Multi-stimulus responsive actuator with GO and carbon nanotube

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Functional Nanostructured Materials (including low-D carbon)

Multi-stimulus responsive actuator with GO and carbon nanotube/PDMS bilayer structure for flexible and smart devices Wen Wang, Chenxue Xiang, Qing Zhu, Weibing Zhong, Mufang Li, Kelu Yan, and Dong Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b08554 • Publication Date (Web): 23 Jul 2018 Downloaded from http://pubs.acs.org on July 24, 2018

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ACS Applied Materials & Interfaces

Multi-stimulus responsive actuator with GO and carbon nanotube/PDMS bilayer structure for flexible and smart devices Wen Wang1, Chenxue Xiang 2, Qing Zhu1, Weibing Zhong1, Mufang Li2, Kelu Yan1, Dong Wang1,2*

1. College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai, 201620, China 2. College of Materials Science and Engineering, Hubei Key Laboratory of Advanced Textile Materials & Application, Wuhan Textile University, Wuhan 430200, China *Corresponding author: Dr. Prof. Dong Wang E-mail: [email protected] or [email protected] Tel: +86-27-59367691 Abstract：：Smart devices with abilities of perceiving, processing, and responding are attracting more and more attentions due to the emerging development of artificial intelligent systems, especially in biomimetic and intelligent robotics fields. Designing a smart actuator with high flexibility and multi-stimulation responsive behaviors to simulate the movement of creatures, such as weight lifting, heavy objects carrying via simple materials, and structural design is highly demanded for the development of intelligent systems. Herein, a soft actuator that can produce reversible deformations under the control of light, thermal, and humidity is fabricated by combining high photo-thermal properties of CNT/PDMS layer with the natural hydrophilic GO layer. Due to the asymmetric double-layer structure, the novel bilayer membrane-based

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actuator showed different bending directions under photothermal and humidity stimulations, resulting in bidirectional controllable bending behaviors. In addition, the actuation behaviors can be well controlled by directionally aligning the graphene oxide onto carbon nanotube/PDMS layer. The actuator can be fabricated into a series of complex biomimetic devices, such as, simulated biomimetic fingers, smart “tweezers”, humidity control switches, which has great potential applications in flexible robots, artificial muscles, and optical control medical devices. Keywords: soft actuator, multi-stimuli response, fast response, shape controllability,

cyclic stability, bionic application. 1 Introduction Smart or intelligent materials which can respond to various kinds of environmental stimuli by changing shapes or internal properties have attracted great research interests.1 Among them, electronic skins,2-3 artificial muscles,4-5 intelligent sensing devices6-8 have promising prospects to be widely applied in multi-functional intelligent systems, artificial intelligence, and medical rehabilitation. In addition, the utilization of green energy resources in nature for driving intelligence systems is a hot topic.9-10 Therefore, the stimuli-responsive actuator (SRA) is especially prominent since they can transform the external energies into dynamic motor behaviors in response to environment stimuli, such as light,11-13 thermal,14-15 humidity,16-18 electricity,

19-21

and magnetism9-10. Different kinds of actuators including gel

types,22-23 liquid crystal structures,8, 27

24

polymers,

25-26

and carbon nanomaterials

18,

have been reported. The capabilities of perception, processing, and responding are


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key properties which may be designed and assembled into a system as independent or separate structure units.28 For example, a fiber-based actuator fabricated by twisting polymer fibers containing the multi-walled carbon nanotubes (MWCNTs) can exhibit a rapid response and large actuation stroke upon contacting with the solvents and vapors.29 A bilayer structured membrane based on graphene /PVDF is made into a fish-like robot which can swim under an electric field.26 The whole actuating process is similar to the response of animals or plants to the environment stimulus. However, there remain significant gaps in responsive performance to stimuli between the bio-systems and currently fabricated actuators, such as single responsive capability to stimulus, long response time or complex structural designs.30 Graphene, a kind of two-dimensional material with high specific surface area, possessing excellent thermal, electrical, mechanical, and optical properties can be a promising candidate for fabricating actuation devices.7, 26, 29 For example, Mu et al1 prepare a graphene monolayer (GM) paper actuator which can generate certain bending and deformation behaviors under ambient light and humidity stimuli. However，graphene films or laminates are very brittle and hard to be bent significantly, especially after long periods of heat and light irradiation, greatly restricting their wide applications. Polydimethylsiloxane (PDMS), a transparent elastomer possessing excellent biocompatibility, high elasticity, hydrophobicity, and low cost, is widely used in bio-electromechanical systems,31 hydrophobic protective covering,

32

filling

agent.33 Furthermore, PDMS has high thermal expansion coefficient and easy bonding with materials at room temperature, which makes it easier to be processed and



utilized.15, 34 Herein, a biomimetic double-layered membrane consisting of the graphene oxide (GO) layer and carbon nanotubes (CNT) embedded PDMS (CNT/PDMS) layer were well designed and fabricated. The membrane showed fast, reversible actuation properties to multiple stimuli, including light irradiation, thermal, and humidity (Fig. 1a). Furthermore, a bilayer structured membrane with controllable actuation behaviors was prepared by directional placement of GO layer in stripe form onto the CNT/PDMS layer, displayed in Fig. 1b. The potential applications of developed stimuli-responsive GO-CNT/PDMS bilayer membrane is demonstrated by assembling it into flexible fingers, tweezers, and bionic reptiles for carrying heavy objects.

Fig. 1 Schematic diagram of the bending/unbending deformation of the bilayer membrane under light irradiation, temperature, and humidity (a), and (b) the directionally curved bilayer membrane. 2 Experimental


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2.1 Materials PDMS was purchased from Suzhou Hai Disi electronic technology CO., Ltd. (Sylagrd 184 silicone elastomer, Dow Corning, USA), Carbon nanotubes (CNT) was obtained from XF nanomaterials technology CO., Ltd. (Nan Jing, China). N-hexane were provided by Sinopharm chemical reagent Co., Ltd. (Shang Hai, China), all of which were used without further purification. 2.2 Preparation of GO film The GO was fabricated by a modified Hummers’ method which is a very common preparation method. Then the prepared GO suspension with a concentration of 5mg/ml was poured into a dish and kept at 40℃. After completely being dried, the GO was peeled off from the dish and well preserved for further use. 2.3 Preparation of the stimuli-responsive bilayer membrane-based actuator N-hexane and CNT were added into PDMS with a quality ratio of 3:0.5:10 and stirred vigorously for 5 hours. Then the viscose solution was degassed in a vacuum after adding curing agent into the PDMS and well mixed (curing agent: PDMS was10:1). The rotation of the CNT/PDMS layer was carried out on the smart coater (Best Tools LLC, USA). After that, the film was put into oven with a temperature of 80℃ for 30 minutes to form a semi-cured CNT/PDMS structure. The pre-prepared GO film was then transferred to the semi-cured CNT/PDMS layer by carefully contacting the GO film with CNT/PDMS layer for 5 minutes and a 200g glass panel was placed horizontally on the surface of the bilayer membrane to provide a certain amount of pressure during the process. The bilayer membrane was then completely



cured at low temperature of 40℃ and cut to a certain size for further measurement. 2.4 Characterization and measurements The morphology and corresponding EDS mapping of the GO-CNT/PDMS bilayer membrane were characterized by JEOL scanning electron microscope. The photograph and video were recorded by a single-lens reflex camera (Sony, Japan). An infrared laser (150W, Philips E27) and NIR light source (50 mW-400 mW, Lei Fu electronic) with the wavelength of 808nm were used to irradiate the bilayer membrane and the light density was recorded by an infrared power meter (LS122, Lin Shang technology). The magnetic heating agitator (IKA, RCT basic) was used for providing heat source to explore the relationship between responsiveness and temperatures. The thermal images and temperatures of the membrane were recorded by an infrared thermometer (FLIR Thermo-Vision A40M). The bending angle was analyzed by adobe Illustrator CS5. 3 Results and discussion 3.1 Morphology characterization of the GO-CNT/PDMS bilayer membrane


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Fig. 2 (a) Schematic illustration of the fabrication of GO-CNT/PDMS bilayer membrane actuator. (b) Flexibility of the GO-CNT/PDMS bilayer membrane. (c) Raman absorption spectrum of the CNT/PDMS composite membrane and pour PDMS membrane (see illustration). (d) SEM image of the cross-section of the GO-CNT/PDMS bilayer membrane. (e) Enlarged SEM images of the cross-section of the GO layer and CNT/PDMS layer in (d). And the illustrations show the surface contact angle of the GO layer (52.19°) and CNT/PDMS layer (113.44°). Fig. 2a shows the fabrication process of the GO-CNT/PDMS bilayer membrane. The CNT was well dispersed into the PDMS solution. The CNT/PDMS solution was then spin-coated into a substrate membrane. The pre-casted GO membrane was then transferred onto the pre-cured CNT/PDMS membrane and formed a tightly adhered bilayer membrane through the subsequent curing process at 40℃. The flexibility of the GO-CNT/PDMS bilayer membrane is illustrated in Fig. 2b by bending to circles



with large curvatures (2.13cm-1) under the external stress. Fig. 2c shows the Raman spectra of the CNT/PDMS layer and the pure PDMS membrane excited at 633nm. Compared with the Raman absorption spectrum of pure PDMS, the main absorption peak in Roman spectra of carbon nanotube materials, including the D peak (near 1350 cm-1), G peak (near 1590 cm-1) and 2D peak (near 2700 cm-1) all appeared on the CNT/PDMS layer, proving that the CNT and PDMS were well combined. Furthermore, the Roman shifts of the three main peaks are in line with the peak range in the Roman spectra of metallic carbon materials.35 The cross-sectional images of the GO-CNT/PDMS bilayer membrane with different magnifications are displayed in Fig. 2d and Fig. 2e. It can be observed that the GO layer and CNT/PDMS layer are tightly adhered. Furthermore, the distinct morphological features of the GO layer with rough surface and loose laminated structure and the PDMS layer with smooth surface were shown in Fig. S1. The illustrations in Fig. 2e shows that the contact angle (CA) of the GO layer is 52°, far less than the 113.44°of the CNT/PDMS layer, which indicates the excellent hydrophilicity of the GO layer. In addition, the corresponding EDS mapping in Fig. S2 shows the uniform distribution of C, N, O and Si elements in CNT/PDMS layer, which enable the CNT/PDMS layer in the bilayer membrane to absorb and conduct thermal energy evenly and rapidly. 3.2 Light actuation of the GO-CNT/PDMS bilayer membrane


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Fig. 3 (a) Schematic illustration of the bending/unbending deformation behaviors under light irradiation. In this process, the relative humidity of the environment is controlled at 30%. (b) Temperature changes as a function of time upon the various CNT concentrations of the GO-CNT/PDMS bilayer under the NIR intensity of 0.5W∙cm-2. (c) Stress generated by irradiating the GO-CNT/PDMS bilayer membrane under the NIR intensity of 0.5W∙cm-2 (red area represents the irradiation on). (d) Maximum bending angle changes of the GO-CNT/PDMS bilayer membrane under different NIR irradiation. (e) The corresponding bending/unbending angles changes as a function of time upon the various CNT concentrations of the GO-CNT/PDMS bilayer under the NIR intensity of 0.5W∙cm-2. (f) Cycling stability test of the bending/unbending behavior under the NIR intensity of 0.5W ∙ cm-2, where the illustration shows the bending angle-time curve of the GO-CNT/PDMS bilayer after 400 cycles (red area represents the irradiation on). (g) The real time bending images of the bilayer membrane in one cycle under the NIR intensity of 0.5W∙cm-2.



Fig. 3a shows the bending/unbending deformation behaviors of the bilayer membrane under photothermal irradiation. When the bilayer membrane is exposed to photothermal stimulation, the CNT/PDMS layer rapidly absorbs light energy and converts it into heat, causing the CNT/PDMS layer to expand. To illustrate the effect of the light irradiation on the temperature increase of the bilayer membrane (7× 20 mm × 80 μm) with different CNT concentrations (0wt%、1wt%、3wt%、 5wt%), the temperature-time curves at the light intensity of 0.5w/cm2 were displayed in Fig. 3b. For the bilayer membrane without CNT, it took longer, about 90s, to reach the maximum temperature of 54℃. However, the addition of CNT into bilayer membranes shortened the time to reach the maximum temperature. Additionally, the maximum temperature could reach 102℃ within 15s for the bilayer membrane having 5% CNT. This result shows that the photothermal conversion efficiency of the bilayer membrane can be greatly accelerated by increasing the CNT concentration. However, the high CNT content makes the CNT/PDMS layer less flexible with the increase of stress and decrease of strain, as shown in Fig. S3. Therefore, the CNT concentration is limited to 5wt%. Moreover, photothermal radiation leads to a significant reduction in environmental humidity. The removal of water molecules in GO layer produces capillary force on GO which makes the GO layer crinkle. 36This causes the GO cell to contract, leading the bilayer membrane to bend to the GO side. Under the combined action of expansion (CNT/PDMS layer) and contraction ( GO layer), the bilayer membrane will bend to the GO face immediately. Fig. 3c shows the mechanical stress of the bilayer membrane during photothermal stimulation.


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It can be observed that the photomechanical stress for this actuator is more than 4.5MPa, which is more than ten times stronger than mammalian skeletal muscles (～ 0.35MPa).37-38 In addition, the change of light intensity has a great influence on the actuating performance of the bilayer membrane. It can be observed from Fig. 3d that with the light irradiation intensity increasing, the maximum bending angles of the bilayer membrane significantly raise. Above the light intensity of 0.1w/cm2, the change of bending angle is gradually level off and finally reach up to the maximum bending angle of 90° at the intensity of 0.5w/cm2 with a CNT concentration of 5wt%, which is mainly restricted by the expansion degree of CNT/PDMS layer and the shrinkage degree of GO layer. In addition, the response time of the bilayer membrane to the maximum bending angle is reduced with the increase of light intensity, which proves that the response speed is accelerated (Fig. S4). The tendency of the maximum bending angles of the bilayer membrane as a function of the CNT concentration fitted well with that of the temperature change (Fig. 3b), as shown in Fig. 3e. Moreover, it could be observed that the bilayer membrane could unbend and recover to its original shape after the photothermal stimulus is removed. During this process, the expansion behavior of the CNT/PDMS layer disappears and the contraction force is generated. At the same time, the ambient humidity around the bilayer membrane rises, water molecules interact with GO cell and permeate the GO layer to make it undergo swelling behavior.

39

Under the action of contraction and

swelling force, the bilayer membrane returns to its original state. ATR-IR spectra in Fig. S5 shows the moisture exchange between GO layer and the ambient air



(RH=30%). Result shows that the GO layer can be quickly saturated with water molecules in minutes under ambient humidity (RH=30%). Fig. S6 shows the bending/unbending process of 5% CNT membrane and the measurement schematic of angles. Moreover, the influence of thickness on bending angles of the bilayer membrane has also been studied. As can be observed from Fig. S7 that the maximum bending angles of the membrane gradually decreased as the thickness increased, which may be attributed to the higher flexible modulus. The cycling performance of actuation is very important for the practical applications. The GO-CNT/PDMS bilayer membrane with 5wt% CNT was used to test the cyclability. From Fig. 3f we can see that after 400 cycles, the actuation of the membrane was nearly unchanged and the bending-recovery performance in the actuating circles was very stable. Furthermore, the response time of the membrane after 400 cycles is also studied. As can be seen from the illustration in Fig3f that after 400 cycles, the film can reach the maximum bending angle (around 90°) in 2.5s and quickly return to the initial state when photothermal stimulus was removed. Fig. 3g showed the reversible bending motion of the GO-CNT/PDMS bilayer membrane in one actuation cycle under the NIR radiation. The bilayer membrane reached the maximum bending angle within 2.48s under light irradiation and recover to the original shape within 9.65s after the irradiation stopped. The transformation process of photo energy to thermal energy and finally to kinetic energy can utilized for soft robots or other smart devices. To evaluate the possibility, the energy conversion efficiency under NIR light irradiation was calculated (Detailed calculations were listed in the Computation part in Supporting


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Information). The energy conversion efficiency of the GO-CNT/PDMS bilayer membrane from photo to thermal and thermal to kinetic under NIR light irradiation was 3.3% and 0.91%, respectively, which are several orders of magnitude larger than the graphene-based bilayer film.40 Detailed calculations were listed in the Computation part in Supporting Information.

3.3 Thermal actuation of the GO-CNT/PDMS bilayer membrane

Fig. 4 The GO-CNT/PDMS bilayer membrane containing 5wt% CNT. In this process, the relative humidity of the environment is controlled at 30%. (a) The corresponding bending/unbending angles changes as a function of time upon various temperatures. (b) The maximum bending angles under different temperature conditions. (c) The real time bending images of the bilayer membrane under different temperatures. To study the effect of thermal stimulus on the bending angles of the bilayer membrane, the curve of bending angle as a function of the time for the bilayer



membrane with 5wt% CNT concentration are shown in Fig. 4a. The different temperatures can be controlled by an electric heater. When the temperatures were set at lower than 50℃，GO-CNT/PDMS bilayer membrane needed to take longer response times, nearly 5s, to reach the maximum bending angles of less than 20°. As the setting temperature increased, the response speed, as well as the maximum bending angles of the bilayer membranes increased sharply. It can achieve a 180° bending angle within 1.72 s when the temperature was set at 80℃. It should be noted that recovering to the original shape took longer time for the bilayer membrane due to the slower heat dissipation. Fig. 4b further displays the rising tendency of the maximum bending angles of the bilayer membrane with the temperature increasing from 40℃ to 80℃. Fig. 4c records the real time bending images of the bilayer membrane actuated at different temperatures, demonstrating the excellent thermal actuation capability of the GO-CNT/PDMS bilayer membrane. 3.3 Humidity actuation of the GO-CNT/PDMS bilayer membrane


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Fig. 5 (a) Schematic illustration of the bending/unbending deformation behaviors when humidity changes. The environment temperature were controlled at 25℃. (b) Bending angle changes of the GO-CNT/PDMS bilayer membrane and CNT/PDMS membrane under different humidity conditions. (c) Stress generated by varying the humidity between 30% and 90%. (d) Bending angle-time curve of the GO-CNT/PDMS bilayer membrane under high (90%) and low (30%) humidity stimulation, where the blue area represents the high humidity of 90%. (e) The real time bending images of the bilayer membrane in one cycle under the stimulation of



humidity changed between 30% and 90%. Fig. 5a illustrates the reversible actuating behavior of the GO-CNT/PDMS bilayer membranes under humidity stimulus, which is an interesting process. When the bilayer membrane was exposed to high humidity, the GO layer, with plenty of oxygen-containing functional groups, can exchange water molecules with the environment to produce rapid water-absorbing behavior. During this process, a large number of water molecules interact with the GO cell and permeate the GO layer. The length and thickness of the GO layer increased significantly with the lamellar space become larger.41 Oppositely, the shape of CNT/PDMS layer can hardly change for its completely hydrophobic structure. As a result of the asymmetric shape change between the GO and CNT/PDMS layers, the bilayer membranes will bend toward the CNT/PDMS layer. Furthermore, the bilayer membrane was exposed to different humidity conditions and the bending angles are recorded in Fig. 5b. It can be observed that, as the ambient humidity changes from 30% to 90%, the bending angles of the membrane increase gradually and eventually reach the maximum bending angle of 137 ° when the relative humidity is 90%. As a comparison, there is no angular change in the CNT/PDMS layer due to the lack of asymmetric deformation structure. Additionally, the entire actuating behavior is reversible. When the ambient humidity drops, the removal of water molecules in GO layer produces capillary force which makes the GO cell to contract, leading the bilayer membrane to restore to its original state. ATR-IR spectra in Fig. S8 shows the structure changes of GO in response to water molecules. Result shows that the hydroxyl peak in GO increases significantly


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after contacting with water and then recovering to its initial state in 3min when the GO layer was placed in the ambient air (RH=30%). This rapid exchange of water moisture proves the excellent adsorption/desorption property between the GO layer and water moisture. In addition, by varying the humidity between 30% and 90%, the stress value of the bilayer membrane varies stably between 0 and 0.59MPa, which indicates the excellent reversible bending performance (Fig. 5c). Fig. 5d shows the bending angle-time curve of the bilayer membrane during the reversible deformation process when the ambient humidity changed between 30% and 90%. It can be observed that the maximum bending angle of the bilayer membrane is up to 137 ° and the whole actuating process can be completed within 3s. This result shows that the GO-CNT/PDMS bilayer membrane has excellent humidity response performance. More actuating performance comparisons between the GO-CNT/PDMS bilayer membrane-based actuator and previously reported membrane-based actuator are shown in Table S1. Fig. 5e shows the reversible bending motion of the GO-CNT/PDMS bilayer membrane in one actuation cycle. Fig. 5e records the deformation of the GO-CNT/PDMS bilayer membrane at various times during the actuating process, as shown in Movie S1. The video file is shown in Movie S1. Moreover, we placed the bilayer membrane on a moist substrate with the GO layer downward to contact the moisture. Results in Fig. S9 displayed that the bilayer membrane quickly bended to the PDMS layer with an increasing bending angle as the water concentration changed from 0wt% to 100wt%. In addition, the effect of interface on the actuating performance of the bilayer membrane have also been



investigated. as shown in Fig. S10.

Fig. 6 (a) The GO-CNT/PDMS bilayer membrane was prepared to simulate the bending/unbending process of a hand and (b) lift heavy objects with light on and off. (c) Series of photographs of a bionic weight-bearing creeper moving forward under the NIR intensity of 0.09w∙cm-2. (d) The circuit diagram of the membrane-based humidity switch and (e) the response of the LED lights under different ambient humidity. The excellent photo-thermal actuation performance of the GO-CNT/PDMS bilayer membrane made it possible to fabricate a series of smart devices or robots. Fig.


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6a shows a glove made by the GO-CNT/PDMS bilayer membrane that can produce a happy posture of “yeah” under the control of NIR light irradiation. Furthermore, a series of actuation behaviors resembles the human fingers are shown in Fig. S12 and Movie S3. Fig. 6b shows that a bionic jack that can lift heavy objects (eight times as much as the mass of itself) in a few seconds under the stimulus of light irradiation. Furthermore, we designed the GO-CNT/PDMS bilayer membrane to be a biomimetic weight-bearing creeper. As shown in Fig. 6c, the creeper can move forward continuously with heavy loads when the NIR irradiation switch on or off. After 45s of regular irradiation, the creeper moved 25mm with a moving speed of around 0.55mm/s (Movie S4 in Supporting Information). Due to the sensitive responsiveness of the bilayer membrane to moisture, a membrane-based humidity switch was fabricated by connecting one end of the bilayer membrane to different colored LED lights, the circuit diagram was shown in Fig. 6d. By varying the ambient humidity, the bending angles of the bilayer membrane can be immediately changed to form closed loops at different heights. Fig. 6e showed that the LED lights with blue, green and red colors were respectively controlled by the relative humidity of 20%, 50% and 80%, which revealed potential applications in humidity detection.



Fig. 7 (a) Schematic of GO-0°, GO-90°and GO-45°bilayer membrane by adjusting the arrangement of GO layer on CNT contained PDMS layer. (b) The crimping process of “intelligent tendrils” under the condition of NIR irradiation. (c) Light-responsive smart “tweezers” picked up a piece of paper driven by infrared light. To make the bilayer membrane more intelligent, we placed the GO layer onto the CNT/PDMS layer in three different directions along the length direction of the bilayer membrane, parallel (0°), perpendicular (GO-90°) and 45° arranged (GO-45°). This specially designed structure realized the controllability of the bilayer membrane in bending direction, and further provided the possibility to fabricate the intelligent


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devices. The GO-45°arranged bilayer membrane can curl like a tendril in a few seconds under external NIR irradiation, as shown in Fig. 7b and Movie S5 in Supporting Information. We fabricated a membrane-based “tweezers”, the free open ends of which were made by the bilayer membrane. Under regular on/off IR irradiation, the “tweezers” performed controllable open/closed behaviors, providing the driving force to pick or release the scrip. The complete operation process is shown in Fig. 7c and Movie S6 in Supporting Information. Furthermore, the photo-responsive smart “crane” and smart “clamp” made by GO-0°and GO-90° arranged membrane were fabricated to simulate a series of biomimetic operations (Fig. S13, Movie S7 and Fig. S14, Movie S8 in Supporting Information). This research has a promising future in the field of intelligent medical treatment.

4 Conclusion In summary, a multi-stimulus responsive soft actuator with bilayer structure was fabricated by simply combining the GO layer with CNT/PDMS layer. The GO-CNT/PDMS bilayer membrane smart actuator demonstrated fast, reversible and stable actuating performance under the environmental stimulus including light irradiation, temperature and humidity. We found that the bilayer membrane with 5wt% CNT content had the fast response performance. When exposed to NIR irradiation, the soft actuator reached a bending angle of 90 in the 2.48s. In addition, the soft actuator displayed reversible bending and unbending deformations under different temperature and humidity conditions. Furthermore, the soft actuator kept an excellent stability after 180 cycles of reversible bending deformation tests. The soft actuator



was tailored and assembled into smart hand, actuator-based jack and weight-bearing creeper which can simulate finger bending, lifting and carrying heavy objects. Besides, we arranged the GO layer orderly to prepare the directionally curved soft actuator. The orientationally arranged bilayer membrane were further made into biomimetic “intelligent tendrils” and smart “tweezers” which had excellent driving performance under light irradiation. This research provided a broad platform for smart medical devices, artificial muscles and actuated weight-bearing robots. Acknowledgements This work was supported by the National Natural Science Foundation of China (Grant No. 51473129, 51503157, 51503160), National Science and Technology support program (2015BAE01B01), Creative research group of Hubei province (2015CFA028) and Nature Science Foundation of Hubei Province (No. 2016CFA076, 2016CFB386). References 1.

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