Underwater dielectric elastomer actuators with large bending deformation for soft robots

Underwater dielectric elastomer actuators with large bending deformation for soft robots | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Underwater dielectric elastomer actuators with large bending deformation for soft robots Chiho Murata, Takumi Shibuya, Naoki A Uemura, Kengo Kusama, Daisuke Nakane, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9133026/v1 This work is licensed under a CC BY 4.0 License Status: Under Revision Version 1 posted 12 You are reading this latest preprint version Abstract Soft robots are promising platforms for underwater exploration and biological sampling because of their compliance and adaptability. Dielectric elastomer actuators (DEAs), particularly bending DEAs, are appealing for underwater soft robots because they enable diverse robotic architectures. However, previously reported underwater bending DEAs still present opportunities for improvement in deformation capability, particularly in terms of deformation magnitude and actuation speed. Therefore, this paper presents an underwater DEA consisting of a layered elastomeric structure with an encapsulated water electrode and inextensible materials, which together generate unidirectional bending deformation when a high voltage is applied between the internal water electrode and the surrounding water. Consequently, the actuator achieves a maximum bending angle of 308.5° (corresponding to a curvature of 0.09/mm), which agrees well with predictions from an analytical model. Additionally, it attains an average actuation speed magnitude of 172.2°/s and a blocked force of 57.2 mN while maintaining stable actuation over 1000 cycles. The actuator was further demonstrated as an electrically driven biohybrid luminescent device incorporating Pyrocystis lunula and as a soft gripper capable of manipulating a live jellyfish. These results highlight the potential of the proposed DEA for advancing underwater soft robotic systems. Physical sciences/Engineering Physical sciences/Materials science Physical sciences/Physics Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Soft robots are constructed from compliant materials and are characterized by their simple structures, high adaptability to surrounding environments, and safe interactions with humans and external objects owing to their low impact upon contact [ 1 – 5 ]. In recent years, underwater soft robotic systems have garnered growing attention due to their diverse potential applications in exploration, environmental monitoring, and biological sampling [ 6 – 10 ]. These robots have demonstrated swimming motions that mimic those of aquatic organisms [ 11 – 13 ], as well as the ability to safely handle delicate marine life by leveraging their structural compliance [ 14 – 16 ]. Actuators play a crucial role in driving underwater soft robots. Among the various types of soft actuators [ 17 – 21 ], dielectric elastomer actuators (DEAs) are considered one of the most promising [ 22 – 26 ]. A DEA consists of an elastomeric membrane sandwiched between two compliant electrodes. When a voltage is applied across the electrodes, an electrostatic force is generated between them, compressing the elastomer membrane in the thickness direction and causing it to expand in the planar directions. This deformation can be harnessed for voltage-controlled actuation. DEAs offer large actuation strains (e.g., 50% linear strain [ 27 ]), fast response times (e.g., 1 kHz [ 28 ]), and high power density (e.g., 600 W/kg [ 29 ]). Their simple structure and electrically driven operation facilitate integration into autonomous soft robots, including those designed for underwater environments [ 30 – 32 ]. Among the various configurations of underwater DEAs, those that achieve bending deformation are particularly versatile and frequently used to drive soft robots inspired by fish [ 30 , 33 , 34 ], jellyfish [ 32 , 35 , 36 ], and rays [ 37 – 39 ]. Nevertheless, the deformation capabilities of previously reported underwater bending DEAs still require further refinement in terms of both deformation magnitude and actuation speed. For example, in the aforementioned studies, the bending angles and actuation speeds range from 5.0° to 48.0° and from 12.6°/s to 102.0°/s, respectively (see Supplementary Table 1 for details). Achieving larger and faster deformations could expand the range of applications, particularly for devices used in sampling tasks. This study aims to provide an underwater DEA capable of generating large deformations. The proposed actuator features an elastomeric layered structure that encapsulates a liquid electrode. An inextensible flexible film and a set of frames are attached to one side of the actuator structure to constrain deformation in the direction orthogonal to bending, thereby enhancing the actuation magnitude. In this study, the proposed actuator concept was demonstrated through modeling, fabrication, and characterization, as well as through its implementation in underwater soft robotic devices. Results and discussion The underwater DEA developed in this study is shown in Fig. 1 a. The actuator comprises a layered structure that encapsulates water as an electrode (Fig. 1 b). The section containing water is hereafter referred to as the chamber. An inextensible flexible film made of oriented polypropylene (OPP) is attached to one side of the structure to act as a strain-limiting layer. Additionally, polyethylene terephthalate (PET) frames are affixed on top of the film to further constrain structural deformation perpendicular to the bending direction. When a high voltage is applied to the chamber while the surrounding water serves as the ground electrode, an electrostatic force (Maxwell stress) is generated between the external water and the chamber. This electrostatic force compresses and induces elongation of the elastomeric layer on the non-constraint side, leading to bending deformation, with the film-covered side forming the inner curve (Fig. 1 b). The actual deformation of the actuator is illustrated in Fig. 1 c,d (see also Supplementary Movie 1). The simplicity of the layered actuator structure enabled the construction of an analytical model based on a hyperelastic material model, which guided the design of the fabricated actuator (see Supplementary Note 1 for the modeling details). The actuator was fabricated using a layer-by-layer lamination process (Fig. 2 ; see the Methods section for details). The chamber was connected to a syringe via a silicone tube. The syringe was used to inject water to fill the chamber, and its needle served as the electrical connection for high-voltage application (Fig. 2 i). During actuation, the syringe was fixed to prevent chamber inflation. The fabricated actuator had a length of 80 mm and a width of 30 mm (see the Supplementary Information for detailed dimensions). Subsequently, the fabricated actuator was characterized in terms of bending angle, blocked force, actuation speed, and cyclic response. The bending angle is defined as the relative displacement with respect to the initial state when no voltage is applied (Fig. 3 a). The blocked force was measured by placing the probe of a load cell against the tip of the actuator (Fig. 3 b). A representative bending angle profile is shown in Fig. 3 c, from which the actuation speed, defined as the peak (maximum) value during bending and unbending, was extracted, as plotted in Fig. 3 d. The details of these measurements are provided in the Methods section. The measured bending angle as a function of the applied voltage, together with the model prediction, is presented in Fig. 4 a. The bending angle increased as the applied voltage increased. At 12 kV, the angle reached 205.9° ± 3.6° after 5 s of voltage application and 308.5° ± 8.8° after 40 s. The corresponding curvature was 0.09/mm. The larger bending angle at 40 s than at 5 s is attributed to the viscoelasticity of the elastomer, which exhibits time-dependent strain. The model prediction showed good agreement with the experimental data, particularly with the data obtained 40 s after voltage application. However, at 11 kV and above, the predicted values were slightly lower than the experimental values measured after 40 s. One possible explanation for this discrepancy is that the actuator was initially tilted rather than perfectly vertical before voltage application, as shown in Fig. 3 a. Potential factors contributing to this initial tilt include fabrication misalignments of the structural materials and variations in the amount of water injected into the chamber. In addition, buoyancy may have lifted the actuator tip, resulting in a larger angle than the predicted value. The measured blocked force as a function of the applied voltage is plotted in Fig. 4 b. The blocked force exhibited a trend similar to that of the bending angle, increasing with the applied voltage and reaching 57.2 ± 0.4 mN at 12 kV. The force was on the order of several tens of millinewtons, indicating that the actuator is well suited for gripper applications that require gentle manipulation of delicate objects because of its large deformation and low mechanical force. As also depicted in Fig. 3 c,d, the rate of change in bending angle was highest immediately after voltage application. Similarly, the angle decreased most rapidly immediately after voltage removal. The maximum speeds during voltage application and voltage removal are plotted as functions of the applied voltage in Fig. 4 c and Fig. 4 d, respectively. At 12 kV, the tip of the actuator came into contact with the fixture shown in Fig. 3 a. Therefore, the maximum speed during voltage cutoff at 12 kV is not included in the plot. In both the voltage application and cutoff phases, the speed increased as the applied voltage increased. Immediately after voltage application, the speed reached 161.1 ± 8.1°/s at 12 kV. Immediately after voltage cutoff, the speed reached − 183.3 ± 6.7°/s at 11 kV. The average magnitude of the peak actuation speed during bending and unbending was 172.2°/s. The actuator demonstrated stable bending actuation over 1000 cycles (Fig. 4 e), with an operating angle of 170.8° in the first cycle and 177.2° in the last cycle. The operating angle increased by 6.4°, indicating high reproducibility of actuation. The bending angle before voltage application increased by 19.1°, while the angle after voltage application increased by 25.6°. The increase in the bending angles before voltage application is likely due to time-dependent behavior. Based on the bending angle measured over time (Fig. 3 c), the actuator continued to deform during voltage application, and the bending angle did not fully return to its initial position even 20 s after voltage removal. This can be attributed to the viscoelasticity of the elastomer, which causes the stretched elastomer to delay in returning to its original shape. The characteristics of the underwater DEA, namely its fast, large, and robust deformation, underscore its significant potential for soft robotic aquatic devices. Similar to many marine organisms, luminescence is a useful function for soft robots because it enables them to signal and communicate their deformation states [ 40 ]. One approach to realizing luminescent functionality is to use light-emitting organisms in biohybrid devices [ 41 , 42 ]. Following this strategy, a culture solution containing Pyrocystis lunula (Fig. 5 a) was injected into the chamber of the underwater DEA. Pyrocystis lunula is a bioluminescent dinoflagellate that emits light in response to deformation of its cell membrane [ 43 – 45 ]. The intensity of light emission depends on the magnitude and rate of the applied force. Insufficient force or slow deformation fails to induce luminescence, whereas large and rapid deformation produces strong luminescence [ 46 , 47 ]. The experimental results indicate that the deformation speed of the actuator is sufficiently high to trigger light emission from Pyrocystis lunula when driven at 12 kV of applied voltage (Fig. 5 b, see also Supplementary Movie 2). Specifically, bioluminescence was generated in the actuator immediately after voltage application and voltage removal (Fig. 5 c,d). The high transparency of the structural materials allowed the light emitted by Pyrocystis lunula inside the actuator to be observed externally. Although previous studies have reported luminescence excitation in biohybrid soft devices using fluidic or magnetic actuation [ 42 ], to our knowledge, there are no reports of actuators that induce Pyrocystis lunula luminescence via voltage-driven actuation. Thus, these results highlight the effectiveness of the underwater DEA as a biohybrid luminescent device capable of producing light without compromising flexibility or structural simplicity. Marine organisms are often collected for research purposes aimed at understanding marine ecosystems. However, jellyfish are delicate and can be easily damaged because they are composed of gelatinous tissue. The fabricated underwater DEA offers a potential solution to this issue owing to its large deformation and low mechanical force. Although a previous study has reported a hydraulically driven soft gripper for capturing live jellyfish [ 14 ], the use of voltage-driven soft grippers for this purpose has not been reported. The developed gripper based on the underwater DEA features a three-fingered configuration, in which one actuator is placed at the center of each side of an equilateral triangle. Upon voltage application, the actuators bend inward, generating a grasping motion. Owing to the high transparency of the actuators, the gripper remains relatively inconspicuous to the target organism and allows for clear observation of the captured target during grasping. To demonstrate this, a jellyfish grasping experiment was performed in a water tank filled with artificial seawater containing a live cannonball jellyfish with a bell diameter of approximately 30 mm (Fig. 6 a; see also Supplementary Movie 3). As the swimming jellyfish approached the center of the gripper, a voltage of 12 kV was applied, causing rapid inward bending of the fingers and enclosing the jellyfish (Fig. 6 b). The jellyfish was then transported while being held by the gripper (Fig. 6 c,d). After voltage removal, the gripper opened its fingers and released the jellyfish, which subsequently swam away normally (Fig. 6 e,f). No visible injury or abnormal swimming behavior was observed after the experiment. These results demonstrate the effectiveness of the proposed actuator for the delicate grasping of aquatic organisms underwater through fast, large, and gentle deformation. Conclusion In this study, an underwater DEA capable of fast and large bending deformation was developed. Characterization of the fabricated actuator revealed a maximum bending angle of 308.5° and an average actuation speed magnitude of 172.2°/s, demonstrating rapid and large deformation in an underwater environment. The actuator was successfully applied to a biohybrid luminescent device incorporating Pyrocystis lunula and to a soft gripper capable of capturing a live jellyfish. These demonstrations highlight the potential of the actuator as a platform for soft robotic devices that combine electrically driven actuation with biohybrid luminescence or delicate underwater grasping. Overall, the results confirm the feasibility of the proposed underwater DEA and underscore its promise for underwater soft robotic applications. Future work will focus on reducing the operating voltage and improving the accuracy of the analytical model. One possible approach to lowering the operating voltage is the elimination of the intermediate layer currently introduced to suppress unintended deformation during actuation. If the elastomer structure can be fabricated with sufficiently low residual strain and high precision, controlled bending may be achieved without this intermediate layer. Such simplification is expected to reduce the energy required for bending and enable comparable deformation at lower voltages. Achieving low-voltage operation would also facilitate the miniaturization of the overall system, including the power supply, thereby improving the practicality of the actuator for underwater environments with strict operational constraints. Methods Fabrication of the actuator All materials were cut using a laser cutting machine (Speedy 300, Trotec). A 0.5 mm-thick acrylic elastomer (VHB4905, 3M) was cut into the designed outline geometry, and a 20 µm-thick OPP film mask (PYLEN Film-OT, TOYOBO) was applied to define the chamber region (Fig. 2 a). Talc was then applied to the elastomer surface within the mask region (Fig. 2 b). This elastomer exhibits high flexibility and transparency, as well as strong adhesion on both sides, which allows for secure bonding between the layered materials. Talc was used to reduce the adhesive strength of the elastomer surface within the chamber region. By selectively applying talc while leaving adhesive regions untreated, chambers could be readily formed during lamination. Subsequently, the mask was removed (Fig. 2 c), and the talc-coated elastomer was laminated onto an intermediate elastomer layer with aligned edges (Fig. 2 d). The intermediate layer contained cutouts for the chamber and the placement of the silicone tube, with the talc-coated surface oriented inward to form the chamber. Next, a silicone tube (MGJG-1×2, MonotaRO) with an inner diameter of 1 mm, an outer diameter of 2 mm, and a length of 80 mm was positioned such that its lower end aligned with the end of the chamber. Finally, another talc-coated elastomer layer was laminated on top, with the talc-coated surface facing inward (Fig. 2 e). This process resulted in an elastomeric structure containing an internal chamber for water encapsulation. To restrict the direction of structural deformation, an OPP film was attached to one side of the elastomeric structure over the chamber region (Fig. 2 f). A 125 µm-thick PET frame (Lumirror #125-S10, TORAY) was then applied on top of the OPP film (Fig. 2 g). The PET frame was preassembled with laterally extending beams connected outside the actuator to ensure uniform spacing along its length. Excess PET frame material was trimmed along the contour of the elastomeric structure using a cutter (Fig. 2 h). To improve waterproofing and insulation, the gaps around the silicone tube–actuator interface were sealed with a silicone adhesive (TSE387-C, Momentive). Water was then injected into the actuator through the silicone tube using a syringe. In this study, tap water was used as the liquid electrode, with a total volume of 0.5 mL injected into the chamber and silicone tube sections. A voltage lead was wrapped around the metal part of the syringe needle connected to the silicone tube. The actuator was 80 mm in length and 30 mm in width. The chamber section measured 60 mm in length and 20 mm in width. A 15 mm margin was left at the top for actuator fixation, while 5 mm margins were provided on both sides and at the bottom to ensure adhesive bonding and electrical insulation under high-voltage operation (see the Supplementary Information for detailed dimension specifications). Measurement of the actuator bending angle and blocked force The rear end of the actuator was fixed vertically using a laser-cut acrylic fixture and placed in a water tank filled with tap water. Voltage was applied to the actuator using a stabilized power supply (PMX32-2QU, Kikusui Electronics) and a DC–DC converter (NHV24-15K450P, Bellnix). The high-voltage side of the DC–DC converter was connected to the water inside the actuator chamber via a syringe needle, while the ground side was connected inside the water tank using a wire with conductive tape. To measure the actuator bending angle, images were captured using a camera (L-835, HOZAN) before voltage application and at 5 s and 40 s after voltage application. The applied voltage was increased from 0 to 12 kV in 1 kV increments. The captured images were analyzed using image processing software (ImageJ). The bending angle was determined as the difference between the tip angles before and after voltage application (Fig. 3 a). The blocked force was measured using an underwater load cell (LSB-210, FUTEK). The actuator tip was fixed between the load cell probe and an acrylic jig in a plane-to-plane configuration (Fig. 3 b). The force value was recorded using a multimeter (Model 2100, Keithley Instruments). The applied voltage was again increased from 0 to 12 kV in 1 kV increments. The blocked force was calculated as the difference between the average force values measured before and after voltage application. These measurements were conducted on three samples, and the average values were reported. Measurement of actuation speed The measurement was conducted in the same setup used for measuring the bending angle and blocked force. A sticker with two markers was attached to the side of the actuator tip, and the deformation was continuously recorded during voltage application using a high-speed camera (INFINICAM, Photron). The two markers were positioned along the centerline of the actuator thickness. The frame rate was set to 50 fps. Voltage application started 3 s after the recording began and lasted for 60 s before being reduced to 0 V. The applied voltage was increased from 0 to 12 kV in 1 kV increments. The coordinates of the two markers in the captured images were determined using video analysis software (Photron FASTCAM Analysis, Photron). A straight line connecting the two marker points was drawn, and its angle was calculated as the bending angle for each frame. The bending angle data were smoothed using a 0.06 s moving average, and the speed of the bending angle was calculated at 0.02 s intervals. In addition to the time-dependent bending angle and speed, the maximum speeds immediately after voltage application and immediately after voltage removal were determined. This measurement was conducted on three samples, and the average value was reported. Measurement of cyclic response The cyclic response was measured using the same setup used for measuring the bending angle and blocked force. A voltage of 8 kV was applied for 5 s, followed by voltage removal for 20 s, and this cycle was repeated 1000 times. During voltage application, the polarity of the water inside the actuator chamber and the external water was alternated to prevent charge accumulation within the actuator. To evaluate variations in the bending angle, images were captured 1 s before voltage application and 5 s after the onset of voltage application. The captured images were analyzed by the image processing software. The bending angle was determined as the difference from the tip angle recorded before voltage application at the first cycle. Preparation of the culture solution containing Pyrocystis lunula The Pyrocystis lunula strain NIES-609 obtained from the Microbial Culture Collection at the National Institute for Environmental Studies was cultured at 21°C in a liquid f/2 medium [ 48 ] under a 12 h light/12 h dark cycle (LD 12:12) using a white fluorescent light at a photon flux density of 10–20 µmol/m 2 /s. To enhance the visibility of bioluminescence, the culture was concentrated before the experiment. On the day before the experiment, the cells were separated from the culture medium using filter paper, and the cells remaining on the filter paper were resuspended in a small amount of the medium to increase the cell density. Since Pyrocystis lunula exhibits circadian regulation of bioluminescence and emits light most strongly during the dark phase [ 45 ], the experiments were conducted during the dark period of the culture cycle. Imaging of the biohybrid actuator The movement and mechanoluminescence of the biohybrid actuator were observed in a darkroom. The image shown in Fig. 5 b was captured by a color CMOS camera (DFK33UX174, Imaging Source) positioned in front of the water tank where the actuator was fixed. The camera was equipped with a wide-angle lens (VS-0618H1, VS Technology) connected via a C-mount adaptor (CML05, Thorlabs) and a 25 mm focal length lens (DLB-12.7-25PM, SIGMAKOKI). The entire experimental setup was slightly visualized by a green-light LED (M530L4, Thorlabs) with a neutral density filter and a diffuser. All optical components were placed on an optical baseplate (OBC-3045-M6, SIGMAKOKI). The actuator was driven at 12 kV and 0.125 Hz, and the image projections were acquired with the imaging software IC Capture (Imaging Source). The images displayed in Fig. 5 c,d were captured by a camera (Z5, Nikon) positioned at the side of the water tank. The actuator was driven at 12 kV and 0.125 Hz, and photographs were captured with an exposure time of 1 s, an aperture of f/3.2, and ISO 51200. Under these conditions, bioluminescence was observed immediately after voltage application and voltage removal. In these experiments, the same setup used for the characterization of the actuator was used to apply the driving voltage. Fabrication of the gripper A three-fingered soft gripper was constructed using three fabricated actuators. The actuators were arranged at the midpoints of the three sides of an equilateral triangular base with a side length of 60 mm and oriented such that inward bending occurred upon voltage application. The base was fabricated via 3D printing (Form 3, Formlabs) using a UV-curable resin (Clear Resin V4, Formlabs). Each actuator was mounted to the base using a plastic torque hinge, which provided sufficient holding force to maintain the initial finger orientation while allowing manual adjustment during assembly. Jellyfish capturing demonstration The demonstration was performed in a water tank filled with artificial seawater at approximately 24°C using a live cannonball jellyfish, which was obtained from Tsuruoka Municipal Kamo Aquarium. The bell diameter of the jellyfish was 30 mm during contraction. During the experiment, the gripper was positioned to allow the jellyfish to approach its center while swimming freely. When the jellyfish entered the grasping region, 12 kV was applied to the actuators to induce inward bending of the three fingers and enclose the organism. The jellyfish was then relocated while being held by the gripper, after which the applied voltage was removed to reopen the fingers and release the animal. Following its release, the jellyfish swam away normally. No visible damage or abnormal swimming behavior was observed after the demonstration. The entire sequence of the demonstration was recorded using a camera (Z5, Nikon). In this demonstration, the voltage was applied using the same setup used for the characterization of the actuator. Use of AI tools ChatGPT (version 5.4, OpenAI) was used solely for language editing support during manuscript preparation. All scientific content, data interpretation, and original writing were independently developed by the authors. All AI-assisted outputs were thoroughly reviewed and verified by the authors. Data availability All data generated and analyzed during this study are available from the corresponding author upon reasonable request. Declarations Competing interests The authors declare no competing interests. Funding This work was supported by the JSPS KAKENHI Grant-in-Aid for Scientific Research (grant numbers 23K26072, 23H01377, 24KJ1131, and 25K01203), the JSPS Research Fellowship for Young Scientists (DC2), the JST Fusion-Oriented Research for Disruptive Science and Technology program (Grant number JPMJFR2126), and the JST SPRING (Grant number MJSP2131). Author Contribution C.M., T.S., and J.S. conceived the main idea. C.M. and T.S. designed and fabricated the actuators and the gripper. C.M., T.S., N.A.U., K.K., D.N., M.S., and J.S. designed the experiments. C.M., T.S., N.A.U., K.K., D.N., and M.S. conducted the experiments and analyzed the data. C.M., T.S., N.A.U., and J.S. generated and edited the figures and media files. C.M. wrote the manuscript. D.N., M.S., and J.S. supervised the project. J.S. edited the manuscript. All authors reviewed the manuscript. Acknowledgments This work was supported by the JSPS KAKENHI Grant-in-Aid for Scientific Research (grant numbers 23K26072, 23H01377, 24KJ1131, and 25K01203), the JSPS Research Fellowship for Young Scientists (DC2), the JST Fusion-Oriented Research for Disruptive Science and Technology program (Grant number JPMJFR2126), and the JST SPRING (Grant number MJSP2131). 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J. & Seliger, H. H. Stimulable and spontaneous bioluminescence in the marine dinoflagellates, Pyrodinium bahamense, Gonyaulax polyedra, and Pyrocystis lunula. J. Gen. Physiol. 54 , 96–122 (1969). Cussatlegras, A. S. & Le Gal, P. Variability in the bioluminescence response of the dinoflagellate Pyrocystis lunula. J. Exp. Mar. Biol. Ecol. 343 , 74–81 (2007). Valiadi, M. & Iglesias-Rodriguez, D. Understanding bioluminescence in dinoflagellates—how far have we come? Microorganisms 1, 3–25 (2013). Tesson, B. & Latz, M. I. Mechanosensitivity of a rapid bioluminescence reporter system assessed by atomic force microscopy. Biophys. J. 108 , 1341–1351 (2015). Jalaal, M. et al. Stress-induced dinoflagellate bioluminescence at the single cell level. Phys. Rev. Lett. 125 , 028102 (2020). Stauber, J. L. et al. Comparison of the Qwiklite™ algal bioluminescence test with marine algal growth rate inhibition bioassays. Environ. Toxicol. 23 , 617–625 (2008). Additional Declarations No competing interests reported. Supplementary Files SupplementaryMovie2.mp4 SupplementaryMovie1.mp4 SupplementaryMovie3.mp4 SRDEASupplementaryInformation.pdf Cite Share Download PDF Status: Under Revision Version 1 posted Editorial decision: Revision requested 06 Apr, 2026 Reviews received at journal 06 Apr, 2026 Reviews received at journal 31 Mar, 2026 Reviewers agreed at journal 27 Mar, 2026 Reviewers agreed at journal 24 Mar, 2026 Reviewers agreed at journal 21 Mar, 2026 Reviewers agreed at journal 19 Mar, 2026 Reviewers invited by journal 19 Mar, 2026 Editor invited by journal 19 Mar, 2026 Editor assigned by journal 17 Mar, 2026 Submission checks completed at journal 17 Mar, 2026 First submitted to journal 16 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9133026","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":610593949,"identity":"6149a2ef-df3e-4281-8c0d-e712e2e94191","order_by":0,"name":"Chiho Murata","email":"","orcid":"","institution":"University of Electro-Communications","correspondingAuthor":false,"prefix":"","firstName":"Chiho","middleName":"","lastName":"Murata","suffix":""},{"id":610593950,"identity":"9e1c061f-eb49-47ca-afe5-abb5ddaa9ade","order_by":1,"name":"Takumi Shibuya","email":"","orcid":"","institution":"University of Electro-Communications","correspondingAuthor":false,"prefix":"","firstName":"Takumi","middleName":"","lastName":"Shibuya","suffix":""},{"id":610593951,"identity":"9f8ee4f0-35d4-4942-ab79-5ace58223943","order_by":2,"name":"Naoki A Uemura","email":"","orcid":"","institution":"University of Electro-Communications","correspondingAuthor":false,"prefix":"","firstName":"Naoki","middleName":"A","lastName":"Uemura","suffix":""},{"id":610593952,"identity":"4d6a3c12-6c58-4928-966d-032f026cdf14","order_by":3,"name":"Kengo Kusama","email":"","orcid":"","institution":"University of Electro-Communications","correspondingAuthor":false,"prefix":"","firstName":"Kengo","middleName":"","lastName":"Kusama","suffix":""},{"id":610593953,"identity":"eb00008d-b5b3-41b6-bf2b-9ba5d80e0e6e","order_by":4,"name":"Daisuke Nakane","email":"","orcid":"","institution":"University of Electro-Communications","correspondingAuthor":false,"prefix":"","firstName":"Daisuke","middleName":"","lastName":"Nakane","suffix":""},{"id":610593954,"identity":"5c515bbe-ea66-417c-85f3-e4837ec4c43f","order_by":5,"name":"Masahiro Shimizu","email":"","orcid":"","institution":"Nagahama Institute of Bio-Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Masahiro","middleName":"","lastName":"Shimizu","suffix":""},{"id":610593955,"identity":"662263e5-b206-4470-ba97-82449bbd3180","order_by":6,"name":"Jun Shintake","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA10lEQVRIiWNgGAWjYDACCcYGIJnAwA8TAPMJajkA1CIJU0mEFiAGaTE4QKy75Gc3tz3+UJMmZ3wj+eAHhho7BubZBKwxuHOw3eDAsRxjsxtpyRIMx5IZGOcQsM9AIrFN4gBbReK2GzlmDAxsBxgYZyQQcNgMkJZ/FfWbZ+R/Y2D4R4QWhhtALQfbchIMJHLYGBjbiNBiANJyti/NcMaZZ8YSiX3JPAT9Ij8j/ZlExbdkef725IcfPnyzkzMkFGKoAOgkHsMZpOiA2CtBspZRMApGwSgY5gAA0FpF1KRsdYsAAAAASUVORK5CYII=","orcid":"","institution":"University of Electro-Communications","correspondingAuthor":true,"prefix":"","firstName":"Jun","middleName":"","lastName":"Shintake","suffix":""}],"badges":[],"createdAt":"2026-03-16 04:53:18","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9133026/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9133026/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":105328193,"identity":"0704a3cd-4edd-4cd4-8250-e4ddd119f952","added_by":"auto","created_at":"2026-03-24 19:44:25","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":4465087,"visible":true,"origin":"","legend":"\u003cp\u003eStructure and working principle of the underwater DEA. (a) Photograph of the fabricated underwater DEA. (b) Working principle of the actuator. When a high voltage difference is applied between the chamber and the surrounding water (ground), the resulting electrostatic force elongates the elastomer layer. Since one side is constrained by the OPP film and PET frames, differential elongation generates bending deformation. (c) Side view of the actuator in water at 0 kV. (d) Bending deformation of the actuator at 12 kV, demonstrating large deformation.\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9133026/v1/ba3aaae9fa77311627d76429.jpeg"},{"id":105328194,"identity":"49fa2ad5-995b-4d46-aac4-eeef30baed6d","added_by":"auto","created_at":"2026-03-24 19:44:25","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1828269,"visible":true,"origin":"","legend":"\u003cp\u003eFabrication process for the actuator. (a) An OPP film mask defining the chamber region is placed on top of an elastomer layer. (b) Talc is applied within the masked region to reduce the tackiness of the elastomer surface. (c) The mask is removed, leaving the elastomer layer with the chamber region covered with talc. (d) An elastomer layer with a hole identical to the chamber dimensions is attached, and a silicone tube is positioned. (e) Another elastomer layer is laminated on top to seal the chamber and form the elastomeric structure. (f) An OPP film is attached to one side of the structure. (g) A PET sheet with multiple holes is placed on top of the OPP film. (h) The excess PET sheet is trimmed along the actuator contour, leaving PET frames. (i) The fabricated actuator connected to a syringe. The syringe enables injection of water into the chamber, and the needle serves as the electrical connection.\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9133026/v1/131b2e2980c51b8764815394.jpeg"},{"id":105328202,"identity":"ea7541a5-18f3-48e5-84dc-3113883dc4ca","added_by":"auto","created_at":"2026-03-24 19:44:26","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1806965,"visible":true,"origin":"","legend":"\u003cp\u003eCharacterization of the actuator. (a) The actuator during bending deformation. The arc indicates the bending angle that was measured. (b) Experimental setup used for measuring the blocked force. (c) Bending angle as a function of elapsed time during voltage application and removal (11 kV). (d) Actuation speed calculated from the time derivative of the bending angle shown in (c), showing peak velocities immediately after voltage application and removal.\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9133026/v1/d857b58a08491e9a1c9fb3be.jpeg"},{"id":105328199,"identity":"92f25acc-f9c6-467a-8095-6523dbedbc92","added_by":"auto","created_at":"2026-03-24 19:44:26","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":948259,"visible":true,"origin":"","legend":"\u003cp\u003eMeasured performance of the actuator. (a) Bending angle as a function of applied voltage. The experimental data acquired 5 s and 40 s after voltage application are compared with predictions from the analytical model. (b) Blocked force as a function of applied voltage. (c) Maximum bending speed immediately after voltage application as a function of applied voltage. (d) Maximum bending speed immediately after voltage removal as a function of applied voltage. (e) Cyclic response of the actuator showing the bending angle before voltage application (V = 0) and during voltage application (V \u0026gt; 0) over repeated cycles up to 1000.\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9133026/v1/df97e84f393d640033d7dccf.jpeg"},{"id":105328197,"identity":"b3ef2d04-8665-41e1-971d-d4c410742b43","added_by":"auto","created_at":"2026-03-24 19:44:25","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":5456932,"visible":true,"origin":"","legend":"\u003cp\u003eBiohybrid luminescent actuator using a \u003cem\u003ePyrocystis lunula\u003c/em\u003e suspension. (a) Microscopy image of \u003cem\u003ePyrocystis lunula\u003c/em\u003e used in this study. (b) Top view and (c) side view of the actuator immediately after voltage application, showing bioluminescence induced by rapid and large deformation. (d) Side view of the actuator immediately after voltage removal, also displaying bioluminescence.\u003c/p\u003e","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9133026/v1/ef2a3eda5ee875a40bfb068e.jpeg"},{"id":105328195,"identity":"aff1f507-3097-476b-be66-003e83cb258f","added_by":"auto","created_at":"2026-03-24 19:44:25","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":3426691,"visible":true,"origin":"","legend":"\u003cp\u003eDemonstration of a soft gripper for manipulating a live jellyfish. The inset shows the target jellyfish (cannonball jellyfish). (a) Initial state of the gripper as the jellyfish approaches the device. (b) Upon voltage application, the gripper is activated and closes its fingers, capturing the jellyfish. (c) The gripper encloses the jellyfish and transports it rightward. (d) The jellyfish is further transported downward. (e) After voltage removal, the gripper opens and releases the jellyfish. (f) The gripper moves upward, and the jellyfish swims away normally.\u003c/p\u003e","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-9133026/v1/f14fbd040aca68c9d3c340f5.jpeg"},{"id":105569159,"identity":"fef301d1-5c7b-4b00-a0c5-46f840d49fdc","added_by":"auto","created_at":"2026-03-27 13:11:33","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":15068332,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9133026/v1/a7bf4809-a96b-43db-b1ab-2dcedbf164a1.pdf"},{"id":105328198,"identity":"e7118029-7ca9-4d69-bcad-6e42644730a8","added_by":"auto","created_at":"2026-03-24 19:44:25","extension":"mp4","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":14770936,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryMovie2.mp4","url":"https://assets-eu.researchsquare.com/files/rs-9133026/v1/728a01548f17c3a173bf2874.mp4"},{"id":105328200,"identity":"5ee64374-b9d2-456d-98bd-d50f66b6970d","added_by":"auto","created_at":"2026-03-24 19:44:26","extension":"mp4","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":21053084,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryMovie1.mp4","url":"https://assets-eu.researchsquare.com/files/rs-9133026/v1/022ad21a15a1662b553c2795.mp4"},{"id":105565141,"identity":"69130074-a9e9-417b-89a8-13d6d8f1c34c","added_by":"auto","created_at":"2026-03-27 12:52:04","extension":"mp4","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":22037531,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryMovie3.mp4","url":"https://assets-eu.researchsquare.com/files/rs-9133026/v1/3eed6d2ab48aa98050f15626.mp4"},{"id":105328196,"identity":"e3bfdeac-6566-4979-9f0f-fb4716bb0b4e","added_by":"auto","created_at":"2026-03-24 19:44:25","extension":"pdf","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":903483,"visible":true,"origin":"","legend":"","description":"","filename":"SRDEASupplementaryInformation.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9133026/v1/400e145d2c7312430941e319.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Underwater dielectric elastomer actuators with large bending deformation for soft robots","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSoft robots are constructed from compliant materials and are characterized by their simple structures, high adaptability to surrounding environments, and safe interactions with humans and external objects owing to their low impact upon contact [\u003cspan additionalcitationids=\"CR2 CR3 CR4\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. In recent years, underwater soft robotic systems have garnered growing attention due to their diverse potential applications in exploration, environmental monitoring, and biological sampling [\u003cspan additionalcitationids=\"CR7 CR8 CR9\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. These robots have demonstrated swimming motions that mimic those of aquatic organisms [\u003cspan additionalcitationids=\"CR12\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], as well as the ability to safely handle delicate marine life by leveraging their structural compliance [\u003cspan additionalcitationids=\"CR15\" citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eActuators play a crucial role in driving underwater soft robots. Among the various types of soft actuators [\u003cspan additionalcitationids=\"CR18 CR19 CR20\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], dielectric elastomer actuators (DEAs) are considered one of the most promising [\u003cspan additionalcitationids=\"CR23 CR24 CR25\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. A DEA consists of an elastomeric membrane sandwiched between two compliant electrodes. When a voltage is applied across the electrodes, an electrostatic force is generated between them, compressing the elastomer membrane in the thickness direction and causing it to expand in the planar directions. This deformation can be harnessed for voltage-controlled actuation. DEAs offer large actuation strains (e.g., 50% linear strain [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]), fast response times (e.g., 1 kHz [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]), and high power density (e.g., 600 W/kg [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]). Their simple structure and electrically driven operation facilitate integration into autonomous soft robots, including those designed for underwater environments [\u003cspan additionalcitationids=\"CR31\" citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAmong the various configurations of underwater DEAs, those that achieve bending deformation are particularly versatile and frequently used to drive soft robots inspired by fish [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e], jellyfish [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e], and rays [\u003cspan additionalcitationids=\"CR38\" citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. Nevertheless, the deformation capabilities of previously reported underwater bending DEAs still require further refinement in terms of both deformation magnitude and actuation speed. For example, in the aforementioned studies, the bending angles and actuation speeds range from 5.0\u0026deg; to 48.0\u0026deg; and from 12.6\u0026deg;/s to 102.0\u0026deg;/s, respectively (see Supplementary Table\u0026nbsp;1 for details). Achieving larger and faster deformations could expand the range of applications, particularly for devices used in sampling tasks.\u003c/p\u003e \u003cp\u003eThis study aims to provide an underwater DEA capable of generating large deformations. The proposed actuator features an elastomeric layered structure that encapsulates a liquid electrode. An inextensible flexible film and a set of frames are attached to one side of the actuator structure to constrain deformation in the direction orthogonal to bending, thereby enhancing the actuation magnitude. In this study, the proposed actuator concept was demonstrated through modeling, fabrication, and characterization, as well as through its implementation in underwater soft robotic devices.\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cp\u003eThe underwater DEA developed in this study is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea. The actuator comprises a layered structure that encapsulates water as an electrode (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). The section containing water is hereafter referred to as the chamber. An inextensible flexible film made of oriented polypropylene (OPP) is attached to one side of the structure to act as a strain-limiting layer. Additionally, polyethylene terephthalate (PET) frames are affixed on top of the film to further constrain structural deformation perpendicular to the bending direction. When a high voltage is applied to the chamber while the surrounding water serves as the ground electrode, an electrostatic force (Maxwell stress) is generated between the external water and the chamber. This electrostatic force compresses and induces elongation of the elastomeric layer on the non-constraint side, leading to bending deformation, with the film-covered side forming the inner curve (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). The actual deformation of the actuator is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec,d (see also Supplementary Movie 1). The simplicity of the layered actuator structure enabled the construction of an analytical model based on a hyperelastic material model, which guided the design of the fabricated actuator (see Supplementary Note 1 for the modeling details).\u003c/p\u003e \u003cp\u003eThe actuator was fabricated using a layer-by-layer lamination process (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e; see the Methods section for details). The chamber was connected to a syringe via a silicone tube. The syringe was used to inject water to fill the chamber, and its needle served as the electrical connection for high-voltage application (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ei). During actuation, the syringe was fixed to prevent chamber inflation. The fabricated actuator had a length of 80 mm and a width of 30 mm (see the Supplementary Information for detailed dimensions).\u003c/p\u003e \u003cp\u003eSubsequently, the fabricated actuator was characterized in terms of bending angle, blocked force, actuation speed, and cyclic response. The bending angle is defined as the relative displacement with respect to the initial state when no voltage is applied (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). The blocked force was measured by placing the probe of a load cell against the tip of the actuator (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). A representative bending angle profile is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec, from which the actuation speed, defined as the peak (maximum) value during bending and unbending, was extracted, as plotted in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed. The details of these measurements are provided in the Methods section.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe measured bending angle as a function of the applied voltage, together with the model prediction, is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea. The bending angle increased as the applied voltage increased. At 12 kV, the angle reached 205.9\u0026deg; \u0026plusmn; 3.6\u0026deg; after 5 s of voltage application and 308.5\u0026deg; \u0026plusmn; 8.8\u0026deg; after 40 s. The corresponding curvature was 0.09/mm. The larger bending angle at 40 s than at 5 s is attributed to the viscoelasticity of the elastomer, which exhibits time-dependent strain. The model prediction showed good agreement with the experimental data, particularly with the data obtained 40 s after voltage application. However, at 11 kV and above, the predicted values were slightly lower than the experimental values measured after 40 s. One possible explanation for this discrepancy is that the actuator was initially tilted rather than perfectly vertical before voltage application, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea. Potential factors contributing to this initial tilt include fabrication misalignments of the structural materials and variations in the amount of water injected into the chamber. In addition, buoyancy may have lifted the actuator tip, resulting in a larger angle than the predicted value.\u003c/p\u003e \u003cp\u003eThe measured blocked force as a function of the applied voltage is plotted in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb. The blocked force exhibited a trend similar to that of the bending angle, increasing with the applied voltage and reaching 57.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4 mN at 12 kV. The force was on the order of several tens of millinewtons, indicating that the actuator is well suited for gripper applications that require gentle manipulation of delicate objects because of its large deformation and low mechanical force.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs also depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec,d, the rate of change in bending angle was highest immediately after voltage application. Similarly, the angle decreased most rapidly immediately after voltage removal. The maximum speeds during voltage application and voltage removal are plotted as functions of the applied voltage in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed, respectively. At 12 kV, the tip of the actuator came into contact with the fixture shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea. Therefore, the maximum speed during voltage cutoff at 12 kV is not included in the plot. In both the voltage application and cutoff phases, the speed increased as the applied voltage increased. Immediately after voltage application, the speed reached 161.1\u0026thinsp;\u0026plusmn;\u0026thinsp;8.1\u0026deg;/s at 12 kV. Immediately after voltage cutoff, the speed reached\u0026thinsp;\u0026minus;\u0026thinsp;183.3\u0026thinsp;\u0026plusmn;\u0026thinsp;6.7\u0026deg;/s at 11 kV. The average magnitude of the peak actuation speed during bending and unbending was 172.2\u0026deg;/s.\u003c/p\u003e \u003cp\u003eThe actuator demonstrated stable bending actuation over 1000 cycles (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee), with an operating angle of 170.8\u0026deg; in the first cycle and 177.2\u0026deg; in the last cycle. The operating angle increased by 6.4\u0026deg;, indicating high reproducibility of actuation. The bending angle before voltage application increased by 19.1\u0026deg;, while the angle after voltage application increased by 25.6\u0026deg;. The increase in the bending angles before voltage application is likely due to time-dependent behavior. Based on the bending angle measured over time (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec), the actuator continued to deform during voltage application, and the bending angle did not fully return to its initial position even 20 s after voltage removal. This can be attributed to the viscoelasticity of the elastomer, which causes the stretched elastomer to delay in returning to its original shape.\u003c/p\u003e \u003cp\u003eThe characteristics of the underwater DEA, namely its fast, large, and robust deformation, underscore its significant potential for soft robotic aquatic devices. Similar to many marine organisms, luminescence is a useful function for soft robots because it enables them to signal and communicate their deformation states [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. One approach to realizing luminescent functionality is to use light-emitting organisms in biohybrid devices [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. Following this strategy, a culture solution containing \u003cem\u003ePyrocystis lunula\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea) was injected into the chamber of the underwater DEA. \u003cem\u003ePyrocystis lunula\u003c/em\u003e is a bioluminescent dinoflagellate that emits light in response to deformation of its cell membrane [\u003cspan additionalcitationids=\"CR44\" citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. The intensity of light emission depends on the magnitude and rate of the applied force. Insufficient force or slow deformation fails to induce luminescence, whereas large and rapid deformation produces strong luminescence [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe experimental results indicate that the deformation speed of the actuator is sufficiently high to trigger light emission from \u003cem\u003ePyrocystis lunula\u003c/em\u003e when driven at 12 kV of applied voltage (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb, see also Supplementary Movie 2). Specifically, bioluminescence was generated in the actuator immediately after voltage application and voltage removal (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec,d). The high transparency of the structural materials allowed the light emitted by \u003cem\u003ePyrocystis lunula\u003c/em\u003e inside the actuator to be observed externally. Although previous studies have reported luminescence excitation in biohybrid soft devices using fluidic or magnetic actuation [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e], to our knowledge, there are no reports of actuators that induce \u003cem\u003ePyrocystis lunula\u003c/em\u003e luminescence via voltage-driven actuation. Thus, these results highlight the effectiveness of the underwater DEA as a biohybrid luminescent device capable of producing light without compromising flexibility or structural simplicity.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eMarine organisms are often collected for research purposes aimed at understanding marine ecosystems. However, jellyfish are delicate and can be easily damaged because they are composed of gelatinous tissue. The fabricated underwater DEA offers a potential solution to this issue owing to its large deformation and low mechanical force. Although a previous study has reported a hydraulically driven soft gripper for capturing live jellyfish [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], the use of voltage-driven soft grippers for this purpose has not been reported.\u003c/p\u003e \u003cp\u003eThe developed gripper based on the underwater DEA features a three-fingered configuration, in which one actuator is placed at the center of each side of an equilateral triangle. Upon voltage application, the actuators bend inward, generating a grasping motion. Owing to the high transparency of the actuators, the gripper remains relatively inconspicuous to the target organism and allows for clear observation of the captured target during grasping. To demonstrate this, a jellyfish grasping experiment was performed in a water tank filled with artificial seawater containing a live cannonball jellyfish with a bell diameter of approximately 30 mm (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea; see also Supplementary Movie 3). As the swimming jellyfish approached the center of the gripper, a voltage of 12 kV was applied, causing rapid inward bending of the fingers and enclosing the jellyfish (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb). The jellyfish was then transported while being held by the gripper (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec,d). After voltage removal, the gripper opened its fingers and released the jellyfish, which subsequently swam away normally (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ee,f). No visible injury or abnormal swimming behavior was observed after the experiment. These results demonstrate the effectiveness of the proposed actuator for the delicate grasping of aquatic organisms underwater through fast, large, and gentle deformation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn this study, an underwater DEA capable of fast and large bending deformation was developed. Characterization of the fabricated actuator revealed a maximum bending angle of 308.5\u0026deg; and an average actuation speed magnitude of 172.2\u0026deg;/s, demonstrating rapid and large deformation in an underwater environment. The actuator was successfully applied to a biohybrid luminescent device incorporating \u003cem\u003ePyrocystis lunula\u003c/em\u003e and to a soft gripper capable of capturing a live jellyfish. These demonstrations highlight the potential of the actuator as a platform for soft robotic devices that combine electrically driven actuation with biohybrid luminescence or delicate underwater grasping. Overall, the results confirm the feasibility of the proposed underwater DEA and underscore its promise for underwater soft robotic applications.\u003c/p\u003e \u003cp\u003eFuture work will focus on reducing the operating voltage and improving the accuracy of the analytical model. One possible approach to lowering the operating voltage is the elimination of the intermediate layer currently introduced to suppress unintended deformation during actuation. If the elastomer structure can be fabricated with sufficiently low residual strain and high precision, controlled bending may be achieved without this intermediate layer. Such simplification is expected to reduce the energy required for bending and enable comparable deformation at lower voltages. Achieving low-voltage operation would also facilitate the miniaturization of the overall system, including the power supply, thereby improving the practicality of the actuator for underwater environments with strict operational constraints.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eFabrication of the actuator\u003c/h2\u003e \u003cp\u003eAll materials were cut using a laser cutting machine (Speedy 300, Trotec). A 0.5 mm-thick acrylic elastomer (VHB4905, 3M) was cut into the designed outline geometry, and a 20 \u0026micro;m-thick OPP film mask (PYLEN Film-OT, TOYOBO) was applied to define the chamber region (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea). Talc was then applied to the elastomer surface within the mask region (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). This elastomer exhibits high flexibility and transparency, as well as strong adhesion on both sides, which allows for secure bonding between the layered materials. Talc was used to reduce the adhesive strength of the elastomer surface within the chamber region. By selectively applying talc while leaving adhesive regions untreated, chambers could be readily formed during lamination. Subsequently, the mask was removed (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec), and the talc-coated elastomer was laminated onto an intermediate elastomer layer with aligned edges (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed). The intermediate layer contained cutouts for the chamber and the placement of the silicone tube, with the talc-coated surface oriented inward to form the chamber. Next, a silicone tube (MGJG-1\u0026times;2, MonotaRO) with an inner diameter of 1 mm, an outer diameter of 2 mm, and a length of 80 mm was positioned such that its lower end aligned with the end of the chamber. Finally, another talc-coated elastomer layer was laminated on top, with the talc-coated surface facing inward (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee). This process resulted in an elastomeric structure containing an internal chamber for water encapsulation. To restrict the direction of structural deformation, an OPP film was attached to one side of the elastomeric structure over the chamber region (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef). A 125 \u0026micro;m-thick PET frame (Lumirror #125-S10, TORAY) was then applied on top of the OPP film (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg). The PET frame was preassembled with laterally extending beams connected outside the actuator to ensure uniform spacing along its length. Excess PET frame material was trimmed along the contour of the elastomeric structure using a cutter (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eh). To improve waterproofing and insulation, the gaps around the silicone tube\u0026ndash;actuator interface were sealed with a silicone adhesive (TSE387-C, Momentive). Water was then injected into the actuator through the silicone tube using a syringe. In this study, tap water was used as the liquid electrode, with a total volume of 0.5 mL injected into the chamber and silicone tube sections. A voltage lead was wrapped around the metal part of the syringe needle connected to the silicone tube. The actuator was 80 mm in length and 30 mm in width. The chamber section measured 60 mm in length and 20 mm in width. A 15 mm margin was left at the top for actuator fixation, while 5 mm margins were provided on both sides and at the bottom to ensure adhesive bonding and electrical insulation under high-voltage operation (see the Supplementary Information for detailed dimension specifications).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eMeasurement of the actuator bending angle and blocked force\u003c/h3\u003e\n\u003cp\u003eThe rear end of the actuator was fixed vertically using a laser-cut acrylic fixture and placed in a water tank filled with tap water. Voltage was applied to the actuator using a stabilized power supply (PMX32-2QU, Kikusui Electronics) and a DC\u0026ndash;DC converter (NHV24-15K450P, Bellnix). The high-voltage side of the DC\u0026ndash;DC converter was connected to the water inside the actuator chamber via a syringe needle, while the ground side was connected inside the water tank using a wire with conductive tape. To measure the actuator bending angle, images were captured using a camera (L-835, HOZAN) before voltage application and at 5 s and 40 s after voltage application. The applied voltage was increased from 0 to 12 kV in 1 kV increments. The captured images were analyzed using image processing software (ImageJ). The bending angle was determined as the difference between the tip angles before and after voltage application (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). The blocked force was measured using an underwater load cell (LSB-210, FUTEK). The actuator tip was fixed between the load cell probe and an acrylic jig in a plane-to-plane configuration (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). The force value was recorded using a multimeter (Model 2100, Keithley Instruments). The applied voltage was again increased from 0 to 12 kV in 1 kV increments. The blocked force was calculated as the difference between the average force values measured before and after voltage application. These measurements were conducted on three samples, and the average values were reported.\u003c/p\u003e\n\u003ch3\u003eMeasurement of actuation speed\u003c/h3\u003e\n\u003cp\u003eThe measurement was conducted in the same setup used for measuring the bending angle and blocked force. A sticker with two markers was attached to the side of the actuator tip, and the deformation was continuously recorded during voltage application using a high-speed camera (INFINICAM, Photron). The two markers were positioned along the centerline of the actuator thickness. The frame rate was set to 50 fps. Voltage application started 3 s after the recording began and lasted for 60 s before being reduced to 0 V. The applied voltage was increased from 0 to 12 kV in 1 kV increments. The coordinates of the two markers in the captured images were determined using video analysis software (Photron FASTCAM Analysis, Photron). A straight line connecting the two marker points was drawn, and its angle was calculated as the bending angle for each frame. The bending angle data were smoothed using a 0.06 s moving average, and the speed of the bending angle was calculated at 0.02 s intervals. In addition to the time-dependent bending angle and speed, the maximum speeds immediately after voltage application and immediately after voltage removal were determined. This measurement was conducted on three samples, and the average value was reported.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eMeasurement of cyclic response\u003c/h2\u003e \u003cp\u003eThe cyclic response was measured using the same setup used for measuring the bending angle and blocked force. A voltage of 8 kV was applied for 5 s, followed by voltage removal for 20 s, and this cycle was repeated 1000 times. During voltage application, the polarity of the water inside the actuator chamber and the external water was alternated to prevent charge accumulation within the actuator. To evaluate variations in the bending angle, images were captured 1 s before voltage application and 5 s after the onset of voltage application. The captured images were analyzed by the image processing software. The bending angle was determined as the difference from the tip angle recorded before voltage application at the first cycle.\u003c/p\u003e \u003cp\u003e \u003cb\u003ePreparation of the culture solution containing\u003c/b\u003e \u003cb\u003ePyrocystis lunula\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThe \u003cem\u003ePyrocystis lunula\u003c/em\u003e strain NIES-609 obtained from the Microbial Culture Collection at the National Institute for Environmental Studies was cultured at 21\u0026deg;C in a liquid f/2 medium [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e] under a 12 h light/12 h dark cycle (LD 12:12) using a white fluorescent light at a photon flux density of 10\u0026ndash;20 \u0026micro;mol/m\u003csup\u003e2\u003c/sup\u003e/s. To enhance the visibility of bioluminescence, the culture was concentrated before the experiment. On the day before the experiment, the cells were separated from the culture medium using filter paper, and the cells remaining on the filter paper were resuspended in a small amount of the medium to increase the cell density. Since \u003cem\u003ePyrocystis lunula\u003c/em\u003e exhibits circadian regulation of bioluminescence and emits light most strongly during the dark phase [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e], the experiments were conducted during the dark period of the culture cycle.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eImaging of the biohybrid actuator\u003c/h3\u003e\n\u003cp\u003eThe movement and mechanoluminescence of the biohybrid actuator were observed in a darkroom. The image shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb was captured by a color CMOS camera (DFK33UX174, Imaging Source) positioned in front of the water tank where the actuator was fixed. The camera was equipped with a wide-angle lens (VS-0618H1, VS Technology) connected via a C-mount adaptor (CML05, Thorlabs) and a 25 mm focal length lens (DLB-12.7-25PM, SIGMAKOKI). The entire experimental setup was slightly visualized by a green-light LED (M530L4, Thorlabs) with a neutral density filter and a diffuser. All optical components were placed on an optical baseplate (OBC-3045-M6, SIGMAKOKI). The actuator was driven at 12 kV and 0.125 Hz, and the image projections were acquired with the imaging software IC Capture (Imaging Source). The images displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec,d were captured by a camera (Z5, Nikon) positioned at the side of the water tank. The actuator was driven at 12 kV and 0.125 Hz, and photographs were captured with an exposure time of 1 s, an aperture of f/3.2, and ISO 51200. Under these conditions, bioluminescence was observed immediately after voltage application and voltage removal. In these experiments, the same setup used for the characterization of the actuator was used to apply the driving voltage.\u003c/p\u003e\n\u003ch3\u003eFabrication of the gripper\u003c/h3\u003e\n\u003cp\u003eA three-fingered soft gripper was constructed using three fabricated actuators. The actuators were arranged at the midpoints of the three sides of an equilateral triangular base with a side length of 60 mm and oriented such that inward bending occurred upon voltage application. The base was fabricated via 3D printing (Form 3, Formlabs) using a UV-curable resin (Clear Resin V4, Formlabs). Each actuator was mounted to the base using a plastic torque hinge, which provided sufficient holding force to maintain the initial finger orientation while allowing manual adjustment during assembly.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eJellyfish capturing demonstration\u003c/h2\u003e \u003cp\u003eThe demonstration was performed in a water tank filled with artificial seawater at approximately 24\u0026deg;C using a live cannonball jellyfish, which was obtained from Tsuruoka Municipal Kamo Aquarium. The bell diameter of the jellyfish was 30 mm during contraction. During the experiment, the gripper was positioned to allow the jellyfish to approach its center while swimming freely. When the jellyfish entered the grasping region, 12 kV was applied to the actuators to induce inward bending of the three fingers and enclose the organism. The jellyfish was then relocated while being held by the gripper, after which the applied voltage was removed to reopen the fingers and release the animal. Following its release, the jellyfish swam away normally. No visible damage or abnormal swimming behavior was observed after the demonstration. The entire sequence of the demonstration was recorded using a camera (Z5, Nikon). In this demonstration, the voltage was applied using the same setup used for the characterization of the actuator.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eUse of AI tools\u003c/h2\u003e \u003cp\u003eChatGPT (version 5.4, OpenAI) was used solely for language editing support during manuscript preparation. All scientific content, data interpretation, and original writing were independently developed by the authors. All AI-assisted outputs were thoroughly reviewed and verified by the authors.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eData availability\u003c/h2\u003e \u003cp\u003eAll data generated and analyzed during this study are available from the corresponding author upon reasonable request.\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis work was supported by the JSPS KAKENHI Grant-in-Aid for Scientific Research (grant numbers 23K26072, 23H01377, 24KJ1131, and 25K01203), the JSPS Research Fellowship for Young Scientists (DC2), the JST Fusion-Oriented Research for Disruptive Science and Technology program (Grant number JPMJFR2126), and the JST SPRING (Grant number MJSP2131).\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eC.M., T.S., and J.S. conceived the main idea. C.M. and T.S. designed and fabricated the actuators and the gripper. C.M., T.S., N.A.U., K.K., D.N., M.S., and J.S. designed the experiments. C.M., T.S., N.A.U., K.K., D.N., and M.S. conducted the experiments and analyzed the data. C.M., T.S., N.A.U., and J.S. generated and edited the figures and media files. C.M. wrote the manuscript. D.N., M.S., and J.S. supervised the project. J.S. edited the manuscript. All authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eThis work was supported by the JSPS KAKENHI Grant-in-Aid for Scientific Research (grant numbers 23K26072, 23H01377, 24KJ1131, and 25K01203), the JSPS Research Fellowship for Young Scientists (DC2), the JST Fusion-Oriented Research for Disruptive Science and Technology program (Grant number JPMJFR2126), and the JST SPRING (Grant number MJSP2131).\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eAll data generated and analyzed during this study are available from the corresponding author upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eYasa, O. et al. An overview of soft robotics. \u003cem\u003eAnnu. Rev. Control Robot Auton. Syst.\u003c/em\u003e \u003cb\u003e6\u003c/b\u003e, 1\u0026ndash;29 (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRich, S. I., Wood, R. 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Toxicol.\u003c/em\u003e \u003cb\u003e23\u003c/b\u003e, 617\u0026ndash;625 (2008).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-9133026/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9133026/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSoft robots are promising platforms for underwater exploration and biological sampling because of their compliance and adaptability. Dielectric elastomer actuators (DEAs), particularly bending DEAs, are appealing for underwater soft robots because they enable diverse robotic architectures. However, previously reported underwater bending DEAs still present opportunities for improvement in deformation capability, particularly in terms of deformation magnitude and actuation speed. Therefore, this paper presents an underwater DEA consisting of a layered elastomeric structure with an encapsulated water electrode and inextensible materials, which together generate unidirectional bending deformation when a high voltage is applied between the internal water electrode and the surrounding water. Consequently, the actuator achieves a maximum bending angle of 308.5\u0026deg; (corresponding to a curvature of 0.09/mm), which agrees well with predictions from an analytical model. Additionally, it attains an average actuation speed magnitude of 172.2\u0026deg;/s and a blocked force of 57.2 mN while maintaining stable actuation over 1000 cycles. The actuator was further demonstrated as an electrically driven biohybrid luminescent device incorporating \u003cem\u003ePyrocystis lunula\u003c/em\u003e and as a soft gripper capable of manipulating a live jellyfish. These results highlight the potential of the proposed DEA for advancing underwater soft robotic systems.\u003c/p\u003e","manuscriptTitle":"Underwater dielectric elastomer actuators with large bending deformation for soft robots","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-24 19:44:20","doi":"10.21203/rs.3.rs-9133026/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-04-06T11:08:34+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-06T07:41:04+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-31T16:16:49+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"297840689875212045239206088737480009798","date":"2026-03-27T04:47:57+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"102068574924694682601612645075842860764","date":"2026-03-24T12:23:14+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"262646903480925616484326860109564352389","date":"2026-03-21T13:28:27+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"100886504573929352850700064036692828626","date":"2026-03-19T12:33:05+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-03-19T12:09:44+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-03-19T11:00:34+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-17T07:24:46+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-17T07:24:40+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2026-03-16T04:37:47+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"7b9a156a-6c59-4a4e-b7bf-e49530f7fb86","owner":[],"postedDate":"March 24th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"in-revision","subjectAreas":[{"id":64962526,"name":"Physical sciences/Engineering"},{"id":64962527,"name":"Physical sciences/Materials science"},{"id":64962528,"name":"Physical sciences/Physics"}],"tags":[],"updatedAt":"2026-04-06T11:25:03+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-24 19:44:20","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9133026","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9133026","identity":"rs-9133026","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}