticles, so twistedfibers containing CNTs and PVA show better affinity with polarsolvents than hybrid fibers containing titania particles. Drivenby 0.05 mL acetone, R-type titania fibers outputted a lower rotorkinetic power (24.3 W kg�1) than those of R-type CNT fibers(45.1 W kg�1) and R-type PVA fibers (26.8 W kg�1). Experimen-tally, CNTs are easily liquid-phase processed, while PVA isdifficult to twist due to its low torsion modulus. Thus, twistedfibers containing CNTs own larger T than PVA fibers, which canbe directly determined from Fig. 5a and Fig. S11 (ESI†). Thelarger T contributes to the higher rotor kinetic power output ofCNT fibers than that of PVA fibers. The rotor kinetic poweroutputs of the hybrid fibers are superior to those of previouslyreported artificial muscles13,15 (Fig. 5b). The nearly equalenergy outputs of R-type fibers and L-type fibers reflected afavorable operating symmetry. In two-unit systems, RR- or LL-typeactuators delivered rotor kinetic power varying from 9.8 W kg�1

to 5.3 W kg�1. RL- or LR-type systems remained inert, since thetwo opposite torques used in the rotor completely cancelledeach other. Similar to the three-unit systems of neat TGFs,nanocomposite-based systems outputted highly controllablepower by adjusting the arrangement of cell units with different

handednesses. In a case study of CNTs, the power outputs ofRRR-, RRL- and RLR-systems showed a gradual decrease from7.9 W kg�1 to 4.1 W kg�1. Through the study on handednanocomposite-based hybrid fibers, we demonstrated thegeneral applicability of handedness-controlled conception inpractical actuating systems.

Conclusions

In summary, we designed handedness-controlled actuatingsystems by programming flexible handed TGFs. IndividualTGFs exhibit high stretchability and mechanical robustness,giving rise to an efficient kinetic energy output driven byvarious polar solvents. As unit cells, TGFs are logically pro-grammed into intricate actuating systems, which operate ashighly controllable soft actuators to handle a heavy object andharvest energy with a high energy conversion efficiency. Thehigh controllability, easy operation, and flexibility of TGFsallow them to be used as high-precision energy harvestersand soft robots. We widely apply handedness-controlled sys-tems to other unit cells, such as hybrid twisted fibers contain-ing nanocomposites and polymers.

Conflicts of interest

The authors declare no conflicts of interest.

Acknowledgements

The authors acknowledge the kind supply of massive giant GOspinning dopes from the company Gaoxi Tech (www.gaoxitech.com). This work was supported by the National Natural ScienceFoundation of China (Grant No. 51533008, 51703194, 51603183,and 21325417), the National Key R&D Program of China(Grant No. 2016YFA0200200), the Fundamental Research Fundsfor the Central Universities (Grant No. 2017XZZX008-06), and the

Fig. 5 (a) Hybrid twisted fibers made with graphene oxide and carbon nanotubes, polyvinyl alcohol, and titania nanoparticles. (b) The power outputs ofthe hybrid twisted fibers in handedness-controlled actuating systems in the presence of 0.05 mL acetone.

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Hundred Talents Program of Zhejiang University (188020*194231701/113).

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