Sun et al.

Microsystems & Nanoengineering (2022)8:37

https://doi.org/10.1038/s41378-022-00363-5
Microsystems & Nanoengineering
www.nature.com/micronano

ARTICLE Open Access

Origami-inspired folding assembly of dielectric

elastomers for programmable soft robots
Yanhua Sun1,2, Dengfeng Li3, Mengge Wu1,3, Yale Yang1,2, Jingyou Su3, Tszhung Wong3, Kangming Xu2, Ying Li2,
Lu Li2 ✉, Xinge Yu 3 ✉ and Junsheng Yu 1 ✉

Abstract
Origami has become an optimal methodological choice for creating complex three-dimensional (3D) structures
and soft robots. The simple and low-cost origami-inspired folding assembly provides a new method for developing
3D soft robots, which is ideal for future intelligent robotic systems. Here, we present a series of materials, structural
designs, and fabrication methods for developing independent, electrically controlled origami 3D soft robots for
walking and soft manipulators. The 3D soft robots are based on soft actuators, which are multilayer structures with
a dielectric elastomer (DE) film as the deformation layer and a laser-cut PET film as the supporting flexible frame.
The triangular and rectangular design of the soft actuators allows them to be easily assembled into crawling soft
robots and pyramidal- and square-shaped 3D structures. The crawling robot exhibits very stable crawling behaviors
and can carry loads while walking. Inspired by origami folding, the pyramidal and square-shaped 3D soft robots
exhibit programmable out-of-plane deformations and easy switching between two-dimensional (2D) and 3D
structures. The electrically controllable origami deformation allows the 3D soft robots to be used as soft
manipulators for grasping and precisely locking 3D objects. This work proves that origami-inspired fold-based
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assembly of DE actuators is a good reference for the development of soft actuators and future intelligent
multifunctional soft robots.

Introduction as an operator in medical robotic systems during clinical

Soft robots have irreplaceable advantages in mechanical surgeries8–10. In addition, soft actuators have been widely
and biomedical engineering1–4. Because of their soft used as manipulators in large demission robots11. In
bodies, soft robots can adapt their body shape to complex practice, to increase their maneuverability for robotic
physical environments and walk through narrow passages walking, medical manipulation, and three-dimensional
that rigid robots cannot5,6. The soft nature of their bodies (3D) object grasping, it is crucial to build soft robots with
also prevents sharp injuries to objects they touch, allowing flexible and variable 3D structures.
them to enter the human body for drug transport7 or act Currently, 3D soft robots are typically manufactured
through 3D printing and assembly with small actua-
tors12,13. Compared to 3D shapes, 2D shapes are more
Correspondence: Lu Li (lli@cqwu.edu.cn) or Xinge Yu (xingeyu@cityu.edu.hk) or space-efficient in terms of their spatial dimension14. Thus,
Junsheng Yu (jsyu@uestc.edu.cn)
1 origami-inspired 3D soft robot construction, derived from
State Key Laboratory of Electronic Thin Films and Integrated Devices, School
of Optoelectronic Science and Engineering, University of Electronic Science an inherent simplified and low-cost folding-based
and Technology of China (UESTC), Chengdu 610054, People’s Republic of assembly technique, is a good strategy due to its ability to
China
2 perform out-of-plane deformations for 3D structure
Chongqing Key Laboratory of Materials Surface & Interface Science,
Chongqing Co-Innovation Center for Micro/Nano Optoelectronic Materials and construction and to switch between 2D and 3D15–19. The
Devices, Micro/Nano Optoelectronic Materials and Devices International detailed advantages of origami robots are as follows: (i)
Science and Technology Cooperation Base of China, School of Materials
Soft, simple preparation process, and low cost. Compared
Science and Engineering, Chongqing University of Arts and Sciences,
Chongqing 402160, People’s Republic of China with traditional robots, origami robots have a more
Full list of author information is available at the end of the article

© The Author(s) 2022

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Sun et al. Microsystems & Nanoengineering (2022)8:37 Page 2 of 11

streamlined structure, eliminating many complex trans- controlled automatically33,34. When combined with
mission gear structures and requiring less production intelligent sensing systems35–38, soft and durable robotic
material. (ii) High degree of collapse and space efficiency. systems can assist humans with long-term tasks through
Origami robots have less transportation and storage human–machine interactions39–43. Electrical actuation
requirements since they are capable of converting from allows robots to be precisely controlled in various envir-
two- to three-dimensional shapes. (iii) Scalability and onments as long as driving programs are established. At
various applications. The diversity of the origami method present, nearly all functional intelligent robots are elec-
enables robots to be highly scalable in terms of structure trically driven due to the advantages of electrical actuation
and functionality. However, more novel designs and in terms of handling precision. In recent years, an
research on origami robots are urgently needed to achieve increasing number of soft robots have been powered by
complex functionality. electrical energy based on electrothermal44, piezo-
Scientists have developed different types of origami- electric45, and dielectric32 principles. Programmable
inspired soft robots with a variety of materials and electrical actuation, such as independent leg control of
actuation methods, each with specific mechanical multilegged robots46 and segmented control of single-
manipulation functions and movement styles20. For body robots47, enables soft robots to move and function in
instance, a battery-free miniature origami robotic arm various ways. In contrast, dielectric elastomers have rarely
based on origami actuation was developed with shape been combined with origami design for electrically actu-
memory alloys and has been used for arm orientation ated paper-folding robots. For the first time, we intro-
control and object grasping21. 2D nanomaterials, such as duced VHB4910 elastomers into origami-inspired robots
MXene22 and graphene23,24, have been used as functional because of their outstanding advantages, such as their
layers in soft actuators and robots, with light fields typi- quick response time and superior resilience.
cally used as an actuation method for 3D structural In this work, we combined origami technology and
control, programmable actuation, movements, and var- electronically controlled actuators to develop program-
ious artistic displays. A new triple-layer dual-chip actuator mable 3D soft robots that can reversibly switch between
based on photothermal actuation was successfully used to 2D and 3D structures. These soft robots rely on a variety
assemble a fast crawling soft robot and a powerful of programming controls to assemble multiple origami
mechanical clamp25. In addition, 3D structures fabricated structures and to perform functions such as walking,
by the kirigami technique in phase-change liquid crystal grasping, and locking objects. These electrical actuators
elastomers are a new type of robotic technology, with light are composed of a pre-stretched dielectric elastomer
beams serving as the actuation source to control motion with conductive carbon grease on both sides, which
and steer the movement direction in 2D26. For the active functions as a stretchable conductive electrode, and a
folding assembly to interchange between 2D and 3D and laser-cut polyethylene terephthalate (PET) film, which
repeatably deform, the actuator must be a soft deforma- functions as a flexible support frame. By designing the
tion material. In addition to the materials mentioned shape of the PET frame, a wide range of 3D origami
above, dielectric elastomers are an excellent choice due to assemblies can be produced in a cost-effective and easy-
their relatively large actuation force with large deforma- to-process manner. These origami-inspired soft robots
tions27,28. Moreover, dielectric elastomers are actuated by based on electronically controlled dielectric elastomers
electrical energy, which is convenient for future integra- perform well in terms of movement, assembly, and
tion with robotic systems. function, serving as good models for future 3D soft
Soft robots should be developed with intelligent sensing robot construction.
systems. A class of actuators that combine tensile and
torsional deformation to achieve sensing and various Results and discussion
motions has been investigated29. Humidity-driven fiber Figure 1 shows the fabrication and actuation principles
muscles detect changes in external humidity while twist- of the origami-inspired soft actuators. As shown in Fig. 1a,
ing and stretching30. Twisted elastomeric fibers fitted with the planar 2D and spatial 3D structures of the origami-
carbon nanotube sheaths and contact clasps for sensing inspired soft robot can be easily switched by four soft
can monitor resistance signals during electrothermally actuators. The soft actuator consists of a dielectric elas-
driven twisting31. In addition, a spiral fiber crawling robot, tomer (DE), which acts as the active deformation layer,
which simulates the musculoskeletal structure of a human and a laser-cut PET film, which acts as the flexible sup-
arm, can detect body deformations while crawling with port frame. To fabricate the soft actuator, a VHB4910 DE
resistive strain sensors32. These findings have been used film was first prestretched to 400% × 400% with a self-
to develop intelligent textiles and soft robots that can designed, precisely adjustable stretching tool (Fig. 1b and
perceive, interact with and adapt to environmental sti- Fig. S1). The thickness of the DE film was reduced from
muli. Future intelligent robotic systems will inevitably be 0.93 to 0.04 mm (Fig. S2). The stretched DE film was fixed
Sun et al. Microsystems & Nanoengineering (2022)8:37 Page 3 of 11

a b

Pre-stretch VHB4910 Fix with acrylic frame Remove retainer clip

2D , planar

Origami
3D , spatial

Attach PET reinforcement Paint carbon grease Attach PET substrate

Paint carbon grease The actuator

c e
OFF State

76° 94° 106°

1 cm
ON State

V
112° 115° 130°

d 180
Experimental data
150 Linear fitting
 (degree)

120
137° 144° 150°

90
R

60

11.5 12.0 12.5 13.0 13.5

R (mm)

Fig. 1 Fabrication and actuation principles of origami soft actuators with dielectric elastomers. a Schematic diagram of the origami-inspired
soft robots. b Flow chart of the fabrication process for the soft actuator. After release, an actuator with a certain initial bending angle was obtained.
c Schematic diagram of the actuation principle and the expanded layered structure of the soft actuator with a dielectric layer (VHB4910), a
reinforcement layer (PET film with a thickness of 0.25 mm), and a flexible substrate (PET film with a thickness of 0.1 mm). d Relationship between the
semicircular radius of the actuation region with the dielectric layer and the bending angle. e Optical images of actuators with different semicircular
radii in the actuation region with different bending angles

to an acrylic frame, and a laser-cut 0.1 mm-thick PET film film in the same position as the reinforcement frame. To
with a circular hole was pasted on it as a flexible frame. apply an actuation voltage to the DE film, conductive
Then, two laser-cut 0.25 mm thick PET films with specific carbon grease was painted on both sides of the middle
semicircular radii were pasted on the other side of the DE round area, which functioned as the actuation region.
Sun et al. Microsystems & Nanoengineering (2022)8:37 Page 4 of 11

A thin wire was placed at the edge of the carbon grease tended to straighten during the actuation process.
electrode, and the soft actuator was actuated by a voltage Therefore, we defined this 120° soft actuator as the tri-
source. After cutting the DE film along the outer edge of angular actuator. Similarly, we used a 90° soft actuator
the PET film and releasing it, a soft actuator with an with an 11.75 mm radius as a rectangular actuator for the
original saddle shape was acquired48. 3D square soft robot. The actuation and deformation
When a voltage is applied to the actuator, charge behaviors of these two soft actuators were critical for the
accumulates on the flexible electrode surfaces on both performance of the 3D soft robots, and the electrical test
sides of the film, as shown in Fig. 1c. When the accu- results are summarized in Fig. 2. After the triangular soft
mulation reaches a certain threshold, the electrostatic actuator was connected to the power supply via thin
force on the positive and negative electrode surfaces wires, the actuation voltage was gradually increased from
squeezes the middle DE film layer, causing it to expand in 0 to 5.52 kV in steps of 0.5 kV. The results show that the
all directions. As the DE film expands in the actuation triangular soft actuator deformed to a horizontal state at
area, the shape of the actuator is no longer in equilibrium, 5.52 kV with a bending angle of only 3° (Fig. 2a). The
resulting in bending and braking effects49. The braking relationship between the bending angle and the actuation
effect is not only voltage-dependent but also related to the voltage is shown in Fig. 2e. The triangular soft actuator
thickness and elastic modulus of the elastomer material. also exhibited excellent cycling consistency. The cycling
Prestretching can greatly reduce the thickness of the DE test results in Fig. 2b, f and Movie S1 show that the soft
film, allowing for braking deformation with a low actua- actuators maintained their original shape after 100 cycles.
tion voltage. In this work, a VHB4910 elastomer film This indicates that soft actuators and 3D soft robots with
(3 M, USA) was used as the actuator due to its high tensile DE films have a stable and reproducible performance
rate, low elastic modulus, and low cost50. during repeated use. For the rectangular actuator, an
As shown in Fig. 1b, e, the actuator exhibits an original excellent deformation performance was also achieved, as
bending angle in its natural state. When an external vol- shown in Fig. 2c–f and Movie S2. Under an actuation
tage is applied, the actuator tends to straighten its body, voltage of 4.09 kV, the rectangular soft actuator deformed
reducing the angle between the actuator and the hor- to a horizontal state with a bending angle of only 1°. After
izontal line, which we define as the bending angle of the 100 cycles, there was no significant difference in the shape
actuator. The original bending angle is crucial for con- of the actuator. We also tested the life cycle of six straight-
structing 3D origami soft robots. For example, a 90° soft edge DE actuators with 90° angles and found that the
actuator can be used to build square 3D origami robots, robots fully recovered to their initial angle within the first
while a 120° soft actuator is the best choice for building 500 cycles. As the number of cycles increased, the
pyramidal 3D origami robots. The original bending angle recovery characteristics of the DE actuators worsened due
could be adjusted by the area of the actuation region. to the bending fatigue of the PET substrates. After 5000
Therefore, we investigated the relationship between the cycles, these DE actuators only recovered to an angle of
bending angle and the semicircular radius of the actuation 60°, while they were expected to recover to 90°. In addi-
region. A set of soft actuators with two semicircular radii tion, the mechanical properties of both actuators were
ranging from 11.5 to 13.5 mm spaced 6 mm apart were investigated by using micromechanical sensors to mea-
fabricated. The obtained soft actuators with different sure the actuator’s force at different voltages (Fig. S4). The
original bending angles are shown in Fig. 1e. The linear result showed that a 3.61 mN force was generated when
relationship between the bending degree and the radius is the triangular soft actuator was actuated by a voltage of
summarized in Fig. 1d. A soft actuator with a radius of 5.52 kV. The rectangular actuator only exhibited a force of
11.75 mm was bent at approximately 90°, while an 2.16 mN under a voltage of 4.09 kV due to the relatively
actuator with a radius of 12.5 mm was bent at approxi- small change in the bending angle.
mately 120°. By adjusting the radius of the actuation In nature, many animals crawl or walk by deforming
region, soft actuators with specific bending angles could and actuating their bodies or joints. The soft actuators in
be easily acquired. This result provides strong support for this work are well suited for use as an artificial muscle in a
the subsequent assembly experiments with crawling crawling robot. Therefore, we designed a 3D crawling soft
robots and 3D folding assemblies with origami-inspired robot with rectangular actuators and studied its walking
soft robots. behavior (Fig. 3). The soft crawling robot has a square
To construct the 3D soft robots, we chose soft actuators body and rectangular bipeds at both ends. Figure S5
with bending angles of 90° and 120° as examples. Figure shows the planar structure design, which included two
S3 presents the planar structure design for these two soft actuation regions with radii of 12.5 mm. The original
actuators. To create a 3D pyramid soft robot, we used a bending angle for the two feet of this soft robot was 120°.
120° soft actuator with a triangular actuation side and a The lengths of the feet and the main body were 40 and
12.5 mm-radius actuation region; the triangular side 60 mm, respectively. Figure 3a shows the crawling
Sun et al. Microsystems & Nanoengineering (2022)8:37 Page 5 of 11

a b
Triangular 0.00 kV 2.05 kV 3.02 kV 1 cycle

118° 110° 97°

117°
1 cm 1 cm

4.01 kV 5.02 kV 5.52 kV 100 cycle

116°
70° 28° 3°

c d
Rectangular 0.00 kV 1.03 kV 2.02 kV 1 cycle

92° 88° 77°

92°
1 cm 1 cm

3.04 kV 4.00 kV 4.09 kV 100 cycle

49° 9° 1° 91°

e f
120 150 Triangular
1 cycle Rectangular 100 cycle
90
 (degree)

 (degree)

100
60

30 50
Triangular
Rectangular
0
0
0 1 2 3 4 5 6 0 10 740 750 760
Voltage (kV) Time (s)

Fig. 2 Study of triangular and rectangular soft actuators. a Photos of the 12.5 mm-radius triangular actuator under different actuation voltages.
b Photos of the triangular actuator after the first and 100th actuation cycles. c Optical images of the 11.75 mm-radius rectangular actuator under
different actuation voltages. d Photos of the rectangular actuator after the first and 100th actuation cycles. e The relationship between the bending
angle and the input voltage for the triangular (blue) and rectangular (orange) actuators. f The stability during 100 actuation cycles for the triangular
(blue) and rectangular (orange) actuators

behaviors of the soft robot at each step, including the foot was stopped, causing it to contract, and the soft robot
actuator’s switching state, the force direction, and the leaned forward, shifting its center of gravity forward again.
displacement direction. By actuating the front and back Finally, the voltage on the rear foot was released, and the
feet separately, the soft robot can move forward on the rear foot contracted and returned to its initial state
sandpaper. Each walking cycle can be separated into four because of the increased friction generated by the front
steps (Fig. 3a and Fig. S6). In the first step, the front foot foot due to the forward shift of the center of gravity.
was actuated against the ground to unfold, and the soft Therefore, the robot’s movement was highly dependent
robot tilted backward. Next, after the front foot com- on the interface friction. The amount of friction generated
pletely unfolded, the rear foot actuated. Due to the on the surface affected the crawling displacement of the
backward shift in the center of gravity, the rear foot soft robot. To further investigate the effect of rough
produced more friction force when it contacted the surfaces on crawling, sandpapers with various grit sizes
ground quickly, causing the soft robot to jump and crawl (P1500, P1000, and P600) were used to study the crawling
forward. Then, the robot’s step stabilized, and its center of speed. The soft robot was actuated by a square-wave
gravity balanced. In the third step, the voltage on the front voltage with a frequency of 0.29 Hz and duty cycle of
Sun et al. Microsystems & Nanoengineering (2022)8:37 Page 6 of 11

a Step 1 Step 2 Step 3 Step 4 Step 5

Volt Off Off Volt Off On Volt On On Volt On Off Volt Off Off

1 cm
P1500 sandpaper 4.3 mm

10.2 mm

f2 f1 f2 f1 f2 f1 f2 f1
P1000

26.4 mm

S S S
P600

b 120
c 40 d 120 Separate actuation
e 4.09
4
Simultaneous actuation

Distance (mm)

Speed (mm/s)
35 3.28
Height (mm)
 (degree)

90 80 3

60 30
40 2 1.71

30 25 1
Front foot Front foot 0
Back foot Back foot
0 20 0
0 1 2 3 0 1 2 3 4 0 5 10 15 20 25 3 4 5
Time (s) Time (s) Time (s) Voltage (kV)

f 1g weights 3.97 mm/s 12.2 mm

1 cm
P600

2g weights 2.80 mm/s 6.2 mm

P600

Fig. 3 Crawling behaviors of the origami-inspired soft robot. a Analysis of the soft robot’s behaviors at each step of the crawling process,
including the actuator’s switching state, the force direction, and the displacement direction. The soft robots walked on sandpaper with different grits,
including P1500, P1000, and P600. b Angle variation of the soft robot’s front and rear feet with time during one motion cycle. c Height variation of
the soft robot’s front and rear foot joints with time during one motion cycle. d Displacement variation with time for the soft robot under separate
and simultaneous actuation. e Crawling speed of the soft robot under different actuation voltages. f Crawling behaviors of the soft robot with
different loads

28.6%. The bandwidth of soft actuators made from front and rear feet generated different friction forces and
VHB4910 elastomers is usually less than 10 Hz due to the crawled to one side during actuation. To verify the
viscoelasticity of VHB elastomers. The results show that superiority of this actuation method, the crawling robot
the average crawling speed of the robot on was also actuated simultaneously at the same voltage for
P600 sandpaper (4.09 mm/s) was nearly 30 times higher comparison (Fig. 3d). When the front and rear feet were
than that on P1500 sandpaper (0.15 mm/s) (Fig. 3a and actuated simultaneously, it was difficult to achieve stable
Movie S3), which indicates that soft robots crawl better on motion in one direction, and the resulting movement was
rough surfaces. In addition, we measured the angle and hesitation in one place (Fig. S7 and Movie S4). In addition
height variations of the front and rear feet of the robot as to the rough sandpaper, we tested the dynamic properties
it crawled on P600 sandpaper during one motion cycle at of soft robots crawling on zigzag surfaces. As shown in
an input voltage of 5 kV. In this intermittent separate Fig. S8, zigzag surfaces with tilt angles of 10°, 20°, and 30°
actuation method, the center of gravity was moved by were built by stacking 300 pieces of 0.9 mm-thick acrylic
changing the height of the robot’s feet separately; thus, the sheets with different zigzag serration widths. It was found
Sun et al. Microsystems & Nanoengineering (2022)8:37 Page 7 of 11

a
Carbon grease (0.1 mm) Carbon grease (0.1 mm)
(i) (ii)

PET reinforcement
(0.25 mm)

VHB 4910 elastomer

PET substrate (0.1 mm)

Carbon grease (0.1 mm) Carbon grease (0.1 mm)

b
1 2 3 4

1 cm

c
1 2 3 4

1 cm

Fig. 4 3D folding assembly of the origami-inspired soft robot. a Expanded multilayered diagrams of the 3D pyramid and square folding
assemblies. b Programmable unfolding process of the pyramid-shaped soft robot. c Programmable unfolding process of the square-shaped
soft robot

that (Fig. S10 and Movie S5) the maximum speed reached stimulate the crawling ability of the soft robot, we used a
5.12 mm/s for a tilt angle of 20°, which was greater than higher actuation voltage of 5.5 kV. The results (Fig. S12)
the speeds of 3.20 and 3.88 mm/s achieved for tilt angles demonstrated that the walking speed first increased and
of 10° and 30° and greater than the maximum speed of then decreased as the power-off frequency increased due to
4.09 mm/s achieved on sandpaper at the same voltage the response time requirement of bipedal charging and
(5 kV) and frequency (0.29 Hz). As shown in Movie S5, discharging. As the frequency increased, the speed of bipedal
the speed of the robot on the zigzag surface with a tilt actuation accelerated. Considering that the power-off time
angle of 10° was lower due to pronounced surface slip- affects the stride angle during contraction, the robots’ pace
page. On the other hand, the 30° angle of inclination per step decreased (Fig. S11) when the power-off time was
formed a wide serration, which hindered bipedal actua- less than the time required for bipedal contraction, reducing
tion and reduced the speed. the crawling speed. According to Tables S1 and S2, the
The actuation voltage also affected the crawling speed of crawling speed of the robots in this paper was at the same
the soft robot. On P600 sandpaper, the soft robot crawled at level (~mm/s) as in previous reports. Table S2 compares the
speeds of 1.71, 3.28, and 4.09 mm/s at actuation voltages of soft robot performance of existing DE actuator-powered
3, 4, and 5 kV (Movie S6). The soft robot clearly exhibited a robots. The clear advantage of our soft robots is their space
larger deformation angle at higher voltages, with one step efficiency and scalability due to the origami assembly.
moving a longer distance. Soft robots can not only crawl on Considering the significant deformation and large
rough surfaces but also carry cargo. The motion status of a actuation forces of DE-based soft actuators, they are ideal
robot with 1 and 2 g loads is shown in Fig. 3f and Movie S7. for developing complex 3D soft robots. Inspired by ori-
The soft robot weighs 2.94 g and could carry up to 2.00 g gami technology, these soft actuators were used to create
while crawling, although its speed decreased from 4.09 to two origami 3D soft robots with different shapes that can
2.80 mm/s. We also investigated the effect of different power switch between 2D and 3D structures. Figure 4a shows
on/off frequencies on the walking state of the robots. To expanded multilayered diagrams of the 3D pyramid- and
Sun et al. Microsystems & Nanoengineering (2022)8:37 Page 8 of 11

a
1 2 3 4 5 6

2 cm

b c d

Maximum loading weight (g)

Without sandpaper P120 sandpaper 15 14.5
Sandpaper 13.5

10.0
10
6.0g 14.5g
6.0
5

2 cm 2 cm 2 cm
Sandpaper 0
None 400 240 120
Sandpaper (P)

e
1 2 3 4 5 6

1 cm

f
1 2 3

1 cm

4 5 6

Fig. 5 Demonstrations of the grasping and locking functions of the origami-inspired 3D soft robot acting on static and dynamic objects.
a A pyramid-shaped soft gripper captures a static ball and transports it to a beaker. b Sandpaper placed on the inside of the soft gripper. c Sandpaper
placed on the inside of the soft gripper. d Maximum gripping weight of the soft gripper with different grit sandpapers. e A square-shaped soft robot
captures a falling ball and locks it in a box. f A square-shaped soft robot captures a rolling ball and then locks it

square-shaped soft robots. The corresponding planar difficult to fold into an ideal closed-form than the shorter
structure designs are presented in Figs. S13 and S14. As edges. Thus, a larger radius was needed to increase the
shown in Fig. 4b, the original shape of the origami- tensile stress when folding. As shown in Fig. S14, a ske-
inspired 3D soft robot is a standard pyramid, and the leton radius of 12.5 mm was chosen to allow the bottom
pyramid-shaped 3D structure consists of four triangular of the long side to fold naturally, and the voltage required
actuators. Each triangular face of the pyramid can be to unfold was increased from 4.1 to 5 kV, allowing a
controlled independently to open into a 2D planar complete 3D square to be assembled (Movie S10).
structure (Movie S9). Similarly, as shown in Fig. 4c, the Soft robots for object manipulation are another important
square-shaped 3D soft robot consists of five rectangular application in the field of soft robotics. The pyramid robot
actuators that can be programmably actuated. Unlike the was transformed into a pyramid-shaped soft gripper
pyramid, the planar structure of the rectangular robot was (Fig. 5a). The back side of the pyramid-shaped gripper was
not centrosymmetric, and it had a longer side that needed attached to a rolled PET stick. The pyramid-shaped soft
to withstand more gravity. The longer edges were more gripper (2.44 g) could transfer spheres (2.73 g) from a petri
Sun et al. Microsystems & Nanoengineering (2022)8:37 Page 9 of 11

dish to a beaker with a finger-like grasping process. As structures and could grasp and lock 3D objects. The 3D
shown in Movie S11, the soft gripper opened quickly after design of the assembly could also be more complex and
the actuation voltage was applied. Then, after the power was versatile, and the DE actuator, with its advantages of a fast
turned off, it took 2–3 s for the “finger” to completely close. response time, light weight, and high durability, offers new
The robot could pick up ping pong balls with weights up to possibilities for the development of origami soft robots.
6.0 g. We improved the gripping ability of the soft gripper by This work provides a good method for the structural and
placing rough sandpaper on the inside of the gripper. The functional design of origami soft robots.
weight of the ping pong ball was continuously increased by
filling it with water, and the gripping experiment was per- Materials and methods
formed in weight steps of 0.5 g. As expected (Fig. 5c, d and Fabrication of the soft actuator
Movie S12), the gripping ability improved due to the First, the PET flexible films, including 0.1 mm-thick
roughness of the sandpaper: 10.0 g for P400, 13.5 g for P240, substrate layers and 0.25 mm-thick reinforcement layers,
and 14.5 g for P120. In addition to the gripper-shaped were cut into specific shapes with a laser cutting machine
manipulator, the square-shaped soft robot can be fabricated (Mintron MC-3020) based on a pattern designed in
as a box to capture static and dynamic objects (Movie S13). AutoCAD. The VHB4910 elastomer (3 M, 60 mm ×
The ball in Fig. 5e fell vertically, and the ball in Fig. 5f was 60 mm) was stretched to 400% × 400% using a pre-
rolled horizontally from the right side. Figure 5e illustrates stretching tool. The prestretched film was fixed using an
the entire process of locking a falling ball. The top lid of the acrylic fixation frame. Then, the PET flexible substrates
box was independently actuated and opened; after the ball and reinforcement layers with preconnected electrodes
fell into the square, the lid closed and locked the ball after were fixed to the center of the actuator. The skeletonized
stopping the actuation voltage. Figure 5f demonstrates the area of the PET film was coated with carbon grease
full process by which the square-shaped soft robot captured (AMKE G-660A). Finally, the soft actuator was obtained
and locked a small ball that rolled in from the side. The long after it was cut and removed from the fixation frame.
side of the rectangle was actuated independently, and it
unfolded rapidly (2 s) with an applied voltage of 5 kV. After Actuation and deformation tests
the ball rolled into the rectangular box from the right side, The fabricated soft actuators were connected to a high-
the long side was closed to lock the ball. The whole process voltage DC power supply. When a certain voltage was
took only 8 s (Movie S14). These results demonstrate the applied, the soft actuator straightened or deformed. During
unlimited potential of origami-inspired soft robots with the cycling test, the triangular and rectangular actuators
dielectric elastomer actuators, which have considerable were continuously charged and discharged to fully deform
advantages for multifunctional field applications in the field and return to their initial states at voltages of 5.5 and 4.1 kV,
of soft robotics. respectively. The cycles were repeated 100 times. All defor-
mation processes were recorded with a camera (SONY).
Conclusion
In this work, we developed DE-based soft actuators with Fabrication of origami robots
stable folding and unfolding functions and designed and The origami robots were designed with CAD software,
fabricated 3D soft robots based on 3D origami folding. The and the PET flexible frame and reinforcement layers were
soft actuator consists of a VHB4910 elastomer, which acts made with a laser cutter. The robots were fabricated by
as the dielectric layer, and a PET film, which acts as the the same process as the soft actuators, but a wire was
flexible substrate and reinforcement layer. The relationship connected to each actuation region to serve as the positive
between the semicircular radius of the actuation region and pole. The negative pole was connected to the actuation
the original bending angle of the soft actuator was inves- region with carbon grease (AMKE G-660A) before it was
tigated. A triangular soft actuator with a 120° bending angle adhered to the soft substrate. Finally, a wire was used as
was suitable for assembling 3D pyramid-shaped soft robots, the common negative electrode.
while a rectangular actuator with a 90° bending angle was
used to construct a crawling soft robot and a square- Movement characterization
shaped 3D soft robot. The stable structure of the soft Two high-voltage DC power supplies were used as
actuator after 100 cycles ensured structural stability during actuation sources to control the front and back feet of the
3D construction and durability during long-term applica- robot. The whole crawling process was recorded using a
tions of the 3D soft robots. For example, a crawling robot camera (SONY).
with rectangular soft actuators demonstrated a stable
crawling ability on different grit papers and can carry cargo Acknowledgements
This work is sponsored by the Regional Joint Fund of the National Science
while walking in a specific direction. The origami-inspired Foundation of China (Grant No. U21A20492), the National Key R&D Program of
3D pyramid- and square-shaped soft robots had stable China (Grant No. 2018YFB0407102), the City University of Hong Kong (Grant Nos.
Sun et al. Microsystems & Nanoengineering (2022)8:37 Page 10 of 11

9667221, 9680322), the Research Grants Council of the Hong Kong Special 15. Rus, D. & Tolley, M. T. Design, fabrication and control of origami robots. Nat.
Administrative Region (Grant No. 21210820, 11213721), the Shenzhen Science and Rev. Mater. 3, 101–112 (2018).
Technology Innovation Commission (Grant No. JCYJ20200109110201713), the 16. Rus, D. & Sung, C. Spotlight on origami robots. Sci. Robot. 3, eaat0938 (2018).
Natural Science Foundation of Chongqing Municipality (Grant No. 17. Kotikian, A. et al. Untethered soft robotic matter with passive control of shape
cstc2019jcyjjqX0021), the Science and Technology Innovation Leading Talents morphing and propulsion. Sci. Robot. 4, eaax7044 (2019).
Program of Chongqing Municipality (No:T04040012) and Science and Technology 18. Miao, L. et al. 3D temporary‐magnetized soft robotic structures for enhanced
of Sichuan Province (Grant No. 2020YFH0181), the National Natural Science energy harvesting. Adv. Mater. 33, 2102691 (2021).
Foundation of China (NSFC) (Grant Nos. U21A20492, 62122002). This work was 19. Kim, B. H. et al. Three-dimensional electronic microfliers inspired by wind-
also sponsored by the Sichuan Province Key Laboratory of Display Science and dispersed seeds. Nature 597, 503–510 (2021).
Technology, and Qiantang Science & Technology Innovation Center. M.W. thanks 20. Ryu, J. et al. Paper robotics: Self‐folding, gripping, and locomotion. Adv. Mater.
the Academic Support Program for PhD students supported by UESTC. Technol. 5, 1901054 (2020).
21. Boyvat, M., Koh, J.-S. & Wood, R. J. Addressable wireless actuation for multijoint
Author details folding robots and devices. Sci. Robot. 2, eaan1544 (2017).
1 22. Cai, G., Ciou, J.-H., Liu, Y., Jiang, Y. & Lee, P. S. Leaf-inspired multiresponsive
State Key Laboratory of Electronic Thin Films and Integrated Devices, School
of Optoelectronic Science and Engineering, University of Electronic Science MXene-based actuator for programmable smart devices. Sci. Adv. 5, eaaw7956
and Technology of China (UESTC), Chengdu 610054, People’s Republic of (2019).
China. 2Chongqing Key Laboratory of Materials Surface & Interface Science, 23. Mu, J. et al. Origami-inspired active graphene-based paper for programmable
Chongqing Co-Innovation Center for Micro/Nano Optoelectronic Materials and instant self-folding walking devices. Sci. Adv. 1, e1500533 (2015).
Devices, Micro/Nano Optoelectronic Materials and Devices International 24. Ling, Y. et al. Laser‐induced graphene for electrothermally controlled,
Science and Technology Cooperation Base of China, School of Materials mechanically guided, 3D assembly and human–soft actuators interaction. Adv.
Science and Engineering, Chongqing University of Arts and Sciences, Mater. 32, 1908475 (2020).
Chongqing 402160, People’s Republic of China. 3Department of Biomedical 25. Li, J. et al. Photothermal actuators: Photothermal bimorph actuators with in-
Engineering, City University of Hong Kong, Hong Kong SAR 999077, People’s built cooler for light mills, frequency switches, and soft robots. Adv. Funct.
Republic of China Mater. 29, 1970184 (2019).
26. Cheng, Y., Lu, H., Lee, X., Zeng, H. & Priimagi, A. Soft actuators: Kirigami‐based
Conflict of interest light‐induced shape‐morphing and locomotion. Adv. Mater. 32, 2070047
The authors declare no competing interests. (2020).
27. Shintake, J., Cacucciolo, V., Shea, H. & Floreano, D. Soft biomimetic fish robot
made of dielectric elastomer actuators. Soft Robot. 5, 466–474 (2018).
Supplementary information The online version contains supplementary 28. Gu, G., Zou, J., Zhao, R., Zhao, X. & Zhu, X. Soft wall-climbing robots. Sci. Robot.
material available at https://doi.org/10.1038/s41378-022-00363-5. 3, eaat2874 (2018).
29. Zou, M. et al. Progresses in tensile, torsional, and multifunctional soft actuators.
Received: 26 November 2021 Revised: 24 January 2022 Accepted: 13 Adv. Funct. Mater. 31, 2007437 (2021).
February 2022 30. Jia, T. et al. Moisture sensitive smart yarns and textiles from self‐balanced silk
fiber muscles. Adv. Funct. Mater. 29, 1808241 (2019).
31. Wang, R. et al. Tensile and torsional elastomer fiber artificial muscle by
entropic elasticity with thermo-piezoresistive sensing of strain and rotation by
a single electric signal. Mater. Horiz. 7, 3305–3315 (2020).
References 32. Liu, Z. et al. Somatosensitive film soft crawling robots driven by artificial
1. Cianchetti, M., Laschi, C., Menciassi, A. & Dario, P. Biomedical applications of muscle for load carrying and multi-terrain locomotion. Mater. Horiz. 8,
soft robotics. Nat. Rev. Mater. 3, 143–153 (2018). 1783–1794 (2021).
2. Hann, S. Y., Cui, H., Nowicki, M. & Zhang, L. G. 4D printing soft robotics for 33. Chen, S., Pang, Y., Cao, Y., Tan, X. & Cao, C. Soft robotic manipulation system
biomedical applications. Addit. Manuf. 36, 101567 (2020). capable of stiffness variation and dexterous operation for safe human-
3. Zhalmuratova, D. & Chung, H.-J. Reinforced gels and elastomers for biome- machine interactions. Adv. Mater. Technol. 6, 2100084 (2021).
dical and soft robotics applications. ACS Appl. Polym. Mater. 2, 1073–1091 34. Dou, W. et al. Soft robotic manipulators: Designs, actuation, stiffness tuning,
(2020). and sensing. Adv. Mater. Technol. 6, 2100018 (2021).
4. Rich, S. I., Wood, R. J. & Majidi, C. Untethered soft robotics. Nat. Electron. 1, 35. Li, D., Yao, K., Gao, Z., Liu, Y. & Yu, X. Recent progress of skin-integrated
102–112 (2018). electronics for intelligent sensing. Light.: Adv. Manuf. 2, 4 (2021).
5. Zhakypov, Z., Mori, K., Hosoda, K. & Paik, J. Designing minimal and scalable 36. Wang, L. et al. A metal-electrode-free, fully integrated, soft triboelectric sensor
insect-inspired multi-locomotion millirobots. Nature 571, 381–386 (2019). array for self-powered tactile sensing. Microsyst. Nanoeng. 6, 59 (2020).
6. Li, G. et al. Self-powered soft robot in the Mariana Trench. Nature 591, 66–71 37. Liu, H. et al. An epidermal sEMG tattoo-like patch as a new human-machine
(2021). interface for patients with loss of voice. Microsyst. Nanoeng. 6, 16 (2020).
7. Fusco, S. et al. An integrated microrobotic platform for on-demand, targeted 38. Li, D. et al. Miniaturization of mechanical actuators in skin-integrated elec-
therapeutic interventions. Adv. Mater. 26, 952–957 (2013). tronics for haptic interfaces. Microsyst. Nanoeng. 7, 85 (2021).
8. Le, H. M., Do, T. N. & Phee, S. J. A survey on actuators-driven surgical robots. 39. Wu, M. et al. Self-powered skin electronics for energy harvesting and
Sens. Actuators A: Phys. 247, 323–354 (2016). healthcare monitoring. Mater. Today Energy 21, 100786 (2021).
9. Ranzani, T., Gerboni, G., Cianchetti, M. & Menciassi, A. A bioinspired soft 40. Liu, Y. et al. Epidermal electronics for respiration monitoring via thermo-
manipulator for minimally invasive surgery. Bioinspiration Biomim. 10, 035008 sensitive measuring. Mater. Today Phys. 13, 100199 (2020).
(2015). 41. Yu, X. et al. Skin-integrated wireless haptic interfaces for virtual and aug-
10. Arezzo, A. et al. Total mesorectal excision using a soft and flexible robotic arm: mented reality. Nature 575, 473–479 (2019).
A feasibility study in cadaver models. Surgical Endosc. 31, 264–273 (2016). 42. Song, E. et al. Miniaturized electromechanical devices for the characterization
11. Mintchev, S., Salerno, M., Cherpillod, A., Scaduto, S. & Paik, J. A portable three- of the biomechanics of deep tissue. Nat. Biomed. Eng. 5, 759–771 (2021).
degrees-of-freedom force feedback origami robot for human-robot interac- 43. Wong, T. H. et al. Tattoo-like epidermal electronics as skin sensors for human
tions. Nat. Mach. Intell. 1, 584–593 (2019). machine interfaces. Soft Sci. 1, 10 (2021).
12. Zhao, W. et al. Vat photopolymerization 3D printing of advanced soft sensors 44. Wang, C. et al. Adaptive soft robots: Soft ultrathin electronics innervated
and actuators: From architecture to function. Adv. Mater. Technol. 6, 2001218 adaptive fully soft robots. Adv. Mater. 30, 1870087 (2018).
(2021). 45. Saikumar, J. et al. Inducing different severities of traumatic brain injury in
13. Ning, X. et al. Mechanically active materials in three-dimensional mesos- Drosophila using a piezoelectric actuator. Nat. Protoc. 16, 263–282
tructures. Sci. Adv. 4, eaat8313 (2018). (2020).
14. Morgan, J., Magleby, S. P. & Howell, L. L. An approach to designing origami- 46. He, Q. et al. Electrically controlled liquid crystal elastomer-based soft tubular
adapted aerospace mechanisms. J. Mech. Des. 138, 052301 (2016). actuator with multimodal actuation. Sci. Adv. 5, eaax5746 (2019).
Sun et al. Microsystems & Nanoengineering (2022)8:37 Page 11 of 11

47. Li, D. et al. Bioinspired ultrathin piecewise controllable soft robots. Adv. Mater. 49. Qiu, Y., Zhang, E., Plamthottam, R. & Pei, Q. Dielectric elastomer artificial
Technol. 6, 2001095 (2021). muscle: Materials innovations and device explorations. Acc. Chem. Res. 52,
48. Lu, X., Wang, K. & Hu, T. Development of an annelid-like peristaltic crawling 316–325 (2019).
soft robot using dielectric elastomer actuators. Bioinspiration Biomim. 15, 50. Chen, D. & Pei, Q. Electronic muscles and skins: A review of soft sensors and
046012 (2020). actuators. Chem. Rev. 117, 11239–11268 (2017).