Skip to main content

Carbon nanotube-graphene hybrids for soft electronics, sensors, and actuators

Abstract

Soft devices that are mechanically flexible and stretchable are considered as the building blocks for various applications ranging from wearable devices to robotics. Among the many candidate materials for constructing soft devices, carbon nanomaterials such as carbon nanotubes (CNTs) and graphene have been actively investigated owing to their outstanding characteristics, including their intrinsic flexibility, tunable conductivity, and potential for large-area processing. In particular, hybrids of CNTs and graphene can improve the performance of soft devices and provide them with novel capabilities. In this review, the advances in CNT-graphene hybrid-based soft electrodes, transistors, pressure and strain sensors, and actuators are discussed, highlighting the performance improvements of these devices originating from the synergistic effects of the hybrids of CNT and graphene. The integration of multidimensional heterogeneous carbon nanomaterials is expected to be a promising approach for accelerating the development of high-performance soft devices. Finally, current challenges and future opportunities are summarized, from the processing of hybrid materials to the system-level integration of multiple components.

Introduction

Carbon nanomaterials composed of a hexagonal lattice of sp2-hybridized carbon atoms have been actively investigated for scalable production in various fields of applications [1, 2]. They are classified into one-dimensional (1D) carbon nanotubes (CNTs) and two-dimensional (2D) graphene according to their dimensional shape. CNTs and graphene exhibit excellent and unique properties, making them attractive candidate materials for electronics, displays, transducers, and other devices. In particular, the high elastic modulus, strength, and aspect ratio of CNTs, along with their high electrical conductivity, allow for mechanically strong and electrically conductive composites with various potential applications [3, 4]. These characteristics of CNTs have also been adopted for microelectromechanical devices by integrating aligned CNTs at specific locations in microstructures [5,6,7,8,9,10]. The incorporation of CNTs has led to improved performance and reliability in structures and devices. In view of the properties of the CNTs, it was expected and eventually discovered that graphene also exhibits extraordinary mechanical, electrical, thermal, and optical properties [11, 12]. Among the many interesting characteristics of graphene, its high carrier mobility outperforms those of other materials, which has accelerated the development of carbon nanoelectronics [13]. Furthermore, owing to their atomic diameter or thickness, both CNTs and graphene can be key components of transparent devices in the form of a monolayer while providing high mechanical compliance [14, 15]. These features have advanced the development of soft and transparent electronics, sensors, and actuators, based on 1D CNTs or 2D graphene as building blocks.

Manufacturing processes have been continuously developed to scale up the excellent properties of individual CNTs and graphene in functional devices. With progress in synthesis, integration, and transfer processes, carbon nanomaterial-based devices have achieved a higher degree of design freedom, including in the selection of substrate materials. Thus, conventional rigid substrates can be replaced by elastomeric substrates, such as rubber and many polymers, leading to the active development of wearable electronics and sensors that can be conformally mounted on curved surfaces based on the low flexural rigidity of thin and soft substrates [16,17,18,19]. In addition, the incorporation of CNTs and graphene into polymeric materials has enabled the realization of soft actuators requiring large deformations by electrical and chemical stimuli [20]. Soft sensors and actuators composed of carbon nanomaterials are expected to be applied in future wearable, implantable devices, and human–machine interfaces. The performance of soft devices can be further improved by heterogeneously integrating multidimensional nanomaterials, as previously demonstrated by combining 1D CNTs and 2D graphene for electronics, optoelectronics, and electromechanical and electrochemical devices [21,22,23,24,25]. CNTs and graphene have intimate lattice structures beneficial for minimizing contact resistance and reinforcing mechanical strength when forming heterostructures [26]. As such, in addition to their own properties, hybrids of 1D CNTs and 2D graphene could synergistically reach improvements in the properties and performance of target devices otherwise unachievable by homogeneous materials. Therefore, CNT-graphene hybrids are an attractive choice for realizing flexible, stretchable, and transparent devices, thereby providing new functionalities and leading to better performance and reliability relative to conventional devices.

This review covers the progress in CNT-graphene hybrid-based soft electronics, sensors, and actuators, highlighting the merits of the heterogeneous integration of carbon nanomaterials in terms of device performance (Fig. 1). As the performance improvement depends on the characteristics of the CNT-graphene hybrid, the properties of a CNT-graphene hybrid film are discussed in addition to their synergistic effects as binary reinforcing fillers for elastomeric composites. Further, we review flexible and stretchable electronic devices composed of CNT-graphene, which can be integrated to operate and control soft sensors and actuators. In addition, CNT-graphene hybrids for soft physical sensors for detecting changes in pressure and strain are discussed, focusing on improvements in the sensitivity and sensing range. Finally, applications for CNT-graphene composites and networks as core components in electrochemical and electrothermal soft actuators are discussed in detail. We conclude the review with current challenges and future perspectives in the field of soft devices potentially consisting of other combinations of nanomaterials, as well as carbon nanomaterial hybrids.

Fig. 1
figure 1

Copyright 2021, Elsevier B.V. Strain sensors: Reproduced with permission [28]. Copyright 2021, American Chemical Society. Electrothermal actuators: Reproduced with permission [29]. Copyright 2018, American Chemical Society. Electrochemical actuators: Reproduced with permission [30]. Copyright 2017, John Wiley and Sons. Electrodes: Reproduced with permission [31]. Copyright 2016, American Chemical Society. Transistors: Reproduced with permission [21]. Copyright 2011, American Chemical Society

Applications of carbon nanotube (CNT)-graphene hybrids for soft electronics, sensors, and actuators. Superior properties and characteristics of multidimensional hybrid carbon nanomaterials significantly improve the performance of soft devices. Pressure sensors: Reproduced with permission [27].

Carbon nanotube (CNT)-graphene-reinforced soft structures

The superior material properties of CNTs and graphene, such as their high Young’s modulus and tensile strength, make them favorable building blocks for various electromechanical applications. Their broad structural applications include thin films on soft substrates and reinforced polymer composites for various types of soft electronics, sensors, and actuators. The mechanical properties of CNT-based structures have been experimentally measured in many studies. The experimentally measured Young’s modulus of CNT-family materials ranges from 4.7 GPa to 1 TPa, depending on the size scale of the structured material and measurement methods [32, 33]. The tensile strengths of these CNT-based structured materials range from 71 MPa to 200 GPa. Extraordinary mechanical properties are generally obtained by using pristine individual nanoscale specimens. However, for scaled-up macrostructures allowing for practical and manufacturable usage of the CNTs, the material properties are generally one to two orders of magnitude smaller. This is mainly because the characteristics of the interconnections and microstructures between the materials dominate the superior intrinsic properties as the material is scaled up into a macro form, resulting in deteriorated mechanical properties in the overall structure on a macro scale. Efforts have been made to overcome this issue, and certain techniques have been developed to enhance material properties on a macro scale [34, 35]. Graphene has attracted significant interest for various applications, and its material properties have been widely tested in many structural forms. An experimentally measured Young’s modulus of 1 TPa as measured by nanoindentation in an atomic force microscopy setup was reported for pristine monolayer graphene [36]. Nonetheless, the Young’s modulus of graphene can decrease to as low as 31.7 GPa for practical macro-scale bulk material configurations, such as in paper forms [37]. Experimental reports have shown that the tensile strength of graphene can range between 223 and 130 GPa [36, 38].

To date, there have been many academic explorations and technical efforts concerning CNT and graphene reinforcements, aiming to find superior structures for soft devices (electronics, sensors, and actuators). These attempts can be classified into many nano and microstructures, but CNT-graphene hybrid thin films and reinforced composite matrices with CNT-graphene fillers [39] are the two most widely explored structural materials. CNT-graphene hybrid films have been widely tested to explore, verify, and utilize their synergetic size and geometrical effects. The Young’s modulus of a CNT-graphene hybrid film has been reported as much higher than that of a super-aligned CNT film. For example, it was reported that a Young’s modulus achieved by a CNT-graphene hybrid film was larger by an order of magnitude (2.34 GPa) than that of a super-aligned CNT film (0.35 GPa) [40]. Graphene fillers generally offer superior mechanical strength to a host material relative to CNT nanofillers [41]. The synergetic effects of CNT-graphene hybrid nanofillers on the mechanical characteristics of composite materials have recently been explored [42]. Efforts have been made to enhance mechanical properties by combining CNTs and graphene nanoplatelets and optimizing the mixing ratio [43]. Others have reported that adding CNT-graphene hybrids as fillers to natural rubber almost doubles its tensile strength [44].

Soft electronics

Electronic components are key parts for the operation of transducers, such as those for signal transmission, power supply, and control. To realize soft sensors and actuators, the mechanical flexibility/stretchability of the electronic materials should be considered along with their electrical performance. Metal and doped Si thin films (the most widely used electronic materials) are unsuitable for such devices, owing to their insufficient flexibility. Thus, the development of flexible and stretchable electronic materials has become an important research topic in recent decades. With recent advances in production techniques, many studies have been performed with the goal of utilizing CNTs and graphene as conductors or semiconducting channels for soft electronics, owing to their remarkable electronic and mechanical properties. Stretchable electrodes based on monolayer graphene with a high fracture strain resistance and low sheet resistance have been proposed [14]. Likewise, the high mobility and on–off ratio of semiconducting CNTs make them an excellent active-channel material for soft electronics [46]. More recently, flexible and stretchable electronic materials utilizing CNT–graphene hybrids have been developed, as the 1D − 2D heterostructure provides novel characteristics such as van der Waals interaction, reinforced mechanical strength, and formation of an efficient percolating network enabling significant improvements in the electrical and mechanical properties [23, 24, 47].

One promising application of the CNT − graphene hybrid is as a flexible and stretchable electrode. Flexible and stretchable electrodes must retain conductivity at a substantial strain level without significant changes in their electrical transport properties. The combination of 1D metallic CNTs and 2D graphene is ideal for achieving these attributes; thus, extensive research has been conducted on developing flexible and stretchable electrodes based on CNT–graphene hybrids [45, 48,49,50,51,52]. Placing both CNTs and graphene on the surfaces of plastics or polymer substrates is one strategy for exploiting hybrid structures as electrodes. Nguyen et al. developed a CNT–graphene hybrid thin film for flexible electrodes [49]. The graphene film was grown via chemical vapor deposition (CVD), and thin networks of CNTs were synthesized on the graphene surface using the same CVD approach. The CNT − graphene hybrid film exhibited a much lower sheet resistance (420 Ω sq−1) than a graphene film (2.15 kΩ sq−1). The considerable improvement in electrical conductivity was attributed to the formation of a CNT network for connecting the gaps between the graphene sheets and the low contact resistance via the π − π interactions between them. The mechano-electrical properties were also investigated. The results showed that the deviation in the resistance of the hybrid film on the polymer substrate was only 7.2% after 100 bending cycles at a bending angle of 150°, owing to the CNTs extending in a bent state without cracking. Another type of CNT-graphene hybrid electrode is a CNT-graphene-elastomer nanocomposite. As shown in Fig. 2a, stretchable electrodes based on CNT − graphene − polydimethylsiloxane (PDMS) nanocomposites were developed via the solution mixing of CNT − graphene fillers with a PDMS matrix, and then the electrical conductivity and stretchability were investigated with respect to the fractions of the filler [45]. The synergistic effects of the 1D − 2D interconnections prevented CNT aggregation and graphene restacking and reduced the contact resistance between them, resulting in the higher electrical conductivity of the nanocomposite with a filler fraction of 0.6% (6.17 × 10−3 S cm−1) compared to CNT-PDMS or graphene − PDMS composites (< 1.85 × 10−3 S cm−1). In addition, the nanocomposite retained its electrical conductivity when strained up to 60%, owing to the high aspect ratio of the CNTs and their homogeneous dispersion with the graphene.

Fig. 2
figure 2

Copyright 2016, American Chemical Society. b Flexible transistor utilizing CNT channel, graphene electrodes, and Al2O3 dielectric. Reproduced with permission [21]. Copyright 2011, American Chemical Society

Electronics based on CNT − graphene hybrid. a Stretchable electrode based on CNT − graphene − polydimethylsiloxane (PDMS) nanocomposite. Reproduced with permission [45].

Flexible and stretchable transistors based on CNT − graphene hybrids have also been actively studied [21, 53,54,55,56,57,58]. The transistors operating in signal processing and control circuits are an essential part of electronic devices, and all components of transistors must be flexible or stretchable to be fully functional for soft electronics. A widely used type of transistor is the field-effect transistor (FET), which comprises active channels, electrodes, and gate dielectrics. To date, flexible and stretchable FETs employing various semiconducting and metallic nanomaterials have been explored. FETs employing CNT–graphene hybrids have several unique advantages over other nanomaterial-based FETs. Yu et al. developed nanocarbon-based transistors on flexible substrates and reported their outstanding characteristics [21]. The device was fabricated using a CNT network channel, monolayer graphene electrodes, and an Al2O3 dielectric (Fig. 2b). The authors revealed that the contact resistance of CNT-graphene is 100 times lower than that of CNT − Au. This was owing to the smaller difference in the work function of CNT-graphene, which allowed the CNT-graphene transistor to exhibit 20-times-higher mobility (81 cm2 V−1 s−1). No appreciable degradation was observed in the conductivity during the bending test, and the change in resistance during stretching (50% strain) was 36%. The change was considerably smaller than that of indium tin oxide (2000% at 5% strain) and graphene (200% at 30% strain). A few years later, stretchable CNT − graphene transistors were developed by the same group [54]. In that study, a geometrically wrinkled Al2O3 layer containing effective built-in air gaps was used to achieve stretchability. A wrinkled structure that can be stretched provides stability to the dielectric under tensile strain, i.e., different from a flat structure. Therefore, the transistors were successfully operated under a high strain (20%) without noticeable leakage current or physical degradation. To validate the potential utility of the transistors, they were mounted on various media such as human skin, aluminum foil, and a plastic heart. These results imply that the CNT-graphene transistor is a promising candidate for the operation of soft sensors and actuators.

Soft sensors

Wearable electronics, including artificial electronic skins, have attracted considerable attention for various applications, such as in human motion detection and physiological monitoring [62,63,64,65,66,67]. Flexible and stretchable physical sensors are key components for such applications, and mechanical flexibility/stretchability, high sensitivity, fast response time, and repeatability are considered as important requirements [68]. However, conventional physical sensors based on thin films and nanowires exhibit insufficient performance for practical applications, such as by having a narrow sensing range and/or low sensitivity [69,70,71,72]. In recent years, CNTs and graphene have been introduced as sensing materials to fabricate flexible physical sensors with a wide sensing range and high sensitivity [73,74,75,76,77,78,79,80,81,82,83,84]. CNT-based physical sensors have high flexibility but suffer from poor sensitivity. In contrast, flexible physical sensors using graphene exhibit strength in sensitivity, although the sensing range is limited. Thus, a CNT-graphene hybrid structure can provide a synergistic electrical network induced by the interconnections between the graphene and CNTs, resulting in superior stretchability and high sensitivity [85,86,87,88,89,90].

Flexible physical sensors based on CNT-graphene hybrids are classified as pressure and strain sensors. Jian et al. demonstrated a flexible pressure sensor using aligned CNTs and graphene hybrid materials [59]. In their study, aligned CNTs were applied to form networks with graphene, resulting in enhanced electrical conductivity (Fig. 3a). The aligned CNTs were prepared from vertically synthesized CNT bundles using a conventional CVD process, and then graphene was grown from a copper (Cu) foil on the prepared aligned CNT films. The fabricated aligned CNT-graphene films showed a good optical transmittance of 81.4% (550 nm) and high sensitivity of 19.8 kPa−1 (< 0.3 kPa) owing to increased conductance from the alignment in the same orientation, providing a very low detection pressure level (0.6 Pa) and superior stability over 35,000 cycles. The CNT-graphene hybrid structure has emerged as a very attractive material for pressure sensors; nevertheless, providing a cost-effective and simple method for fabricating such materials remains a challenging issue. To overcome this difficulty, Zhao et al. reported asymmetric pressure sensors based on multiwalled CNT (MWCNT)-graphene fabricated using direct laser writing [27]. As shown in Fig. 3b, a combined structure of MWCNTs and graphene was formed using a laser direct-writing technique, providing convenience, high reliability, good efficiency, and the ability for mass production. A MWCNT-embedded polyimide film was graphitized into MWCNT-embedded laser-induced graphene using the laser direct-writing method. The fabricated sensor exhibited a high sensitivity of 2.41 kPa−1, low detection limit of 1.2 Pa, and fast response recovery time of 2 ms. Tran et al. introduced a quantum resistive pressure sensor comprising 3D-sprayed CNT-graphene, and showed a very large pressure sensitivity range (0–8 MPa) [91]. Thus, these flexible pressure sensors have shown good potential for applications such as artificial skins.

Fig. 3
figure 3

Copyright 2017, John Wiley and Sons. b multi-walled CNT (MWCNT)-graphene fabricated laser direct writing (Reproduced with permission [27]. Copyright 2021, Elsevier B.V. c, d Strain sensors using CNT-graphene networks: c E-textile based on CNT-reduced graphene oxide (rGO) hybrids incorporated in non-woven fabric. Reproduced with permission [60]. Copyright 2021, Elsevier B.V. d Spyder web-like conductive polymer composites containing MWCNT-graphene nanoplatelets. Reproduced with permission [61]. Copyright 2021, Elsevier B.V

Various flexible physical sensors (pressure sensor and strain sensor) based on CNT-graphene hybrids. a, b Pressure sensors using combined CNT-graphene: a Aligned CNT with graphene. Reproduced with permission [59].

In addition to flexible pressure sensors, CNT-graphene hybrid materials have been widely used as flexible wearable strain sensors. Yao et al. reported an electronic textile-based wearable and washable strain sensor composed of a CNT-reduced graphene oxide (rGO) hybrid incorporated in a non-woven fabric [60]. Many studies combining CNT-graphene and textiles have been proposed for electronic textile sensors, but these methods have several drawbacks (e.g., requiring additional harmful treatments or specific experimental conditions, and/or showing weak adhesion between the CNT-graphene and textiles). Therefore, a washable, durable, and wearable e-textile sensor based on CNT-rGO was fabricated using an ultrasonic nano-soldering method, resulting in strong adhesion between the rGO-CNT and non-woven fabric (Fig. 3c). Previous flexible strain sensors have generally been used to measure unidirectional strain, thus showing limitations in application. Flexible strain sensors usable for various applications require multidirectional sensing, high sensitivity, and a wide detection range. Chen et al. demonstrated a spider web-like 3D-printed flexible strain sensor constructed using conductive polymer composites, including MWCNT-graphene nanoplatelets [61]. This sensor exhibited a large strain range (0%–300%), good linearity, a gauge factor of over 1000, and good stability (Fig. 3d). Li et al. reported graphene nanoplatelets and CNTs forming hierarchical hybrid networks fabricated by spray coating. These were demonstrated in flexible wearable strain sensors by applying them to a human finger and front neck area [92]. In general, the enhanced sensitivity of the graphene from introducing the CNTs allows for the detection of subtle motions. There are other strain sensors that use porous PDMS with CNT-graphene as a hybrid filler to control the sensitivity and stretchability using the Soxhlet extraction method [28]. Thus, strain sensors based on CNT-graphene-PDMS show promise for wearable smart electronics.

Soft actuators

Soft actuators play a critical role in soft robotics and bionics, with broader impacts in wearable and flexible electronics, robotic exoskeletons and prosthetics, artificial organs, and implantable medical devices. Along with advances in actuation mechanisms, innovative materials with unique physical and chemical characteristics have been vigorously explored. Carbon-based nanomaterials are known for their outstanding electrical and mechanical properties, high surface-to-volume ratios, and light specific weights; these aspects are critical for building high-performance soft actuators. CNT/graphene hybrid composites have been reported to offer the synergistic enhancement of such material properties for even larger actuation strains, faster response times, and greater stability and durability.

Ion polymer metal composite (IPMC) actuators are a type of electro-chemo-mechanical actuator that consist of an ionic polymer layer coated with conductive layers on both sides (Fig. 4a). Ion migration and redistribution occur when a potential is applied to the conductive layers. This induces an asymmetric volume expansion of the conductive layers and consequent structural deformation. Because CNT/graphene composites have advantages over metals when used as conductive layers, different structural designs and fabrication processes have been reported. Yang et al. fabricated ionic polymer actuators using an electrospray-coated MWCNT/graphene mixture with carboxymethyl cellulose on a Nafion membrane [95]. Compared to conventional IPMC actuators with platinum electrodes, the MWCNT/graphene actuators achieved a larger actuation displacement of ± 2.33 mm. The increasing ratio of graphene in the MWCNT/graphene composites led to decreasing in the actuation displacement and increasing in the fundamental natural frequency owing to the increased electrical resistance and mechanical stiffness, respectively. Lu et al. revealed that an rGO/MWCNT hybrid had a porous structure and exhibited more efficient electrochemical charging and discharging characteristics (Fig. 4b) [93]. An electrochemical actuator fabricated using the rGO/MWCNT hybrid in the electrodes demonstrated a larger bending displacement than those with only rGO or MWCNTs at frequencies ranging from ~ 0.1 to 1 Hz, with no signs of significant performance degradation even after 106 cycles. To further increase the specific surface areas of the conductive layers to promote faster ion diffusion and higher electrochemical responses for improved actuation performance, three-dimensional rGO/MWCNT-based hierarchical nanostructures have been synthesized and adapted for ionic actuators. rGO/MWCNT hybrid films with vertically aligned NiO nanowalls on the surface have achieved large displacements and fast responses (18.4 mm bending peak-to-peak deformation at 10 Hz), with long-term stability over 5 × 105 cycles [96]. rGO sheets with vertically grown MWCNTs with Ni dots at the tips (Fig. 4c) have also shown significant performance enhancements, with a bending strain, blocking force, and cyclic duration of 6.59 mm, 4.53 mN, and 4 h, respectively [30].

Fig. 4
figure 4

Copyright 2014, John Wiley and Sons. b Scanning electron microscope (SEM) image of rGO/MWCNT hybrid layer showing porous surface structures and displacement of bending actuation with different conductive materials over the frequency range from 0.01 to 1 Hz. Reproduced with permission [93]. Copyright 2012, John Wiley and Sons. c Fabrication process of graphene-carbon nanotube-nickel (G-CNT-Ni) heterostructures. Reproduced with permission [30]. Copyright 2017, John Wiley and Sons. d Coiled CNT/rGO hybrid yarns: a schematic diagram of the working mechanism, a SEM image showing the structure of the yarn, and an illustration of the testing setup. Reproduced with permission [94]. Copyright 2018, John Wiley and Sons. e Illustration of the bending and recovery actuation of the graphene oxide (GO)-CNT/PDMS bilayer membrane in response to light and temperature stimulations and the controlled bending behaviors with the aligned GO patterns in different directions. Reproduced with permission [29]. Copyright 2018, American Chemical Society

a Illustration of the working mechanism of an ion polymer metal composite (IPMC) actuator. Reproduced with permission [20].

CNT artificial muscles are another type of electrochemical actuator able to generate torsional or tensile motions with high energy conversion efficiency and controllability. CNT yarns, which are the main building blocks of CNT artificial muscles, can be fabricated by twist-spinning electrolyte-filled CNTs. Similar to IPMC actuators, ions migrate and fill the electrical double layer at the applied voltages (Fig. 4d). This causes a volumetric expansion of the yarns, resulting in untwisting and contraction. The capacitance of CNT yarns is one of the critical factors determining the actuation performance, and it can be increased by the addition of graphene. Qiao et al. fabricated coiled CNT/rGO hybrid yarns using a bioscrolling method. The yarns were driven in an aqueous inorganic electrolyte with a maximum tensile contraction of 8.1%, contractile stress of 16 MPa, and work capacity of 236 J/kg [94]. Similarly, Hyeon et al. fabricated coiled graphene/CNT yarns containing 80 wt% graphene and recorded an order-of-magnitude larger tensile stroke and work capacity of ~ 19% and 2.6 J/g, respectively [97].

Carbonaceous nanomaterials and their composites are promising candidates for flexible heating elements, owing to their excellent electrical, thermal, and mechanical properties. Wang et al. developed simple electrothermal actuators by integrating CNTs and graphene oxides (GOs) into a polyvinyl alcohol matrix to spin composite fibers [98]. When a voltage was applied to the fiber, the single-walled CNT/GO networks generated heat, and the fibers underwent thermal expansion. Another type of thermal actuator consisting of bilayer membranes with different thermal expansion coefficients can generate more sophisticated motions (Fig. 4e) [29]. A GO-CNT/PDMS bilayer structure was obtained by spin coating a CNT/PDMS mixture onto a GO layer. When exposed to light or heat, the membrane bent toward the GO layer and was also responsive to moisture changes. Bending was controlled by patterning the GO layer into ordered strips in different directions, and various soft robotic applications, such as smart tweezers and tendrils, were demonstrated.

Conclusion

Soft electronics, sensors, and actuators are expected to be essential components in robotics, wearable devices, and implantable devices, as these devices can be integrated with arbitrary structures and surfaces based on their flexibility and stretchability. Among the many materials and structures developed so far, hybrids of multidimensional carbon nanomaterials have shown great potential, given their compelling properties suitable for soft devices. The integration of carbon nanomaterials into elastomers would also provide new functionalities compared to conventional metals or semiconductors, such as transparency. Furthermore, hybrids of CNT and graphene could complement each other, resulting in improved device performance, e.g., in regards to sensitivity, sensing range, and actuation displacement. Thus, devices based on CNT-graphene hybrids can outperform others comprising homogeneous materials. Hybrids of nanomaterials are not limited to CNT and graphene; other combinations of multidimensional materials such as 1D metallic nanowires and 2D semiconducting transition metal dichalcogenides can be designed for new device architectures and functionalities.

In addition to the considerable achievements in hybrid carbon nanomaterial-based soft devices, several challenges and opportunities remain for future work. From a materials perspective, controlling defects and the number of walls or layers of CNTs and graphene during scalable and low-cost production may expand the applicability of carbon nanomaterials. Moreover, providing effective and simple purification between metallic and semiconducting CNTs would enhance the performance of carbon-based transistors and be useful for other applications, such as in transparent conductors and electromagnetic wave shielding. In terms of the performance of soft devices, improved structural and electronic design would enable a high-density sensor array for measuring and processing multiple stimuli without crosstalk, and an actuator for generating large displacements and forces with high resolution. To realize a standalone soft device, the development of manufacturing and packaging processes for integrating all components (such as electronics, sensors, and actuators) into a single system is another important challenge. Flexible and stretchable energy storage devices and wireless communication modules can also be integrated with such soft systems. Overall, high-performance, reliable, and biocompatible soft devices composed of carbon nanomaterial hybrids will be available in many fields through interdisciplinary efforts to address these challenges.

Availability of data and materials

Not applicable.

Abbreviations

1D:

One-dimensional

2D:

Two-dimensional

CNT:

Carbon nanotube

CVD:

Chemical vapor deposition

PDMS:

Polydimethylsiloxane

FET:

Field-effect transistor

MWCNT:

Multi-walled carbon nanotube

GO:

Graphene oxide

rGO:

Reduced graphene oxide

IPMC:

Ion polymer metal composite

References

  1. Geim AK (2009) Graphene: status and prospects. Science 324:1530–1534. https://doi.org/10.1126/science.1158877

    Article  Google Scholar 

  2. De Volder MFL, Tawfick SH, Baughman RH, Hart AJ (2013) Carbon nanotubes: present and future commercial applications. Science 339:535–539. https://doi.org/10.1126/science.1222453

    Article  Google Scholar 

  3. Coleman JN, Khan U, Blau WJ, Gun’ko YK, (2006) Small but strong: a review of the mechanical properties of carbon nanotube–polymer composites. Carbon N Y 44:1624–1652. https://doi.org/10.1016/j.carbon.2006.02.038

    Article  Google Scholar 

  4. Li C, Thostenson ET, Chou TW (2008) Sensors and actuators based on carbon nanotubes and their composites: a review. Compos Sci Technol 68:1227–1249. https://doi.org/10.1016/j.compscitech.2008.01.006

    Article  Google Scholar 

  5. Choi J, Lee JI, Eun Y et al (2011) Aligned carbon nanotube arrays for degradation-resistant, intimate contact in micromechanical devices. Adv Mater 23:2231–2236. https://doi.org/10.1002/adma.201100472

    Article  Google Scholar 

  6. Eun Y, Lee JI, Choi J et al (2011) Integrated carbon nanotube array as dry adhesive for high-temperature silicon processing. Adv Mater 23:4285–4289. https://doi.org/10.1002/adma.201102331

    Article  Google Scholar 

  7. Choi J, Eun Y, Pyo S et al (2012) Vertically aligned carbon nanotube arrays as vertical comb structures for electrostatic torsional actuator. Microelectron Eng 98:405–408. https://doi.org/10.1016/j.mee.2012.05.033

    Article  Google Scholar 

  8. Eun Y, Choi J, Lee JI et al (2013) Reversible and continuous latching using a carbon internanotube interface. ACS Appl Mater Interfaces 5:7465–7469. https://doi.org/10.1021/am401777u

    Article  Google Scholar 

  9. Choi J, Eun Y, Kim J (2014) Investigation of interfacial adhesion between the top ends of carbon nanotubes. ACS Appl Mater Interfaces 6:6598–6605. https://doi.org/10.1021/am500252s

    Article  Google Scholar 

  10. Choi J, Pyo S, Baek DH et al (2014) Thickness-, alignment- and defect-tunable growth of carbon nanotube arrays using designed mechanical loads. Carbon N Y 66:126–133. https://doi.org/10.1016/j.carbon.2013.08.050

    Article  Google Scholar 

  11. Geim AK, Novoselov KS (2010) The rise of graphene. Nanoscience and technology: a collection of reviews from nature journals. World Scientific, Singapore, pp 11–19

    Google Scholar 

  12. Chang H, Wu H (2013) Graphene-based nanomaterials: Synthesis, properties, and optical and optoelectronic applications. Adv Funct Mater 23:1984–1997. https://doi.org/10.1002/adfm.201202460

    Article  Google Scholar 

  13. Schwierz F (2010) Graphene transistors. Nat Nanotechnol 5:487–496. https://doi.org/10.1038/nnano.2010.89

    Article  Google Scholar 

  14. Kim KS, Zhao Y, Jang H et al (2009) Large-scale pattern growth of graphene films for stretchable transparent electrodes. Nature 457:706–710. https://doi.org/10.1038/nature07719

    Article  Google Scholar 

  15. Yu L, Shearer C, Shapter J (2016) Recent development of carbon nanotube transparent conductive films. Chem Rev 116:13413–13453. https://doi.org/10.1021/acs.chemrev.6b00179

    Article  Google Scholar 

  16. Sun DM, Liu C, Ren WC, Cheng HM (2013) A review of carbon nanotube- and graphene-based flexible thin-film transistors. Small 9:1188–1205. https://doi.org/10.1002/smll.201203154

    Article  Google Scholar 

  17. Chen K, Gao W, Emaminejad S et al (2016) Printed Carbon Nanotube Electronics and Sensor Systems. Adv Mater 28:4397–4414. https://doi.org/10.1002/adma.201504958

    Article  Google Scholar 

  18. Wang C, Xia K, Wang H et al (2019) Advanced carbon for flexible and wearable electronics. Adv Mater 31:1–37. https://doi.org/10.1002/adma.201801072

    Article  Google Scholar 

  19. Jung Y, Jung K, Park B et al (2019) Wearable piezoresistive strain sensor based on graphene-coated three-dimensional micro-porous PDMS sponge. Micro Nano Syst Lett 7:20. https://doi.org/10.1186/s40486-019-0097-2

    Article  Google Scholar 

  20. Kong L, Chen W (2014) Carbon nanotube and graphene-based bioinspired electrochemical actuators. Adv Mater 26:1025–1043. https://doi.org/10.1002/adma.201303432

    Article  Google Scholar 

  21. Yu WJ, Lee SY, Chae SH et al (2011) Small hysteresis nanocarbon-based integrated circuits on flexible and transparent plastic substrate. Nano Lett 11:1344–1350. https://doi.org/10.1021/nl104488z

    Article  Google Scholar 

  22. Zhu Y, Li L, Zhang C et al (2012) A seamless three-dimensional carbon nanotube graphene hybrid material. Nat Commun 3:1225–1227. https://doi.org/10.1038/ncomms2234

    Article  Google Scholar 

  23. Pyo S, Kim W, Il JH et al (2017) Heterogeneous integration of carbon-nanotube–graphene for high-performance, flexible, and transparent photodetectors. Small 13:1700918. https://doi.org/10.1002/smll.201700918

    Article  Google Scholar 

  24. Pyo S, Choi J, Kim J (2019) A fully transparent, flexible, sensitive, and visible-blind ultraviolet sensor based on carbon nanotube-graphene hybrid. Adv Electron Mater 5:1800737. https://doi.org/10.1002/aelm.201800737

    Article  Google Scholar 

  25. Kumar V, Lee G, Singh K et al (2020) Structure-property relationship in silicone rubber nanocomposites reinforced with carbon nanomaterials for sensors and actuators. Sensors Actuators, A Phys 303:111712. https://doi.org/10.1016/j.sna.2019.111712

    Article  Google Scholar 

  26. Yan Z, Peng Z, Casillas G et al (2014) Rebar graphene. ACS Nano 8:5061–5068. https://doi.org/10.1021/nn501132n

    Article  Google Scholar 

  27. Zhao J, Luo J, Zhou Z et al (2021) Novel multi-walled carbon nanotubes-embedded laser-induced graphene in crosslinked architecture for highly responsive asymmetric pressure sensor. Sensors Actuators, A Phys 323:112658. https://doi.org/10.1016/j.sna.2021.112658

    Article  Google Scholar 

  28. He Y, Wu D, Zhou M et al (2021) Wearable strain sensors based on a porous polydimethylsiloxane hybrid with carbon nanotubes and graphene. ACS Appl Mater Interfaces 13:15572–15583. https://doi.org/10.1021/acsami.0c22823

    Article  Google Scholar 

  29. Wang W, Xiang C, Zhu Q et al (2018) Multistimulus responsive actuator with GO and carbon nanotube/PDMS bilayer structure for flexible and smart devices. ACS Appl Mater Interfaces 10:27215–27223. https://doi.org/10.1021/acsami.8b08554

    Article  Google Scholar 

  30. Kim J, Bae S, Kotal M et al (2017) Soft but powerful artificial muscles based on 3D graphene–CNT–Ni Heteronanostructures. Small 13:1701314. https://doi.org/10.1002/smll.201701314

    Article  Google Scholar 

  31. Kim T, Park J, Sohn J et al (2016) Bioinspired, highly stretchable, and Conductive dry Adhesives based on 1D–2D hybrid carbon nanocomposites for All-in-One ECG electrodes. ACS Nano 10:4770–4778. https://doi.org/10.1021/acsnano.6b01355

    Article  Google Scholar 

  32. Hossain MM, Islam MA, Shima H et al (2017) Alignment of carbon nanotubes in carbon nanotube fibers through nanoparticles: a route for controlling mechanical and electrical properties. ACS Appl Mater Interfaces 9:5530–5542. https://doi.org/10.1021/ACSAMI.6B12869/ASSET/IMAGES/AM-2016-12869V_M004.GIF

    Article  Google Scholar 

  33. Wernik JM, Meguid SA (2014) On the mechanical characterization of carbon nanotube reinforced epoxy adhesives. Mater Des 59:19–32. https://doi.org/10.1016/J.MATDES.2014.02.034

    Article  Google Scholar 

  34. Lu X, Hiremath N, Hong K et al (2017) Improving mechanical properties of carbon nanotube fibers through simultaneous solid-state cycloaddition and crosslinking. Nanotechnology. https://doi.org/10.1088/1361-6528/AA6223

    Article  Google Scholar 

  35. Zhang X, Li Q (2010) Enhancement of friction between carbon nanotubes: An efficient strategy to strengthen fibers. ACS Nano 4:312–316. https://doi.org/10.1021/NN901515J

    Article  Google Scholar 

  36. Lee C, Wei X, Kysar JW, Hone J (2008) Measurement of the elastic properties and intrinsic strength of monolayer graphene. Science 321:385–388. https://doi.org/10.1126/SCIENCE.1157996/SUPPL_FILE/LEE-SOM.PDF

    Article  Google Scholar 

  37. Ranjbartoreh AR, Wang B, Shen X, Wang G (2011) Advanced mechanical properties of graphene paper. J Appl Phys 109:014306. https://doi.org/10.1063/1.3528213

    Article  Google Scholar 

  38. Sheng L, Wei T, Liang Y et al (2017) Ultra-high toughness all graphene fibers derived from synergetic effect of interconnected graphene ribbons and graphene sheets. Carbon N Y 120:17–22. https://doi.org/10.1016/J.CARBON.2017.05.033

    Article  Google Scholar 

  39. Kinloch IA, Suhr J, Lou J et al (2018) Composites with carbon nanotubes and graphene: an outlook. Science 362:547–553. https://doi.org/10.1126/science.aat7439

    Article  Google Scholar 

  40. Lin X, Liu P, Wei Y et al (2013) (2013) Development of an ultra-thin film comprised of a graphene membrane and carbon nanotube vein support. Nat Commun 41(4):1–7. https://doi.org/10.1038/ncomms3920

    Article  Google Scholar 

  41. Kumar A, Sharma K, Dixit AR (2021) A review on the mechanical properties of polymer composites reinforced by carbon nanotubes and graphene. Carbon Lett 31:149–165. https://doi.org/10.1007/s42823-020-00161-x

    Article  Google Scholar 

  42. Shukla MK, Sharma K (2019) Effect of functionalized graphene/CNT ratio on the synergetic enhancement of mechanical and thermal properties of epoxy hybrid composite. Mater Res Express 6:085318. https://doi.org/10.1088/2053-1591/AB1CC2

    Article  Google Scholar 

  43. Chatterjee S, Nafezarefi F, Tai NH et al (2012) Size and synergy effects of nanofiller hybrids including graphene nanoplatelets and carbon nanotubes in mechanical properties of epoxy composites. Carbon N Y 50:5380–5386. https://doi.org/10.1016/J.CARBON.2012.07.021

    Article  Google Scholar 

  44. Li H, Yang L, Weng G et al (2015) Toughening rubbers with a hybrid filler network of graphene and carbon nanotubes. J Mater Chem A 3:22385–22392. https://doi.org/10.1039/C5TA05836H

    Article  Google Scholar 

  45. Oh JY, Jun GH, Jin S et al (2016) Enhanced Electrical Networks of Stretchable Conductors with Small Fraction of Carbon Nanotube/Graphene Hybrid Fillers. ACS Appl Mater Interfaces 8:3319–3325. https://doi.org/10.1021/acsami.5b11205

    Article  Google Scholar 

  46. Sun DM, Timmermans MY, Tian Y et al (2011) Flexible high-performance carbon nanotube integrated circuits. Nat Nanotechnol 6:156–161. https://doi.org/10.1038/nnano.2011.1

    Article  Google Scholar 

  47. Liang X, Cheng Q (2018) Synergistic reinforcing effect from graphene and carbon nanotubes. Compos Commun 10:122–128. https://doi.org/10.1016/j.coco.2018.09.002

    Article  Google Scholar 

  48. Peng L, Feng Y, Lv P et al (2012) Transparent, conductive, and flexible multiwalled carbon nanotube/graphene hybrid electrodes with two three-dimensional microstructures. J Phys Chem C 116:4970–4978. https://doi.org/10.1021/jp209180j

    Article  Google Scholar 

  49. Nguyen DD, Tai NH, Chen SY, Chueh YL (2012) Controlled growth of carbon nanotube-graphene hybrid materials for flexible and transparent conductors and electron field emitters. Nanoscale 4:632–638. https://doi.org/10.1039/c1nr11328c

    Article  Google Scholar 

  50. Chen M, Zhang L, Duan S et al (2014) Highly stretchable conductors integrated with a conductive carbon nanotube/graphene network and 3D porous poly (dimethylsiloxane). Adv Funct Mater 24:7548–7556. https://doi.org/10.1002/adfm.201401886

    Article  Google Scholar 

  51. Foroughi J, Spinks GM, Antiohos D et al (2014) Highly conductive carbon nanotube-graphene hybrid yarn. Adv Funct Mater 24:5859–5865. https://doi.org/10.1002/adfm.201401412

    Article  Google Scholar 

  52. Barshutina MN, Volkov VS, Arsenin AV et al (2021) Biocompatible, electroconductive, and highly stretchable hybrid silicone composites based on few-layer graphene and cnts. Nanomaterials. https://doi.org/10.3390/nano11051143

    Article  Google Scholar 

  53. Jang S, Jang H, Lee Y et al (2010) Flexible, transparent single-walled carbon nanotube transistors with grapheme electrodes. Nanotechnology 21:425201. https://doi.org/10.1088/0957-4484/21/42/425201

    Article  Google Scholar 

  54. Chae SH, Yu WJ, Bae JJ et al (2013) Transferred wrinkled Al2O3 for highly stretchable and transparent graphene–carbon nanotube transistors. Nat Mater 12:403–409. https://doi.org/10.1038/nmat3572

    Article  Google Scholar 

  55. Kim SH, Song W, Jung MW et al (2014) Carbon nanotube and graphene hybrid thin film for transparent electrodes and field effect transistors. Adv Mater 26:4247–4252. https://doi.org/10.1002/adma.201400463

    Article  Google Scholar 

  56. Shi E, Li H, Yang L et al (2015) Carbon nanotube network embroidered graphene films for monolithic all-carbon electronics. Adv Mater 27:682–688. https://doi.org/10.1002/adma.201403722

    Article  Google Scholar 

  57. Yang L, Zhao Y, Xu W et al (2017) Highly crumpled all-carbon transistors for brain activity recording. Nano Lett 17:71–77. https://doi.org/10.1021/acs.nanolett.6b03356

    Article  Google Scholar 

  58. Zhang Y, Huang Q, Huang W, Zhang M (2021) Ultra-flexible high-k transparent integratable fully-carbon-based capacitor arrays for sharp-switching transistors. Carbon N Y 182:117–123. https://doi.org/10.1016/j.carbon.2021.05.065

    Article  Google Scholar 

  59. Jian M, Xia K, Wang Q et al (2017) Flexible and highly sensitive pressure sensors based on bionic hierarchical structures. Adv Funct Mater. https://doi.org/10.1002/adfm.201606066

    Article  Google Scholar 

  60. Yao D, Tang Z, Zhang L et al (2021) Gas-permeable and highly sensitive, washable and wearable strain sensors based on graphene/carbon nanotubes hybrids e-textile. Compos Part A Appl Sci Manuf 149:106556. https://doi.org/10.1016/j.compositesa.2021.106556

    Article  Google Scholar 

  61. Chen X, Zhang X, Xiang D et al (2022) 3D printed high-performance spider web-like flexible strain sensors with directional strain recognition based on conductive polymer composites. Mater Lett 306:130935. https://doi.org/10.1016/j.matlet.2021.130935

    Article  Google Scholar 

  62. Pyo S, Choi J, Kim J (2018) Flexible, transparent, sensitive, and crosstalk-free capacitive tactile sensor array based on graphene electrodes and air dielectric. Adv Electron Mater 4:1700427

    Article  Google Scholar 

  63. Pyo S, Lee J, Kim W et al (2019) Multi-layered, hierarchical fabric-based tactile sensors with high sensitivity and linearity in ultrawide pressure range. Adv Funct Mater 29:1–9. https://doi.org/10.1002/adfm.201902484

    Article  Google Scholar 

  64. Lee J, Pyo S, Kwon D-S et al (2019) Ultrasensitive strain sensor based on separation of overlapped carbon nanotubes. Small. https://doi.org/10.1002/smll.201805120

    Article  Google Scholar 

  65. Bae K, Jeong J, Choi J et al (2021) Large-Area, Crosstalk-Free, Flexible Tactile Sensor Matrix Pixelated by Mesh Layers. ACS Appl Mater Interfaces 13:12259–12267. https://doi.org/10.1021/acsami.0c21671

    Article  Google Scholar 

  66. Oh D, Seo J, Kim HG et al (2022) Multi-height micropyramids based pressure sensor with tunable sensing properties for robotics and step tracking applications. Micro Nano Syst Lett 10:7. https://doi.org/10.1186/s40486-022-00149-4

    Article  Google Scholar 

  67. de Oliveira JG, Muhammad T, Kim S (2020) A silver nanowire-based flexible pressure sensor to measure the non-nutritive sucking power of neonates. Micro Nano Syst Lett 8:18. https://doi.org/10.1186/s40486-020-00121-0

    Article  Google Scholar 

  68. Pyo S, Lee J, Bae K et al (2021) Recent progress in flexible tactile sensors for human-interactive systems: from sensors to advanced applications. Adv Mater 33:1–26. https://doi.org/10.1002/adma.202005902

    Article  Google Scholar 

  69. Amjadi M, Pichitpajongkit A, Lee S et al (2014) Highly stretchable and sensitive strain sensor based on silver nanowire-elastomer nanocomposite. ACS Nano 8:5154–5163. https://doi.org/10.1021/nn501204t

    Article  Google Scholar 

  70. Yan C, Wang J, Kang W et al (2014) Highly stretchable piezoresistive graphene-nanocellulose nanopaper for strain sensors. Adv Mater 26:2022–2027. https://doi.org/10.1002/adma.201304742

    Article  Google Scholar 

  71. Zhou J, Gu Y, Fei P et al (2008) Flexible piezotronic strain sensor. Nano Lett 8:3035–3040. https://doi.org/10.1021/nl802367t

    Article  Google Scholar 

  72. Pyo S, Lee JI, Kim MO et al (2019) Polymer-based flexible and multi-directional tactile sensor with multiple nicr piezoresistors. Micro Nano Syst Lett 7:1–8. https://doi.org/10.1186/s40486-019-0085-6

    Article  Google Scholar 

  73. Zheng S, Wu X, Huang Y et al (2020) Multifunctional and highly sensitive piezoresistive sensing textile based on a hierarchical architecture. Compos Sci Technol 197:108255. https://doi.org/10.1016/j.compscitech.2020.108255

    Article  Google Scholar 

  74. Shajari S, Mahmoodi M, Rajabian M et al (2020) Highly sensitive and stretchable carbon nanotube/fuoroelastomer nanocomposite with a double-percolated network for wearable electronics. Adv Electron Mater 6:1–13. https://doi.org/10.1002/aelm.201901067

    Article  Google Scholar 

  75. Tian H, Shu Y, Wang XF et al (2015) A graphene-based resistive pressure sensor with record-high sensitivity in a wide pressure range. Sci Rep 5:1–6. https://doi.org/10.1038/srep08603

    Article  Google Scholar 

  76. Wang L, Choi W, Yoo K et al (2020) Stretchable carbon nanotube dilatometer for in situ swelling detection of lithium-ion batteries. ACS Appl Energy Mater 3:3637–3644. https://doi.org/10.1021/acsaem.0c00114

    Article  Google Scholar 

  77. Afroj S, Tan S, Abdelkader AM et al (2020) Highly conductive, scalable, and machine washable graphene-based e-textiles for multifunctional wearable electronic applications. Adv Funct Mater. https://doi.org/10.1002/adfm.202000293

    Article  Google Scholar 

  78. Xie X, Huang H, Zhu J et al (2020) A spirally layered carbon nanotube-graphene/polyurethane composite yarn for highly sensitive and stretchable strain sensor. Compos Part A Appl Sci Manuf 135:105932. https://doi.org/10.1016/j.compositesa.2020.105932

    Article  Google Scholar 

  79. Abshirini M, Charara M, Liu Y et al (2018) 3D printing of highly stretchable strain sensors based on carbon nanotube nanocomposites. Adv Eng Mater 20:1–9. https://doi.org/10.1002/adem.201800425

    Article  Google Scholar 

  80. Chen Y, Pötschke P, Pionteck J et al (2018) Smart cellulose/graphene composites fabricated by: In situ chemical reduction of graphene oxide for multiple sensing applications. J Mater Chem A 6:7777–7785. https://doi.org/10.1039/c8ta00618k

    Article  Google Scholar 

  81. Park J, Lee Y, Hong J et al (2014) Tactile-direction-sensitive and stretchable electronic skins based on human-skin-inspired interlocked microstructures. ACS Nano 8:12020–12029. https://doi.org/10.1021/nn505953t

    Article  Google Scholar 

  82. Yeom C, Chen K, Kiriya D et al (2015) Large-area compliant tactile sensors using printed carbon nanotube active-matrix backplanes. Adv Mater 27:1561–1566. https://doi.org/10.1002/adma.201404850

    Article  Google Scholar 

  83. Bin YH, Ge J, Wang CF et al (2013) A flexible and highly pressure-sensitive graphene-polyurethane sponge based on fractured microstructure design. Adv Mater 25:6692–6698. https://doi.org/10.1002/adma.201303041

    Article  Google Scholar 

  84. Hou C, Wang H, Zhang Q et al (2014) Highly conductive, flexible, and compressible all-graphene passive electronic skin for sensing human touch. Adv Mater 26:5018–5024. https://doi.org/10.1002/adma.201401367

    Article  Google Scholar 

  85. Song Q, Ye F, Yin X et al (2017) Carbon nanotube–multilayered graphene edge plane core–shell hybrid foams for ultrahigh-performance electromagnetic-interference shielding. Adv Mater 29:1–8. https://doi.org/10.1002/adma.201701583

    Article  Google Scholar 

  86. Li J, Li W, Huang W et al (2017) Fabrication of highly reinforced and compressible graphene/carbon nanotube hybrid foams via a facile self-assembly process for application as strain sensors and beyond. J Mater Chem C 5:2723–2730. https://doi.org/10.1039/c7tc00219j

    Article  Google Scholar 

  87. Kuang J, Dai Z, Liu L et al (2015) Synergistic effects from graphene and carbon nanotubes endow ordered hierarchical structure foams with a combination of compressibility, super-elasticity and stability and potential application as pressure sensors. Nanoscale 7:9252–9260. https://doi.org/10.1039/c5nr00841g

    Article  Google Scholar 

  88. Afroze JD, Tong L, Abden MJ et al (2021) Hierarchical honeycomb graphene aerogels reinforced by carbon nanotubes with multifunctional mechanical and electrical properties. Carbon N Y 175:312–321. https://doi.org/10.1016/j.carbon.2021.01.002

    Article  Google Scholar 

  89. Liu K, Yao Y, Lv T et al (2020) Textile-like electrodes of seamless graphene/nanotubes for wearable and stretchable supercapacitors. J Power Sources 446:227355. https://doi.org/10.1016/j.jpowsour.2019.227355

    Article  Google Scholar 

  90. Shi J, Li X, Cheng H et al (2016) Graphene reinforced carbon nanotube networks for wearable strain sensors. Adv Funct Mater 26:2078–2084. https://doi.org/10.1002/adfm.201504804

    Article  Google Scholar 

  91. Tran MT, Tung TT, Sachan A et al (2020) 3D sprayed polyurethane functionalized graphene / carbon nanotubes hybrid architectures to enhance the piezo-resistive response of quantum resistive pressure sensors. Carbon N Y 168:564–579. https://doi.org/10.1016/j.carbon.2020.05.086

    Article  Google Scholar 

  92. Li Y, Ai Q, Mao L et al (2021) Hybrid strategy of graphene/carbon nanotube hierarchical networks for highly sensitive, flexible wearable strain sensors. Sci Rep 11:21006. https://doi.org/10.1038/s41598-021-00307-5

    Article  Google Scholar 

  93. Lu L, Liu J, Hu Y et al (2012) Highly stable air working bimorph actuator based on a graphene nanosheet/carbon nanotube hybrid electrode. Adv Mater 24:4317–4321. https://doi.org/10.1002/adma.201201320

    Article  Google Scholar 

  94. Qiao J, Di J, Zhou S et al (2018) Large-Stroke Electrochemical Carbon Nanotube/Graphene Hybrid Yarn Muscles. Small 14:1801883. https://doi.org/10.1002/smll.201801883

    Article  Google Scholar 

  95. Yang W, Choi H, Choi S et al (2012) Carbon nanotube–graphene composite for ionic polymer actuators. Smart Mater Struct 21:055012. https://doi.org/10.1088/0964-1726/21/5/055012

    Article  Google Scholar 

  96. Wu G, Li GH, Lan T et al (2014) An interface nanostructured array guided high performance electrochemical actuator. J Mater Chem A 2:16836–16841. https://doi.org/10.1039/C4TA04268A

    Article  Google Scholar 

  97. Hyeon JS, Park JW, Baughman RH, Kim SJ (2019) Electrochemical graphene/carbon nanotube yarn artificial muscles. Sensors Actuators B Chem 286:237–242. https://doi.org/10.1016/j.snb.2019.01.140

    Article  Google Scholar 

  98. Wang R, Sun J, Gao L et al (2011) Fibrous nanocomposites of carbon nanotubes and graphene-oxide with synergetic mechanical and actuative performance. Chem Commun 47:8650. https://doi.org/10.1039/c1cc11488c

    Article  Google Scholar 

Download references

Acknowledgements

Not applicable.

Funding

This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Science, ICT, and Future Planning (2022R1A2C4001577) and by the Korean government (MSIT) (2020R1G1A1099812). This research was also supported by the Korea Institute of Industrial Technology as “In-line real-time monitoring system in Lens manufacturing (KITECH JH-22–0018)” and by the Institute Project of the Korea Institute of Machinery and Materials (NK238E).

Author information

Authors and Affiliations

Authors

Contributions

All authors contributed to writing and editing the manuscript. All authors read and approved the final manuscript.

Corresponding authors

Correspondence to Jaesam Sim, Kwanoh Kim or Jungwook Choi.

Ethics declarations

Competing interests

The authors declare that they have no competing interests.

Additional information

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Rights and permissions

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Pyo, S., Eun, Y., Sim, J. et al. Carbon nanotube-graphene hybrids for soft electronics, sensors, and actuators. Micro and Nano Syst Lett 10, 9 (2022). https://doi.org/10.1186/s40486-022-00151-w

Download citation

  • Received:

  • Accepted:

  • Published:

  • DOI: https://doi.org/10.1186/s40486-022-00151-w

Keywords