Joint Mechanics Research Articles

Accuracy tradeoffs between individual bone and joint-level statistical shape models of knee morphology

Statistical shape models (SSMs) are useful tools in evaluating variation in bony anatomy to assess pathology, plan surgical interventions, and inform the design of orthopaedic implants and instrumentation. Recently, by considering multiple bones spanning a joint or the whole lower extremity, SSMs can support studies investigating articular conformity and joint mechanics. The objective of this study was to assess tradeoffs in accuracy between SSMs of the femur or tibia individually versus a combined joint-level model. Three statistical shape models were developed (femur-only, tibia-only, and joint-level) for a training set of 179 total knee arthroplasty (TKA) patients with osteoarthritis representing both genders and several ethnicities. Bone geometries were segmented from preoperative CT scans, meshed with triangular elements, and registered to a template for each SSM. Principal component analysis was performed to determine modes of variation. The statistical shape models were compared using measures of compactness, accuracy, generalization, and specificity. The generalization evaluation, assessing the ability to describe an unseen instance in a leave-one-out analysis, showed that errors were consistently smaller for the individual femur and tibia SSMs than for the joint-level model. However, when additional modes were included in the joint-level model, the errors were comparable to the individual bone results, with minimal additional computational expense. When developing more complex SSMs at the joint, lower limb, or whole-body level, the use of an error threshold to inform the number of included modes, instead of 95 % of the variation explained, can help to ensure accurate representations of anatomy.

Implementation of a passive bi-articular ankle-knee exoskeleton during maximal squat jumping.

Owing to the unexplored potential to harness knee extension power during jumping, the current study aimed to examine how joint mechanics were altered with a biologically inspired, passive bi-articular ankle-knee exoskeleton, which could potentially facilitate greater jump height by increasing work production about the knee and ankle. Twenty-five participants (16 males and 9 females, 175.2 ± 8.2 cm, 72.9 ± 10.3 kg, 24.0 ± 3.4 years) performed maximal squat jumping with and without the exoskeletal device and we compared jump height, joint moment and joint work of the lower limbs. Despite a low exoskeleton stiffness and therefore a limited capacity to store energy, the bi-articular device resulted in decreased jump height (1.9 ± 3.1 cm, p = 0.006), decreased net work about the knee (0.23 J/kg, p < 0.001) and no increase in ankle joint work (p = 0.207), compared with jumping with no exoskeleton. Based on our findings, to mimic unassisted ankle joint moment profiles, a future bi-articular device would need increased elastic element slack length, greater stiffness and a larger moment arm about the ankle. Future designs could also employ attachment sites that have minimal overlying soft tissue, such as the pelvis, to improve comfort of the device.

Interfacial microstructure characteristics and failure mechanism of the laser welding-brazing steel-Al joints with various welding parameters

The microstructure details of the interface, mechanical properties and failure mechanism of laser welding-brazing (LWB) steel-Al joints with various welding parameters were comparatively investigated. The emergence of ternary Fe–Al–Si intermetallic compounds (IMCs) was observed in the interfacial area of the joints prepared utilizing ER4047 filler. In contrast, only the binary Fe–Al IMCs were formed in the interfacial area of the joints prepared employing ER5356 filler. With the same laser tilt angle, the IMCs layer of the joints prepared with ER4047 was thinner than that of the joints prepared with ER5356, implying the rapid growth of the IMCs welded via the ER5356 filler. The tensile strength exhibited by the former surpassed that of the latter. Employing the same filler metal, the average thickness of the IMCs layer of the joints with laser tilt angle of 10° was smaller than that of the joints with laser tilt angle of 20°. The strength of the joints with smaller tilt angle was better than that of the ones with bigger tilt angle. The tensile test outcomes revealed that there existed failure competition among the Al alloy base metal (Al-BM), weld metal (WM) and interface structure. If the interface structure was Fe–Al IMC with high brittleness, the cracks propagated along the interface, and finally fractured at the interface. If the interface structure was Fe–Al–Si IMC with good toughness, the crack propagation in the interface region could be hampered. In this case, the joint was prone to occur via WM failure or even Al-BM failure modes.

Application of Friction Riveting technique for the assembly of electronic components on printed circuit boards (PCB)

This study focuses on the effects of reducing the diameter of rivets used in Friction Riveting due to the need for downscaling when joining assemblies on a smaller scale. The Friction Riveting process has shown promising feasibility for a variety of material combinations and applications in the transportation industry. Recent research has explored the potential application of this technique in electronics, specifically for the assembly of printed circuit boards (PCBs), using AA-2024-T351 rivets on thin glass-fiber-reinforced epoxy substrates (FR4). The joint formation of joints produced with PCBs was investigated in terms of process temperature evolution, microstructural changes, and mechanical properties. Joints were obtained at process temperatures ranging from 285 ºC to 368 ºC. The use of 4 mm rivets resulted in extensive delamination, weak joint mechanisms, and cracking, impaired by the different coefficients of thermal expansion of the materials involved. Reducing the rivet diameter to 3 mm significantly improved joint quality. A further reduction to 2.5 mm minimized delamination but led to insufficient anchorage and cracking. Joints produced with a 3 mm rivet diameter achieved the highest ultimate tensile force of 276 N. This study sets the foundation for applying the Friction Riveting process to practical PCB assemblies, demonstrating that optimizing the process parameters to the diameter-to-thickness ratio can balance sufficient rivet anchoring, minimize delamination, and reduce cracking.

Ankle mechanics during jump landings across different foot positions in professional ballet dancers

ABSTRACT This study aimed to investigate the effect foot position on ankle joint mechanics and vertical ground reaction forces (vGRF) across jump landings in professional ballet dancers. Twenty-seven professional ballet dancers (men: 14; women: 13) attended one data collection session, completing five maximal countermovement jumps in parallel, first, second, fourth, and fifth positions. Three-dimensional ankle mechanics, landing vGRF variables, and jump height were recorded via a seven-camera motion capture system and one force platform. A repeated measures multivariate analysis of variance was used to assess the main effects foot position across all target variables. A linear discriminate analysis was conducted to investigate target variables across foot positions. Frontal and transverse plane ankle mechanics had the largest impact when discriminating between foot positions. Ankle power in the transverse plane during jump landing in fourth was double that of all other positions. Our findings suggest that ankle range of motion should be restored before returning to jumps in fourth and fifth positions following distal lower extremity injury. The multiplanar energy transfer observed indicates a need for specific exercises to develop multiplanar force and rate of force development of local structures around the ankle.

Contact stress ultrasonic detection method based on contact acoustic resistance model

The size and distribution of the contact stress at the assembly interface will directly affect the connection performance of the mechanical joint. However, the rough assembly interface presents strong dielectric discontinuity and material nonlinearity, which become the bottleneck restricting the development of contact stress detection. How to obtain contact stress by nondestructive testing means has become an urgent problem to be solved. In this paper, a multi-layer interface contact stress detection method based on contact acoustic resistance model is proposed to solve the difficult problem of rough interface contact stress detection. Firstly, based on the formation mechanism of contact acoustic resistance of rough assembly interface, the equivalent contact acoustic resistance expression of contact layer is derived. Secondly, the contact mechanism of rough assembly interface is clarified, and the mapping relationship model between contact acoustic resistance and contact stress is constructed. On this basis, according to the transmission law of ultrasonic wave at different interfaces of multilayer acoustic impedance, the expression of acoustic transmission coefficient at the interface of variable acoustic impedance is obtained. A contact stress detection method based on contact stress-contact acoustic resistance coefficient and acoustic transmission coefficient is proposed. The correctness of the theoretical model is verified by the tensile testing machine, and the maximum error is 15.52 %. This method will provide powerful data support for the evaluation of assembly interface connection state.

Shear mechanism of RCS joints with whole column-section diaphragm

The authors proposed a new precast RC column-steel beam (RCS) joint with whole column-section diaphragm, aiming to address the shortcomings including bearing failure and difficulty in prefabrication of the RCS joint details available in the existing literature. Due to its unique details, the proposed RCS joint may have a dissimilar force-transferring mechanism from the conventional beam-through type RCS joint. Moreover, the effect of various parameters on this novel joint was still unclear by limited test results. The objective of this study was to clarify the shear mechanism of the proposed joint and the impact of critical parameters. Specimens with different axial load ratios and thickness of parallel FBPs were tested under cyclic loading. The results showed that the increase in axial load ratio and thickness of parallel FBPs improved joint strength in this test. A detailed three-dimensional finite element (FE) model was developed and verified using the experimental results. The difference in the force transferring between the proposed joint and conventional beam-through RCS joints was explained in detail based on the numerical results. The dowel action of longitudinal column bars were evident in the proposed joint and the orthogonal FBPs were ineffective in activating the inner concrete strut. A parametric study was further conducted. The impacts of width of parallel FBPs, thickness of orthogonal FBPs, and axial load ratio were investigated. The joint strength linearly increased with the width of parallel FBPs. A parabolic distribution of shear stress in the parallel FBP section was obtained, while the yield zone was concentrated in the central area of the parallel FBP. The ductility could be improved with the thickness of orthogonal FBPs when the thickness was less than 10 mm. Further increasing the thickness of orthogonal FBP beyond 10 mm did not significantly affect the overall joint behavior. The joint may attain the optimal shear strength when the axial load ratio is between 0.3 and 0.4. The modeling approach in this study could be adopted as an effective tool to assess joint behavior. Moreover, the conclusions obtained by numerical study potentially promoted the application of the proposed joint.

Cracking behavior of segmented-casting joint in steel-UHPC composite bridge deck system: Experiment and numerical simulation

The cracking of the pre-/post-casting UHPC joint in the steel-UHPC composite bridge deck system can lead to continuous tensile damage in the UHPC layer, reducing its ability to stiffen the steel deck. This study aims to clarify the cracking mechanism of the segmented-casting UHPC joint, and to provide design recommendations for cracking control. Axial tension tests on full-scale composite deck specimens were conducted, in which the influence of with and without joint, and varying reinforcement ratios on cracking response were identified. Moreover, the nonlinear numerical model for the composite deck, where the UHPC-UHPC interface was simulated in three methods, i.e. unbonded case, cohesive zone model (CZM), and perfectly bonded case, was developed and validated to simulate the crack initiation and propagation of the UHPC layer. Based on the validated numerical model incorporating CZM, improving the bond strength of CZM is more effective in controlling crack opening at the interface than increasing the failure displacement. Finally, optimized reinforcement arrangement and joint shape recommendations were provided to enhance construction convenience, minimize stress concentration, and limit crack opening.

Mechanical loading and orthobiologic therapies in the treatment of post-traumatic osteoarthritis (PTOA): a comprehensive review.

The importance of mechanical loading and its relationship to orthobiologic therapies in the treatment of post-traumatic osteoarthritis (PTOA) is beginning to receive attention. This review explores the current efficacy of orthobiologic interventions, notably platelet-rich plasma (PRP), bone marrow aspirate (BMA), and mesenchymal stem/stromal cells (MSCs), in combating PTOA drawing from a comprehensive review of both preclinical animal models and human clinical studies. This review suggests why mechanical joint loading, such as running, might improve outcomes in PTOA management in conjunction with orthiobiologic administration. Accumulating evidence underscores the influence of mechanical loading on chondrocyte behavior and its pivotal role in PTOA pathogenesis. Dynamic loading has been identified as a key factor for optimal articular cartilage (AC) health and function, offering the potential to slow down or even reverse PTOA progression. We hypothesize that integrating the activation of mechanotransduction pathways with orthobiologic treatment strategies may hold a key to mitigating or even preventing PTOA development. Specific loading patterns incorporating exercise and physical activity for optimal joint health remain to be defined, particularly in the clinical setting following joint trauma.

Fluoroscopy: Taking a closer look at joint motion in osteoarthritis

BackgroundKnowledge of joint biomechanics is crucial for understanding the pathophysiology of osteoarthritis (OA). Biomechanical changes, especially in early-stage OA, are subtle and therefore require highly accurate and precise ways of measuring joint loading (i.e., forces) and kinematics (i.e., motion). Most OA research investigating kinematics to date using conventional measurement methods, has been restricted either to measures of functional, weight-bearing activities with limited precision, or to highly precise measures of non-functional activities. X-ray fluoroscopy, however, is a medical imaging modality that can be used to precisely measure high-speed dynamic human movement in vivo under weight-bearing conditions. ObjectiveTo illustrate the potential of fluoroscopy to measure human movement and study joint biomechanics in OA by highlighting several exemplary applications in studies on knee OA. DesignWe searched PubMed to identify a selection of relevant studies with fluoroscopic evaluation of joint mechanics in individuals with, or at risk of developing, knee OA. ResultsFluoroscopy has been utilized in biomechanical studies in populations with early stages of knee OA or at risk of developing knee OA, as well as in studies evaluating conservative treatment strategies for knee OA. Due to its ability to capture highly accurate and precise kinematic measures, fluoroscopy holds great promise in providing new insights in the role of biomechanics in OA pathogenesis. ConclusionsThe use of fluoroscopy in larger cohorts and longitudinal (interventional) studies may lead to more robust and generalizable results and could clarify the mediation pathways of joint biomechanics in the onset and progression of OA.

Correlation Between Radiological Grading and Clinical Scoring in Knee Osteoarthritis Patients.

Osteoarthritis is characterized by mechanical joint abnormalities, primarily involving articular cartilage and subchondral bone degradation. Diagnosis of knee osteoarthritis relies on American College of Rheumatology criteria, and severity assessment utilizes the Western Ontario and McMaster Universities Osteoarthritis Index score and Kellgren and Lawrence grading. Despite reported associations, discrepancies persist in the correlation between Western Ontario and McMaster Universities Osteoarthritis Index and Kellgren and Lawrence grade. Descriptive cross-sectional study was conducted at the National Trauma Centre, over six months with consecutive convenience sampling. Demographic and clinico-radiological data were collected. Mean, SD and correlation coefficient was calculated. Consecutive convenient sampling yielded 80 participants meeting American College of Rheumatology criteria, aged 52-81 years, predominantly female (67.50%). Significant positive correlations were identified between age, Western Ontario and McMaster Universities Osteoarthritis Index score, and KL grade. Results showed most cases with Kellgren and Lawrence grade III and strong correlations (r=0.73, p=0.00) between total Western Ontario and McMaster Universities Osteoarthritis Index scores and Kellgren and Lawrence grading. Notably, pain, stiffness and physical functions individually exhibited a significant possitive correlation with Kellgren and Lawrence grading. The study affirms age-related influences on osteoarthritis, emphasizes female predilection, and underscores the importance of assessing both clinical and radiological parameters. In conclusion, this study supports Western Ontario and McMaster Universities Osteoarthritis Index efficacy in dynamic disease assessment and management, especially in settings where radiological examinations may be impractical, thus establishing Western Ontario and McMaster Universities Osteoarthritis Index as a versatile tool for systematic monitoring and intervention in knee osteoarthritis.

Compliant control of biomimetic parallel torso based on musculoskeletal control

Compliant movement and stress buffering of the torso are particularly important for state transition during high-speed locomotion in quadrupedal mammals. Currently, passive compliant control is commonly used in bionic torsos of quadruped robots, while active compliant control remains rare and immature. In previous research, we developed an active six-Degree-of-Freedom (DoF) bionic parallel torso. In this paper, we establish a muscle model that includes four biomechanical elements representing muscle characteristics (muscle force-fiber length and muscle velocity relationships) from the perspective of biology and physiology. We propose a musculoskeletal model that simulates the biological motion control system to control the compliant movement of each joint of the parallel mechanism. This model includes: 1) a neural equilibrium point controller that represents the transmission of motion commands, 2) activation dynamics that describe the activation of stimulated muscles, 3) contraction dynamics that emphasize the biomechanical characteristics of muscle tendons, 4) skeletal dynamics that describe bone movement. The effects of flexor and extensor stimulation on muscle activation, force, length, and velocity were analyzed. The results showed that both the flexor and extensor muscles will contract after corresponding stimulation. Furthermore, adjusting muscle stimulation through the musculoskeletal model can drive the parallel mechanism to reach the desired position. The musculoskeletal control method based on external force feedback can establish new torque balance in joints and drive the parallel torso to achieve compliant movements. Simulation and experiments have demonstrated the feasibility of the musculoskeletal control method. This method enhances the compliance and environmental adaptability of the parallel torso in practical applications.

A randomised controlled trial of the effect of intra-articular lidocaine on pain scores in inflammatory arthritis.

Chronic pain in inflammatory arthritis (IA) reflects a complex interplay between active disease in a peripheral joint and central pronociceptive mechanisms. Because intra-articular lidocaine may be used to abolish joint-specific peripheral input to the central nervous system, we aimed to validate its use as a clinical tool to identify those patients with IA whose pain likely incorporates centrally mediated mechanisms. We began by investigating whether there was a placebo response of intra-articular injection in patients with IA 1:1 randomised to receive intra-articular lidocaine or control (0.9% saline). After, in a larger patient cohort not randomized to placebo vs lidocaine groups, we tested whether patients with IA could be stratified into 2 cohorts based on their response to intra-articular lidocaine according to markers of centrally mediated pain. To this end, we evaluated postlidocaine pain numerical rating scale (NRS) scores alongside baseline painDETECT, fibromyalgia criteria fulfillment, and quantitative sensory testing outcomes. Numerical rating scale scores were collected at baseline and 3-, 5-, and 10-minutes postinjection. Firstly, the placebo effect of intra-articular injection was low: compared to baseline, the mean pain NRS score 5-minutes postinjection was reduced by 3.5 points in the lidocaine group vs 1.2 points in the control group. Secondly, postlidocaine NRS scores were significantly higher in those with a high (>18) baseline painDETECT score, fibromyalgia, and low-pressure pain threshold at the trapezius (P = 0.002, P = 0.001, P = 0.005, respectively). Persistent high pain after intra-articular lidocaine injection could be used as an indicator of pronociceptive mechanisms that are centrally mediated, informing centrally targeted analgesic strategies.

Experimental and numerical study on the effect of load direction on the bolt loosening failure

The loosening is one of the main failure modes of bolted joints. Currently, researchers only focused on bolt loosening behavior under simple axial or transverse loads. Understanding the loosening failure mechanism of bolted joints under complex load is important for improving reliability. A multi-directional loading test device was designed, and bolt loosening experiments were conducted. The effect of load direction and amplitude on bolt loosening behavior were investigated. The results indicate that bolt loosening can be divided into two stages. Load direction and load amplitude are critical factors determining the loosening trend in the later stage. In addition, a refined finite element model of bolted joints was established to verify and explain the experimental results. The FEA results show that the relative sliding between internal and external threads and the stress redistribution on the threads are the main reasons for the bolt loosening. The smaller the angle between the load direction and the tangential direction of the contact surface, the relative sliding more likely to occur.

Fire performance enhancement of cold-formed steel walls: experimental and numerical study

Cavity-insulated cold-formed steel (CFS) walls, with gypsum plasterboard (GP) on both sides, are widely used in the construction industry. However, their fire performance is compromised by the faster rise in the temperature of the hot flange (HF), which is influenced by cavity insulation and board joints. This study aims to optimize cavity insulation configuration to enhance fire performance. Two mid-scale, non-load-bearing fire experiments on CFS walls were conducted, employing double-layered GP boards and rock wool insulation, under ISO834 time-temperature fire conditions. Meanwhile, a finite element model of physical space fluid-heat coupling of furnace-CFS walls considering joints with time was developed to reveal joint mechanisms and configurations. The results showed that non-insulated stud CFS walls had slower HF temperature rise and similar insulation compared to insulated counterparts, delaying HF temperature reach to 537 °C by 14 min. The base-layer joints had the least adverse impact on the HF temperature rise than overlapped joints and face-layer joints. The HF temperatures for various joint configurations reached 537 °C at different times: 57 min for the face layer, 62 min for the base layer, and 49 min for overlapped joints. Considering the construction cost-effectiveness, it was found that adding steel strips (the same width as the flange) at the joint position could significantly decelerate the HF temperature rise. In 60 min, the HF temperature in the model with additional steel strips dropped by 94 °C lower than in the 10 mm overlapped joint model. Finally, based on finite element results, design equations were proposed for predicting HF temperature variation over time across joint types.

Study of the mechanical properties and propagation mechanisms of non-coplanar and discontinuous joints via numerical simulation experiments

Non-coplanar and discontinuously jointed rock masses are more complex than coplanar and discontinuously jointed rock masses. The mechanical properties and propagation mechanisms of non-coplanar and discontinuous joints were studied via direct shear tests with microscopic numerical simulation experiments. The numerical simulation tests were performed under different normal stresses, joint inclination angles, and shear rates. The numerical experimental results show that the microscale failure of non-coplanar and discontinuously jointed rock masses is mainly caused by tensile cracks. Additionally, when the peak shear stress is reached, the growth rate of cracks increases rapidly, and the number of cracks increases with increasing normal stress. The shear strength of non-coplanar and discontinuously jointed rock masses increases with increasing normal stress. Under the same normal stress, the variation curves of the shear strength of non-coplanar and discontinuously jointed rock masses with respect to the dip angle exhibit an “S”-shaped nonlinear pattern. Rock masses with joint inclination angles of approximately 15° and 65° have minimum and maximum shear strengths, respectively. The joint dip angle has a significant impact on the final failure mode of rock bridges in the rock mass. As the joint dip angle increases, the final failure modes of rock bridges change from “end-to-end” connection to a combination of “head-to-head” and “tail-to-tail” connections. The shear rate has a certain impact on the peak shear stress, but the impact is not significant. The spatial distribution of the tensile force chains changes as shearing progresses, and stress concentration occurs at the tips of the original joints, which is the reason for the development of long tensile cracks in the deeper parts.

Conventionally instrumented inverse kinematic alignment for total knee arthroplasty: How is it done?

For primary total knee arthroplasty (TKA), there is an increasing trend towards patient-specific alignment strategies such as kinematic alignment (KA) and inverse kinematic alignment (iKA), which by restoring native joint mechanics may yield higher patient satisfaction rates. Second, the most recent Australian joint registry report describes favourable revision rates for conventionally instrumented TKA compared to technology-assisted techniques such as those using navigation, robotics or custom-cutting blocks. The aim of this technique article is to describe in detail a surgical technique for TKA that: (1) utilises the principles of iKA and (2) uses conventionally instrumented guided resections thereby avoiding the use of navigation, robotics or custom blocks. A TKA technique is described, whereby inverse kinematic principles are utilised and patient-specific alignment is achieved. Additionally, the patellofemoral compartment of the knee is restored to the native patellofemoral joint line. The sequenced technical note provided may be utilised for cemented or cementless components; cruciate retaining or sacrificing designs and for fixed or rotating platforms. An uncomplicated, robust and reproducible technique for TKA is described. Knee arthroplasty surgeons may wish to harness the emerging benefits of both a conventionally instrumented technique and a patient-specific alignment strategy. Level V.

Effect of laser texturing and thermomechanical joining parameters on bond strength of steel-flax fiber reinforced vitrimer composites

The study examines laser texturing's impact on metal-composite hybrid joint mechanics formed via heat compression. It focuses on sustainable composite fabrication, utilizing flax fibers and a recyclable vitrimer resin known for dynamic covalent bond exchange capabilities, enhancing recyclability, repairability, and reshaping. Simulated heating conditions determined optimal bonding between the composite and laser-textured surfaces, considering the glass transition temperature for minimum temperature and time requirements. Deviations from initial heat pressing conditions (135 °C, 0.6 MPa, 5 min) reduced bonding strength, underscoring parameter sensitivity. Cross-tensional tests under varied laser texturing conditions, supported by microscopic examinations, revealed optimal strength (1680 N) with a 150 μm hatch distance and 9 repetitions, ensuring consistent ablation volume and time. Supplementary ANSYS simulations pinpointed stress concentration regions in cross-tensional joints, guiding adjustments in laser texturing within the region of interest to assess mechanical properties. The hybrid cross-tensional and lap shear joints were also reconnected after each fracture via heat compression, allowing for the evaluation of degradation in bonding strength over each cycle.

A Stretchable and Tough Graphene Film Enabled by Mechanical Bond.

The pursuit of fabricating high-performance graphene films has aroused considerable attention due to their potential for practical applications. However, developing both stretchable and tough graphene films remains a formidable challenge. To address this issue, we herein introduce mechanical bond to comprehensively improve the mechanical properties of graphene films, utilizing [2]rotaxane as the bridging unit. Under external force, the [2]rotaxane cross-link undergoes intramolecular motion, releasing hidden chain and increasing the interlayer slip distance between graphene nanosheets. Compared with graphene films without [2]rotaxane cross-linking, the presence of mechanical bond not only boosted the strength of graphene films (247.3 vs 74.8 MPa) but also markedly promoted the tensile strain (23.6 vs 10.2 %) and toughness (23.9 vs 4.0 MJ/m3). Notably, the achieved tensile strain sets a record high and the toughness surpasses most reported results, rendering the graphene films suitable for applications as flexible electrodes. Even when the films were stretched within a 20 % strain and repeatedly bent vertically, the light-emitting diodes maintained an on-state with little changes in brightness. Additionally, the film electrodes effectively actuated mechanical joints, enabling uninterrupted grasping movements. Therefore, the study holds promise for expanding the application of graphene films and simultaneously inspiring the development of other high-performance two-dimensional films.

A Stretchable and Tough Graphene Film Enabled by Mechanical Bond

AbstractThe pursuit of fabricating high‐performance graphene films has aroused considerable attention due to their potential for practical applications. However, developing both stretchable and tough graphene films remains a formidable challenge. To address this issue, we herein introduce mechanical bond to comprehensively improve the mechanical properties of graphene films, utilizing [2]rotaxane as the bridging unit. Under external force, the [2]rotaxane cross‐link undergoes intramolecular motion, releasing hidden chain and increasing the interlayer slip distance between graphene nanosheets. Compared with graphene films without [2]rotaxane cross‐linking, the presence of mechanical bond not only boosted the strength of graphene films (247.3 vs 74.8 MPa) but also markedly promoted the tensile strain (23.6 vs 10.2 %) and toughness (23.9 vs 4.0 MJ/m3). Notably, the achieved tensile strain sets a record high and the toughness surpasses most reported results, rendering the graphene films suitable for applications as flexible electrodes. Even when the films were stretched within a 20 % strain and repeatedly bent vertically, the light‐emitting diodes maintained an on‐state with little changes in brightness. Additionally, the film electrodes effectively actuated mechanical joints, enabling uninterrupted grasping movements. Therefore, the study holds promise for expanding the application of graphene films and simultaneously inspiring the development of other high‐performance two‐dimensional films.