Rigid Components Research Articles

Tongue-inspired gelatin/poly(acrylate-co-acrylamide)-Fe3+ organic hydrogel with tunable mechanical, electrical, and sensory properties

Conductive hydrogels have emerged as one of the most promising candidates for the next generation of wearable soft electronics. However, they face limitations during practical implementation owing to their unbalanced overall properties. In this study, we present a dynamic cross-linked gelatin/poly(acrylic acid-co-acrylamide) (GxPyFez) hydrogel with tunable mechanical strength, self-healing, freezing resistance, electrical conductivity, and high sensitivity, which was prepared by incorporating Fe3+ ions. The hydrogel was prepared based on the tongue, in which gelatin/poly(acrylic acid-co-acrylamide) and Fe3+ ions mimic the connective tissue and receptor cells of the human tongue. The synergistic effect of reversible crosslinking, along with the modulation of rigid and flexible components enabled tunable flexible structures that exhibit excellent mechanical properties such as elongation at break (569 %) and toughness (8.82 MJ m−3). Notably, the G2P3Fe0.1 hydrogel exhibited remarkable self-healing ability, even at room temperature, while maintaining a good freezing resistance. Furthermore, the G2P3Fe0.1 demonstrated fast response characteristics along with a high sensitivity (GF = 2.75). Consequently, it could be assembled into sensors capable of effectively detecting various movements of the human body; it serves as an electronic skin that responds to diverse external stimuli and monitors underwater motion signals. This study provides new insights into the design of conductive hydrogels with tunable overall properties that can be modified to suit specific application scenarios.

A new statistical-quality-control methodology for panel line monitoring in shipyards

The construction of cruise ship hulls is a complex process that involves various stages: it begins with the fabrication of panels, which involves marking, cutting, and shaping metal plates of considerable length, followed by the welding of rigid structural components onto these panels. To minimize delays and cost overruns, it is crucial to detect any anomalies early on and rectify them through appropriate repair work. Therefore, real-time conformity verifications and effective Statistical Quality Control (SQC) methodologies are necessary. This paper proposes a novel SQC methodology, specifically tailored for monitoring the panel line in cruise-ship shipyards. This methodology, while adopting a traditional standardized p control chart with samples of variable size, integrates two original aspects: (i) it accounts for the significant level of customization and specific quality characteristics inherent in the different panels and (ii) it rigorously considers the measurement uncertainty associated with the large-volume metrology instruments (such as state-of-the-art total stations, laser trackers or laser scanners) used for conformity verification, following the ISO 14253-1:2017 standard. The methodology is exemplified through a real-world case study, providing practical insights into its application.

Reverberation ray matrix analysis for wave propagation in beam structures with rigid components

The method of reverberation-ray matrix (MRRM) is modified for the dynamic response analysis of beam structures with rigid components. The wave expressions for the beam structures are derived based on the Timoshenko beam theory, and the MRRM formulations are obtained through the compatibility conditions of displacements and joint coupling equations by considering the effects of rigid components. An application of this method is considered in the context of a phononic crystal with spring-mass-like resonators. The proposed resonant unit consists of a large mass-like central component connected to thin beams that serve as springs. The large central component can be approximated as a rigid body. Using the MRRM and the finite element method (FEM), the band diagrams and the transmission spectrums are calculated. The innovative cell offers the advantage of producing lower and wider bandgaps when compared to traditional lattice structures. The accuracy of the MRRM is verified with the FEM. The current research provides a vibration analysis approach for beam structures with rigid components and the analysis of phononic crystals serves as a reference for structural design.

The Claw: An Avian-Inspired, Large Scale, Hybrid Rigid-Continuum Gripper

Most robotic hands have been created at roughly the scale of the human hand, with rigid components forming the core structural elements of the fingers. This focus on the human hand has concentrated attention on operations within the human hand scale, and on the handling of objects suitable for grasping with current robot hands. In this paper, we describe the design, development, and testing of a four-fingered gripper which features a novel combination of actively actuated rigid and compliant elements. The scale of the gripper is unusually large compared to most existing robot hands. The overall goal for the hand is to explore compliant grasping of potentially fragile objects of a size not typically considered. The arrangement of the digits is inspired by the feet of birds, specifically raptors. We detail the motivation for this physical hand structure, its design and operation, and describe testing conducted to assess its capabilities. The results demonstrate the effectiveness of the hand in grasping delicate objects of relatively large size and highlight some limitations of the underlying rigid/compliant hybrid design.

The synthesis method of series-based bistable compliant mechanisms for rigid-body guidance problem based on geometrical similarity transformation of pole maps

Abstract Designing guidance mechanisms using bistable mechanisms with two stable positions is a common low-power solution for maintaining the guidance position without continuous external energy input. However, the coupling between kinematics and statics in compliant bistable mechanisms poses a challenge for their application in mechanism synthesis. To address this issue, this paper introduces the pole similarity transformation theory into the synthesis of compliant mechanisms and proposes a general synthesis method for planar serial-based compliant bistable mechanisms. This method models the compliant mechanism using the strain energy method and analyzes the bistable characteristics of the mechanism within its motion plane using the saddle point searching method. By doing so, the proposed method can identify stable positions without predetermined motion trajectories, making it more suitable for designing compliant bistable mechanisms with general planar motion. Additionally, this method utilizes the pole map to describe the stable positions of the rigid components in the compliant mechanism and establishes an information database for compliant bistable mechanisms. Through leveraging the pole similarity transformation, the pole maps of the mechanisms in the information database are matched with the pole map of the motion task, thus achieving the synthesis of planar serial-based compliant bistable mechanisms for the rigid-body guidance problem. The paper provides a detailed explanation of the mechanism synthesis process and demonstrates its application through a case study.

Stereolithographic Process for Embedding of Electronic Components into Multi-material Flexible and Stretchable Polymer Substrate to Reduce Stress During Stretching

The integration of rigid electronic components into stretchable materials is a complex challenge due to contrary material properties. This paper shows a novel approach for the embedding of electronic components into flexible and stretchable polymer substrates using a stereolithographic process that leads to stress reduction during stretching. The key factor is the multi-material printing with various elastic material properties. The paper shows a miniaturized packaged component (e.g. 0201 LED) in a flexible and stretchable substrate based on three different materials. The first material has rigid properties (stiffness 42.25 N/mm) and surrounds a small area of the LED with about 500 μm peripheral frame. The main purpose of this material is to round up the sharp edges of the LED to the next material. The second material is more elastic (stiffness 0.11 N/mm) and surrounds the first embedded LED. The purpose of the implementation of the second intermediate material is to spread the load between the LED and stretchable substrate caused by stretching. The third material has even higher elastic properties (stiffness 0.05 N/mm) and builds up the main part of the stretchable substrate (size of (4.5x34) mm2). After the fabrication of the multi-material substrate with the embedded LED, horseshoe conductive traces are screen printed with conductive paste. Finally, the embedded LED substrate with the conductive traces is cured at 125 °C. The final stretchable substrate with the embedded LED was able to stretch up to about 25 % for 30 cycles without disturbing the electrical function.

Selective Detection of Intermediate-Amplitude Motion by Solid-State NMR.

The coexistence of rigid and mobile molecules or molecular segments abounds in biomolecular assemblies. Examples include the carbohydrate-rich cell walls of plants and intrinsically disordered proteins that contain rigid β-sheet cores. In solid-state nuclear magnetic resonance (NMR) spectroscopy, dipolar polarization transfer experiments are well suited for detecting rigid components, whereas scalar-coupling experiments are well suited for detecting highly mobile components. However, few NMR methods are available to detect the segments that undergo intermediate-amplitude fast motion. Here, we introduce two NMR experiments, a two-dimensional T2H-filtered CP-hCH correlation and a three-dimensional J-INADEQUATE CCH correlation, to observe this intermediate-amplitude motion. Both experiments involve 1H detection under fast magic-angle spinning (MAS). By combining 1H transverse relaxation (T2H) filters with dipolar polarization transfer, we suppress the signals of both highly rigid and highly mobile species, thus revealing the signals of intermediate mobile species. 1H detection under fast MAS is crucial for distinguishing the different motional amplitudes. We demonstrate these techniques on several plant cell wall samples and show that they allow the selective detection and resolution of certain hemicellulose and pectin signals, which are usually masked by the signals of the rigid cellulose and the highly dynamic pectins in purely dipolar and scalar NMR spectra.

Porous Conductive Textiles for Wearable Electronics.

Over the years, researchers have made significant strides in the development of novel flexible/stretchable and conductive materials, enabling the creation of cutting-edge electronic devices for wearable applications. Among these, porous conductive textiles (PCTs) have emerged as an ideal material platform for wearable electronics, owing to their light weight, flexibility, permeability, and wearing comfort. This Review aims to present a comprehensive overview of the progress and state of the art of utilizing PCTs for the design and fabrication of a wide variety of wearable electronic devices and their integrated wearable systems. To begin with, we elucidate how PCTs revolutionize the form factors of wearable electronics. We then discuss the preparation strategies of PCTs, in terms of the raw materials, fabrication processes, and key properties. Afterward, we provide detailed illustrations of how PCTs are used as basic building blocks to design and fabricate a wide variety of intrinsically flexible or stretchable devices, including sensors, actuators, therapeutic devices, energy-harvesting and storage devices, and displays. We further describe the techniques and strategies for wearable electronic systems either by hybridizing conventional off-the-shelf rigid electronic components with PCTs or by integrating multiple fibrous devices made of PCTs. Subsequently, we highlight some important wearable application scenarios in healthcare, sports and training, converging technologies, and professional specialists. At the end of the Review, we discuss the challenges and perspectives on future research directions and give overall conclusions. As the demand for more personalized and interconnected devices continues to grow, PCT-based wearables hold immense potential to redefine the landscape of wearable technology and reshape the way we live, work, and play.

Sample-tracking vibration isolation with rigid negative stiffness for broad bandwidth

Sample-tracking vibration isolators position their mover such that the distance to a targeted sample is constant to provide a vibration-free environment, for example, for inline metrology with high resolution. To achieve high vibration isolation and rejection especially at low frequencies, this paper proposes a sample-tracking vibration isolator that integrates a flexure-guided hybrid reluctance actuator (HRA) with a negative stiffness for quasi-zero stiffness (QZS). The negative stiffness cancels the flexure stiffness for QZS, by which vibrations transmitted from the actuator’s stator can be significantly reduced. Unlike conventional QZS systems, the negative stiffness is magnetically realized with rigid components such as a permanent magnet and ferromagnetic cores. Consequently, the proposed vibration isolator has mechanical resonant frequencies of around 2.5kHz and higher. This hardware design with a feedback controller realizes a motion with nanometer resolution and a high closed-loop control bandwidth of 991Hz for further vibration isolation and sample tracking. To evaluate the performances of the proposed vibration isolator, the negative stiffness is tuned to cancel a flexure stiffness at experiments. Experimental results show that the fine tuning decreases transmissibility from −30dB to −62dB by a factor of 40 at a low frequency of 10Hz. Furthermore, the tracking error of the mover position is measured for a demonstration of the vibration rejection performance in the time domain. The results also show that the stiffness cancellation decreases the tracking error with feedback control from 2.7 nm (rms) to 1.3 nm (rms) by 52% at a steady state. The proposed sample-tracking vibration isolator successfully demonstrates high vibration isolation performance by utilizing the rigid negative stiffness of the HRA.

Monolithic Soft Fibrous Valves Capable of Generating Air Pressure Cutoff, Maintaining, and Oscillation for Pneumatic Systems

AbstractSoft pneumatic robotics are designed for safe and compliant interaction with the environment or humans. However, the pneumatic systems used for actuation and protection are still relatively bulky and rely on rigid components such as solenoid valves and pressure regulators. This study presents the design and analysis of soft fibrous valves (SFVs) with internal tiny channels and external helical structures, which could be used in soft pneumatic systems. Made from soft material, SFVs demonstrate unique capabilities in controlling pressure by partial expansion under specific pressure. Three types of SFVs are designed: 1) SFV‐C is designed to protect soft pneumatic actuators by cutting off airflow under excessive pressure; 2) SFV‐M maintains pressure in actuators when the input pressure abruptly drops, preventing potential damage to the operated object; 3) SFV‐O produces oscillating pressure output without electronic control supplied by constant pressure source. Theoretical modeling and experimental validations are conducted to investigate the performance of the SFVs under various stretching, twisting, and pressure conditions. Furthermore, fully flexible SFVs are designed to enhance their compliance and resistance to external impacts. Overall, the SFVs offer promising solutions for pressure control and protection in soft pneumatic systems, enabling safer and more effective operations in various scenarios.

Multimodal Soft Robotic Actuation and Locomotion.

Diverse and adaptable modes of complex motion observed at different scales in living creatures are challenging to reproduce in robotic systems. Achieving dexterous movement in conventional robots can be difficult due to the many limitations of applying rigid materials. Robots based on soft materials are inherently deformable, compliant, adaptable, and adjustable, making soft robotics conducive to creating machines with complicated actuation and motion gaits. This review examines the mechanisms and modalities of actuation deformation in materials that respond to various stimuli. Then, strategies based on composite materials are considered to build toward actuators that combine multiple actuation modes for sophisticated movements. Examples across literature illustrate the development of soft actuators as free-moving, entirely soft-bodied robots with multiple locomotion gaits via careful manipulation of external stimuli. The review further highlights how the application of soft functional materials into robots with rigid components further enhances their locomotive abilities. Finally, taking advantage of the shape-morphing properties of soft materials, reconfigurable soft robots have shown the capacity for adaptive gaits that enable transition across environments with different locomotive modes for optimal efficiency. Overall, soft materials enable varied multimodal motion in actuators and robots, positioning soft robotics to make real-world applications for intricate and challenging tasks.

Enhancing Electrical and Mechanical Properties of Conductive Textile for Wearable Embedded Systems Through Copper Electroplating

Wearable electronics, particularly electronic textiles, hold promise for significant advancements, yet their limited electrical conductivity hinders widespread application. This study examines the application of copper electrodeposition to enhance the electromechanical attributes of textronics. The conductive fabric undergoes copper electroplating for varying durations, assessing the increase in electrical conductivity relative to copper thickness. Experimental conditions span current densities from 0.2 to 20 A dm−2. Additionally, the research evaluates the mechanical resistance of the resulting interconnection with conventional electronic components. Voltammetric measurements, sheet resistance, and microscope observations establish optimal copper deposition conditions. As hypothesized, an inverse proportionality between the sheet resistance of the electrodeposited fabric and the thickness of the copper layer has been observed. This improvement raises a query: does the electromechanical reliability of e‐textiles improve with the addition of only a few micrometers of copper? The study reveals the significant enhancement of the mechanical resistance of soldered interconnections with rigid components after a few seconds of electrodeposition as well as an improvement of the quality factor of a textile antenna. In conclusion, electroplating significantly improves the electromechanical properties of textronics without compromising their wearability. This discovery paves the way for novel applications such as wireless fast charging with textile antennas.

Highly Flexible, High-Performance, and Stretchable Piezoelectric Sensor Based on a Hierarchical Droplet-Shaped Ceramics with Enhanced Damage Tolerance.

Stretchable self-powered sensors are of significant interest in next-generation wearable electronics. However, current strategies for creating stretchable piezoelectric sensors based on piezoelectric polymers or 0-3 piezoelectric composites face several challenges such as low piezoelectric activity, low sensitivity, and poor durability. In this paper, a biomimetic soft-rigid hybrid strategy is used to construct a new form of highly flexible, high-performance, and stretchable piezoelectric sensor. Inspired by the hinged bivalve Cristaria plicata, hierarchical droplet-shaped ceramics are manufactured and used as rigid components, where computational models indicate that the unique arched curved surface and rounded corners of this bionic structure can alleviate stress concentrations. To ensure electrical connectivity of the piezoelectric phase during stretching, a patterned liquid metal acts as a soft circuit and a silicone polymer with optimized wettability and stretchability serves as a soft component that forms a strong mechanical interlock with the hierarchical ceramics. The novel sensor design exhibits excellent sensitivity and durability, where the open circuit voltage remains stable after 5000 stretching cycles at 60% strain and 5000 twisting cycles at 180°. To demonstrate its potential in heathcare applications, this new stretchable sensor is successfully used for wireless gesture recognition and assessing the progression of knee osteoarthritis.

Structure and dynamics heterogeneity in poly(vinyl acetal)s: The effect of side group length

Understanding on the structure and dynamics of poly(vinyl acetal)s is insufficient due to the complicated chemical structure and amorphous nature of this type of polymers. In this work, we investigate the effect of side group length on structure and dynamics heterogeneity at different length scales spanning from side group, segment, and polymer network by combing dynamic mechanical analysis (DMA), dielectric relaxation spectroscopy (DRS), solid-state NMR, and differential scanning calorimetry analysis (DSC). By increasing the length of acetal side group, its intrinsic dynamics slows down. Taking into account the scale of segment and networks, with the increase of acetal group length, the formation of cross-linking sites formed by the hydroxyl-rich domain is suppressed, the relaxation distribution of the segment widens, and the volume fraction of rigid component decreases. The effect of side group length on the structure and dynamics heterogeneity of poly(vinyl acetal)s at different scales results in significant changes in material properties such as the non-monotonic change in loss factor value (tan δ) and a monotonous reduction in glass transition temperature (Tg).

Biomimetic Design of a New Semi-Rigid Spatial Mesh Antenna Reflector.

The reflective surface accuracy (RSA) of traditional space mesh antennas typically ranges from 0.2 to 6 mmRMS. To improve the RSA, an active control scheme can be employed, although it presents challenges in determining the installation position of the actuator. In this study, we propose a novel design for a semi-rigid cable mesh that combines rigid members and a flexible woven mesh, drawing inspiration from both rigid ribbed antennas and biomimicry. Initially, we investigate the planar mesh topology of spider webs and determine the bionic cable surface's mesh topology based on the existing hexagonal meshing method, with RSA serving as the evaluation criterion. Subsequently, through motion simulations and careful observation, we establish the offset angle as the key design parameter for the bionic mesh and complete the design of the bionic cable mesh accordingly. Finally, by analyzing the impact of the node quantity on RSA, we determine a layout scheme for the flexible woven mesh with a variable number of nodes, ultimately settling for 26 nodes. Our results demonstrate that the inclusion of numerous rigid components on the bionic cable mesh surface offers viable installation positions for the actuator of the space mesh antenna. The reflector accuracy achieved is 0.196 mmRMS, slightly surpassing the lower limit of reflector accuracy observed in most traditional space-space mesh antennas. This design presents a fresh research perspective on combining active control schemes with reflective surfaces, offering the potential to enhance the RSA of traditional rigid rib antennas to a certain extent.

Morphological Entanglement in Living Systems.

Many organisms exhibit branching morphologies that twist around each other and become entangled. Entanglement occurs when different objects interlock with each other, creating complex and often irreversible configurations. This physical phenomenon is well studied in nonliving materials, such as granular matter, polymers, and wires, where it has been shown that entanglement is highly sensitive to the geometry of the component parts. However, entanglement is not yet well understood in living systems, despite its presence in many organisms. In fact, recent work has shown that entanglement can evolve rapidly and play a crucial role in the evolution of tough, macroscopic multicellular groups. Here, through a combination of experiments, simulations, and numerical analyses, we show that growth generically facilitates entanglement for a broad range of geometries. We find that experimentally grown entangled branches can be difficult or even impossible to disassemble through translation and rotation of rigid components, suggesting that there are many configurations of branches that growth can access that agitation cannot. We use simulations to show that branching trees readily grow into entangled configurations. In contrast to nongrowing entangled materials, these trees entangle for a broad range of branch geometries. We, thus, propose that entanglement via growth is largely insensitive to the geometry of branched trees but, instead, depends sensitively on timescales, ultimately achieving an entangled state once sufficient growth has occurred. We test this hypothesis in experiments with snowflake yeast, a model system of undifferentiated, branched multicellularity, showing that lengthening the time of growth leads to entanglement and that entanglement via growth can occur for a wide range of geometries. Taken together, our work demonstrates that entanglement is more readily achieved in living systems than in their nonliving counterparts, providing a widely accessible and powerful mechanism for the evolution of novel biological material properties.

Pristine Ti3C2Tx MXene Enables Flexible and Transparent Electrochemical Sensors.

In the era of the internet of things, there exists a pressing need for technologies that meet the stringent demands of wearable, self-powered, and seamlessly integrated devices. Current approaches to developing MXene-based electrochemical sensors involve either rigid or opaque components, limiting their use in niche applications. This study investigates the potential of pristine Ti3C2Tx electrodes for flexible and transparent electrochemical sensing, achieved through an exploration of how material characteristics (flake size, flake orientation, film geometry, and uniformity) impact the electrochemical activity of the outer sphere redox probe ruthenium hexamine using cyclic voltammetry. The optimized electrode made of stacked large Ti3C2Tx flakes demonstrated excellent reproducibility and resistance to bending conditions, suggesting their use for reliable, robust, and flexible sensors. Reducing electrode thickness resulted in an amplified faradaic-to-capacitance signal, which is advantageous for this application. This led to the deposition of transparent thin Ti3C2Tx films, which maintained their best performance up to 73% transparency. These findings underscore its promise for high-performance, tailored sensors, marking a significant stride in advancing MXene utilization in next-generation electrochemical sensing technologies. The results encourage the analytical electrochemistry field to take advantage of the unique properties that pristine Ti3C2Tx electrodes can provide in sensing through more parametric studies.

Hybrid Printed Rigidity‐Programmable Substrate/Liquid Metal 3D Circuits Toward Stretchable Electronics

AbstractStretchable electronics have the unique capability of 3D (three dimensional) deformation, overcoming the brittleness of traditional inorganic electronics. However, during large deformations, different scale strains between the rigid and stretchable components lead to mismatch, causing interconnect failures. Therefore, the development of the rigidity‐programmable substrate with effective strain shielding capabilities has become a research hotspot. Furthermore, the exponential growth in electronic density presents challenges in the circuit design of stretchable electronics. The urgent need is to develop highly integrated stretchable electronic systems. In this study, a highly integrated stretchable pulse sensor with effective strain shielding capabilities using hybrid 3D printing technology is developed, which comprises electronic chips, a rigidity‐programmable substrate/encapsulation layer printed by using PSC (polydimethylsiloxane/silica‐nanoparticles composite)‐based ink, and LM (liquid metal)‐based 3D circuits. First, the PSC‐based ink is optimized to enhance the strain shielding effectiveness of the rigidity‐programmable substrate. Meanwhile, 3D printing parameters are optimized to achieve high printing precision with minimum line widths below 100 µm. The resulting stretchable pulse sensor demonstrated good mechanical and electrical stability under complex 3D deformations, including bending, twisting, and stretching. The PSC region strain of the sensor is only ≈2% when the global strain is up to ≈65%, which exhibited effective strain shielding capabilities.

A Flexible and Electrically Conductive Liquid Metal Adhesive for Hybrid Electronic Integration

AbstractElectrical and mechanical integration approaches are essential for emerging hybrid electronics that must robustly bond rigid electrical components with flexible circuits and substrates. However, flexible polymeric substrates and circuits cannot withstand the high temperatures used in traditional electronic processing. This constraint requires new strategies to create flexible materials that simultaneously achieve high electrical conductivity, strong adhesion, and processibility at low temperature. Here, an electrically conductive adhesive is introduced that is flexible, electrically conductive (up to 3.25×105S m−1) without sintering or high temperature post‐processing, and strongly adhesive to various materials common to flexible and stretchable circuits (fracture energy 350 <Gc< 700 J m−2). This is achieved through a multiphase soft composite consisting of an elastomeric and adhesive epoxy network with dispersed liquid metal droplets that are bridged by silver flakes, which form a flexible and conductive percolated network. These inks can be processed through masked deposition and direct ink writing at room temperature. This enables soft conductive wiring and robust integration of rigid components onto flexible substrates to create hybrid electronics for emerging applications in soft electronics, soft robotics, and multifunctional systems.

Fabric Pressure Sensors for Fine-Grained Interaction Detection in Plush Toys

Recent advances in fabric-based sensors have made it possible to densely instrument plush toys without altering their aesthetic or tactile appeal, unlike traditional sensors whose rigid components can negatively impact the interactive experience. This innovation opens a new realm of interaction possibilities, allowing for the detection of nuanced gestures and movements that are crucial for understanding behavior, enhancing engagement, and potentially monitoring cognitive functions in therapeutic contexts.