Soft Structures Research Articles

Piezoresistive properties for soft structures using hybrid CCB/CNT-based natural rubber latex composites

This study explores the development of flexible sensors for soft structures. Conductive carbon black (CCB) and carbon nanotubes (CNT) were incorporated into a natural rubber (NR) matrix using glutaraldehyde (GA) as a curing system. The sensor properties of latex-NR composites with 20 phr of CCB, including variations of CNT content (0.5 to 3 phr), were examined. Increasing CNT content beyond 0.5 phr decreased tensile strength and elongation at break, but improved sensitivity and gauge factor (GF). Additionally, applying a voltage over 5 V caused a joule heating of the latex-NR composite strip elements. When integrated onto a soft tendon-based TPU bending actuator, higher CNT content reduced electrical signal drift during cyclic bending, enhancing long-term monitoring. This research highlights the potential of CCB/CNT-based latex-NR composites for soft structure applications, including soft robotics and health monitoring.

Cure-on-demand 3D printing of complex geometries for enhanced tactile sensing in soft robotics and extended reality

Replicating the tactile sensing mechanisms, conformity, and feel of real skin is essential for next-generation human–machine interfaces. However, producing tissue-like multilayered geometries and integrating them as e-skin systems requires simplifying and standardizing their manufacture. Here, we present a scalable and cost-effective cure-on-demand strategy for 3D printing nanocomposite silicone rubbers and integrating them into complex soft structures with 1200 % enhanced pressure-strain sensitivity. By utilizing a controlled in-situ mixing of catalyst-cured silicones and shear-driven alignment of carbon nanofibers (CNF), we construct percolated networks with conductivities up to 130 S m−1 layer-by-layer. We investigate the influence of ink composition, printing parameters, geometrical design, and material density on the mechanical properties, stretchability, sensitivity, and antimicrobial activity of 3D printed piezoresistive sensors and build skin-like interfaces that detect minimal deformations like human physiological signs. This customizable, biocompatible, and robust e-skin holds promise for cost-effective integration in rehabilitation medicine, smart robotics applications, and extended reality (XR) interactive experiences.

Experimental study on failure mechanism of soft rock-coal bodies in abandoned mines under cyclic dynamic loading

During the construction and operation of a pumped storage power station in an abandoned mine, the soft rock-coal body structure, comprising the roof and the residual coal pillars, encounters a complex stress environment characterized by cyclic loads. The study of its failure mechanism under cyclic dynamic loading holds significant theoretical and practical importance to stay the safety and stability of the abandoned mine pumped storage power station. In this paper, we take “roof-residual coal pillar” soft rock-coal combinations with different percentages of rock as the research object, and study their mechanical properties, failure mechanism, energy evolution characteristics and acoustic emission distribution characteristics through cyclic dynamic loading experiments. The results of the experiment indicate that: (1) Both weak cyclic dynamic loading and high rock percentage enhance the deformation resistance of soft rock-coal combinations. Under low-disturbance horizontal cyclic loading, its peak strength and modulus of elasticity increase with increasing rock percentage. (2) Under low-disturbance horizontal cyclic loading, an increasing trend is observed in the average total strain energy density, dissipation energy density, and elastic energy density of the combinations as the percentage of rock increases. (3) Under low-disturbance horizontal cyclic loading, as the percentage of rock increases in the soft rock-coal combinations, the degree of failure in the rock body part progressively intensifies, while the destruction of the coal portion progressively decreases. (4) The large number of acoustic emission signals are generated at the instant of destabilization and destruction of the coal-rock combinations, mainly dominated by the signals generated by the destruction of the coal body. Acoustic emission counts and absolute energy at key point N2 decrease as the percentage of rock increases. The b value is primarily distributed in the cyclic dynamic loading stage and the failure stage, both displaying zones of sudden increase and sudden decrease in b value.

Application of Residual Structure Time Convolutional Network Based on Attention Mechanism in Remaining Useful Life Interval Prediction of Bearings.

In the context of Industry 4.0, bearings, as critical components of machinery, play a vital role in ensuring operational reliability. The detection of their health status is thus of paramount importance. Existing predictive models often focus on point predictions of bearing lifespan, lacking the ability to quantify uncertainty and having room for improvement in accuracy. To accurately predict the long-term remaining useful life (RUL) of bearings, a novel time convolutional network model with an attention mechanism-based soft thresholding decision residual structure for quantifying the lifespan interval of bearings, namely TCN-AM-GPR, is proposed. Firstly, a spatio-temporal graph is constructed from the bearing sensor signals as the input to the prediction model. Secondly, a residual structure based on a soft threshold decision with a self-attention mechanism is established to further suppress noise in the collected bearing lifespan signals. Thirdly, the extracted features pass through an interval quantization layer to obtain the RUL and its confidence interval of the bearings. The proposed methodology has been verified using the PHM2012 bearing dataset, and the comparison of simulation experiment results shows that TCN-AM-GPR achieved the best point prediction evaluation index, with a 2.17% improvement in R2 compared to the second-best performance from TCN-GPR. At the same time, it also has the best interval prediction comprehensive evaluation index, with a relative decrease of 16.73% in MWP compared to the second-best performance from TCN-GPR. The research results indicate that TCN-AM-GPR can ensure the accuracy of point estimates, while having superior advantages and practical significance in describing prediction uncertainty.

Permanently magnetized elastomer rotating actuator using traveling waves

We report a soft actuator that generates continuous rotation of an object placed on it by electromagnetically exciting circular travelling waves in a soft disk. The disk, that serves as the stator, is made of a stretchable composite consisting of segments of silicone elastomer in which hard ferromagnetic particles are embedded. Inspired by piezoelectric traveling wave rotary actuators, the disk’s 16 sections are driven by underlying printed circuit board coils to create a flexural traveling wave on the disk’s surface. The rotor can be any object directly placed on the stator: the traveling wave in the stator leads by friction to the rotation of the rotor. Unlike conventional electromagnetic motors that rely on a precisely controlled gap between stator and rotor, a concept incompatible with soft robotics, our device exploits the contact between rotor and stator and the associated dry friction to generate torque. Rotation speeds of over 6 rpm were obtained for a partially rice-filled balloon, 30 cm diameter, weighing 17 g. We report detailed speed and performance metrics when rotating plastic disks. With this rotating actuator, we demonstrate an innovative way to transmit torques and rotations within soft structures.

Strain to shine: stretching-induced three-dimensional symmetries in nanoparticle-assembled photonic crystals

Stretching elastic materials containing nanoparticle lattices is common in research and industrial settings, yet our knowledge of the deformation process remains limited. Understanding how such lattices reconfigure is critically important, as changes in microstructure lead to significant alterations in their performance. This understanding has been extremely difficult to achieve due to a lack of fundamental rules governing the rearrangements. Our study elucidates the physical processes and underlying mechanisms of three-dimensional lattice transformations in a polymeric photonic crystal from 0% to over 200% strain during uniaxial stretching. Corroborated by comprehensive experimental characterizations, we present analytical models that precisely predict both the three-dimensional lattice structures and the macroscale deformations throughout the stretching process. These models reveal how the nanoparticle lattice and matrix polymer jointly determine the resultant structures, which breaks the original structural symmetry and profoundly changes the dispersion of photonic bandgaps. Stretching induces shifting of the main pseudogap structure out from the 1st Brillouin zone and the merging of different symmetry points. Evolutions of multiple photonic bandgaps reveal potential optical singularities shifting with strain. This work sets a new benchmark for the reconfiguration of soft material structures and may lay the groundwork for the study of stretchable three-dimensional topological photonic crystals.

Total Internal Reflection (TIR) Behavior of Heterogeneous Interface Shear Waves in Layered Soft Structure

Total Internal Reflection (TIR) Behavior of Heterogeneous Interface Shear Waves in Layered Soft Structure

Symmetrical Modeling of Physical Properties of Flexible Structure of Silicone Materials for Control of Pneumatic Soft Actuators

With the ongoing advancements in material technology, the domain of soft robotics has garnered increasing attention. Soft robots, in contrast to their rigid counterparts, offer superior adaptability to the environment, enhanced flexibility, and improved safety, rendering them highly suitable for complex application scenarios such as rescue operations and medical interventions. In this paper, a new type of pneumatic software actuator is proposed. The actuator adopts a combination of a soft structure and pneumatic control, which is highly flexible and versatile. By using the flow of gas inside the soft structure, high-precision and flexible motion control is realized. In the design process, the extensibility and adaptability of the structure are considered, so that the actuator can adapt to different working environments and task requirements. The experimental results show that the pneumatic soft actuator exhibits excellent performance in terms of accuracy, response speed, and controllability. This research provides new ideas and methods for the development of the field of pneumatic actuators and has wide application prospects. The main research content of this paper is as follows: first, the soft pneumatic actuator is modeled and simulated, the structure is optimized on the basis of simulation, and finally, the performance of the actuator is tested.

Classification and Evaluation of Octopus-Inspired Suction Cups for Soft Continuum Robots.

The emergence of the field of soft robotics has led to an interest in suction cups as auxiliary structures on soft continuum arms to support the execution of manipulation tasks. This application poses demanding requirements on suction cups with respect to sensorization, adhesion under non-ideal contact conditions, and integration into fully soft systems. The octopus can serve as an important source of inspiration for addressing these challenges. This review aims to accelerate research in octopus-inspired suction cups by providing a detailed analysis of the octopus sucker, determining meaningful performance metrics for suction cups on the basis of this analysis, and evaluating the state-of-the-art in suction cups according to these performance metrics. In total, 47 records describing suction cups are found, classified according to the deployed actuation method, and evaluated on performance metrics reflecting the level of sensorization, adhesion, and integration. Despite significant advances in recent years, the octopus sucker outperforms all suction cups on all performance metrics. The realization of high resolution tactile sensing in suction cups and the integration of such sensorized suction cups in soft continuum structures are identified as two major hurdles toward the realization of octopus-inspired manipulation strategies in soft continuum robot arms.

Gene flow throughout the evolutionary history of a colour polymorphic and generalist clownfish.

Even seemingly homogeneous on the surface, the oceans display high environmental heterogeneity across space and time. Indeed, different soft barriers structure the marine environment, which offers an appealing opportunity to study various evolutionary processes such as population differentiation and speciation. Here, we focus on Amphiprion clarkii (Actinopterygii; Perciformes), the most widespread of clownfishes that exhibits the highest colour polymorphism. Clownfishes can only disperse during a short pelagic larval phase before their sedentary adult lifestyle, which might limit connectivity among populations, thus facilitating speciation events. Consequently, the taxonomic status of A. clarkii has been under debate. We used whole-genome resequencing data of 67 A. clarkii specimens spread across the Indian and Pacific Oceans to characterize the species' population structure, demographic history and colour polymorphism. We found that A. clarkii spread from the Indo-Pacific Ocean to the Pacific and Indian Oceans following a stepping-stone dispersal and that gene flow was pervasive throughout its demographic history. Interestingly, colour patterns differed noticeably among the Indonesian populations and the two populations at the extreme of the sampling distribution (i.e. Maldives and New Caledonia), which exhibited more comparable colour patterns despite their geographic and genetic distances. Our study emphasizes how whole-genome studies can uncover the intricate evolutionary past of wide-ranging species with diverse phenotypes, shedding light on the complex nature of the species concept paradigm.

Evaluation of a chitosan-based hydrogel containing graphene oxide and Scrophularia striata extract as an antimicrobial wound dressing

In the realm of wound care, hydrogels have emerged as a promising treatment option owing to their properties such as high water absorption, biocompatibility, and soft structure. This research focuses on the development of a chitosan/guar gum/ polycaprolactone (CS/GG/PCL) hydrogel treated with graphene oxide (GO) and Scrophularia striata (SS) extract for burn wound healing applications. The synergistic combination of these components aims to enhance the hydrogel's efficacy in delivering herbal medicines for wound treatment. Scrophularia striata, known for its diverse biological activities, was incorporated into the hydrogel due to its antimicrobial, antitumor, biliary stimulation, hemodynamic, analgesic, anti-inflammatory, and hepatoprotective effects. The network structure and functional group interactions of CS/GG/PCL hydrogel were investigated by FE-SEM and FTIR. Subsequent evaluations revealed that the hydrogel exhibited over 135 % swelling in water, with the SS extract enhancing its hydrophilicity. Additionally, the release of SS extract from the composite hydrogel reached 98 % in phosphate-buffered saline (PBS) solution after 180 min at pH 7.4. Notably, SS extract demonstrated excellent antibacterial activity against both Staphylococcus aureus and Escherichia coli bacteria. Furthermore, the hydrogel exhibited no cytotoxic effects on human foreskin fibroblast (HFF) cells, with the cell proliferation actually improving. Therefore, the CS/GG/PCL composite hydrogel enriched with GO and SS extract presents a promising avenue for delivering herbal medicines, positioning it as a potential candidate for advanced wound healing applications.

Magnetic Hair Tactile Sensor for Directional Pressure Detection

Tactile sensing in the human body is achieved via the skin. This has inspired the fabrication of synthetic skins with pressure sensors for potential applications in robotics, bio‐medicine, and human–machine interfaces. Tactile sensors based on magnetic elements are promising as they provide high sensitivity and a wide dynamic range. However, current magnetic tactile sensors mostly detect pressures of solid objects and operate at relatively high forces about 100 mN. Herein, these limitations are addressed by manufacturing soft, stretchable, and hair‐like structures that are permanently magnetized to achieve high‐resolution, cost‐effective, and high‐resolution pressure sensing. Combining these hair‐like structures with advances in 3D magnetic‐field measurements allows us to monitor directional tactile pressures without solid contact. To prove the concept of this technology, a bio‐inspired soft device is built with a hairy structure that senses and reports environmental mechanical stresses, similar to that of human skin. Simple self‐assembly of the soft magnetic hair structure makes our approach easy to scale for large‐area applications.

Designing, modeling and controlling the angular bending of a foldable soft actuator without using a curvature sensor

Soft actuators have recently attracted considerable attention owing to their inherent flexibility and adaptability. Nevertheless, for a soft robot to successfully engage with its surroundings and perform tasks with optimal effectiveness, it encounters a range of obstacles, including the need for precise and skillful movement, the capacity to perceive its own position and motion and the ability to effectively regulate its flexible structures. Researchers have developed techniques to integrate curvature sensors onto flexible devices, enabling them to detect and react to their positions. However, the integration of curvature sensors into flexible structures presents a substantial challenge in the structural manufacturing process. To address these concerns, this article presents a technique for designing, dynamic modeling and controlling the bending angle of foldable soft actuator without the need for curvature sensors. An optimal design for the geometric dimensions of the soft structure utilizing origami concepts to guarantee the requisite bending properties is suggested. A model-based control method that considers both the motion dynamic and the air dynamic is proposed for controlling the angular bending of the actuator. The motion dynamic was developed using the constant volume principle of the elastomer material and the neo-Hookean hyperelastic theory to establish the correlation between the applied pressure and bending angle. This dynamic model incorporates both the hyperelastic material characteristics of silicone rubber and the geometry of the actuator. Soft actuators have variations in the air chamber’s volume during operation and accurately measuring this variation is challenging. In order to tackle this problem, the fuzzy active disturbance rejection controller is used to predict these variations. The controller possesses exceptional position-tracking capability. This control strategy exhibited excellent responsiveness throughout the range of steady-state error values from approximately 1°–2°. Removing the curvature sensor increases the longevity of this soft actuator and promotes the efficiency of the manufacturing process, hence enhancing the practical application possibilities for the soft actuator made from super elastic material.

Study on physiological injuries of occupants under vertical impact loads

Under vertical impact loads, such as explosions, serious compressive deformation occurs in the pelvic bones and lumbar vertebrae of the human body leading to injuries or fatalities for occupants. This study focuses on the occupant-seat model in military vehicles, establishes a biomechanical model of the human spine, and establishes the relationship between vertical impact loads and human injuries. Subsequently, a C-shaped energy-absorbing cushioning structure is designed for application at the bottom support of the seat. Using a peak value of 50 g explosion-simulated triangular wave loading, the study compares the attenuation effects of different structural characteristics of cushioning energy-absorbing structures on impact loads. The results indicate that a 50 g peak vertical impact load can cause significant human injuries. The designed energy-absorbing cushioning structure can greatly reduce human response, but both excessively soft and rigid energy-absorbing cushioning structures fail to achieve effective impact attenuation.

A multipurpose, adolescent idiopathic scoliosis-specific, short MRI protocol: A feasibility study in volunteers

IntroductionVisualization of scoliosis typically requires ionizing radiation (radiography and CT) to visualize bony anatomy. MRI is often additionally performed to screen for neural axis abnormalities. We propose a 14-minutes radiation-free scoliosis-specific MRI protocol, which combines MRI and MRI-based synthetic CT images to visualize soft and osseous structures in one examination. We assess the ability of the protocol to visualize landmarks needed to detect 3D patho-anatomical changes, screen for neural axis abnormalities, and perform surgical planning and navigation. Methods18 adult volunteers were scanned on 1.5 T MR-scanner using 3D T2-weighted and synthetic CT sequences. A predefined checklist of relevant landmarks was used for the parameter assessment by three readers. Parameters included Cobb angles, rotation, torsion, segmental height, area and centroids of Nucleus Pulposus and Intervertebral Disc. Precision, reliability and agreement between the readers measurements were evaluated. Results91 % of Likert-based questions scored ≥ 4, indicating moderate to high confidence. Precision of 3D dot positioning was 1.0 mm. Precision of angle measurement was 0.6° (ICC 0.98). Precision of vertebral and IVD height measurements was 0.4 mm (ICC 0.99). Precision of area measurement for NP was 8 mm2 (ICC 0.55) and for IVD 18 mm2 (ICC 0.62) for IVD. Precision of centroid measurement for NP was 1.3 mm (ICC 0.88–0.92) and for IVD 1.1 mm (ICC 0.88–91). ConclusionsThe proposed MRI protocol with synthetic CT reconstructions, has high precision, reliability and agreement between the readers for multiple scoliosis-specific measurements. It can be used to study scoliosis etiopathogenesis and to assess 3D spinal morphology.

Macroscopic and mesoscopic mechanism of hydration instability of the rock-grout coupled structure

In order to investigate the macroscopic and mesoscopic mechanism of hydration instability of rock-grout structure under the influence of moisture content, a direct shear test combined with particle flow code (PFC) simulation was conducted subject to various moisture content levels and normal stresses. The results show that a higher moisture content would compromise the load bearing capacity of soft rock anchorage structures by deteriorating the structural integrity of the surrounding rock and the bonding effect between the anchorage interfaces. The load bearing capacity of the surrounding rock is also rapidly reduced. The rock-grout structure has four main shear damage modes, which are influenced by both moisture content and normal stress. When the saturated moisture content is reached, the anchorage structure has lost its bearing capacity, and the rock is muddied and subsequently debonded from the bolt. The energy required to break the internal adhesion of the rock-grout structure under the effect of hydration is greatly reduced, resulting in easy decoupling and dispersion between the rock skeleton particles. In turn, the rock surface particles bonded by the anchor agent are separated from the deeper particles, resulting in the failure of the bonding surface and weakening the coupling effect between the anchor and the surrounding rock. According to the test results, the control measures for surrounding rock of muddy roadway are put forward.

Shaken and Stirred: A Comparative Study of Earthquake‐Triggered Soft‐Sediment Deformation Structures in Lake Sediments

AbstractSubaqueous paleoseismic studies used soft sediment deformation structures (SSDS) to discern the shaking strength of past earthquakes, as the deformation degree of SSDS related to Kelvin Helmholtz Instability evolves from disturbed lamination and folds to intraclast breccia with higher peak ground accelerations (PGA). We lack comparative studies of different sediment types with SSDS related to earthquakes from different seismogenic sources to comprehend how these factors modulate earthquake‐induced deformation. Here, we compile sediment records with seven earthquake‐triggered SSDS from 10 lakes with organic‐, carbonate‐, siliciclastic‐, and diatom‐rich sediment from three subduction zones and one collisional setting. We target basin sequences with slope angles <0.65° to reduce the influence of gravitational downslope stress. We find that even minimal increases in slope angle, maximal 1°, lead to higher deformation degrees and, for some earthquakes, SSDS are only present at >0.65°. Fine‐grained clastics enhance sediment susceptibility to deformation, whereas abundant diatoms reduce it, demonstrating the influence of composition. Deformation correlates best with PGA and the vicinity of the earthquakes, suggesting that high frequency shaking promotes deformation. In addition, deformation only occurs above a minimum magnitude dependent on sediment composition, and higher deformation degrees in our studied basin sedimentary sequences only above Mw 4.9 for all sediment types, suggesting that sufficient duration of shaking—magnitude correlates with duration—is essential for SSDS development. We advise taking multiple cores on gentle slopes to study SSDS—additional to basin cores—to resolve small magnitude local earthquakes and relative differences in frequency content of past events.

Composite strengthening via stress-concentration regions softening: The proof of concept with Schwarzites and Schwarzynes inspired multi-material additive manufacturing

Inspired by nature, porous graded topological structures based on carbon, like Schwarzites and Schwartzynes, exhibit a distinctive radial-gradient distribution of pores. The pores are strategically arranged in two patterns: small pores at the centre and larger pores in the outer region (ψ), and larger pores at the centre with smaller pores in the outer region (Ω). This type of topological engineering, with its unique deformation behaviour, makes these structures highly suitable for engineering applications requiring high energy absorption. However, the existence of stress-concentration regions within the porous graded structures leads to premature structural failure during uni-axial compression. To enhance the mechanical properties of such porous graded structures, this study proposes a strategy of tailoring their pores' deformation characteristics by replacing the stress concentration regions with soft/flexible materials. The selective reinforcing two (ψ2) and three layers (Ω3) soft material enhances the specific yield strength of the multi-material composite by 187.27 % and 230.22 %, respectively compared to the respective porous soft structures. Specific resilience is heightened by 289.93 % and 323.82 % for multi-material composite ψ2 and Ω3, w.r.t the respective porous hard structure(ψ0′ and Ω0,). Our results present a unique strategy for improving the structural performance of the porous graded structures by tailoring the deformation characteristics. Engineered multi-material-based advanced composites, resulting from this approach, exhibit significant potential for applications requiring energy absorption without failure.

Study on Structural Design and Motion Characteristics of Magnetic Helical Soft Microrobots with Drug-Carrying Function.

Magnetic soft microrobots have a wide range of applications in targeted drug therapy, cell manipulation, and other aspects. Currently, the research on magnetic soft microrobots is still in the exploratory stage, and most of the research focuses on a single helical structure, which has limited space to perform drug-carrying tasks efficiently and cannot satisfy specific medical goals in terms of propulsion speed. Therefore, balancing the motion speed and drug-carrying performance is a current challenge to overcome. In this paper, a magnetically controlled cone-helix soft microrobot structure with a drug-carrying function is proposed, its helical propulsion mechanism is deduced, a dynamical model is constructed, and the microrobot structure is prepared using femtosecond laser two-photon polymerization three-dimensional printing technology for magnetic drive control experiments. The results show that under the premise of ensuring sufficient drug-carrying space, the microrobot structure proposed in this paper can realize helical propulsion quickly and stably, and the speed of motion increases with increases in the frequency of the rotating magnetic field. The microrobot with a larger cavity diameter and a larger helical pitch exhibits faster rotary advancement speed, while the microrobot with a smaller helical height and a smaller helical cone angle outperforms other structures with the same feature sizes. The microrobot with a cone angle of 0.2 rad, a helical pitch of 100 µm, a helical height of 220 µm, and a cavity diameter of 80 µm achieves a maximum longitudinal motion speed of 390 µm/s.

An SMA-actuated soft robot with encircling gripping by adjustable grasping span

Shape Memory Alloy (SMA) actuators are used in the soft robots, which were used to crawl objects with fragile surfaces due to the flexibility and small volume of the SMA. However, the actuator is disadvantaged in providing output force due to the SMA material’s own property, like high power-to-weight ratio. In this article, a novel SMA-driven soft gripper structure is designed and validated, which realizes the adjustment of the initial angle of the actuator and the positioning distance through an adjustment mechanism. The gripper encircles gripping with a 100/% success rate achieved for (20–70 mm) objects, with a maximum gripping span of 150 mm. In addition, combined with the FEM (finite element method) to capture the best parameters for the device, many design details are considered, like the drive model and the gripper structure. Finally, a validation test for the device to achieve a 100/% success rate in grasping targets in the shape of a sphere and cone, and grasp a maximum of 670 g of a bottle of water. The results show that the gripper can reliably grasp the object, and has the potential to grab uneven and fragile objects by adjusting the mechanism.