Liquid metal nano-gyroid stretchable transparent conductor for ultra-resilient optoelectronics and electroluminescence

Abstract

The brittle nature of today’s displays, solar cells, and touchscreens leads to adverse economic and environmental impacts, driving the need for thin-film, flexible optoelectronics that are resistant to strain, impact, sharp objects, and liquids. This vision requires cost-effective, scalable production of ultra-resilient transparent conductors capable of withstanding millions of deformation cycles—challenges that nanowire-based electrodes have yet to overcome. In nature, particular insect wings achieve a unique blend of transparency, resilience, and lightness. This inspired us to develop liquid metal-based transparent conductors with nature-inspired gyroid-like nanostructures that outperformed nanowire-based counterparts significantly in conductivity and stretchability (7×), withstanding a record-breaking strain of 1400% and unprecedented stability over 100,000 strain cycles. Unlike nanowire-based electrodes, this electrode is simple, low-cost, scalable, and recyclable. The formation of such a nano-scaffold is beyond the reach of lithographic techniques but is enabled by our unconventional technique: graphene-assisted self-assembly of liquid metal nanodroplets into a porous 3D microstructure. We demonstrate mechanically resilient soft-matter electroluminescent displays with high light intensity and extend their applications to soft robotics, light-emitting muscles, energy harvesting, transparent heaters, and UV sensors. By harnessing the deformability of liquid metal, we demonstrate a transparent pressure-sensing film that converts any display into a pressure-sensing interface.

Introduction

Skin-alike electronics¹ that are soft, thin, and stretchable, envision futuristic applications in virtual and augmented reality², e-skins for soft machines^3–5, health monitoring stickers^6–10, e-textiles^11,12, and hybrid electronics¹³. Despite rapid progress in fabrication methods for stretchable interconnects, developing more advanced e-skins that can emit light, display information, or harvest energy remains challenging, as such functionalities require a stretchable transparent conductor (STC).

A soft-matter transparent conductor (TC) can also address the growing number of smartphones and tablets that end up in landfills due to cracked screens. The next generation of displays is expected to have a thinner form factor and support bending, rolling, twisting, and stretching, as well as support impact, sharp objects, and/or humidity.

Moreover, by exploiting the mechanical compliance of transparent electrodes, one can envisage a transparent pressure-sensing film that converts any screen into a pressure-sensitive one. A pressure-sensitive screen provides a richer human–machine interface, compared to current touchscreens.

However, unlike the flexible TCs based on nanometric films of indium tin oxide (ITO), which are commonplace, fabricating STCs remains a significant challenge. Recent progress in transparent and, in some cases, stretchable electronics has demonstrated transparent conductors and devices for soft actuators, wearable sensors, energy‑storage systems, and transparent heaters^14–17. Few works showed optoelectronic devices such as LEDs and photovoltaics based on PEDOT:PSS¹⁸, AgNWs¹⁹, and ITO²⁰ that are flexible or slightly stretchable. Hydrogels are stretchable^21,22 but lack the desired long-term stability, suffer from water evaporation, and their ionic conductivity limits their applications in electronics²³. Other efforts have focused on high-aspect ratio conductive fillers, such as silver nanowires (AgNWs)^24,25, carbon nanotubes (CNTs)^26,27, and graphene^28,29. Despite the high electrical conductivity of AgNW-based TCs, they are vulnerable to UV radiation^30,31, and suffer from high electromechanical coupling and hysteresis³² when subjected to mechanical strain, due to fragile wire-wire junctions. AgNW inks are costly, and their deposition is challenging due to the low ink concentration and adhesion, which limits their industrial application.

Unlike engineered TCs, in biology, a combination of mechanical resilience, optical transparency, and lightweight function is common. Among them, we studied the transparent layers in dragonfly wings, which are known for their remarkable flapping-wing aerodynamic performance, optical transparency (which aids in camouflage), lightweight design, and excellent resilience, enabling them to fly over 10,000 km. In insects, such transparency has been associated with camouflage and stealth during hunting, while the underlying nano-porous structure simultaneously optimizes strength-to-weight ratio and influences thermal regulation, so transparency can be regarded largely as a byproduct of this structural optimization.

Using scanning electron microscopy (SEM), we observed a 3D porous nanostructure (Fig. 1a and Supplementary Fig. 30) that provides optical transparency, lightweight properties, and excellent mechanical properties. Engineering a similar nanostructure is beyond the reach of lithographic techniques but is made possible in this work through nanoscale self-assembly.

Fig. 1. Overview of this work.

a Microscopic structure of translucent dragonfly wing vs. microscopic structure of the stretchable transparent conductor. Dragonfly illustration from FreeSVG (public domain). b Comparison between non-sintered and sintered LMND composite GO-Free (i–iii) and with GO@EGaIn (iv–vi). c, d Ashby graphs comparing this work with SOTA in terms of sheet conductivity as a function of maximum strain achieved (c), and mechanical strain cycling (d). The SOTA works are referenced as follows: 1-²⁹, 2-⁶⁰, 3-²⁷, 4-²⁶, 5-⁶¹, 6-⁶², 7-²⁵, 8-³², 9-⁶³, 10-⁶⁴. e Liquid-metal STC enables translucent pressure-sensing film to enable pressure-sensing on displays for a richer interface. f Examples of implemented electroluminescent devices that are resilient to sharp objects, impact, liquids, and >600% of strain.

As a conductor, we used eutectic gallium indium (EGaIn) liquid metal (LM), as it offers an excellent combination of electrical conductivity (3.4 × 10⁶ Sm⁻¹)³³, fluidic deformability, intrinsic self-healing properties, low gauge factor, and stability when subjected to repetitive mechanical strain. Therefore, the development of STCs based on EGaIn LM is highly desirable. Two works demonstrated visually imperceptible LM electrodes, through the patterning of LM with a linewidth as low as ~5 µm^32,34. These are promising advances, but not easily scalable in size and quantity due to the need for sputter deposition of Cr and Cu³², or a highly controlled and slow printing process using a glass-capillary nozzle³⁴. Moreover, the reported electrical conductivity and cyclic performance are a fraction of what is achieved with bulk LM conductors.

Here, we present an unconventional technique for forming STCs by self-assembling LM nanodroplets (LMNDs) into a 3D percolating network assisted by graphene oxide (GO). GO sheets act as large anchoring planes for LM droplets and considerably alter the arrangement of LMNDs after deposition and laser sintering. This anchoring behavior arises from electrostatic self-assembly followed by galvanic replacement and Ga-O-C bonding at the GO-LM interface, as detailed in Supplementary Note 1. Unlike GO-free LM nanodroplets, which spread evenly on the surface, an engineered, optimized GO@EGaIn composite forms a porous microstructure. Upon laser sintering, the microstructure further packs, resulting in increased porosity, leaving behind a light-transmitting 3D micro-scaffold similar to the gyroid-like structure in the translucent dragonfly’s wings (Supplementary Fig. 30).

This technique enables rapid, scalable, and low-cost fabrication of highly conductive, ultra-stretchable conductors with an unprecedented maximum strain tolerance of 1380% (Supplementary Fig. 29), withstanding >100,000 cycles at 150% strain. Using this electrode, we are advancing e-skins that can sense, display information, harvest energy, heat, and actuate. Compared to high-aspect-ratio conductors, this technique is readily scalable to large areas and enables higher sheet conductivity and a significant improvement in mechanical stretchability.

Figure 1b shows SEM images of non-sintered and laser-sintered films of LMNDs without GO (i–iii) and with GO (iv–vi). Only the latter results in a light-transmitting film due to its porous micro-scaffold. The formation of such microstructure is beyond the reach of conventional lithographic techniques but is enabled by simple self-assembly, laser-assisted packing, and aggregation behavior induced by GO sheets.

During ink preparation, positively charged EGaIn droplets assemble on negatively charged GO sheets (Supplementary Information Note 1 and Fig. S1). Yet, the deposited GO@EGaIn film is not conductive prior to laser sintering, as both ultrathin (~3 nm) Ga₂O₃ shells around LMNDs and GO sheets prevent a conductive path between droplets. A low-cost fiber laser with an infrared (IR) wavelength can simultaneously reduce GO and sinter LMNDs. LMNDs sintering is due to the thermal expansion of the droplets when hit by the laser, resulting in the rupture of the oxide shell around LMNDs, and the coalescence of droplets into conductive paths^35–37. Similar ns‑pulsed laser sintering and patterning approaches have been widely used to process liquid metal conductors for soft and stretchable electronics^38–40.

Simultaneously, the IR laser performs laser reduction and laser thinning of the GO (reducing the thickness of the GO layer), both contributing to improved electrical conductivity²⁸. At this stage, the correct composite nomination is rGO@EGaIn, as the GO is reduced. To achieve high electrical conductivity and optical transparency simultaneously, a careful selection of material synthesis and laser sintering parameters is required, as will be detailed later.

High-aspect ratio GO sheets act as a backbone structure with adhesive forces to attract the LMNDs (Fig. 1b-iv). These ultrathin backbone sheets determine the final geometry of the liquid metal 3D scaffold after laser sintering. The resulting STC using this method has a significantly higher sheet conductivity and stretchability compared to AgNWs, CNTs, or graphene, and their maximum strain at break (~1380%) is >7 times higher than the best works reported so far (Fig. 1c). Besides, for the first time, we show the long-term stability of an STC that could withstand at least 100k cycles of 150% strain (Fig. 1d). Moreover, the GO@EGaIn network is considerably less smearing to touch and mechanical pressure, compared to GO-free EGaIn nanoparticles (Supplementary Note 10 and Supplementary Fig. 22). Supplementary Table 4 shows some of the recent works in the field of STC, including their conductivity, stretchability, and optical transmittance.

Soft-matter TC obtained with this technique can be used to develop a transparent pressure-sensing e-skin by exploiting the liquid metal’s deformability. Such transparent pressure-sensing film can add pressure-sensing capability to any touchscreen display (Fig. 1e). This significantly enriches the human–machine interface and permits new possibilities in game and music applications.

We also demonstrate the development of ultra-resilient electroluminescent (EL) e-skins and e-textiles that can withstand mechanical strain, mechanical impact, sharp objects, and liquids. The developed EL devices show higher luminous intensity and strain tolerance (>600%) than the state of the art, and benefit from simpler fabrication and fewer layers, as will be detailed. Supplementary Fig. 35 shows an e-textile that incorporates an EL display and a stretchable thin-film battery.

Other applications shown in this work include transparent heaters, energy harvesting, UV sensors, and bio-inspired light-emitting actuators. In electrostatic actuators, having a low-stiffness electrode is critical. The GO@LMNDs electrode combines high electrical conductivity with low stiffness, thanks to its porosity and fluidic deformability, making it an ideal electrode material for soft robotics.

Results

Ink preparation, deposition, and laser processing

Encapsulation of EGaIn LMNDs using GO^41–43 was shown recently in a few works. These efforts focused on the synthesis of a stable GO-coated EGaIn colloid and did not report electrical conductivity, stretchability, or transparency. In one work⁴⁴, we showed the spray coating of a stable GO@EGaIn colloidal solution. However, despite a GO/EGaIn weight ratio of only ≈0.08, the laser-sintered electrodes exhibited high sheet resistance (several kΩ/square) and no stretchability.

We studied the microstructure of various GO@EGaIn composites and their electromechanical properties intensively after sintering. We found that the electrical, mechanical, and optical properties of the electrodes are sensitive to the synthesis, deposition, and sintering parameters. We found that there is a very narrow window of parameter values that yield high conductivity, stretchability, and transparency (Supplementary Fig. 23). The route for the successful fabrication of STC is to reduce the GO amount to the minimum possible, which is enough to drive the self-assembly of liquid metal droplets into 3D scaffolds, but not too little that it resembles the behavior of GO-free LMNDs (Fig. 1c-ii). A slight increase in GO above the optimal amount results in kΩ sheet resistance and reduced stretchability. These parameters were carefully engineered to achieve a balance between high electrical conductivity and optical transparency and are discussed in detail in Supplementary Note 1. This includes the role of sonication solution based on zeta potential measurements, the ratio between GO and EGaIn, the sonication time, and how we could coat GO over LMNDs sonicated in ethanol (which was previously reported as not possible in ethanol^43,45), using a double solvent solution.

Previous works on GO-free LM droplets and GO-coated droplets were prepared as stable colloidal solutions, which require a low concentration of the colloidal phase, which are typically spray-coated⁴⁶. In comparison, the highly concentrated GO@EGaIn network enables the scalable fabrication of uniform, large-area films using scalable techniques, such as rod/blade coating and stencil printing.

Referring to Fig. 2a, we synthesized EGaIn droplets (0.1–1 µm) in ethanol through probe sonication and added zero to four drops of low-concentrated (4 mg/ml) aqueous solution of GO (Dv90 5–7 µm), leading to a GO/EGaIn weight ratio of 0 to 0.002. LMNDs anchor to GO sheets via electrostatic interactions, forming small clusters of LMNDs. By optimizing synthesis and mixing parameters (Supplementary Fig. 2), we can promote the formation of large networks of GO@LMND that precipitate by gravity within less than 2 min (Supplementary Movie 1). Additionally, during settling, aggregates spontaneously stack, further increasing the settling rate. This will force all the dispersed droplets to settle at the bottom of the container, in a group of aggregates bonded to GO sheets. Finally, there is a complete phase separation between the solvent and GO@EGaIn clusters. We then remove the remaining solvent, leaving a highly concentrated GO@EGaIn ink (Fig. 2a-iv). Supplementary Fig. 31 shows the significant increase in the volume of GO@LMNDs compared to bulk LM, demonstrating the porosity of the resulting ink. Figure 2c illustrates how LM droplets assemble on the GO sheets, as well as the schematic design of the GO@EGaIn network after deposition, after sintering, and after elastomer encapsulation.

Fig. 2. GO@EGaIn composite.

a Synthesis process. b Deposition (i), rod coating (ii), and laser sintering (iii). c Illustration of GO@EGaIn network before and after laser sintering, and after polymer encapsulation d GO sheets (darker) over LM droplets (lighter). e Close-up on a GO sheet conformally adhering over the LM droplet. f Cross-section of a sintered GO@EGaIn film. g Close-up of the LMNDs aggregation thanks to GO sheets. h Comparison between non-sintered (left) and sintered (right) composite. i stretchable transparent conductor electrode.

We calculated that the specific surface area of GO is ~1200 higher than that of LMNDs with a diameter of 500 nm (SI Note 1). Thus, to obtain a 1:1 surface ratio for GO/EGaIn, the weight ratio should be ~0.0008. Based on this, we studied composites with GO/EGaIn surface ratios ranging from 0 to 0.002. Interestingly, the calculation matched the experimental results quite well. A GO/LM weight ratio of 0.0004 (surface ratio ~0.5) was found to be sufficient to cause self-stacking and resulted in an excellent sheet resistance of ~1 Ω/sq. Increasing GO by up to three times increases hole size and quantity (i.e., higher transmittance), with only minor changes in conductivity (Supplementary Figs. 3 and 4). However, a 4× increase in GO leads to ~13× sheet resistance, and a further rise in GO leads to kΩ range sheet resistance. The optimal GO/EGaIn ratio for precipitating the GO@LMND network and forming STC increases as LMND size decreases, with longer sonication time. However, smaller LMNDs form excessive Ga₂O₃ shells and are thus unsuitable (see Supplementary Note 1). SEM images in Fig. 2d and Supplementary Figs. 5–7 show that the GO sheets coated almost the entire surface of the LMNDs at a GO/EGaIn surface ratio of 1.5.

After the deposition of the film, we perform laser sintering using a MOPA (master oscillator power amplifier) IR wavelength fiber laser, an accessible equipment ( ~ 3000€) often used in print shops (see Supplementary Note 16 for laser parameters and fluence calculations). The laser beam breaks the oxide shell of LMNDs, resulting in the formation of highly conductive and optically translucent electrodes (Fig. 2c). An evaluation of the uniformity of the GO@EGaIn film in terms of electrical resistance and transmittance is presented in Supplementary Note 12 and Supplementary Fig. 25. We then pour a solution of hyperplastic styrene-isoprene (SIS) block copolymers over the particles, which infiltrates the porous structure, allowing the electrode to be lifted from the substrate. SIS also protects the LM scaffolds from coalescing during mechanical strain (Supplementary Fig. 31). Unlike the STCs based on AgNWs that require complex synthesis and deposition steps, GO@EGaIn STCs are formed in a few minutes using ordinary low-cost equipment.

We performed high-contrast SEM using Inlens scatter and backscattered electron detectors to distinguish GO sheets in the composite. GO sheets over the LMNDs are visible all over the composite (Fig. 2d, e and Supplementary Figs. 5–8). Notably, the droplets self-organize in a specific arrangement even before sintering. In Fig. 2d, one can see zones free of droplets. Interestingly, the GO sheets’ adhesive forces firmly hold droplets together, yet they do not coalesce, leading to the formation of an interesting porous structure. The particle arrangement is governed by the size and size distribution of LMNDs, and the quantity of GO sheets (Supplementary Information Note 1B and 1D). Figure 2e and Supplementary Fig. 6 show a GO-coated droplet. Figure 2g shows clearly how the binding between GO sheets and LMNDs holds together a long line of droplets, without causing the particles’ coalescence. The thickness of the film applied through rod coating is ~10 µm, which is reduced to ~7 µm after laser sintering (Fig. 2f and Supplementary Fig. 32). Cross-section microscope images from samples of GO@LMNDs and GO-Free LMNDs, prior to and after sintering, are presented in Supplementary Fig. 32 (sintered layer is at the bottom). Deposited films on glass were laser-sintered, infiltrated with SIS polymer, and then peeled from the glass. The sintering depth is ~3.5 µm; thus, some of the droplets remain non-sintered. Previous works that studied laser sintering of LMNDs (GO-free) demonstrated conductivity but not stretchability of the electrodes^36,37. GO replaces the brittle Ga₂O₃ semiconductor layer, thus contributing to the reduction of electromechanical coupling when subjected to mechanical strain³⁶ (Supplementary Figs. 18–20).

Upon laser sintering, the vacant spots in the composite become larger, as the LMNDs aggregate and pack around the GO sheets, resulting in a porous gyroid-like 3D structure (Fig. 2h–i). Therefore, the overall geometry of the 3D scaffold is dictated by the size and number of GO sheets, underscoring the importance of precisely controlling GO quantity and size.

Impact of the LMND size on self-assembly

In order to produce the transparency of the electrode, unlike the GO-free LMNDs that have a relatively uniform deposition over the surface (Fig. 1b-i, ii), the GO-coated LMNDs should have a porous structure, which results in the formation of STCs after laser sintering. For this purpose, it is necessary to establish the self-assembly of multiple LMNDs assisted by GO. Our analysis, further detailed in Supplementary Note 8, shows that such an effect only happens if the diameter of LMNDs is ~2-20x smaller than the GO sheet, which can be adjusted by sonication time. In this case, GO sheets help aggregate several LMNDs, thus resulting in the formation of a porous structure. See Supplementary Note 8 and Supplementary Fig. 21 for the detailed analysis.

Electromechanical and optical characterization

Samples produced with this technique can be stretched to a record-breaking 1380% before electrical failure (Fig. 3a). In addition, the STC benefits from a low gauge factor (<2 over 0–200%). Figure 3b shows the electromechanical coupling of the sample when subjected to an unprecedented number of 100,000 strain cycles at 150% strain, >10× the strain levels reported previously (Fig. 1e). The improved electrical conductivity, compared to previous works, is essential for applications such as energy harvesting and transparent heaters. The liquid deformability of the electrodes enhances the STC’s resilience against mechanically or thermally induced strains and can potentially address microcracks in solar panel current collectors. Moreover, the deformability of LM conductors can be exploited to form transparent resistive pressure sensors for pressure-sensitive screens.

Fig. 3. Translucid electrode characterization.

a Electrical resistance of STCs when subjected to mechanical strain until failure. b Electrical resistance against 100k cycles of 150% mechanical strain. c Examples of laser-patterned samples. d Optical transparency measurement of various samples. e Ashby graph comparing this work (both non-patterned STC with ~60% transmittance and patterned STC with ~90% transmittance) with SOTA in terms of sheet conductivity and optical transmittance. The SOTA works are referenced as follows: 1-⁶³, 2-²⁵, 3-⁶¹, 4-⁶², 5-⁶⁰, 6-²⁶, 7-²⁷, 8-²⁹, 9-³², 10-⁶⁴. f SEM images of line pattern (i), high magnification image from the remaining line after ablation (ii), and angled view of the same showing the sidewalls (iii). g Sheet resistance of several line patterns, varying the linewidth of the pattern, and comparison with the theoretical model. The experimental initial sheet resistance is R₀ = 1.02 ± 0.13 Ω/sq. h Sheet resistance of the sintered STC as a function of the laser power. i SEM images from the sintered but not-patterned STC using an Inlens detector.

Referring to Fig. 3d, the optical transmittance measurement showed a transmittance of ~70% at a wavelength of 400 nm and ~55% at higher wavelengths. This transparency is enough for EL devices and displays (Figs. 1g, h and 4a, b). Additionally, the evaluation of transmittance after repeated stretching is presented in Supplementary Fig. 27 and shows stable optical performance. Higher optical transparency can be readily achieved by laser patterning with the same fiber laser equipment used for sintering. We studied various pattern shapes (e.g., point, line, hexagon) (Fig. 3c), resulting in an optical transparency of up to 90% (Fig. 3d). Figure 3e compares the optical transparency and sheet conductivity of this work with previous works. Furthermore, Supplementary Note 13 presents the evaluation of the optical haze of the GO@EGaIn transparent samples, with a calculated value of 53.53% at 550 nm, and Supplementary Fig. 26 shows the calculated haze for one representative sample in the wavelength range from 400 to 700 nm.

Fig. 4. Applications.

a Schematics of stretchable EL device, comprised of a phosphor layer (ZnS:Cu) and two GO@EGaIn electrodes (i), the fabricated device under a mechanical strain of 600% (ii), examples of thin-film EL devices over polymer (iii, iv). Wearable EL blinker for bike/scooter riders with fluorescent oval frames, that serve as always-on markers surrounding each EL arrow to maintain visibility when the arrows are off (vi), and a 25-pixel e-textile EL device (vii); Maximum brightness (cd/m²) vs maximum strain tolerance of this work compared to state of the art (viii), and brightness as a function of strain (ix). The SOTA works are referenced as follows: 1-⁵⁴, 2-⁶³, 3-⁵⁵, 4-⁶⁵, 5-⁶⁶, 6-⁶⁷, 7-⁶⁸, 8-⁶⁹. b Energy-autonomous UV sensor skin. c Optical pressure-sensing matrix. d GO@EGaIn STC enabled translucent pressure-sensing film for pressure-sensing displays, taking advantage of the liquid deformability of liquid metal (i). Concept of pressure-sensing matrix (ii), and application of pressure-sensing film in games and music applications (iii). Transparent pressure-sensitive skin on a display for commanding the archery game (iv), and an array of transparent pressure sensors for a pressure-sensitive DJ application (v). Force is measured by the formation of a transparent strain gauge that acts as a force-sensitive resistor (vi, vii, viii).

We expected that laser patterning would cause a significant increase in the sheet resistance, proportional to the ablated area. Surprisingly, this was not the case. Figure 3g shows the sheet resistance of several 10 × 10 mm electrodes patterned as parallel lines, with a linewidth from 50 to 190 µm, showing nearly constant sheet resistance. Further analysis showed that this is due to ablation-induced sintering and packing.

We studied the dimensions of different zones of the electrodes through a comprehensive SEM analysis and developed a mathematical model that considers ablation-induced sintering and predicts the sheet resistance of the electrodes with ablated patterns (Supplementary Note 2, Supplementary Figs. 9–12, and Supplementary Tables 1–3). Referring to Fig. 3g and Supplementary Fig. 13, this model predicts the sheet resistance of the electrodes more precisely, compared to the model that does not consider the packed zone. Supplementary Fig. 33 clearly shows the packed edges of the traces. Supplementary Fig. 33 shows a 3D reconstruction of a patterned line, in which the sides of the patterned line also have a higher height than the center of the line.

Applications

Multiple applications were developed to demonstrate the versatility of this electrode for sensors, actuators, and displays.

Electroluminescent (EL) devices

A stretchable EL device was fabricated by sandwiching an emissive layer (ZnS:Cu-filled elastomer) between two GO@EGaIn electrodes (Fig. 4a). Having a transparent conductor on both sides permits double-sided light emission. The fabrication process is fast and straightforward, and the EL device can withstand >600% of strain (Fig. 4a and Supplementary Movie 2). Figure 4a, iii, iv, and v show examples of a developed ultrathin and ultra-resilient EL e-skin through high-resolution laser patterning. Figure 4a-vi shows an example of a wearable textile display for a scooter rider to give a turn right/left signal to the drivers behind (Supplementary Fig. 34 and Supplementary Movie 3).

Figure 4a-viii shows the measured luminance intensity compared to the SOTA, obtaining a maximum value of 413.1 cd/m². Supplementary Movie 3 shows a visual comparison between our EL device and a commercial EL device. Figure 4a-ix shows the luminance as a function of mechanical strain, which increases by 2× at 100% strain.

E-textile display

We also fabricated a 25-pixel e-textile display by laser patterning two STC grids sandwiching the intermediate EL layer (Fig. 4a-vii). Figure 4b, Supplementary Fig. 35, and Supplementary Movie 7 show an e-textile that combines an EL display and a battery. It incorporates a printed stretchable Ag-Ga battery^47–49 that powers a lung-shaped EL device and displays the respiration cycle.

Transparent temperature sensor and heater

Using the same GO@LMNDs composite but switching from an IR fiber to a CO₂ laser, we created a considerably different composite in which GO is reduced, but LM droplets do not coalesce. Supplementary Fig. 37 shows a considerable difference in microstructure. CO₂ laser-sintered GO@EGaIn has a sheet resistance in the kΩ range and permits the fabrication of both a joule heater and a temperature sensor (Supplementary Note 4 and Supplementary Fig. 16). Figure 4c, Supplementary Fig. 37, and Supplementary Movie 4 show a soft, transparent heater under a thermal camera. The improved electrical conductivity and mechanical resilience of GO@LMNDs compared to TCs based on metal oxide films enable applications for rapid heating of glass or car mirrors.

Energy-autonomous UV sensor

Thanks to their optical transparency, STC electrodes can be used to construct an energy harvesting film that generates a current in response to light. Here, we demonstrate this by fabricating an energy-autonomous UV sensor. We fabricated a zinc oxide (ZnO)-elastomer composite and placed it between two STC electrodes. This device generates a current in response to UV light (Supplementary Fig. 36a). This UV sensor can operate in two modes: photoresistor mode and self-powered mode (Supplementary Fig. 28). See Supplementary Note 15 for details.

We showed a deformable energy-autonomous UV light sensor that can be used as a wearable UV exposure patch (Fig. 4b and Supplementary Fig. 36). Supplementary Fig. 36 and Supplementary Movie 6 show a rotating sunflower-inspired machine that turns toward the light. By exploring the deformability of the UV sensor, we developed an innovative multi-node light-assisted pressure-sensing device (Fig. 4c, Supplementary Fig. 40, and Supplementary Movie 9).

Transparent pressure-sensing films for the next generation of human–machine interfaces (HMIs)

Taking advantage of the electrode’s transparency and deformability, we fabricated a transparent pressure-sensitive resistor that can convert a display into a pressure-sensitive screen (Fig. 4d-i-ii and Supplementary Fig. 17), showing the concept of pressure-sensitive film through resistive sensing. By measuring pressure, the transparent e-skin provides a richer interface than current tactile displays. Figure 4d-iv and Supplementary Movie 5 show this e-skin over a screen to adjust bow power in an archery game. The fluidic nature of the liquid metal enables pressure sensing through electrode deformation. Figure 4d-v and Supplementary Movie 5 demonstrate the pressure-sensitive film as an interface in pressure-sensitive buttons in a DJ application. By combining pressure-sensitive input and a visual 3D effect on the screen, we created a rich HMI. Figure 4d-vi-viii shows the functioning concept. Sensing elements are created by isolating a serpentine geometry from the overall TC electrode to act as a force-sensitive resistor.

Nature-inspired light-emitting actuators and jellyfish-inspired soft robot

Electrostatic actuators, such as dielectric elastomer actuators, require low-stiffness, ultra-stretchable electrodes. Currently, most works use carbon grease, which is impractical due to its tendency to smear. Here, we show the utilization of our STC to develop HASEL actuators⁵⁰. Moreover, we combine actuation with sensing and light emission to develop an integrated jellyfish-like soft robot (Fig. 5a).

Fig. 5. Jellyfish-inspired “robot” with integrated actuator, display, and sensors.

a Schematics of various components of the robot including GO@EGaIn electrode (i), Two light-emitting “muscles” (right and left) composed of dielectric liquid and phosphor particles inside a thin stretchable bag, sandwiched between STC electrodes (ii), the UV sensors (iii), the EL display (iv), the proximity and touch sensors (v), and the PDMS mold (vi). b Image from coleoidea (Squid) (Photo Credit: Shutterstock), and its chromatophores at expanded and punctate states (reproduced by permission from ref. ⁵²). c Schematics of chromatophores-inspired light-emitting actuator and sensor skin. Light emission occurs simultaneously with actuation. d Light emitting during actuation of the right-side soft actuator in a jellyfish-inspired robot. e The fabricated jellyfish-inspired robot with GO@LMNDs-based actuators, sensors, and EL. In the hand: STC that was later integrated into the robot to form the simultaneous actuation and lighting (i), other light-emitting jellyfish prototypes (ii, iii).

Certain animal species produce colors on their skin for camouflage or to signal opposite-sex attraction (Fig. 5b). This is achieved by chromatophores (color-producing cells), which use actuation mechanisms to disperse or aggregate pigments. In Doryteuthis pealeii, each chromatocyte has radially arranged muscles that pull the pigmented cell outward into a flat-colored disc⁵¹. When actuated, dorsal mantle chromatophores transit from a punctate to an expanded state in response to visual cues (Fig. 5b)⁵². This inspired us to fabricate light-emitting actuators. We incorporated ZnS:Cu particles in the dielectric liquid of the HASEL actuator. Upon actuation, the HASEL electrodes get closer, resulting in EL light emission (Fig. 5c, d). Supplementary Movie 8 and Supplementary Fig. 38 show examples of HASEL actuators we developed.

Furthermore, we can incorporate proximity, touch, pressure, and light sensors in the e-skin by laser patterning the same STC. Figure 5a shows schematics of a soft robot inspired by a jellyfish (Fig. 5h) that incorporates a HASEL actuator that emits light upon actuation, two UV sensors that act as “eyes”, a touch/proximity e-skin, and another non-actuating EL layer. Figure 5e shows the developed robot that reacts to proximity, touch, and UV light direction (Supplementary Movie 8).

In summary, GO@LMNDs STCs were demonstrated for sensing proximity, pressure, temperature, and light; for harvesting energy; as electrodes for EL displays; for heating; and for soft actuators that emit light.

Pol-gel universal method for plug-and-play fusion of multi-layer devices

Advanced e-skin with sensing, actuation, or display functions requires fabricating multiple independent ultrathin (<100 µm) e-skin layers and integrating them into a single film. Here, we show a universal approach for the fusion of independently manufactured ultrathin layers by leveraging the porosity of the STC electrode, whose surface is composed of conductive GO@EGaIn and styrenic block copolymer (BCPs) (Supplementary Fig. 15). The existing non-permanent physical cross-linkers in styrenic BCPs permit a reversible polymer-gel transition, which we previously employed for room temperature microchip soldering⁵³, which is here adapted for e-skin layer fusion. The pol-gel transition is triggered by the polymer’s solvent and results in an adhesive gel. Once at the gel state, we unite the functional layers. This results in a seamless fusion of the layers. Supplementary Note 3 further describes this technique, and Supplementary Fig. 14 provides a schematic of the process used to develop EL devices and e-skin sensors.

Supplementary Fig. 34 shows the cross-section of the EL device that was developed by fusing the STC electrode and the ZnS:Cu-TPU composite. We first coated a few drops of the polymer solvent onto the STC surface using a rod, forming a thin layer of adhesive gel, and then joined the layers. Prior to this method, when we applied the STC directly over the ZnS:Cu-TPU composite, we experienced low light intensity and light degradation over time. The pol-gel fusion technique addresses both problems. Moreover, the EL devices developed in this work did not require the integration of a high-dielectric intermediate layer, as reported in previous works^54,55. We hypothesize that this improvement is due to the approximation of STC to the ZnS particles, reaching a distance <20 µm. Moreover, both GO and gallium oxide may contribute to improved dielectric properties of the composite^56,57. It is known that the quality of the interface is essential in multi-layer circuits. This technique guarantees an excellent mechanical and electrical interface between the layers.

In summary, the pol-gel technique enables “plug-and-play” fabrication of complex e-skins and can be extended as a universal technique for multi-layer sensors, actuators, energy harvesting, and energy storage devices, as well as for integrating e-skins onto textiles or plastics.

The GO@EGaIn can also be recovered and recycled from the fabricated SIS-based circuits by using an environmentally friendly solvent (2-methyltetrahydrofuran) to dissolve the SIS block copolymer from the circuits and extract the GO@EGaIn in the form of an agglomerated chunk. Supplementary Fig. 39 shows the recovery process of the ink and fabrication of a resistive pressure sensor using the recycled metal.

Discussion

This study presents a novel STC that combines high electrical conductivity with exceptional mechanical resilience, enabling applications in optoelectronics, flexible displays, soft robotics, and electronic skins. The STC exhibits remarkable durability under repeated strain cycles, outperforming previous works. While the current level of optical transparency requires further optimization, it is worth noting that traditional transparent conductors such as ITO are ultrathin films (100–200 nm). In contrast, the increased thickness of the conductive layer in our system, though less favorable for transparency, is crucial for functionalities such as stretchable transparent sensors and heaters. Furthermore, we demonstrate that transparency can be significantly enhanced through laser patterning, offering a tunable pathway to balance optical and electrical performance.

Further improvements in transparency are expected through optimization at both the material and fabrication levels. At the material level, one key approach is to control the porosity of the conductive network by tuning the size and distribution of the GO sheets. As discussed previously, the geometry and pore structure of the final conductor are strongly influenced by GO sheet dimensions. While we systematically varied the size of the LMNDs, our work was limited by the size range of commercially available GO. Future studies will focus on using GO sheets with tailored lateral dimensions to further enhance transparency.

At the fabrication level, advanced laser processing techniques—such as femtosecond laser sintering and ablation—offer promising routes to enhance transparency. These methods can improve the packing density of the liquid metal and introduce controlled porosity, enabling precise tuning of structural parameters and potentially leading to a significant increase in optical transmittance.

The use of a laser for sintering liquid metal nanoparticles can also bring other possibilities for optoelectronics. For instance, one recent work showed that the infrared emissivity of films made with LMNDs can be tuned using an IR laser⁵⁸. Moreover, laser-induced graphene with a high surface can be formed in situ, over the LMNDs, if they are coated with proper polymers, such as poly(amic acid)⁵⁹.

Furthermore, the substrate has an important role in the uniform deposition and patterning of STCs. Good surface adhesion facilitates ink deposition and patterning. In order to eliminate this limitation, in this work, we used the “inverse” fabrication technique. The “inverse” fabrication technique consists of back-filling the sintered electrode with the pre-polymer solution, which fills the gaps in porous electrodes. This allows for protection of the microstructure, and also results in electrodes that are considerably smoother, compared to the direct method, i.e., coating the ink over the polymer film. Moreover, through this technique, our options for choosing the substrate are broader, which is important for subsequent layer deposition.

As this study introduces a novel approach for fabricating STCs, further investigation is warranted into aspects such as long-term stability, cytotoxicity, and manufacturing reparability.

Methods

GO@EGaIn composite preparation

To produce EGaIn liquid metal, a mixture of gallium (75.5 wt%) and indium (24.5 wt%) was placed in a glass container and heated on a hot plate at 250 °C for 4 h. To prepare a suspension of LM Nano Droplets (LMND), 0.4 g of EGaIn was added to a container containing ethanol (Chemlab, 100%) to a final volume of 20 ml. We employed a probe sonication (LAWSON scientific, 650 W, 25 KHz) process to generate LMND, for 10 min at 90% in an ice bath. After sonication, the GO@EGaIn composite was obtained by mixing different quantities of graphene oxide water dispersion (50, 100, 150, 200 µg) (Graphenea, 0.4 wt.% GO) depending on the GO/LM ratios required. The mixture is left to rest for ≈2 min to allow the GO-LMND aggregates to form, interact, and finally settle to the bottom of the container. After that time, the phase separation between ethanol and the highly concentrated ink is distinguishable. The excess solvent is removed using a pipette until the phase separation is no longer noticeable, leaving the GO@EGaIn particles and some residual ethanol.

PVA

A poly(vinyl alcohol) (PVA) solution is synthesized by mixing 5 g of PVA powder (SEKISU, Selvol 523S) with 50 mL of H₂O. The mixture was stirred at 90 °C on a hot plate (AGIMATIC-N) until it formed a clear, homogeneous solution.

Film deposition

First, two pieces of tape (Miarco, ≈55-µm thick) are stuck to the glass to create a gap between the applicator rod and the glass during material deposition. Then, the PVA solution is applied to a glass and left to dry for ≈1 h in the oven at 60 °C. The PVA layer functions as a sacrificial layer to facilitate the film removal at the end of device fabrication. Afterward, the GO@EGaIn composite is transferred over the PVA layer using a pipette and spread using the rod. The uniformity of the thin film is achieved by repeatedly pushing the GO@EGaIn particles in different directions. The film is then dried with a hot-air gun or in an oven at 60 °C.

Laser sintering and ablation

The GO@EGaIn film is laser sintered using a MOPA (Master Oscillator Power Amplifier) infrared wavelength fiber laser (UNICHCNC, 1064 nm, 20 W), with a hatch pattern of 0.01 mm line spacing (power = 20% (4 W), frequency = 200 KHz, pulse width = 9 ns). Laser ablation of the film was performed with a hatch pattern of 0.05 mm line space (power = 100%, frequency = 50 KHz, pulse width = 20 ns).

Line and hexagonal pattern ablation

Laser ablation patterns were performed with the MOPA laser configured with a 3-loop count (power = 70%, frequency = 50 KHz, pulse width = 20 ns, start TC = −25, laser off = 200 us, end TC = 0 us, polygon TC = 75 us).

Scanning electron microscopy

Four field-emission microscopes were used to analyze the samples, achieving the required resolution and contrast. Hitachi SU8600 was used in samples in Supplementary Fig. 5a.i and Supplementary Fig. 33c. Zeiss Sigma 360 was used in Figs. 1c, 2h, 3f and Supplementary Figs. 5a.ii-iii, 8a, and 32c. Zeiss Gemini 360 was used in the Figs. 1a and 2d, e, g and Supplementary Figs. 2a, 4, and 6. Thermofischer was used in Figs. 2f. i and 3c and Supplementary Figs. 3a, 5b, 14e, 15, 33b, 37a, b.

Electromechanical characterization

The GO@EGaIn film was deposited onto the sacrificial PVA layer and then laser-sintered. Laser ablation isolated rectangular areas measuring 10 × 70 mm from the sintered film. Then, the substrate solution of SIS polymer or Ecoflex™ (Smooth-On, 00-30) is applied over the samples using the thin-film applicator (ZUA 2000, ZEHNTNER) adjusted to 700 µm. SIS-based samples are dried at room temperature for 3 h, and Ecoflex™ in the oven at 60 °C for 1 h. The film containing the samples and PVA is peeled from the glass and placed in water for 1 h to fully dissolve the sacrificial PVA layer. The individual samples are then cut by a CO₂ laser (VLS 3.50, Universal Laser Systems Inc.).

For electromechanical testing, we used an Instron 5969 with a 100 N load cell and a data acquisition system composed of a multimeter (GW Instek GDM-8351) and 16-bit DAQ (NI USB 6002). Electrical resistance measurements were performed on each sample using a desktop multimeter (GW Instek GDM-8351).

Optical characterization

A GO@EGaIn film is deposited over a sacrificial PVA layer, then laser-sintered and/or patterned. Rectangles with a size of 60 × 90 mm are isolated from the sintered film by laser ablation. Then, PDMS is applied to the samples using the thin-film applicator set to 700 µm. The samples are dried in the oven at 60 °C for 2 h, then peeled from the glass and placed in water for 1 h to dissolve the sacrificial PVA layer.

For the visible spectroscopy test, a detector (Spectroradiometer Opsytec SR900) was used from 200 to 1100 nm, along with a 150 W Dolan-Jenner DC950 quartz-halogen light source. The samples are placed between the light source and the detector using a sample holder, and the sample’s transmittance is measured. An isolated PDMS layer was used as a reference.

Electroluminescent composite blend

A blend of 1.65 g of EL phosphor (KPT Co., D310CT) and 1 g of waterborne polyurethane (ALBERDINGK^®, U 4101) was mixed using the planetary mixer (THINKY, ARE-250) at 2000 rpm for 3 min.

Electroluminescent light devices

The electroluminescent (EL) device consists of two separate layers bonded together. The first layer of the EL device starts with a glass coated with PVA, on which the GO@EGaIn film is deposited via rod coating, followed by laser sintering of the entire EL area. Next, design patterns were ablated with the MOPA laser at the places of the EL that should not light up. Then, the EL blend was rod-coated over the pattern and dried in the oven at 60 °C for 1 h. On a separate glass, a layer of SIS-based GO@EGaIn was fabricated using the same procedure as described in the section “Electromechanical characterization”. To bind the two layers of the EL device, a thin layer of toluene was rod-coated onto the phosphor composite, and the second layer was then gently applied immediately after. The exposed ink side of the second layer was glued to the phosphor due to slight SIS dissolution, promoted by toluene. After drying in the oven, the two layers are strongly attached. To connect the EL device to the power source (a pocket EL inverter, ≈360 Vpkpk at ≈2 KHz), electrical contacts were made with copper tape and silver ink.

EL driving circuit

A custom-made EL inverter power source was developed using a repurposed transformer (SMT-28V-NB 42 A). A pulsed voltage was applied to its primary side, controlled by a MOSFET (IPA80R1K0CE). By using a PWM (Pulse Width Modulation) signal with a frequency of 47 KHz and a 20% duty cycle, produced by a signal generator (MFG-2230M, GW Instek), the amplitude of the AC voltage output at the transformer’s secondary side was adjusted by varying the DC voltage source from 0 to 45 V.

EL newspaper

The EL newspaper was fabricated using a process similar to that of the previously described EL device, i.e., by sandwiching the EL layer between GO@EGaIn layers to make the base EL device. Then an opaque layer was prepared by mixing 1 g of WPU with 0.2 g of black pigment (FabTone™, Holden’s Latex) in a planetary mixer at 2000 RPM for 3 min. A uniform 50 µm thick layer of this mixture was applied using a spiral bar coater and then dried in an oven at 60 °C for 1 h, and then patterned with a newspaper design using a UV laser (INNO laser 5 W, Advanced Optowave) set to 99% power, with a speed of 800 mm/s, a frequency of 20 KHz, and a pitch of 0.05 mm.

Display textile

Each EL blinker follows the same procedure as described in the section Electroluminescent light devices using an arrow design pattern. The fluorescent oval frame that was attached around each EL arrow used a fluorescent blend of 1.65 g of ZnS:Cu particles (ONYXMET, CAS Nr: 150361-05-0) and 1 g of waterborne polyurethane (ALBERDINGK®, U 4101), mixed at 2000 rpm for 3 min. A thermoplastic polyurethane sheet (BEMIS™, ST604 TPU) with one side heat-activated adhesive was coated with the fluorescent blend on the non-adhesive side. After curing in an oven at 60 °C for 1 h, the oval design was laser-cut using a CO₂ laser and glued to the textile, along with the EL arrow, using a heat press. The power source (pocket EL inverter, ≈360 Vpkpk at ≈2 KHz) was configured to blinking mode, and the arrow selection was done using an electric switch.

25-pixel display

The 25-pixel display was fabricated layer by layer rather than making two separate parts that are joined afterward (section Electroluminescent light devices). The display uses a matrix configuration, lines, and columns sandwiched in the intermediate EL layer. First, the fabrication process starts with a glass coated with PVA, where a thin layer of SIS solution (20 wt% SIS) is applied by rod coating. Then, the GO@EGaIn film is deposited via rod coating, followed by laser sintering of the whole area. Next, the matrix lines were isolated by ablation with the MOPA laser. Then, the EL blend was rod-coated over the lines and dried in the oven at 60 °C for 1 h. Afterward, the matrix columns were printed on paper using a paper stencil with SIS-Silver-EGaIn ink and dried in the oven at 60 °C for 10 min. Then, a PDMS layer was deposited using the thin-film applicator set to 700 µm, and the sample was placed in the oven at 60 °C for 2 h to cure. Finally, the display was peeled from the glass and placed in water to dissolve the PVA sacrificial layer. Additional flexible printed circuit boards (FPCB) were added to establish connections to the external driving circuit. SIS-Silver-EGaIn ink was used to promote the electrical interface between the display and the FPCBs. The external driving circuit consists of a microcontroller (µC) (Cypress, PSOC 4) that uses ten digital outputs to control the 25 EL lights. The µC outputs are isolated via triac driver optocouplers (MOC3063SM), which are connected to triacs (Z0103MN) to control the EL inverter output to the matrix. The microcontroller scans each EL “pixel” and updates it according to the desired display number.

Luminance characterization

The EL samples are prepared as described in the “Electroluminescent light devices” methods section. To measure the luminance of the samples, the test is conducted in a dark room and consists of two steps: (1) Reference measure with the EL device turned off; (2) Luminance measurement with the EL device turned on using a spectroradiometer (Apacer Technology Inc., AL100/AL110). The device was placed over the sample, and the measurements were taken for different applied input voltages. The measurements were made with the device set to auto-sampling rate, with the luminance value displayed in cd/m² on the screen.

SIS-silver-EGaIn ink

The ink is prepared by dissolving SIS into toluene (20 wt% SIS) until a clear solution is obtained. For each 1 g of the SIS solution, 1.65 g of Ag flakes (Technic Inc., Silflake 071) and 1.65 g of EGaIn are added and mixed using the mixer at 2000 rpm for 3 min.

Pressure-sensitive display

The GO@EGaIn deposition uses the procedure described in the section “Film deposition” followed by laser sintering and circuit isolation by laser ablation. After that, a PDMS layer was deposited using the thin-film applicator adjusted to 700 µm and left to cure in the oven at 60 °C for 2 h. Finally, the display was peeled from the glass and placed in water to dissolve the PVA sacrificial layer. The pressure resistor sensor device was acquired using an analog-to-digital converter (ADS122C04) and an Arduino board (ESP8266-12F), both connected to the PC via USB. The archery game was made using the Unity development platform, which receives pressure data from a USB device and controls the arch.

Transparent heater

The GO@EGaIn deposition follows the procedure described in the “Film deposition” section. The heater consists of a thin line (heating element) created by the MOPA laser using selective sintering, with the wavy line corresponding to the non-sintered region. To make the heating element conductive, the central zone of the non-sintered GO@EGaIn line was exposed to a CO₂ laser (Universal Laser Systems Inc., VLS 3.50) in rast mode (power = 10%, speed = 30% ppi = 1000). Then, PDMS is cast over the device using the thin-film applicator set to 700 µm, and the device is placed in the oven at 60 °C for 2 h. After peeling the circuit and removing the PVA sacrificial layer, additional PDMS was poured onto the exposed ink side. The heating was controlled using a power supply (Elektro-Automatik, EA-PS 2384-05 B), regulating the voltage between 0 and 80 V. Thermal images were taken by (XEAST®, XE-33).

Liquid gallium battery

An SIS layer used as the battery substrate is coated with a thin film, with a thickness of 700 µm. The battery was digitally printed using a Voltera V1 printer, in the following order: first current collector (Ag-EGaIn-SIS), second current collector (Carbon-SIS), and electrodes (cathode: Ag₂O-Carbon-SIS, anode: Ga-Carbon-SIS). The composites used in each layer were fabricated as in ref. ⁴⁹. After printing, the hydrogel electrolyte is placed on top of the electrodes. For the encapsulation, an SIS film is placed on top of the whole battery. Two sets of batteries are printed with seven cells connected in parallel. Then, these two sets are connected in series. This way, the necessary current (105 mA) and voltage (3.3 V) are ensured to be provided for powering the EL patch.

Integrated battery and electroluminescent patch

The EL patch was fabricated using the procedure described in the “Electroluminescent light devices” section, and the battery as described in the “Liquid gallium battery” section. To create the lung shape, a design was drawn and applied to the laser during ink ablation. The EL patch is encapsulated with SIS and placed on top of the battery. The circuitry used to control the EL patch was constructed with a PSOC 4 Bluetooth module (CY8CKIT-042-BLE, Cypress), programmed to modulate the EL light intensity in a pulsing pattern. Additionally, a triac driver optocoupler (MOC3063SM) and a triac (Z0103MN) were employed as the driving circuit in conjunction with an EL power source (pocket EL inverter, ≈360 Vpkpk at ≈2 KHz).

HASEL actuator

The dielectric shell of the hydraulically amplified self-healing electrostatic (HASEL) actuators was made from a TPU film with a thickness of 50 µm (BEMIS™, TPU 3412). The dielectric shells were heat-sealed using a fabrication process similar to ref. ⁵⁰ by using a commercially available 3D printer (Creality, CR10S PRO) that was repurposed as a CNC heat-sealing device. A 2D drawing of the heat-seal design defined the path of the heated extruder tip on the printer. The backpaper of the TPU film was left during the heat-sealing process to help evenly distribute the force of the heat-sealing tip. Two sheets of TPU were joined with the backpaper pointing outside and placed on the base plate of the printer. A general-purpose mold release (Mann, Ease Release™ 200) was sprayed onto the TPU layers before joining to prevent strong adhesion between the layers. The backpaper of the TPU was used to distribute heat during the sealing process evenly and to prevent the TPU from melting through. All heat-seal designs included a one-sided opening serving as a fill port. A silicon oil (Silicones, 5 cSt) was used as the liquid dielectric. A syringe with a needle was used to fill the chamber(s) of the heat-sealed dielectric shell with the liquid dielectric through this port. The fill port was sealed with food sealer equipment (Qilive) repurposed for TPU sealing.

Energy harvesting /UV sensing e-skin

These e-skins were created from two separate layers that were bonded together. The first layer of the sensor starts with a glass coated with PVA, where the GO@EGaIn film is applied using rod coating, followed by laser sintering of the entire sensor area. Then, the two sensors were separated by ablation using the MOPA laser. After that, the UV-sensitive material, prepared by mixing 0.2 g of SIS with 1.8 g of toluene and 0.2 g of ZnO powder using a planetary mixer, was applied with a rod coating over the pattern and dried in an oven at 60 °C for 15 min. A layer of SIS-based GO@EGaIn was created on another piece of glass using the method described in the section “Samples for characterization fabrication.” To connect the two layers of the sensor device, a thin layer of toluene was applied with a rod over the ZnO composite, and the second layer was then gently applied immediately afterward. After drying in the oven, the two layers became firmly attached.

Jellyfish-inspired robot

The jellyfish-inspired soft robot comprised distinct components (see Fig. 5a): an EL layer, two HASEL actuators, and two ZnO sensors. These components were fabricated using the methods previously described and then manually assembled layer by layer. Phosphor particles were added to the dielectric liquid of the HASEL actuator before the filling process to illuminate during actuation. Software running on a PC was developed to control the actuators and measure the UV sensors. A microcontroller (PSOC 4, Cypress) was utilized to read the analog voltage output of the UV sensors. Additionally, a signal generator (MFG-2230M, Gw Instek), a power supply (EA-PS 2384-05, Elektro-Automatik), and two DC/DC converters (Q50-5, XP Power) were employed to excite the HASEL actuators independently.

Author contributions

P.A.L. and M.C.F. contributed equally to this work. They conceived and performed the experiments, carried out the data analysis, and contributed to writing the manuscript. A.S. provided analytical support, including image analysis. J.V. assisted with 3D design and with capturing photographic and video documentation. M.M. assisted with optical characterization and related measurements. M.T. acquired funding, supervised the research, guided project direction, and wrote the majority of the manuscript. All authors read and approved the final manuscript.

Data availability

All data generated or analyzed during this study are included in this published article or in the supplementary information files. The codes used in the prototypes of Figs. 4 and 5, are available from the corresponding author on reasonable request.

Code availability

The codes used in the prototypes of Figs. 4 and 5, are available from the corresponding author on reasonable request.

Competing interests

The authors declare no competing financial or non-financial interests. Pending patent application “Suspension, colloid or network comprising liquid metal droplets bound with graphene-based particles, respective ink, transparent stretchable conductor and obtention process thereof” (US application no. 18/860,738, filed 26 April 2023) is co–invented by the undersigned and co–inventors Mahmoud Tavakoli, Pedro Filipe Alhais Lopes, Alexandre Chambel, Marta Sofia Calisto Freitas, and Afsaneh Lalsanati, and is filed by Universidade de Coimbra. This patent application is currently pending and covers the composition of the liquid metal/graphene-based conductive suspensions and inks, as well as the processes used to fabricate the transparent, stretchable conductors that are employed in the devices reported in this manuscript. Author M.T. is a Guest Editor of npj flexible electronics collection Liquid Metals-Based Devices for Flexible Electronics. M.T. was not involved in the journal’s review of, or decisions related to, this manuscript.

Supplementary information

The online version contains supplementary material available at 10.1038/s41528-026-00586-w.