Supplementary Materials for

Peano-HASEL actuators: Muscle-mimetic, electrohydraulic transducers

that linearly contract on activation

Nicholas Kellaris, Vidyacharan Gopaluni Venkata, Garrett M. Smith, Shane K. Mitchell,

Christoph Keplinger*

*Corresponding author. Email: christoph.keplinger@colorado.edu

Published 5 January 2018, Sci. Robot. 3, eaar3276 (2018)

DOI: 10.1126/scirobotics.aar3276

The PDF file includes:

Materials and Methods

Fig. S1. Heat-press used for sealing BOPP pouches.

Fig. S2. Fabrication process for Peano-HASEL actuators with hydrogel

electrodes.

Fig. S3. Fabrication process for Peano-HASEL actuators with aluminum

electrodes.

Fig. S4. Voltage signal with reversing polarity used during force-strain tests.

Fig. S5. Example of damage to aluminum electrodes after voltage cycling.

Fig. S6. High-speed contraction of Peano-HASEL actuators.

Fig. S7. Experimental setup used for frequency response tests of Peano-HASEL

actuators.

Fig. S8. Full actuation signal for lever arm tests.

Fig. S9. Lifetime test for Peano-HASEL actuators.

Fig. S10. Dielectric breakdown tests for KOH-etched BOPP film.

Legends for Movies S1 to S6

References (47, 48)

Other Supplementary Material for this manuscript includes the following:

(available at robotics.sciencemag.org/cgi/content/full/3/14/eaar3276/DC1)

Movie S1 (.mp4 format). Demonstration of actuation characteristics.

Movie S2 (.mp4 format). Actuation using integrated aluminum electrodes.

Movie S3 (.mp4 format). Scaling up forces with Peano-HASEL actuators.

Movie S4 (.mp4 format). Frequency response of Peano-HASEL actuators.

robotics.sciencemag.org/cgi/content/full/3/14/eaar3276/DC1

Movie S5 (.mp4 format). Demonstration of precise and rapid actuation.

Movie S6 (.mp4 format). Transparent Peano-HASEL actuators.

Materials and Methods

Actuator materials

The three basic components of Peano-HASEL actuators are:

1) A flexible and inextensible shell

2) A liquid dielectric

3) Flexible electrodes

Below we describe the materials used for fabrication of Peano-HASEL actuators:

1) Shell: The actuator shell is constructed from a metallized coextruded biaxially-oriented

polypropylene (BOPP) film (Impex films, MSB 20). BOPP was chosen for being inexpensive, thin,

strong, and for possessing a high dielectric strength (~ 700 V/μm) (35), which increases the

maximum field that can be applied across the actuator before dielectric breakdown. The BOPP films

were 21 μm thick with a vacuum-deposited aluminum metallization layer on one side of the BOPP

core and a thin (< 1 μm) copolymer layer on the other side to facilitate heat-sealing.

2) Liquid dielectric: A vegetable-based transformer oil called Envirotemp FR3 was purchased from

Cargill to serve as the liquid dielectric for its high dielectric breakdown strength, chemical

compatibility with BOPP, and for being environmentally-friendly.

3) Electrodes: Since Peano-HASEL actuators only require flexible, rather than stretchable,

electrodes, many materials are possible. In this work, two types of electrode materials were

demonstrated:

a) Hydrogel electrodes: The first type of electrode demonstrated is an ionic conductor made

from polyacrylamide (PAAm) hydrogel swollen with an 8 M LiCl electrolyte solution to

provide conductivity and high water-retention (37). Hydrogels have been demonstrated as

effective electrode materials in electrostatic actuators previously (36). The process for

creating electrodes from conductive hydrogels is detailed in the following section.

b) Aluminum electrodes: The second type of electrode demonstrated is an ultrathin aluminum

metallized layer that is vacuum-deposited on the BOPP during industrial manufacturing,

estimated to be 30 nm thick (47), based on the manufacturer’s reported optical density of

2.2 (48). The process for creating electrodes from this layer is described in the following

section.

Fabrication processes for Peano-HASEL actuators

The main steps involved in the fabrication of actuators are:

1) Heat-sealing of BOPP sheets to form the flexible and inextensible pouches

2) Filling the pouches with liquid dielectric

3) Fabricating and attaching electrodes on the surface

Heat-press used to create actuator pouches:

Actuator pouches were sealed using a custom heat-press fitted with a brass-rod die that defined

the desired pouch geometry (fig. S1A). The die (shown in fig. S1B) is comprised of an aluminum

plate with 1.57-mm-thick brass rods epoxied onto the surface. These rods were arranged to define

a three-unit Peano-HASEL actuator with pouches that were 2 cm tall and 4 cm wide. A 2 mm-wide

gap was left in the seal of each pouch for filling. The die was placed in a cutout on the top plate of

the heat-press near the integrated heating element (fig. S1C). Springs held the die firmly in place,

while a temperature sensor pressed against the back of the die to monitor the sealing temperature.

The base plate of the heat-press used two acrylic layers separated by elastomeric pads to help

accommodate uneven loading (fig. S1D). The top layer of acrylic had a 1 mm elastomeric pad over

it for distributing the pressure of the die on the sealable films.

Creating and filling pouch structures:

The process for sealing pouches is depicted in Fig. 2 of the main text. To prepare for sealing,

two sheets of BOPP were cleaned with methanol and sandwiched between two layers of Kapton

film, as shown in fig. S1E. The bottom layer of Kapton film was marked to provide an alignment

guide, while the top layer acted as a heat-distributing layer during sealing. Figure S1F shows this

setup for aluminum-electrode actuators ready to be sealed. Die temperature was set to 375 oF on

the heat-press (on the front-left dial shown in fig. S1A); the top plate was lowered and pressed

against the sealable materials with moderate pressure for three seconds to achieve a proper seal.

The pouches were then filled with liquid dielectric through the filling ports using a needle and

syringe. Each pouch was filled with 1.4 mL of liquid dielectric, followed by careful removal of any

bubbles. The amount of liquid dielectric in each pouch was determined by assuming that the

uncovered portion of each pouch forms a perfectly circular cross-section when fully contracted

(shown in Fig. 1A). This cross-section was multiplied by the pouch width to get total volume of

liquid needed. From here we adjusted the fill amount slightly based on observed performance. After

filling, a heated aluminum bar was used to seal the filling ports to create sealed pouches. After

filling and sealing the pouches, the shell was cleaned using soap and water to remove oil residue.

Fabricating and placing hydrogel electrodes:

Hydrogel electrodes consist of a 160-μm-thick layer of conductive PAAm hydrogel that was

cast onto a 160-μm-thick layer of polydimethylsiloxane (PDMS). The fabrication process for these

electrodes is outlined in fig. S2 and described below.

PDMS prepolymer (Sylgard 184, 10:1 base-to-curing agent ratio) was blade-cast on an

acrylic plate using a 160-μm-thick PET spacer and cured in an oven at 75 oC for 30 min to produce

a PDMS sheet (fig. S2 step 1). The cured PDMS sheet was treated with a solution of 10 wt%

benzophenone in ethanol as in (38) for 2 min in order to promote bonding between the hydrogel

and PDMS surface (fig. S2 step 2). After this, hydrogels were prepared as described by Bai et al.

(37). First, lithium chloride salt (LiCl; The Science Company, NC-48518M) was dissolved in

deionized water to form an 8 M solution; the LiCl provides the ionic conductivity to the hydrogel

network. The solution was allowed to cool to room temperature. Next we combined the four

ingredients that form the hydrogel network: Acrylamide (AAm; Sigma A88887) was the monomer,

N,N-methylenebisacrylamide (MBAA; Sigma, 146072) acted as a crosslinker, Ammonium

persulfate (AP; Sigma, 248614) was the photo-initiator, and N,N,N’,N’-

tetramethylethylenediamine (TEMED; Sigma, T9281) was added as the crosslinking accelerator.

Acrylamide (2.2 M) was dissolved in the 8 M LiCl solution along with MBAA (0.06 wt% of AAm)

and AP (0.17wt% of AAm). The solution was mixed on a stir plate for 5 minutes then degassed for

10 minutes. To initiate polymerization, TEMED (0.05wt% of AAm) was added to the solution

immediately before casting the hydrogels. The hydrogels were cast on to the treated PDMS sheet

using a second PET spacer (160-μm thick) (fig. S2 step 3). A glass plate was placed on top to spread

the solution evenly. It was placed under a 365-nm UV light (3UV-38, UVP) and cured for 1h (fig.

S2 step 4). After the conductive PAAm hydrogel layer was cured and bonded to the PDMS sheet,

it was cut into the desired electrode shape using a CO2 laser (Epilog Legend 36EXT, 75W) at ~

10% of full power and 100% speed (fig. S2 step 5). Excess material was removed (fig. S2 step 6)

to expose the completed PDMS-backed hydrogel electrode. The electrode was then peeled off the

acrylic plate and placed on the actuator pouches with the hydrogel side contacting the BOPP. The

PDMS backing served to protect the hydrogel electrode from environmental factors such as dust,

and to prevent accidental adhesion to other surfaces (countertops, gloves, etc.), while maintaining

the flexibility of the electrode.

Fabrication process for aluminum electrodes

We demonstrated an alternate electrode material that is comprised of a thin, flexible layer

of aluminum that is vacuum-deposited on the BOPP. This metallization layer was selectively-

etched in KOH to define an electrode pattern on the pouches. The full process (shown in fig. S3A)

is as follows:

Sheets of metallized BOPP were rinsed with methanol and air-dried to remove any dust

particles. Wiping was avoided, as it caused noticeable abrasion in the metallization layer. The BOPP

sheet was then taped flat onto an acrylic plate with the metallized layer facing upwards. A soft

PDMS stamp cast in the shape of the electrodes was pressed onto the metallized layer; this stamp

acted as a protective mask during etching. This assembly was then placed in a petri dish with a 1.5

wt.% KOH solution to etch away the aluminum in the unprotected areas (fig. S3A step 1). The

sheets were rinsed with deionized water and air dried. Two etched BOPP sheets were then heat-

sealed together with the aluminum electrodes facing outwards (fig. S3A step 2). The stamped

actuator was filled with liquid dielectric using a needle and syringe inserted through the filling ports

(fig. S3A step 3). Finally, the filling ports were sealed using a heated aluminum bar (fig. S3A step

4) to create a completed actuator - shown in fig. S3B. After fabrication, the completed actuator was

gently cleaned with soapy water to remove any oil residue.

Final actuator dimensions

Our actuator consisted of three pouches in series. Each pouch was 2 cm high and 4 cm wide,

and filled with 1.4 mL of liquid dielectric. Electrodes were 0.9 cm high x 3.8 cm wide with 3-mm-

wide strips to connect the electrodes between pouches. Electrodes were placed with about 1 mm

separation from the top and sides of each pouch, to decrease the likelihood of electrical arcing

through any defects in the pouch seal. This design made the contracting area one centimeter high,

with an aspect ratio of ~ 4:1 (width-to-height). This aspect ratio helped reduce the effect of the

constrained edges which prevent the actuating area from forming an ideal cylindrical shape (15).

Creating connections to completed actuators

Electrical connection points were made with thin strips of copper tape attached to the

electrode leads at the top of each actuator (seen in Fig. 3B-C). In the case of aluminum electrodes,

small strips of hydrogel or carbon grease were added to reinforce the electrical connection between

the bottom of the leads and the top of the electrode on the uppermost pouch, which was prone to

disconnecting due to mechanical fatigue while operating or handling.

For physical connections to the actuators, two main types of mounting supports were

demonstrated - rigid acrylic and flexible tape. For rigid acrylic mounting, acrylic pieces of the

desired shape were laser cut and attached to the top and bottom of the actuator on either side using

strips of VHB tape. These were fastened with plastic screws and nuts. This rigid mounting was

useful in situations where the actuator needed precise mounting for testing, had a large applied

mechanical load, or needed to be integrated with other rigid components (as in the lever arm

demonstration). For flexible mounting, strips of fiberglass-reinforced tape were attached on

opposing sides of the actuator, at both the top and bottom (seen in Fig. 1C). A hole punch was used

to make holes in the tape on the top and bottom for mounting.

Testing Peano-HASEL actuators

Generating high-voltage signals

To provide the high voltage signals necessary for actuation, a Trek Model 50/12 high

voltage amplifier was used. Input signals were generated using custom LabVIEW VIs (version

15.0.1f2), then fed into the high voltage amplifier through an NI Model 6212 DAQ.

Force versus strain testing

For force vs. strain tests, the actuators were mounted on an acrylic stand and fastened with

plastic screws. Single-actuator tests used acrylic mounts, while parallel-actuator tests used the

fiberglass-reinforced tape. Standard copper weights ranging from 10 g to 1 kg were suspended from

the bottom of the actuator. A modified square-wave voltage signal with long rise and fall times (~

1 s) was applied (fig. S4), with maximum voltages of 6 kV, 8 kV, and 10 kV. This modification

increased the charging time and reduced the maximum current in the aluminum electrodes, since

fast charging was observed to ablate the thin metallized layer. Figure S5 shows the damage in the

aluminum electrodes due to fast charging. Even with slow charging, damage to the aluminum

electrodes was observed after ~ 100 cycles. For this reason, all other tests used only hydrogel-

electrode actuators. Videos of the actuation at different weights were captured using a DSLR

camera (Canon EOS 6D), and Tracker video analysis and modeling software (version 4.96) was

used to optically determine the linear actuation for each load, at a given voltage. The force-strain

curves presented in Fig. 3A were then constructed from these data points at different discrete loads.

Movie S1 and Movie S2 show actuation characteristics for hydrogel and aluminum electrodes,

respectively.

High speed contraction of pouches

Tests were performed on an actuator with hydrogel electrodes in order to characterize the

contraction speed with various inertial loads (i.e. hanging masses) attached to the bottom of the

actuator. The test setup was similar to the actuation tests described above, with a schematic shown

in fig. S6A. A 0.5 Hz square wave with reversed polarity between each cycle was used to excite the

actuators and a video of the actuation was captured with a Vision Research high-speed camera

(Phantom v710) at 800 FPS. Tracker video analysis and modeling software was used to determine

the contraction as a function of time. A Savitsky-Golay filter was applied to smooth the contraction

data, using third-order polynomials fit to subsets of data that were seven points long. Figure S6B

shows the initial portion of the filtered contraction curve for a 100 g load, with the time of initial

contraction (ts) and equilibrium contraction (te) labeled. The derivatives of the Savitsky-Golay

coefficients were taken to determine velocity (fig. S6C) and acceleration (fig. S6D) curves. From

these data, we calculated the peak strain rate, peak specific power, and average specific power of

our actuators, with results shown in Fig. 5C-D of the main text. To determine these quantities, we

only considered the period of initial movement (ts) to equilibrium contraction (te). An overshoot

was observed in the contraction response of the actuator - due to the inertia of the system - after

which the actuator settled towards an equilibrium position. This overshoot was fairly consistent

across cycles. To calculate peak strain rate, we found the peak velocity from our velocity curve and

normalized to the length, L, of our actuator (6.4 cm, which included the pouch heights and seal

widths between pouches):

Peak strain rate =𝑣peak

𝐿⋅ 100% (1)

To calculate the specific power of the actuator, we first determined the forces on the hanging

weight, which are shown in fig. S6A:

𝐹net(𝑡) = 𝑚applied ⋅ 𝑎(𝑡) = 𝐹act(𝑡) − 𝐹g(𝑡) (2)

𝐹act(𝑡) = 𝐹net(𝑡) + 𝐹g(𝑡) (3)

= 𝑚applied ⋅ 𝑎(𝑡) + 𝑚applied ⋅ 𝑎g (4)

= 𝑚applied(𝑎(𝑡) + 𝑎g) (5)

Here, ag is the acceleration due to gravity, and a(t) is the measured acceleration of the mass. From

here we calculate specific power from force and velocity, normalized to actuator mass (5 g):

𝑃sp(𝑡) =𝑃(𝑡)

𝑚act=

𝐹act(𝑡)⋅𝑣(𝑡)

𝑚act (6)

Here, v(t) is the measured velocity. The plot for specific power versus time is shown in fig. S6E.

Average specific power is determined by finding the total specific work performed by the actuator

between the start of contraction ts and equilibrium contraction te, and dividing by the change in

time:

𝑃sp−avg =𝑊total

𝑚act(𝑡e−𝑡s) (7)

Frequency testing

To characterize the frequency response of the hydrogel-electrode actuators, we used a

custom setup, depicted in fig. S7A. This setup consisted of tensioned elastic bands that were

attached to the bottom of the actuator with hooks and anchored to a fixed acrylic base plate. The

bands were calibrated such that they collectively exerted 1 N of downward force on the actuator.

These elastic bands exerted a roughly constant restoring force on the actuator along the entire

actuation stroke, unlike suspending an inertial weight of the desired value. The bands prevented

unnecessary wobbling and ensured that the actuation was limited only to an up-down motion. A

square wave voltage signal of 8 kV (fig. S7B) was then applied at various frequencies. Videos of

the actuation were captured using a high-speed camera (Vision Research, Phantom v710) at a frame

rate of 30x the actuation frequency. Tracker video analysis and modeling software was then used

to calculate the actuation strain corresponding to various frequencies. Movie S4 shows a Peano-

HASEL actuator operating at a range of frequencies between 1 Hz and 50 Hz.

Lever arm testing

To demonstrate the speed and accurate positional control of Peano-HASEL actuators, a

parallel stack of two actuators was assembled and attached to an acrylic lever arm with a 1:7 input-

to-output displacement. This setup allowed us to take advantage of the large force-generating

capabilities of Peano-HASEL actuators and translate it to large actuation strokes at the free end of

the arm. A small circular ‘hand’ was attached to one end of the arm and a table-tennis ball was

placed in it. The applied voltage signal as a function of time is shown in fig. S8 and the

demonstration of actuation is shown in Movie S5.

Lifetime testing

To estimate the lifetime for our hydrogel-electrode actuators, we used our frequency test

setup to continuously cycle actuators until failure. The voltage signal shown in fig. S7B was used

to excite the actuator using a LabVIEW VI that included a counter to track the number of actuation

cycles. Two different samples were tested at a maximum voltage of 8 kV at frequencies of 6 Hz

and 50 Hz, and the lifetime in number of cycles was measured. 6 Hz was chosen as the highest

observed frequency to still achieve full actuation compared to a DC voltage of 8 kV. 50 Hz was

tested to investigate lifetime at higher frequencies with lower strain. Actuation strain versus number

of actuation cycles is shown in fig. S9 for 6 Hz cycling. Actuation remained consistent throughout

the lifetime of the actuator. Failure occurred at around 20,000 cycles for both 6 Hz and 50 Hz. In

both cases, failure occurred via electrical arcing through the heat seal of the pouches near the edge

of the electrodes.

Dielectric breakdown measurements of BOPP

The dielectric strength of BOPP is a crucial factor in determining performance of Peano-

HASEL actuators, since it can limit maximum safe operating voltage, which in turn determines the

Maxwell pressure generated in the devices. These tests were conducted to verify the dielectric

strength of BOPP and to determine if the KOH etching treatment affected the dielectric strength of

the BOPP; given that BOPP has excellent chemical resistance to high concentrations (up to 50 wt%)

of KOH, we did not expect dielectric breakdown strength to be significantly affected. Two samples

of metallized BOPP were etched in 1.5 wt% KOH solution for 4 min and 60 min. For each data

point, two strips of conductive PAAm hydrogel were placed on either side of the BOPP sheets

perpendicular to each other to serve as electrodes. This setup created a square test window 2.5 mm2.

A voltage ramp signal with a ramp rate of 500 V/s was generated using a LabVIEW custom VI and

was supplied as the input signal to the high voltage source through a DAQ (NI 6212). The signal

was stopped through the program when it sensed an electrical short due to dielectric breakdown,

and the breakdown voltage was recorded. Fifteen tests were performed for each sample and the

results were fit to a two-parameter Weibull distribution (fig. S10). The characteristic breakdown

strength (evaluated at 63.2% likelihood of failure) was estimated statistically for both etch times. A

slight increase in breakdown strength was observed in the samples treated for 60 minutes in KOH.

Fig. S1. Heat-press used for sealing BOPP pouches. (A) The heat-press assembly used to seal

sheets of BOPP to form the actuator pouch, made from a converted grill press with the lower heating

element removed. The labelled components are explained in the subfigure with the corresponding

letter. (B) Metal die, made from brass rods epoxied onto an aluminum plate for creating the seal

geometry. (C) Cut-away section for holding the die plate: The temperature sensor (central circular

piece) is installed to press against the back of the die. Temperature is set using a control knob on

the front of the assembly. Springs (shown at the four corners) hold the die in place while allowing

for some uneven load compensation. (D) Base acrylic plates for holding materials to be sealed. A

PDMS sheet on top, and soft spacers between, are included for uneven load compensation and load

distribution. (E) Exploded view of the stack used for sealing: the bottom Kapton provides an

alignment guide, followed by two BOPP sheets to be sealed, and finally the top layer of Kapton for

avoiding direct contact to the metal die. (F) Stacked view of aluminum-electrode BOPP sandwiched

between Kapton sheets for sealing.

Fig. S2. Fabrication process for Peano-HASEL actuators with hydrogel electrodes.

Fig. S3. Fabrication process for Peano-HASEL actuators with aluminum electrodes. (A)

Overview of the fabrication process for actuators with vacuum-deposited aluminum electrodes,

including use of the heat-press described in fig. S1. (B) Completed and unmounted aluminum

Peano-HASEL, before trimming excess BOPP.

Fig. S4. Voltage signal with reversing polarity used during force-strain tests.

Science Robotics Supplementary Materials Page 13 of 20

Fig. S5. Example of damage to aluminum electrodes after voltage cycling. The two dotted white

boxes show areas on the connector for an aluminum electrode that sustained damage during

repeated charging and discharging while actuating a Peano-HASEL. The very thin aluminum layers

(~ 30 nm thick) are prone to ablation during fast charging and discharging.

Fig. S6. High-speed contraction of Peano-HASEL actuators. (A) Schematic of actuator with

quantities relevant for determining the dynamic actuation characteristics. (B) Zoomed view of

initial portion of the contraction curve in Fig. 5B, with a 100 g hanging weight. A Savitsky-Golay

filter was applied to position (contraction) data to provide smoothing; derivatives of the Savitsky-

Golay fits at each point provided velocity (C) and acceleration (D) data. (E) Specific power was

calculated using equation (6). Contraction time was treated as the time from the start of contraction

𝑡s to equilibrium contraction 𝑡e, ignoring the subsequent overshoot.

Fig. S7. Experimental setup used for frequency response tests of Peano-HASEL actuators.

(A) Physical set-up for determining the frequency response of actuators. Two elastic bands are

attached to the bottom of the pouch and slightly angled outward to provide torsional stability as

well as a constant restoring force of 1 N throughout the stroke. (B) Voltage signal used during

testing, which was applied at a range of frequencies. T is the period of one actuation cycle.

Fig. S8. Full actuation signal for lever arm tests. The full signal used in testing the lever arm

setup (Fig. 6 of the main text). The three regions are meant to show the versatility of actuation for

Peano-HASELs. I demonstrates voltage steps of 1-kV increments from 0 to 12 kV with 0.75 s hold

time at each voltage to show the accurate positional control with respect to input voltage. II is an

offset sine wave constructed by reflecting every other cycle over the x-axis. This waveform is meant

to demonstrate smooth and muscle-mimetic actuation. III is a 13-kV voltage step to demonstrate

the high-speed operation of the actuators.

Fig. S9. Lifetime test for Peano-HASEL actuators. A hydrogel-electrode actuator was cycled at

6 Hz until failure, using the frequency test setup. Around 20,000 actuation cycles were observed

before electrical arcing occurred through the seal on the side of a pouch. As shown by the blue

circles in the plot, no degradation in actuation strain was observed throughout the test. A test

performed at 50 Hz gave similar results, with 21,000 actuation cycles before failure.

Fig. S10. Dielectric breakdown tests for KOH-etched BOPP film. Breakdown voltages of

single-layer BOPP film with thin heat-sealing copolymer layer on one side. One sample was etched

for 4 minutes in 1.5 wt% aqueous KOH solution, while the other was etched for 60 minutes in the

same solution. These conditions were meant to verify that our KOH etch did not degrade the

breakdown strength of BOPP samples. Electrodes were PAAm hydrogels swollen with an 8 M LiCl

solution. A voltage ramp of 500 V/s was applied until breakdown occurred, with 15 tests conducted

under each condition. The data was fit to a two-parameter Weibull distribution to determine the

characteristic breakdown voltages of 650 V/μm (4 minutes) and 685 V/μm (60 minutes).

Movie S1. Demonstration of actuation characteristics.

A hydrogel-electrode Peano-HASEL actuator was suspended from an acrylic frame. Fiberglass-

reinforced tape was added to the actuator to create secure mounting points while maintaining a soft

design; a 20 g weight was hung from the bottom of the actuator, which was then actuated at 8 kV

with a 1 Hz modified square wave; a skewed view shows the geometry changes in the contracting

area of the pouch. The same demonstrations were repeated using the voltage signal depicted in fig.

S4 to show the progressive closing of the electrodes.

Movie S2. Actuation using integrated aluminum electrodes.

A Peano-HASEL actuator with integrated aluminum electrodes was suspended from an acrylic

frame with a 20 g weight hanging from the bottom. The actuator was then operated at 8 kV and 0.3

Hz using the voltage signal depicted in fig. S4. A skewed view of an aluminum-electrode actuator

clearly shows the geometry changes in the contracting area. A side view of the actuator further

demonstrates the geometry changes in the cross-section.

Movie S3. Scaling up forces with Peano-HASEL actuators.

Six Peano-HASEL actuators were stacked in a parallel configuration to scale up actuation force. A

500g weight was attached to the bottom of the stack, which was actuated at 8 kV with a 1 Hz

reversing-polarity square wave; a side view of the actuating stack shows the offset pouches

efficiently filling the space between the actuators during contraction. Next, a filled one-liter water

bottle (~ 1 kg) was attached to the bottom of the stack, which was actuated at 10 kV with a 2 Hz

reversing-polarity square wave.

Movie S4. Frequency response of Peano-HASEL actuators.

Actuation frequency of a Peano-HASEL actuator was varied from 1 Hz to 50 Hz at 8 kV; at 50 Hz,

actuation strain remained > 50% of its value at low frequencies.

Movie S5. Demonstration of precise and rapid actuation.

Two actuators were connected in parallel and mounted on an acrylic frame. The bottoms of the

actuators were attached to a lever arm. The end of the arm had a circular acrylic ‘hand’ which held

a table-tennis ball (2.7 g). We provided three distinct signals: First, we stepped voltage from 0 kV

to 12 kV in 1-kV increments, with 0.75 s hold time at each voltage. Second, we provided a modified

sine wave to demonstrate smooth muscle-like actuation. Finally, we provided a 13-kV voltage step,

which led to rapid contraction that threw the table-tennis ball 24 cm into the air.

Movie S6. Transparent Peano-HASEL actuators.

A three-unit Peano-HASEL actuator was placed in an acrylic box, with a 10 g weight hanging off

the bottom. A colorful image (Claude Monet’s ‘Water Lilies’) was placed in the background. The

actuator was submerged in a liquid dielectric (Drakeol 19 LT mineral oil); once submerged, the

actuator was nearly invisible – only bubbles trapped along the skirt during filling were apparent.

After clearing away trapped bubbles, the actuator was operated at 8 kV at frequencies of 1 Hz and

2 Hz. Only a faint outline of the electrodes was visible while lifting the weight.