Preparation of magnetorheological elastomers and their application in mollusk-inspired bionic systems

Preparation of magnetorheological elastomers and their application in mollusk-inspired bionic systems | 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 Preparation of magnetorheological elastomers and their application in mollusk-inspired bionic systems Zhihong Lin, Zhe Gao, Yuedong Huang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8698891/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 17 Apr, 2026 Read the published version in Scientific Reports → Version 1 posted 10 You are reading this latest preprint version Abstract This study focuses on the biomimetic design, structurally controllable fabrication, and performance regulation of magnetorheological elastomers (MREs) for soft robotics applications. Firstly, by designing a 24-sided polygon orientation control fixture, we achieved precise preparation of magnetic particle chain structures at a series of key angles, including 0°, 15°, 30°, 45°, 60°, 75°, and 90°. Subsequently, scanning electron microscopy confirmed that the MRE microstructure exhibited well-defined chain-like features. Based on this, the dynamic mechanical properties of 50% MRE iron powder with varying carbonyl angles were tested using a rheometer. Finally, MRE was applied to biomimetic designs for manta ray tail fin undulations and chameleon tongue curling. Research findings indicate that chain orientation exerts a significant regulatory effect on the storage modulus (G'), loss modulus (G''), complex viscosity (|η*|), and loss factor (tanδ). Through spatial programming of gradient components and orientation distribution, MREs prepared under a uniform magnetic field drive can successfully reproduce continuous biomimetic motion that closely matches biological prototypes. Physical sciences/Engineering Physical sciences/Materials science Magnetorheological elastomer Preparation Chain-like characteristics Bionic Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 1 Introduction Magnetorheological fluid (MRF) is a classic magnetically responsive smart material that has been widely applied in precision vibration damping and motion control fields [ 1 – 3 ]. However, the inherent challenges of particle settling and sealing severely limit the reliability of this technology in long-term stable operation. To overcome this bottleneck, researchers developed magnetorheological elastomers (MRE). MRE immobilizes micron- or nanometer-sized magnetic particles (such as iron (II) carbonyl powder or magnetite) within flexible polymer matrices like silicone rubber or polyurethane, thereby resolving issues of leakage and sedimentation. Applying an external magnetic field during the curing process induces magnetic particles to align orderly along magnetic field lines, forming chain-like or columnar microstructures. The influence of magnetic fields causes materials to exhibit significant anisotropic mechanical properties. Based on the reversible, rapid, and continuously tunable mechanical behavior of MRE, it demonstrates significant application potential in intelligent vibration reduction systems [ 4 , 5 ], adaptive damping devices [ 6 ], aerospace structural vibration control [ 7 – 9 ], and biomedical minimally invasive instruments [ 10 , 11 ]. Inspired by traditional biomimetic soft robots [ 12 – 15 ], significant progress has also been made in the biomimetic applications of magnetorheological elastomers. MRE offers advantages such as controllability [ 16 ], responsiveness [ 17 ], and adaptability [ 18 ]. The core advantage of MRE lies in its ability to actively design its internal microstructure through an external magnetic field. When a magnetic field is applied during curing, particles align along magnetic field lines to form anisotropic MREs [ 19 ]; without a magnetic field, particles distribute randomly, exhibiting isotropic behavior [ 20 ]. Among these, anisotropic MREs are more suitable for biomimetic applications [ 21 , 22 ]. Regarding the preparation process of MREs, extensive research has been conducted to enhance their performance by optimizing material composition and process conditions. Regarding filler regulation, Salem [ 23 ] found that increasing the content of carbonyl iron powder leads to an overall increase in both the storage modulus and magnetorheological effect of MRE. However, excessively high filler content can easily lead to particle agglomeration, which in turn compromises performance stability. Jolly[ 24 ] earlier revealed the significant effect of magnetic field-induced curing on the microstructure and mechanical properties of MRE. Salem [ 23 ] and Jolly [ 24 ] confirmed that the anisotropic structure formed in MRE under magnetic fields can effectively enhance the material modulus. Zhao[ 25 ] enhanced the interfacial bonding between magnetic particles and the polymer matrix through surface chemical modification, thereby improving the overall mechanical properties of the magnetic-reactive elastomer. Additionally, Marcin [ 26 ] effectively enhanced the uniformity of magnetic particle distribution within the matrix by introducing specific additives and optimizing the dispersion process, thereby reducing performance fluctuations caused by agglomeration. The above studies demonstrate that the combined application of particle surface modification, dispersion process optimization, and external field-induced orientation can synergistically enhance the mechanical properties and stability of magnetic rare-earth materials. In the performance regulation of MREs, the spatial orientation of the particle chains is a key factor determining their anisotropy and field-induced response. Research indicates that minor adjustments to the orientation of particle chains can induce significant changes in material properties. Zhang[ 27 ] found that adjusting the orientation of particle chains by a finite angle significantly enhances the magnetorheological effect of MRE. Lin[ 28 ] further demonstrated that complex programmable biomimetic motions can be achieved by integrating MRE units with different magnetization directions. Tian’s [ 29 ] research reveals that specific-orientation MRE exhibits distinct stiffness differences under different loading directions, demonstrating its potential for directional load-bearing applications. Additionally, Wu[ 30 ] systematically compared the response mechanisms of different oriented structures from a mechanical perspective, deepening the understanding of the relationship between orientation and performance. Although numerous studies have analyzed chain-like MREs from various perspectives, detailed investigations into the angle-specific preparation processes remain scarce. MRE exhibits programmable anisotropic properties, with its applications expanding from traditional vibration control to cutting-edge fields such as flexible sensing, programmable metamaterials, and intelligent bionic systems. By programming the orientation distribution of particle chains, MRE enables dynamic reconfiguration of structural functions [ 28 , 31 ]. Lin[ 32 ] developed a programmable metamaterial plate based on MRE, enabling real-time control of elastic wave guided behavior and vibrational bandgap solely by adjusting the driving current. In the field of biomimetic motion, researchers have successfully achieved complex behaviors such as inchworm-like crawling [ 33 , 34 ] and snake-inspired locomotion [ 28 ] by magnetically programming MREs at specific angles. Additionally, by integrating origami structural design with magnetic moment programming technology, a three-dimensional reconfigurable magnetically driven system has been developed, including rolling robots and jellyfish robots [ 35 ]. For applications requiring non-contact precision operation, MRE's rapid magnetic response and compliant properties make it an ideal new drive material. Through composite structural design, MRE actuators enable adaptive grasping and controllable deformation, allowing damage-free manipulation of irregular objects in diverse environments [ 36 , 37 ]. Furthermore, the integration of 3D printing technology with magnetization distribution programming has opened new avenues for programmable deformation and motion control of soft materials. Through 3D technology, precise control over complex deformation patterns such as octopus tentacles and butterfly wing movements has been achieved [ 38 , 39 ]. Similarly, Qi [ 40 ] employed 3D printing to embed magnetically oriented units within a flexible substrate, further validating the feasibility of achieving biomimetic motion through spatial arrangement control. This study provides a novel approach for optimizing the preparation and expanding the functionalities of MRE by innovatively designing a 24-sided polygonal fixture. The 24-sided polygonal fixture leverages its symmetry to achieve precise control over the chain-like structure of magnetic particles at a series of specific angles: 0°, 15°, 30°, 45°, 60°, 75°, and 90°. These angles cover the range required for common research and applications, meeting the needs of multidimensional experimental analysis such as shear characteristics, magnetic torque, and tilted chain structures. Compared to traditional fixtures, this design significantly enhances the accuracy of angle control and the convenience of preparation, while also helping to reduce material consumption and shorten the research and development cycle. In the field of biomimetic applications, this study designed the functional magnetic particle content of MREs by drawing inspiration from the tail undulation of manta rays and the tongue curling motion of chameleons. For critical motion function components, a carbonyl iron powder content of 60%-70% is employed, while for non-critical motion function components, a carbonyl iron powder content of 40%-50% is utilized. This method overcomes the limitations of traditional MRE biomimicry, which typically employs uniform particle distribution throughout the entire structure and can only mimic a single morphology. It achieves the requirement for differential mechanical property allocation across different regions to match complex biological motions. 2 Experimental sections 2.1 Materials and equipment Magnetic particles are typically prepared from raw materials such as metals and magnetic oxides, providing precise magnetic property support for the target system. The experiment selected iron carbonyl powder from Germany's BASF as the magnetic particles (exhibiting regular spherical morphology, density ≥ 2.5g/cm³, average particle size approximately 3.8–5.3µm); Select Smooth-on's Ecoflex silicone rubber (Grade: Ecoflex 00–20, mixed viscosity: 3000 cps, density: 1.07 g/cm³);Select dimethyl silicone oil (350CS) for easy demolding of the prepared magnetorheological elastomer. Additionally, use the DXKDP series programmable DC power supply to adjust the magnetic field strength, then employ the DX-102F handheld RTN gaussmeter to verify whether the magnetic field meets the required specifications. 2.2 Preparation of MRE The Fig. 1 illustrates the four steps involved in preparing magnetorheological elastomers: Material Preparation: Taking the preparation of MRE with 50% iron powder mass fraction as an example, precisely weigh each component according to the mass ratio of Silicone Rubber A: Silicone Rubber B: Silicone Oil: Carbonyl Iron Powder = 10:10:1:20. Mixing and degassing: Thoroughly stir the mixture with an electric mixer until uniform and free of lumps. Subsequently, place the mixture in a vacuum pump to remove air bubbles. Injection and orientation curing: Rapidly inject the degassed mixture into the mold. Place the mold into the specific angle slot of the 24-sided polygon fixture, ensuring the mold orientation aligns with the preset particle chain orientation angle (e.g., 0°, 45°). Then place it into the preset magnetic field environment until the silicone rubber fully cures. Demolding and post-processing: After the mold has cooled to room temperature, carefully remove the sample. Use a metal craft knife to carefully cut along the edges to obtain a complete MRE sample. Meanwhile, Fig. 2 shows the core experimental equipment used to prepare MRE in this study. 2.3 Programming methods for bionic applications of MRE Following the preparation process shown in Fig. 3 , the intact MRE is cut out using a custom-made punch. Secondly, place MREs with varying concentrations into 3D-printed molds and position them according to the desired angles of the biomimetic animals; Finally, adjust the spacing between each MRE. After placing them all, pour in fully transparent silicone AB adhesive (20°C) to bond them together. Leave it at room temperature for 2–3 hours to cure. Once solidified, use a metal craft knife to score along the desired dimensions before removing. After sampling the MRE specimens, their microstructures were observed using a scanning electron microscope (SEM). Before the experiment, the acceleration voltage, magnification, and working distance of the electron microscope were set to consistent values to eliminate the influence of equipment parameter variations on the observation results. The primary objective of this experiment is to verify whether magnetic particles in the material form chain-like structures consistent with the anticipated preparation. Figure 4 shows the microstructure of MRE as observed by scanning electron microscopy (SEM). Combining multiple SEM images in Fig. 4 reveals that as the magnetic field induction angle (i.e., the angle between the red coordinate system's x-axis and the particle chain direction) gradually increases from 0° to 90°, the chain-like structures formed by iron powder particles within the matrix exhibit highly consistent orientation aligned with the pre-set magnetic field direction. Particle chains in each angular group are uniformly arranged along their respective predetermined directions, with no noticeable agglomeration, disordered arrangement, or random dispersion observed. As shown in the SEM images in Fig. 4 , the prepared magnetorheological elastomer has successfully formed chains of magnetic particles with distinct morphology, continuous structure, and highly uniform orientation. Therefore, the prepared MRE chain-like structure exhibits the desired directional alignment characteristics, achieving the intended material design objectives. 2.4 Rheometer testing and characterization of 50% carbonyl iron powder MRE To investigate the dynamic mechanical behavior of MRE at different magnetic particle chain orientation angles, rheological testing systems were employed. Three representative angles were selected for comparison: 0° and 45°, 15° and 60°, and 30° and 75°. Since the magnetorheological properties of MREs are highly dependent on the orientation structure of magnetic particle chains, a 24-sided polygonal fixture was employed in the experiment to achieve precise control over multi-angle orientation. The aforementioned angle pairings cover key feature orientations ranging from parallel direction (0°), low-angle inclination (15°, 30°), critical angle (45°), to high-angle inclination (60°, 75°). The objective is to systematically capture the evolution of material properties with orientation changes and avoid the randomness that may arise from single-angle testing. The MRE samples were tested using an Anton Paar rheometer to obtain key rheological parameters including storage modulus (G′), loss modulus (G″), complex viscosity (|η*|), and loss factor (tanδ). By analyzing these parameters, the system evaluated the mechanical properties of MRE under different chain orientation angles. The corresponding test results are shown in Figs. 5 and 6 . As shown in Fig. 5 , both the storage modulus (G′) and loss modulus (G″) gradually increase with rising angular frequency (ω). At the same angular frequency, the values of the G′ and G″ curves corresponding to lower magnetic field angles are generally higher than those obtained at higher magnetic field angles. Specifically (Fig. 6 ): (a) Both G′ and G″ at 0° orientation exceed 45°; (b) G′ and G″ at 15° are significantly higher than at 60°; (c) G′ and G″ at 30° remain consistently above 75° across the entire frequency range. Furthermore, for the same orientation angle, the value of G′ consistently remains significantly higher than that of G″, and the gap between the two remains essentially stable as frequency increases. This phenomenon can be attributed to the microstructure formed by carbonyl iron powder particles within the MRE, which facilitates stress transfer and consequently enhances both the elastic and viscous responses of the material. As shown in the test results of Fig. 6 , both the complex viscosity (|η|) and loss factor (tan δ) of the MRE containing 50% carbonyl iron powder exhibit a consistent decreasing trend with increasing angular frequency (ω). Regardless of whether at low or high magnetic field angles, both |η*| and tan δ decrease continuously with increasing ω. Moreover, their variation curves at the same angle are nearly identical, indicating that under these test conditions, their frequency dependence is highly consistent. Additionally, at the same angular frequency, both the |η*| and tan δ values corresponding to the lower magnetic field angle are significantly higher than those at the higher magnetic field angle. Specifically manifested as follows (Fig. 7 ): (a) The curve under 0° conditions is consistently higher than that under 45° conditions; (b) The curve under 15° conditions is significantly higher than that under 60° conditions; (c) The curve under 30° conditions remains higher than that under 75° conditions. Analysis of Figs. 5 and 6 reveals that the dynamic mechanical properties of the MRE with 50% carbonyl iron powder content result from the synergistic interaction between angular frequency and test angle (magnetic field strength). Among these, the angular frequency determines the fundamental trend of viscoelastic response, specifically manifested as G' and G'' increasing with rising frequency, while |η*| and tanδ decrease with increasing frequency. The test angle precisely regulates the strength of performance levels by altering the intensity of magnetic interactions and microstructure within the material's carbonyl iron powder particles, with the regulatory effect becoming more pronounced as ω increases. 3 Spatial assembly and programmable control of magnetically controlled MRE materials 3.1 Manta ray tail flapping biomimicry When swimming, manta rays generate large-amplitude flexible undulations in the middle and rear sections of their pectoral fins to efficiently propel water. Meanwhile, the base region near the body maintains high structural rigidity, providing a stable foundation for force transmission during wave-like movements. This biomechanical property fundamentally stems from the gradient mechanical properties of the tail tissue—the distal region exhibits lower fiber density and dynamic regulation of elastic modulus. The base consists of dense collagen fiber bundles, exhibiting high stiffness and low variability in mechanical properties. To precisely replicate the aforementioned biological characteristics, a segmented chain-type MRE with a biomimetic flexible fin structure was designed. The structure consists of eight independent MRE units connected along the extension direction via flexible chains. The four units in the middle-rear section corresponding to the critical zone of pectoral fin undulation are set to a high-content gradient of 60%, 60%, 70%, and 70%. The four units at the base corresponding to the stable support zone are set to a low-content gradient of 40%, 40%, 50%, and 50%. Since the magnetostrictive shear modulus of MREs is positively correlated with magnetic particle content, units with different iron powder concentrations exhibit differentiated stiffness responses under uniform magnetic field excitation. Therefore, the modulus increase is more pronounced in high-content units, while the change in low-content units is relatively limited. Consequently, under the influence of a single magnetic field, this biomimetic structure spontaneously generates a mechanical gradient characterized by “remote adjustability and base stability” within its interior. This enables the structure to exhibit dynamic mechanical behavior highly consistent with that of the manta ray's pectoral fins at the structural level. Figure 7 comprehensively illustrates the development process of the biomimetic manta ray tail structure through four modules: A1 to A4. Module A1 takes the manta ray's tail as its biological prototype, using contour annotations to highlight its naturally curved form, thereby providing morphological reference for subsequent biomimetic design. Module A2 defines the target curve based on this profile and utilizes segmented structural diagrams to specify the angular parameters and installation direction rules for each segment, thereby completing the geometric design and assembly logic definition of the structure. The A3 module demonstrates the actual assembly state of this biomimetic structure on the experimental platform, achieving the transition from design to physical form. The A4 module's locally magnified experimental results clearly reveal the final dynamic morphology of the biomimetic structure, whose morphological characteristics form a distinct correspondence with the biological prototype in A1. Figure 8 shows a comparison of the deformation of structures with three different iron powder mass fractions under static magnetic field excitation. Where B1-B5 correspond to a uniform structure with an iron powder mass fraction of 40%. Under magnetic field excitation starting at 0.5 A and incrementing in 0.25 A steps up to 1.5 A, the entire structure undergoes bending; However, the difference in bending angles between the middle-to-rear section and the base is not significant, which clearly does not align with the biological movement patterns of manta ray pectoral fins. Due to the overall low iron powder content, the base lacks sufficient rigidity and fails to provide rigid support within the magnetic field; Therefore, the entire structure undergoes lateral buckling displacement, leading to structural instability and failure of the biomimetic function. C1-C5 correspond to a uniform structure with an iron powder mass fraction of 60%. The higher particle content significantly limits the deformation capability of the polymer matrix, resulting in reduced magneto-responsive flexibility. Under identical magnetic field excitation, the structure exhibits only minimal overall deformation, maintaining a highly rigid and taut state throughout. In the mid-to-late stages, no significant fluctuation trends are discernible. Meanwhile, the overall bending amplitude is significantly lower than that of a uniform 40% structure. Consequently, effective biomimetic wave propagation cannot be achieved. D1–D5 correspond to gradient distribution structures (iron powder mass fractions of 40%, 40%, 50%, 50%, 60%, 60%, 70%, and 70%, respectively). Under a 1.5 A magnetic field excitation, the structure exhibits a morphology highly consistent with its biological prototype. The mid-to-rear high-content units achieve large-amplitude flexible bending, while the low-content units at the base undergo only small-angle deformation, enabling biomimetic functionality. Figure 9 compares the response processes of structures with different iron powder contents under dynamic magnetic field excitation. Where Fig. 9 (a) corresponds to a uniform structure with 40% iron powder content. The structure exhibits minimal deformation across the entire current range, with a very low slope of deformation as the current increases. It is evident that the magnetic response performance of the 40% iron powder content is insufficient, failing to produce effective deformation in response to magnetic field excitation. Figure 9 (b) corresponds to a uniform structure with 60% iron powder content. As the excitation current gradually increases from 0.5 A to 1.5 A, the overall bending of the structure progressively increases. However, the difference in bending angles between the mid-to-rear section and the base of the MRE is minimal, failing to simulate the temporal characteristics of the manta ray's pectoral fin movement. When the current exceeds 1 A, the structure even undergoes overall distortion and instability, losing the controllability of its biomimetic form. Figure 9 (c) corresponds to the gradient-content structure, fully illustrating its dynamic biomimetic process. At a current of 0.75 A, the bending angle of the high-content units in the middle and rear sections of the MRE is significantly greater than that of the low-content units at the base, exhibiting a start-up pattern characterized by “slight oscillation in the middle and rear sections—straightening at the base.” When the current rises to 1.0 A, the amplitude of fluctuations in the middle and late stages of the MRE increases significantly, forming wide-amplitude oscillations consistent with the biological prototype. Meanwhile, the MRE base maintains a slight angle of curvature, with no reduction in support. As the current further increased to 1.5 A, the mid-to-rear section of the MRE exhibited enhanced oscillation, achieving highly efficient water flow propulsion while maintaining stable base stiffness. The entire dynamic response not only replicates the morphological changes of the manta ray's pectoral fins, but its “activation-oscillation-propulsion” temporal rhythm also closely matches that of its biological prototype. A comprehensive analysis of the static and dynamic responses shown in Figs. 8 and 9 reveals that when the iron powder content in the critical motion segment (mid-to-rear section) is insufficient (e.g., a uniform 40% structure throughout), the magnetostrictive modulus exhibits minimal variation, making it difficult for the structure to generate effective oscillations. Conversely, if the iron powder content at the base is excessively high (such as a uniform 60% structure throughout), the resulting excessive variation in stiffness leads to a loss of support and induces buckling distortion. By adopting a gradient distribution combining the mid-to-rear section (60%, 70%) with the base section (40%, 50%), the structure achieves both large-amplitude oscillations at the tip and stable support at the base under uniform magnetic field excitation. Its static and dynamic morphologies closely match the movement characteristics of manta ray pectoral fins. 3.2 Chameleon tongue curling biomimicry The chameleon's highly efficient hunting ability stems from its tongue's unique mechanism of active curling at the front end and stable support at the rear end, enabling non-uniform motion. To precisely replicate this biological function, the study designed a biomimetic rod structure based on segmented chain MREs. The structure consists of seven independent MRE units connected axially via flexible chains. Among these, the functional gradient distribution of the mass fraction of carbonyl iron powder in MRE. Set the front four units of the key zone of the chameleon's tongue to a high-content gradient of 60%, 60%, 70%, and 70%. Meanwhile, the rear three units of the stable support zone on the chameleon's tongue are configured with a low-content gradient of 40%, 40%, and 50%. Figure 10 systematically illustrates the design and validation process of the biomimetic chameleon tongue curling mechanism through four modules: A1 to A4. Module A1 draws inspiration from the dynamic coiling motion of a chameleon's tongue during predation. Documenting this coiling behavior, it provides a function-driven morphological basis for biomimetic design. Module A2 first defines the target fitting curve based on the biological contour; Subsequently, through segmented structural design, the continuous deformation of the tongue was discretized into five gradient angles: 0°, 15°, 30°, 45°, and 75°. Simultaneously, positive and negative signs clearly indicate the installation orientation of each segment, thereby completing the geometric and assembly logic definition of the structure. Module A3 demonstrates the physical assembly state of this biomimetic structure on the experimental platform, achieving the transition from parametric design to physical assembly. The A4 module's locally magnified experimental results clearly reveal the ring-shaped curling morphology of the biomimetic structure under excitation, exhibiting high consistency with the biological prototype in A1. This validates the parametric design's capability to accurately reproduce biological functional morphology. Figure 11 shows a comparison of the deformation responses of three different iron powder content structures under static magnetic field excitation. B1-B5 exhibit a uniform structure with an iron powder mass fraction of 40%. Due to the low iron powder content, the magnetic modulus of MRE exhibits only a slight change. Therefore, under a 1.5 A magnetic field, the structure exhibits only minimal deformation, with no curling tendency at the front end, and the biomimetic function remains unachieved. C1-C5 exhibit a uniform structure with an iron powder mass fraction of 60%. Under magnetic field excitation ranging from 0.5 A to 1.5 A (in 0.25 A increments), the MRE structure exhibits disordered deformation characteristics. Within the 0.5–1.0 A range, the structure does not exhibit directed bending but instead displays distorted, loose, and irregular deviations. When the current rises to 1.25 A, the structure exhibits overall bending; However, the uniform deformation before and after MRE shows no difference, and bending is accompanied by lateral deviation and sagging. At 1.5 A, the bending amplitude increases, but instability and sagging worsen, failing to demonstrate the biomimetic characteristics of rear-end support throughout the entire process. D1-D5 represent a gradient content structure. Under a 1.5 A magnetic field excitation, the MRE exhibits morphology highly consistent with its biological prototype. The front-end high-content units achieve large-curvature curling, while the rear-end low-content units undergo only minor angular deformation. Throughout the process, a holistic bionic posture was achieved, integrating front-end packaging with back-end support. Therefore, this verifies that the gradient-based structure of D1-D5 plays a key role in enabling functional partitioning. Figure 12 compares the response processes of structures with different iron powder contents under dynamic magnetic field excitation. Figure 12 (a) corresponds to a uniform structure with 40% iron powder content. This structure exhibits minimal deformation across the entire current range, with a very low slope of deformation increasing with current. This indicates insufficient magnetic response performance, rendering it incapable of effectively responding to excitation and failing to achieve biomimetic functionality. Figure 12 (b) corresponds to a uniform structure with 60% iron powder content. As the current gradually increased from 0.5 A to 1.5 A, the overall bending of the structure continued to increase, but it consistently exhibited uniform deformation without any gradient. Meanwhile, the difference in bending angles between the front and rear ends is minimal, failing to replicate the movement sequence characteristic of a chameleon's tongue, where the front end actively curls while the rear end passively follows. When the current exceeds 1.25 A, the structure undergoes overall distortion and instability, causing the biomimetic form to lose complete control. Figure 12 (c) corresponds to the gradient-content structure, fully illustrating its dynamic biomimetic process. At a current of 0.5 A, the bending angle of the high-content units at the front end is significantly greater than that of the low-content units at the rear end, exhibiting a pre-stretch morphology characterized by “slight curling at the front end and straightening at the rear end.” When the current increased to 1.0 A, the bending angle of the front end unit significantly increased, forming a curled shape consistent with the biological prototype (Fig. 10A1), while the rear end maintained a small-angle deformation. As the current further increases to 1.5 A, the curvature of the front end continues to grow, achieving a tight wrap around the prey. This dynamic process not only replicates the morphological characteristics of a chameleon's tongue but also closely matches the biological prototype's sequential rhythm of pre-extension, coiling, and envelopment. A comprehensive analysis of Fig. 11 (static deformation) and Fig. 12 (dynamic process) reveals that for the uniform structure with 40% iron powder content (corresponding to Fig. 12 (a)), the insufficient total magnetic particles result in a negligible change in the magnetostrictive modulus. Under excitation ranging from 0.5 A to 1.5 A, it consistently fails to generate effective curling, with the morphology severely deviating from the biomimetic target. The uniform structure with 60% iron powder content (corresponding to Fig. 12 (b)) exhibits excessive rear-end stiffness variation during excitation due to the absence of a mechanical gradient. This results in irregular deflection and sagging, causing it to lose its support function. The gradient content structure (corresponding to Fig. 12 (c)), characterized by a “front-high, rear-low” iron powder distribution, exhibits a deformation pattern of “front-end flexible curling and rear-end stable extension” under different currents. This behavior closely matches the kinematic characteristics of a chameleon's tongue. Above results validate the material's ability to encode biomimetic motion characteristics into MRE units, demonstrating spontaneous self-replication of target biomimetic morphologies under a single uniform magnetic field without requiring complex external control. 4 Conclusion This study investigates the control of chain-like structural orientation in MRE and their potential applications in biomimetic soft robots. Through the innovative design of a 24-sided polygonal orientation control fixture, magnetic particles were precisely aligned at 0°, 15°, 30°, 45°, 60°, 75°, and 90°. Microscopic morphology observations confirmed excellent orientation consistency. Rheological testing further revealed the significant regulatory effect of orientation angle on the dynamic mechanical properties of MRE. Building upon this foundation, the MRE composite structure was engineered using gradient material design and spatial angle programming, drawing inspiration from the undulating tail fins of manta rays and the curling tongues of chameleons as biomimetic prototypes. This design successfully replicates continuous motion that closely matches the biological models. The conclusions of this study include: (1) The proposed orientation control process enables precise preparation of the MRE microstructure, providing a reliable foundation for material property customization; (2) Based on a spatial splicing strategy utilizing gradient iron powder distribution and chain-like orientation, programmable deformation of the MRE structure was achieved, simplifying the control logic for biomimetic motion. (3) The designed MRE biomimetic structure can effectively simulate the characteristic movements of manta ray tail fin undulation, propulsion and chameleon tongue curling for prey capture under magnetic field excitation, validating the practical application potential of this material system in soft biomimetic animals. Declarations Conflict of interest: The authors declare that they have no conflict of interest. Funding information: This research has been supported by the funding: Supported by Fujian Provincial Natural Science Foundation of China (Project Number: 2024J01317, 2022J011183). Author Contribution Zhihong Lin is responsible for the methodology proposal and the writing of the draft paper. Zhe Gao and Yuedong Huang contributed to the grammar check and Article processing fee. Data Availability All data included in this study are available upon request from the corresponding author. References Kumar, J. S. et al. 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The magneto viscoelastic response of elastomer composites consisting of ferrous particles embedded in a polymer matrix[J]. J. Intell. Mater. Syst. Struct. 7 (6), 613–622 (1996). Zhao, J. et al. Surface modification of carbonyl iron particles using dopamine and silane coupling agent for high-performance magnetorheological elastomers[J]. Polym. Test. 119 , 107935 (2023). Maslowski, M. et al. Effect of ionic liquids on the selected properties of magnetic composites filled with micro-sized iron oxide (Fe3O4)[J]. Polimery,2016, 61 (2):117–124 . Zhang, J. et al. The magneto-mechanical properties of off-axis anisotropic magnetorheological elastomers[J]. Compos. Sci. Technol. 191 , 108079 (2020). Lin, D. et al. Characterization of the translational shear properties of the magnetorheological elastomers embedding the tilt chain-like structure[J]. Appl. Rheology . 34 (1), 20240022 (2024). Tian, T. F. & Nakano, M. Fabrication and characterization of anisotropic magnetorheological elastomer with 45° iron particle alignment at various silicone oil concentrations[J]. J. Intell. Mater. Syst. Struct. 29 (2), 151–159 (2018). Wu, H. et al. Chain formation mechanism of magnetic particles in magnetorheological elastomers during pre-structure[J]. J. Magn. Magn. Mater. 527 , 167693 (2021). Ijaz, S. et al. Magnetically actuated miniature walking soft robot based on chained magnetic microparticles-embedded elastomer[J]. Sens. Actuators A: Phys. 301 , 111707 (2020). Lin, Y. et al. Investigation of a new magnetorheological elastomer metamaterial plate with continuous programmable properties for vibration manipulation[J]. J. Sound Vib. 573 , 118215 (2024). Hua, D. et al. A magnetorheological fluid-filled soft crawling robot with magnetic actuation[J]. IEEE/ASME Trans. Mechatron. 25 (6), 2700–2710 (2020). Joyee, E. B. & Pan, Y. A fully three-dimensional printed inchworm-inspired soft robot with magnetic actuation[J]. Soft Rob. 6 (3), 333–345 (2019). Tang, D. et al. Origami-inspired magnetic-driven soft actuators with programmable designs and multiple applications[J]. Nano Energy . 89 , 106424 (2021). Gao, W. et al. Magnetic Driving Flowerlike Soft Platform: Biomimetic Fabrication and External Regulation[J]. ACS Appl. Mater. Interfaces . 8 (22), 14182–14189 (2016). Choi, D. S. et al. Beyond Human Hand: Shape-Adaptive and Reversible Magnetorheological Elastomer-Based Robot Gripper Skin[J]. ACS Appl. Mater. Interfaces . 12 (39), 44147–44155 (2020). Cao, X. et al. 3D printing magnetic actuators for biomimetic applications[J]. ACS Appl. Mater. Interfaces . 13 (25), 30127–30136 (2021). Chen, Z. et al. Programmable transformation and controllable locomotion of magnetoactive soft materials with 3D-patterned magnetization[J]. ACS Appl. Mater. Interfaces . 12 (52), 58179–58190 (2020). Qi, S. et al. 3D printed shape-programmable magneto-active soft matter for biomimetic applications[J]. Compos. Sci. Technol. 188 , 107973 (2020). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 17 Apr, 2026 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 09 Feb, 2026 Reviews received at journal 08 Feb, 2026 Reviews received at journal 02 Feb, 2026 Reviewers agreed at journal 02 Feb, 2026 Reviewers agreed at journal 30 Jan, 2026 Reviewers invited by journal 30 Jan, 2026 Editor invited by journal 30 Jan, 2026 Editor assigned by journal 27 Jan, 2026 Submission checks completed at journal 27 Jan, 2026 First submitted to journal 26 Jan, 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-8698891","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":584481506,"identity":"cb95c421-8822-41af-a9f8-75b317cf7a9d","order_by":0,"name":"Zhihong Lin","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA7klEQVRIiWNgGAWjYBACPmYGhgMffhwAsdkYEiok5OQJaWFjZmA8OLMHpuWMhbFhAyEtDAzMh3nYoFoY2yoSGQ4Q0sLOe+AAD88dOXP+5c8ePJwnkcDYwPzw0Q28DuNLOCBh8czYcsaDdIPEbRJ57AxsxsY5eLXwGBww4DmcuOHGgWMSQC3FjA08bNIEtSSwgbQcbJNInCOR2HCAGC0HQFrON7MB1ROp5WBjz2FjgxtsbBIJxySMDZsJ+IWf/4zx5z8/DssZnD/+TPJHTZ2cPHvzw8f4tCCARAKUwUyUcrB9B4hWOgpGwSgYBSMMAAC8w02loYkvowAAAABJRU5ErkJggg==","orcid":"","institution":"Sanming University","correspondingAuthor":true,"prefix":"","firstName":"Zhihong","middleName":"","lastName":"Lin","suffix":""},{"id":584481507,"identity":"7b6d45fa-edb8-499c-b143-a302ee1eb7a2","order_by":1,"name":"Zhe Gao","email":"","orcid":"","institution":"Sanming University","correspondingAuthor":false,"prefix":"","firstName":"Zhe","middleName":"","lastName":"Gao","suffix":""},{"id":584481508,"identity":"7575bcd8-9b0f-4fd7-9bb0-519743497282","order_by":2,"name":"Yuedong Huang","email":"","orcid":"","institution":"Xiamen Ocean Vocational College","correspondingAuthor":false,"prefix":"","firstName":"Yuedong","middleName":"","lastName":"Huang","suffix":""}],"badges":[],"createdAt":"2026-01-26 09:54:41","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8698891/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8698891/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-026-48818-3","type":"published","date":"2026-04-17T15:58:13+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":101880701,"identity":"098cdb94-4683-4c11-bd18-be8cdeb47859","added_by":"auto","created_at":"2026-02-04 15:05:28","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":205757,"visible":true,"origin":"","legend":"\u003cp\u003eMRE preparation process\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8698891/v1/02498d8ee02649973ceded5d.png"},{"id":101761815,"identity":"574ae6f6-9cda-4c72-9093-82dc75ed7f0c","added_by":"auto","created_at":"2026-02-03 11:22:59","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":547828,"visible":true,"origin":"","legend":"\u003cp\u003ePrimary Experimental Instruments for MRE Preparation: (a) Excitation device; (b) 5×2 mm punch; (c) Vacuum pump; (d) DX-102F handheld RTN gaussmeter; (e) MRE preparation mold; (f) Electric stirring rod; (g) Electronic balance; (h) DXKDP series programmable DC power supply.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8698891/v1/9c6433b62d187b6c206ec7cf.png"},{"id":101761812,"identity":"c611e46c-46c2-4465-82d4-45ef545b6442","added_by":"auto","created_at":"2026-02-03 11:22:59","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":165265,"visible":true,"origin":"","legend":"\u003cp\u003eProcess for preparing and utilizing MRE composites for bionic applications\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8698891/v1/81066ec211a4bd41d2d2668c.png"},{"id":101761821,"identity":"4ccb8c46-1a78-422f-abcb-61a6d094ec95","added_by":"auto","created_at":"2026-02-03 11:23:00","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1229030,"visible":true,"origin":"","legend":"\u003cp\u003eMicrographs of MRE electron microscope at various angles\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8698891/v1/8de06e75ce1c1812a28d3fc3.png"},{"id":101880662,"identity":"693b6505-16f6-4d50-bbdf-1d0d4c5b5791","added_by":"auto","created_at":"2026-02-04 15:04:55","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":224610,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of angular frequency and magnetic field angle on the storage and loss moduli of 50% carbonyl iron powder MRE (a) Comparison of storage and loss moduli at 0° and 45° MRE (b) Comparison of storage and loss moduli at 15° and 60° MRE (c) Comparison of storage and loss moduli at 30° and 75° MRE\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8698891/v1/8fa7e1d38ac7d3372e7e21ec.png"},{"id":101761819,"identity":"3cc0cf35-d631-4706-bf70-6c0a0f4bce1f","added_by":"auto","created_at":"2026-02-03 11:23:00","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":175963,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of angular frequency and magnetic field angle on the complex viscosity and loss factor of 50% carbonyl iron powder MRE (a) Comparison of complex viscosity and loss factor at 0° and 45° MRE (b) Comparison of complex viscosity and loss factor at 15° and 60° MRE (c) Comparison of complex viscosity and loss factor at 30° and 75° MRE\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-8698891/v1/67b5ce3cd975611d7e83b276.png"},{"id":101880460,"identity":"589c0418-30e2-4163-b8e5-457b4e7abfbd","added_by":"auto","created_at":"2026-02-04 15:02:17","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":227217,"visible":true,"origin":"","legend":"\u003cp\u003eA1-A4: Schematic diagrams of the structural composition of the manta ray and experimental results.\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-8698891/v1/8e0740ca4a724bfe29a09a05.png"},{"id":101880461,"identity":"1150bdcd-4e97-4895-b16d-bb30491964ec","added_by":"auto","created_at":"2026-02-04 15:02:18","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":1067692,"visible":true,"origin":"","legend":"\u003cp\u003eB1-B5 shows biomimetic experiments of magnetorheological elastomers with 40% carbonyl iron powder content; Figure C1-C5 shows biomimetic experiments of magnetorheological elastomers with 60% carbonyl iron powder content; Figure D1-D5 shows biomimetic experiments of magnetorheological elastomers with varying carbonyl iron powder contents (front end: 40%, rear end: 70%\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-8698891/v1/6ced9918495e6159fbe90417.png"},{"id":101761818,"identity":"7cf1c19d-feb2-4e7a-bfeb-f173d9b1fd5a","added_by":"auto","created_at":"2026-02-03 11:22:59","extension":"jpeg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":441542,"visible":true,"origin":"","legend":"\u003cp\u003eDynamic response simulation of manta ray tail undulation using magnetorheological elastomer. (a) Schematic of magnetic field variation with 40% carbonyl iron powder content; (b) Schematic diagram of magnetic field variation with 60% carbonyl iron powder content; (c) Schematic diagram of magnetic field variation with different carbonyl iron powder contents (40% and 50% at the front end of the tail, 60% and 70% at the rear end\u003c/p\u003e","description":"","filename":"floatimage9.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8698891/v1/441dc2a7b88cb0edd6ca300a.jpeg"},{"id":101880574,"identity":"cecc66ca-25ad-4808-b208-6180ba499415","added_by":"auto","created_at":"2026-02-04 15:03:44","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":259254,"visible":true,"origin":"","legend":"\u003cp\u003eA1-A4 schematic diagram of the structural composition of the chameleon and schematic diagram of the experimental results\u003c/p\u003e","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-8698891/v1/612bfa1fa5568f1d65fa9189.png"},{"id":101880516,"identity":"c06b40c3-408f-4a0e-9bdc-ea27bbaf77e7","added_by":"auto","created_at":"2026-02-04 15:03:07","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":1464690,"visible":true,"origin":"","legend":"\u003cp\u003eB1-B5 shows biomimetic experiments of magnetorheological elastomers with 40% carbonyl iron powder content, while Figure C1-C5 depicts biomimetic experiments of magnetorheological elastomers with 60% carbonyl iron powder content. Figures D1-D5 show biomimetic experiments of magnetorheological elastomers with varying carbonyl iron powder contents (the front end of the tongue represents 60%, 60%, 70%, and 70% content, while the rear end represents 40%, 40%, and 50%).\u003c/p\u003e","description":"","filename":"floatimage11.png","url":"https://assets-eu.researchsquare.com/files/rs-8698891/v1/13a68718a30fa61d14a4fc67.png"},{"id":101880742,"identity":"211a516b-4c96-4997-93c8-902b1ecec35c","added_by":"auto","created_at":"2026-02-04 15:05:48","extension":"jpeg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":277691,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagrams of the dynamic response of chameleon tongue curling simulated using magnetorheological elastomers: (a) Schematic diagram of magnetic field variation with 40% carbonyl iron powder content, (b) Schematic diagram of magnetic field variation with 60% carbonyl iron powder content, (c) Schematic diagrams of magnetic field variation for different carbonyl iron powder contents (tongue tail sections represent 40%, 50%, head: 60%, 70%) under varying magnetic fields.\u003c/p\u003e","description":"","filename":"floatimage12.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8698891/v1/95c13330e95d4235483fc3b5.jpeg"},{"id":107352080,"identity":"5fbdb731-461d-41d3-b393-ff8b8a6d58d9","added_by":"auto","created_at":"2026-04-20 16:13:04","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6951381,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8698891/v1/29ee2cb6-a8fe-431f-bd4a-1b1441d4a938.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Preparation of magnetorheological elastomers and their application in mollusk-inspired bionic systems","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eMagnetorheological fluid (MRF) is a classic magnetically responsive smart material that has been widely applied in precision vibration damping and motion control fields [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. However, the inherent challenges of particle settling and sealing severely limit the reliability of this technology in long-term stable operation. To overcome this bottleneck, researchers developed magnetorheological elastomers (MRE). MRE immobilizes micron- or nanometer-sized magnetic particles (such as iron (II) carbonyl powder or magnetite) within flexible polymer matrices like silicone rubber or polyurethane, thereby resolving issues of leakage and sedimentation. Applying an external magnetic field during the curing process induces magnetic particles to align orderly along magnetic field lines, forming chain-like or columnar microstructures. The influence of magnetic fields causes materials to exhibit significant anisotropic mechanical properties. Based on the reversible, rapid, and continuously tunable mechanical behavior of MRE, it demonstrates significant application potential in intelligent vibration reduction systems [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], adaptive damping devices [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], aerospace structural vibration control [\u003cspan additionalcitationids=\"CR8\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], and biomedical minimally invasive instruments [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Inspired by traditional biomimetic soft robots [\u003cspan additionalcitationids=\"CR13 CR14\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], significant progress has also been made in the biomimetic applications of magnetorheological elastomers. MRE offers advantages such as controllability [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e], responsiveness [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e], and adaptability [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The core advantage of MRE lies in its ability to actively design its internal microstructure through an external magnetic field. When a magnetic field is applied during curing, particles align along magnetic field lines to form anisotropic MREs [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]; without a magnetic field, particles distribute randomly, exhibiting isotropic behavior [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Among these, anisotropic MREs are more suitable for biomimetic applications [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eRegarding the preparation process of MREs, extensive research has been conducted to enhance their performance by optimizing material composition and process conditions. Regarding filler regulation, Salem [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e] found that increasing the content of carbonyl iron powder leads to an overall increase in both the storage modulus and magnetorheological effect of MRE. However, excessively high filler content can easily lead to particle agglomeration, which in turn compromises performance stability. Jolly[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] earlier revealed the significant effect of magnetic field-induced curing on the microstructure and mechanical properties of MRE. Salem [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e] and Jolly [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] confirmed that the anisotropic structure formed in MRE under magnetic fields can effectively enhance the material modulus. Zhao[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] enhanced the interfacial bonding between magnetic particles and the polymer matrix through surface chemical modification, thereby improving the overall mechanical properties of the magnetic-reactive elastomer. Additionally, Marcin [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] effectively enhanced the uniformity of magnetic particle distribution within the matrix by introducing specific additives and optimizing the dispersion process, thereby reducing performance fluctuations caused by agglomeration. The above studies demonstrate that the combined application of particle surface modification, dispersion process optimization, and external field-induced orientation can synergistically enhance the mechanical properties and stability of magnetic rare-earth materials.\u003c/p\u003e \u003cp\u003eIn the performance regulation of MREs, the spatial orientation of the particle chains is a key factor determining their anisotropy and field-induced response. Research indicates that minor adjustments to the orientation of particle chains can induce significant changes in material properties. Zhang[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] found that adjusting the orientation of particle chains by a finite angle significantly enhances the magnetorheological effect of MRE. Lin[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] further demonstrated that complex programmable biomimetic motions can be achieved by integrating MRE units with different magnetization directions. Tian\u0026rsquo;s [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e] research reveals that specific-orientation MRE exhibits distinct stiffness differences under different loading directions, demonstrating its potential for directional load-bearing applications. Additionally, Wu[\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e] systematically compared the response mechanisms of different oriented structures from a mechanical perspective, deepening the understanding of the relationship between orientation and performance. Although numerous studies have analyzed chain-like MREs from various perspectives, detailed investigations into the angle-specific preparation processes remain scarce.\u003c/p\u003e \u003cp\u003eMRE exhibits programmable anisotropic properties, with its applications expanding from traditional vibration control to cutting-edge fields such as flexible sensing, programmable metamaterials, and intelligent bionic systems. By programming the orientation distribution of particle chains, MRE enables dynamic reconfiguration of structural functions [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. Lin[\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e] developed a programmable metamaterial plate based on MRE, enabling real-time control of elastic wave guided behavior and vibrational bandgap solely by adjusting the driving current. In the field of biomimetic motion, researchers have successfully achieved complex behaviors such as inchworm-like crawling [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] and snake-inspired locomotion [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] by magnetically programming MREs at specific angles. Additionally, by integrating origami structural design with magnetic moment programming technology, a three-dimensional reconfigurable magnetically driven system has been developed, including rolling robots and jellyfish robots [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. For applications requiring non-contact precision operation, MRE's rapid magnetic response and compliant properties make it an ideal new drive material. Through composite structural design, MRE actuators enable adaptive grasping and controllable deformation, allowing damage-free manipulation of irregular objects in diverse environments [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Furthermore, the integration of 3D printing technology with magnetization distribution programming has opened new avenues for programmable deformation and motion control of soft materials. Through 3D technology, precise control over complex deformation patterns such as octopus tentacles and butterfly wing movements has been achieved [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. Similarly, Qi [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e] employed 3D printing to embed magnetically oriented units within a flexible substrate, further validating the feasibility of achieving biomimetic motion through spatial arrangement control.\u003c/p\u003e \u003cp\u003eThis study provides a novel approach for optimizing the preparation and expanding the functionalities of MRE by innovatively designing a 24-sided polygonal fixture. The 24-sided polygonal fixture leverages its symmetry to achieve precise control over the chain-like structure of magnetic particles at a series of specific angles: 0\u0026deg;, 15\u0026deg;, 30\u0026deg;, 45\u0026deg;, 60\u0026deg;, 75\u0026deg;, and 90\u0026deg;. These angles cover the range required for common research and applications, meeting the needs of multidimensional experimental analysis such as shear characteristics, magnetic torque, and tilted chain structures. Compared to traditional fixtures, this design significantly enhances the accuracy of angle control and the convenience of preparation, while also helping to reduce material consumption and shorten the research and development cycle. In the field of biomimetic applications, this study designed the functional magnetic particle content of MREs by drawing inspiration from the tail undulation of manta rays and the tongue curling motion of chameleons. For critical motion function components, a carbonyl iron powder content of 60%-70% is employed, while for non-critical motion function components, a carbonyl iron powder content of 40%-50% is utilized. This method overcomes the limitations of traditional MRE biomimicry, which typically employs uniform particle distribution throughout the entire structure and can only mimic a single morphology. It achieves the requirement for differential mechanical property allocation across different regions to match complex biological motions.\u003c/p\u003e"},{"header":"2 Experimental sections","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials and equipment\u003c/h2\u003e \u003cp\u003eMagnetic particles are typically prepared from raw materials such as metals and magnetic oxides, providing precise magnetic property support for the target system. The experiment selected iron carbonyl powder from Germany's BASF as the magnetic particles (exhibiting regular spherical morphology, density\u0026thinsp;\u0026ge;\u0026thinsp;2.5g/cm\u0026sup3;, average particle size approximately 3.8\u0026ndash;5.3\u0026micro;m); Select Smooth-on's Ecoflex silicone rubber (Grade: Ecoflex 00\u0026ndash;20, mixed viscosity: 3000 cps, density: 1.07 g/cm\u0026sup3;);Select dimethyl silicone oil (350CS) for easy demolding of the prepared magnetorheological elastomer. Additionally, use the DXKDP series programmable DC power supply to adjust the magnetic field strength, then employ the DX-102F handheld RTN gaussmeter to verify whether the magnetic field meets the required specifications.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Preparation of MRE\u003c/h2\u003e \u003cp\u003eThe Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e illustrates the four steps involved in preparing magnetorheological elastomers:\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eMaterial Preparation: Taking the preparation of MRE with 50% iron powder mass fraction as an example, precisely weigh each component according to the mass ratio of Silicone Rubber A: Silicone Rubber B: Silicone Oil: Carbonyl Iron Powder\u0026thinsp;=\u0026thinsp;10:10:1:20.\u003c/p\u003e \u003cp\u003eMixing and degassing: Thoroughly stir the mixture with an electric mixer until uniform and free of lumps. Subsequently, place the mixture in a vacuum pump to remove air bubbles.\u003c/p\u003e \u003cp\u003eInjection and orientation curing: Rapidly inject the degassed mixture into the mold. Place the mold into the specific angle slot of the 24-sided polygon fixture, ensuring the mold orientation aligns with the preset particle chain orientation angle (e.g., 0\u0026deg;, 45\u0026deg;). Then place it into the preset magnetic field environment until the silicone rubber fully cures.\u003c/p\u003e \u003cp\u003eDemolding and post-processing: After the mold has cooled to room temperature, carefully remove the sample. Use a metal craft knife to carefully cut along the edges to obtain a complete MRE sample. Meanwhile, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the core experimental equipment used to prepare MRE in this study.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Programming methods for bionic applications of MRE\u003c/h2\u003e \u003cp\u003eFollowing the preparation process shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, the intact MRE is cut out using a custom-made punch. Secondly, place MREs with varying concentrations into 3D-printed molds and position them according to the desired angles of the biomimetic animals; Finally, adjust the spacing between each MRE. After placing them all, pour in fully transparent silicone AB adhesive (20\u0026deg;C) to bond them together. Leave it at room temperature for 2\u0026ndash;3 hours to cure. Once solidified, use a metal craft knife to score along the desired dimensions before removing.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAfter sampling the MRE specimens, their microstructures were observed using a scanning electron microscope (SEM). Before the experiment, the acceleration voltage, magnification, and working distance of the electron microscope were set to consistent values to eliminate the influence of equipment parameter variations on the observation results. The primary objective of this experiment is to verify whether magnetic particles in the material form chain-like structures consistent with the anticipated preparation. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows the microstructure of MRE as observed by scanning electron microscopy (SEM).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eCombining multiple SEM images in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e reveals that as the magnetic field induction angle (i.e., the angle between the red coordinate system's x-axis and the particle chain direction) gradually increases from 0\u0026deg; to 90\u0026deg;, the chain-like structures formed by iron powder particles within the matrix exhibit highly consistent orientation aligned with the pre-set magnetic field direction. Particle chains in each angular group are uniformly arranged along their respective predetermined directions, with no noticeable agglomeration, disordered arrangement, or random dispersion observed. As shown in the SEM images in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, the prepared magnetorheological elastomer has successfully formed chains of magnetic particles with distinct morphology, continuous structure, and highly uniform orientation. Therefore, the prepared MRE chain-like structure exhibits the desired directional alignment characteristics, achieving the intended material design objectives.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Rheometer testing and characterization of 50% carbonyl iron powder MRE\u003c/h2\u003e \u003cp\u003eTo investigate the dynamic mechanical behavior of MRE at different magnetic particle chain orientation angles, rheological testing systems were employed. Three representative angles were selected for comparison: 0\u0026deg; and 45\u0026deg;, 15\u0026deg; and 60\u0026deg;, and 30\u0026deg; and 75\u0026deg;. Since the magnetorheological properties of MREs are highly dependent on the orientation structure of magnetic particle chains, a 24-sided polygonal fixture was employed in the experiment to achieve precise control over multi-angle orientation. The aforementioned angle pairings cover key feature orientations ranging from parallel direction (0\u0026deg;), low-angle inclination (15\u0026deg;, 30\u0026deg;), critical angle (45\u0026deg;), to high-angle inclination (60\u0026deg;, 75\u0026deg;). The objective is to systematically capture the evolution of material properties with orientation changes and avoid the randomness that may arise from single-angle testing.\u003c/p\u003e \u003cp\u003eThe MRE samples were tested using an Anton Paar rheometer to obtain key rheological parameters including storage modulus (G\u0026prime;), loss modulus (G\u0026Prime;), complex viscosity (|η*|), and loss factor (tanδ). By analyzing these parameters, the system evaluated the mechanical properties of MRE under different chain orientation angles. The corresponding test results are shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e and \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, both the storage modulus (G\u0026prime;) and loss modulus (G\u0026Prime;) gradually increase with rising angular frequency (ω). At the same angular frequency, the values of the G\u0026prime; and G\u0026Prime; curves corresponding to lower magnetic field angles are generally higher than those obtained at higher magnetic field angles. Specifically (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e): (a) Both G\u0026prime; and G\u0026Prime; at 0\u0026deg; orientation exceed 45\u0026deg;; (b) G\u0026prime; and G\u0026Prime; at 15\u0026deg; are significantly higher than at 60\u0026deg;; (c) G\u0026prime; and G\u0026Prime; at 30\u0026deg; remain consistently above 75\u0026deg; across the entire frequency range. Furthermore, for the same orientation angle, the value of G\u0026prime; consistently remains significantly higher than that of G\u0026Prime;, and the gap between the two remains essentially stable as frequency increases. This phenomenon can be attributed to the microstructure formed by carbonyl iron powder particles within the MRE, which facilitates stress transfer and consequently enhances both the elastic and viscous responses of the material.\u003c/p\u003e \u003cp\u003eAs shown in the test results of Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, both the complex viscosity (|η|) and loss factor (tan δ) of the MRE containing 50% carbonyl iron powder exhibit a consistent decreasing trend with increasing angular frequency (ω). Regardless of whether at low or high magnetic field angles, both |η*| and tan δ decrease continuously with increasing ω. Moreover, their variation curves at the same angle are nearly identical, indicating that under these test conditions, their frequency dependence is highly consistent. Additionally, at the same angular frequency, both the |η*| and tan δ values corresponding to the lower magnetic field angle are significantly higher than those at the higher magnetic field angle. Specifically manifested as follows (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e): (a) The curve under 0\u0026deg; conditions is consistently higher than that under 45\u0026deg; conditions; (b) The curve under 15\u0026deg; conditions is significantly higher than that under 60\u0026deg; conditions; (c) The curve under 30\u0026deg; conditions remains higher than that under 75\u0026deg; conditions.\u003c/p\u003e \u003cp\u003eAnalysis of Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e and \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e reveals that the dynamic mechanical properties of the MRE with 50% carbonyl iron powder content result from the synergistic interaction between angular frequency and test angle (magnetic field strength). Among these, the angular frequency determines the fundamental trend of viscoelastic response, specifically manifested as G' and G'' increasing with rising frequency, while |η*| and tanδ decrease with increasing frequency. The test angle precisely regulates the strength of performance levels by altering the intensity of magnetic interactions and microstructure within the material's carbonyl iron powder particles, with the regulatory effect becoming more pronounced as ω increases.\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Spatial assembly and programmable control of magnetically controlled MRE materials","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Manta ray tail flapping biomimicry\u003c/h2\u003e \u003cp\u003eWhen swimming, manta rays generate large-amplitude flexible undulations in the middle and rear sections of their pectoral fins to efficiently propel water. Meanwhile, the base region near the body maintains high structural rigidity, providing a stable foundation for force transmission during wave-like movements. This biomechanical property fundamentally stems from the gradient mechanical properties of the tail tissue\u0026mdash;the distal region exhibits lower fiber density and dynamic regulation of elastic modulus. The base consists of dense collagen fiber bundles, exhibiting high stiffness and low variability in mechanical properties.\u003c/p\u003e \u003cp\u003eTo precisely replicate the aforementioned biological characteristics, a segmented chain-type MRE with a biomimetic flexible fin structure was designed. The structure consists of eight independent MRE units connected along the extension direction via flexible chains. The four units in the middle-rear section corresponding to the critical zone of pectoral fin undulation are set to a high-content gradient of 60%, 60%, 70%, and 70%. The four units at the base corresponding to the stable support zone are set to a low-content gradient of 40%, 40%, 50%, and 50%. Since the magnetostrictive shear modulus of MREs is positively correlated with magnetic particle content, units with different iron powder concentrations exhibit differentiated stiffness responses under uniform magnetic field excitation. Therefore, the modulus increase is more pronounced in high-content units, while the change in low-content units is relatively limited. Consequently, under the influence of a single magnetic field, this biomimetic structure spontaneously generates a mechanical gradient characterized by \u0026ldquo;remote adjustability and base stability\u0026rdquo; within its interior. This enables the structure to exhibit dynamic mechanical behavior highly consistent with that of the manta ray's pectoral fins at the structural level.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e comprehensively illustrates the development process of the biomimetic manta ray tail structure through four modules: A1 to A4. Module A1 takes the manta ray's tail as its biological prototype, using contour annotations to highlight its naturally curved form, thereby providing morphological reference for subsequent biomimetic design. Module A2 defines the target curve based on this profile and utilizes segmented structural diagrams to specify the angular parameters and installation direction rules for each segment, thereby completing the geometric design and assembly logic definition of the structure. The A3 module demonstrates the actual assembly state of this biomimetic structure on the experimental platform, achieving the transition from design to physical form. The A4 module's locally magnified experimental results clearly reveal the final dynamic morphology of the biomimetic structure, whose morphological characteristics form a distinct correspondence with the biological prototype in A1.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e shows a comparison of the deformation of structures with three different iron powder mass fractions under static magnetic field excitation. Where B1-B5 correspond to a uniform structure with an iron powder mass fraction of 40%. Under magnetic field excitation starting at 0.5 A and incrementing in 0.25 A steps up to 1.5 A, the entire structure undergoes bending; However, the difference in bending angles between the middle-to-rear section and the base is not significant, which clearly does not align with the biological movement patterns of manta ray pectoral fins. Due to the overall low iron powder content, the base lacks sufficient rigidity and fails to provide rigid support within the magnetic field; Therefore, the entire structure undergoes lateral buckling displacement, leading to structural instability and failure of the biomimetic function.\u003c/p\u003e \u003cp\u003eC1-C5 correspond to a uniform structure with an iron powder mass fraction of 60%. The higher particle content significantly limits the deformation capability of the polymer matrix, resulting in reduced magneto-responsive flexibility. Under identical magnetic field excitation, the structure exhibits only minimal overall deformation, maintaining a highly rigid and taut state throughout. In the mid-to-late stages, no significant fluctuation trends are discernible. Meanwhile, the overall bending amplitude is significantly lower than that of a uniform 40% structure. Consequently, effective biomimetic wave propagation cannot be achieved.\u003c/p\u003e \u003cp\u003eD1\u0026ndash;D5 correspond to gradient distribution structures (iron powder mass fractions of 40%, 40%, 50%, 50%, 60%, 60%, 70%, and 70%, respectively). Under a 1.5 A magnetic field excitation, the structure exhibits a morphology highly consistent with its biological prototype. The mid-to-rear high-content units achieve large-amplitude flexible bending, while the low-content units at the base undergo only small-angle deformation, enabling biomimetic functionality.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e compares the response processes of structures with different iron powder contents under dynamic magnetic field excitation. Where Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(a) corresponds to a uniform structure with 40% iron powder content. The structure exhibits minimal deformation across the entire current range, with a very low slope of deformation as the current increases. It is evident that the magnetic response performance of the 40% iron powder content is insufficient, failing to produce effective deformation in response to magnetic field excitation.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(b) corresponds to a uniform structure with 60% iron powder content. As the excitation current gradually increases from 0.5 A to 1.5 A, the overall bending of the structure progressively increases. However, the difference in bending angles between the mid-to-rear section and the base of the MRE is minimal, failing to simulate the temporal characteristics of the manta ray's pectoral fin movement. When the current exceeds 1 A, the structure even undergoes overall distortion and instability, losing the controllability of its biomimetic form.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(c) corresponds to the gradient-content structure, fully illustrating its dynamic biomimetic process. At a current of 0.75 A, the bending angle of the high-content units in the middle and rear sections of the MRE is significantly greater than that of the low-content units at the base, exhibiting a start-up pattern characterized by \u0026ldquo;slight oscillation in the middle and rear sections\u0026mdash;straightening at the base.\u0026rdquo; When the current rises to 1.0 A, the amplitude of fluctuations in the middle and late stages of the MRE increases significantly, forming wide-amplitude oscillations consistent with the biological prototype. Meanwhile, the MRE base maintains a slight angle of curvature, with no reduction in support. As the current further increased to 1.5 A, the mid-to-rear section of the MRE exhibited enhanced oscillation, achieving highly efficient water flow propulsion while maintaining stable base stiffness. The entire dynamic response not only replicates the morphological changes of the manta ray's pectoral fins, but its \u0026ldquo;activation-oscillation-propulsion\u0026rdquo; temporal rhythm also closely matches that of its biological prototype.\u003c/p\u003e \u003cp\u003eA comprehensive analysis of the static and dynamic responses shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e and \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e reveals that when the iron powder content in the critical motion segment (mid-to-rear section) is insufficient (e.g., a uniform 40% structure throughout), the magnetostrictive modulus exhibits minimal variation, making it difficult for the structure to generate effective oscillations. Conversely, if the iron powder content at the base is excessively high (such as a uniform 60% structure throughout), the resulting excessive variation in stiffness leads to a loss of support and induces buckling distortion. By adopting a gradient distribution combining the mid-to-rear section (60%, 70%) with the base section (40%, 50%), the structure achieves both large-amplitude oscillations at the tip and stable support at the base under uniform magnetic field excitation. Its static and dynamic morphologies closely match the movement characteristics of manta ray pectoral fins.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Chameleon tongue curling biomimicry\u003c/h2\u003e \u003cp\u003eThe chameleon's highly efficient hunting ability stems from its tongue's unique mechanism of active curling at the front end and stable support at the rear end, enabling non-uniform motion. To precisely replicate this biological function, the study designed a biomimetic rod structure based on segmented chain MREs. The structure consists of seven independent MRE units connected axially via flexible chains. Among these, the functional gradient distribution of the mass fraction of carbonyl iron powder in MRE. Set the front four units of the key zone of the chameleon's tongue to a high-content gradient of 60%, 60%, 70%, and 70%. Meanwhile, the rear three units of the stable support zone on the chameleon's tongue are configured with a low-content gradient of 40%, 40%, and 50%.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e systematically illustrates the design and validation process of the biomimetic chameleon tongue curling mechanism through four modules: A1 to A4. Module A1 draws inspiration from the dynamic coiling motion of a chameleon's tongue during predation. Documenting this coiling behavior, it provides a function-driven morphological basis for biomimetic design. Module A2 first defines the target fitting curve based on the biological contour; Subsequently, through segmented structural design, the continuous deformation of the tongue was discretized into five gradient angles: 0\u0026deg;, 15\u0026deg;, 30\u0026deg;, 45\u0026deg;, and 75\u0026deg;. Simultaneously, positive and negative signs clearly indicate the installation orientation of each segment, thereby completing the geometric and assembly logic definition of the structure. Module A3 demonstrates the physical assembly state of this biomimetic structure on the experimental platform, achieving the transition from parametric design to physical assembly. The A4 module's locally magnified experimental results clearly reveal the ring-shaped curling morphology of the biomimetic structure under excitation, exhibiting high consistency with the biological prototype in A1. This validates the parametric design's capability to accurately reproduce biological functional morphology.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e shows a comparison of the deformation responses of three different iron powder content structures under static magnetic field excitation. B1-B5 exhibit a uniform structure with an iron powder mass fraction of 40%. Due to the low iron powder content, the magnetic modulus of MRE exhibits only a slight change. Therefore, under a 1.5 A magnetic field, the structure exhibits only minimal deformation, with no curling tendency at the front end, and the biomimetic function remains unachieved.\u003c/p\u003e \u003cp\u003eC1-C5 exhibit a uniform structure with an iron powder mass fraction of 60%. Under magnetic field excitation ranging from 0.5 A to 1.5 A (in 0.25 A increments), the MRE structure exhibits disordered deformation characteristics. Within the 0.5\u0026ndash;1.0 A range, the structure does not exhibit directed bending but instead displays distorted, loose, and irregular deviations. When the current rises to 1.25 A, the structure exhibits overall bending; However, the uniform deformation before and after MRE shows no difference, and bending is accompanied by lateral deviation and sagging. At 1.5 A, the bending amplitude increases, but instability and sagging worsen, failing to demonstrate the biomimetic characteristics of rear-end support throughout the entire process.\u003c/p\u003e \u003cp\u003eD1-D5 represent a gradient content structure. Under a 1.5 A magnetic field excitation, the MRE exhibits morphology highly consistent with its biological prototype. The front-end high-content units achieve large-curvature curling, while the rear-end low-content units undergo only minor angular deformation. Throughout the process, a holistic bionic posture was achieved, integrating front-end packaging with back-end support. Therefore, this verifies that the gradient-based structure of D1-D5 plays a key role in enabling functional partitioning.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e compares the response processes of structures with different iron powder contents under dynamic magnetic field excitation. Figure\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e(a) corresponds to a uniform structure with 40% iron powder content. This structure exhibits minimal deformation across the entire current range, with a very low slope of deformation increasing with current. This indicates insufficient magnetic response performance, rendering it incapable of effectively responding to excitation and failing to achieve biomimetic functionality.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e(b) corresponds to a uniform structure with 60% iron powder content. As the current gradually increased from 0.5 A to 1.5 A, the overall bending of the structure continued to increase, but it consistently exhibited uniform deformation without any gradient. Meanwhile, the difference in bending angles between the front and rear ends is minimal, failing to replicate the movement sequence characteristic of a chameleon's tongue, where the front end actively curls while the rear end passively follows. When the current exceeds 1.25 A, the structure undergoes overall distortion and instability, causing the biomimetic form to lose complete control.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e(c) corresponds to the gradient-content structure, fully illustrating its dynamic biomimetic process. At a current of 0.5 A, the bending angle of the high-content units at the front end is significantly greater than that of the low-content units at the rear end, exhibiting a pre-stretch morphology characterized by \u0026ldquo;slight curling at the front end and straightening at the rear end.\u0026rdquo; When the current increased to 1.0 A, the bending angle of the front end unit significantly increased, forming a curled shape consistent with the biological prototype (Fig.\u0026nbsp;10A1), while the rear end maintained a small-angle deformation. As the current further increases to 1.5 A, the curvature of the front end continues to grow, achieving a tight wrap around the prey. This dynamic process not only replicates the morphological characteristics of a chameleon's tongue but also closely matches the biological prototype's sequential rhythm of pre-extension, coiling, and envelopment.\u003c/p\u003e \u003cp\u003eA comprehensive analysis of Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e (static deformation) and Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e (dynamic process) reveals that for the uniform structure with 40% iron powder content (corresponding to Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e(a)), the insufficient total magnetic particles result in a negligible change in the magnetostrictive modulus. Under excitation ranging from 0.5 A to 1.5 A, it consistently fails to generate effective curling, with the morphology severely deviating from the biomimetic target. The uniform structure with 60% iron powder content (corresponding to Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e(b)) exhibits excessive rear-end stiffness variation during excitation due to the absence of a mechanical gradient. This results in irregular deflection and sagging, causing it to lose its support function. The gradient content structure (corresponding to Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e(c)), characterized by a \u0026ldquo;front-high, rear-low\u0026rdquo; iron powder distribution, exhibits a deformation pattern of \u0026ldquo;front-end flexible curling and rear-end stable extension\u0026rdquo; under different currents. This behavior closely matches the kinematic characteristics of a chameleon's tongue. Above results validate the material's ability to encode biomimetic motion characteristics into MRE units, demonstrating spontaneous self-replication of target biomimetic morphologies under a single uniform magnetic field without requiring complex external control.\u003c/p\u003e \u003c/div\u003e"},{"header":"4 Conclusion","content":"\u003cp\u003eThis study investigates the control of chain-like structural orientation in MRE and their potential applications in biomimetic soft robots. Through the innovative design of a 24-sided polygonal orientation control fixture, magnetic particles were precisely aligned at 0\u0026deg;, 15\u0026deg;, 30\u0026deg;, 45\u0026deg;, 60\u0026deg;, 75\u0026deg;, and 90\u0026deg;. Microscopic morphology observations confirmed excellent orientation consistency. Rheological testing further revealed the significant regulatory effect of orientation angle on the dynamic mechanical properties of MRE. Building upon this foundation, the MRE composite structure was engineered using gradient material design and spatial angle programming, drawing inspiration from the undulating tail fins of manta rays and the curling tongues of chameleons as biomimetic prototypes. This design successfully replicates continuous motion that closely matches the biological models.\u003c/p\u003e \u003cp\u003eThe conclusions of this study include: (1) The proposed orientation control process enables precise preparation of the MRE microstructure, providing a reliable foundation for material property customization; (2) Based on a spatial splicing strategy utilizing gradient iron powder distribution and chain-like orientation, programmable deformation of the MRE structure was achieved, simplifying the control logic for biomimetic motion. (3) The designed MRE biomimetic structure can effectively simulate the characteristic movements of manta ray tail fin undulation, propulsion and chameleon tongue curling for prey capture under magnetic field excitation, validating the practical application potential of this material system in soft biomimetic animals.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eConflict of interest:\u003c/h2\u003e \u003cp\u003eThe authors declare that they have no conflict of interest.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding information:\u003c/h2\u003e \u003cp\u003eThis research has been supported by the funding: Supported by Fujian Provincial Natural Science Foundation of China (Project Number: 2024J01317, 2022J011183).\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eZhihong Lin is responsible for the methodology proposal and the writing of the draft paper. Zhe Gao and Yuedong Huang contributed to the grammar check and Article processing fee.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eAll data included in this study are available upon request from the corresponding author.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eKumar, J. S. et al. A review of challenges and solutions in the preparation and use of magnetorheological fluids[J]. \u003cem\u003eInt. J. Mech. Mater. Eng.\u003c/em\u003e \u003cb\u003e14\u003c/b\u003e (1), 1\u0026ndash;18 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, Y. et al. A state-of-the-art review on magnetorheological elastomer devices[J]. \u003cem\u003eSmart Mater. Struct.\u003c/em\u003e \u003cb\u003e23\u003c/b\u003e (12), 123001\u0026ndash;123001 (2014).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWahid, S. et al. Magneto-rheological defects and failures: A review[J]. \u003cem\u003eMater. Sci. 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Technol.\u003c/em\u003e \u003cb\u003e188\u003c/b\u003e, 107973 (2020).\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":true,"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":"Magnetorheological elastomer, Preparation, Chain-like characteristics, Bionic","lastPublishedDoi":"10.21203/rs.3.rs-8698891/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8698891/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study focuses on the biomimetic design, structurally controllable fabrication, and performance regulation of magnetorheological elastomers (MREs) for soft robotics applications. Firstly, by designing a 24-sided polygon orientation control fixture, we achieved precise preparation of magnetic particle chain structures at a series of key angles, including 0\u0026deg;, 15\u0026deg;, 30\u0026deg;, 45\u0026deg;, 60\u0026deg;, 75\u0026deg;, and 90\u0026deg;. Subsequently, scanning electron microscopy confirmed that the MRE microstructure exhibited well-defined chain-like features. Based on this, the dynamic mechanical properties of 50% MRE iron powder with varying carbonyl angles were tested using a rheometer. Finally, MRE was applied to biomimetic designs for manta ray tail fin undulations and chameleon tongue curling. Research findings indicate that chain orientation exerts a significant regulatory effect on the storage modulus (G'), loss modulus (G''), complex viscosity (|η*|), and loss factor (tanδ). Through spatial programming of gradient components and orientation distribution, MREs prepared under a uniform magnetic field drive can successfully reproduce continuous biomimetic motion that closely matches biological prototypes.\u003c/p\u003e","manuscriptTitle":"Preparation of magnetorheological elastomers and their application in mollusk-inspired bionic systems","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-03 11:22:54","doi":"10.21203/rs.3.rs-8698891/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-02-09T09:55:20+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-08T07:38:26+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-02-02T15:53:12+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"44999355696189347538859153339848948108","date":"2026-02-02T12:06:10+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"117224099653989099394484466478443541602","date":"2026-01-31T01:34:56+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-01-30T18:09:31+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-01-30T09:18:41+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-01-27T15:10:55+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-01-27T15:05:37+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2026-01-26T09:33:22+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":"43b06295-6224-4de6-a622-713c92b15b6c","owner":[],"postedDate":"February 3rd, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":62177373,"name":"Physical sciences/Engineering"},{"id":62177374,"name":"Physical sciences/Materials science"}],"tags":[],"updatedAt":"2026-04-20T16:11:15+00:00","versionOfRecord":{"articleIdentity":"rs-8698891","link":"https://doi.org/10.1038/s41598-026-48818-3","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2026-04-17 15:58:13","publishedOnDateReadable":"April 17th, 2026"},"versionCreatedAt":"2026-02-03 11:22:54","video":"","vorDoi":"10.1038/s41598-026-48818-3","vorDoiUrl":"https://doi.org/10.1038/s41598-026-48818-3","workflowStages":[]},"version":"v1","identity":"rs-8698891","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8698891","identity":"rs-8698891","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}