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Abstract Studies focusing on the kinematics of the ankle joint complex (AJC) have long been a key area of interest for biomechanists and orthopedic surgeons. However, it is not clear how additional weight-bearing walking affects the motion of the AJC compared to walking with a normal body weight (BW) or what adjustments the AJC would instinctively make to accommodate the additional load. To address this gap in knowledge, advanced dynamic biplane radiography combined with a model-based 2D-3D tracking technique was employed to elucidate the inherent kinematics of the AJC during the stance phase while walking with and without additional weight-bearing. It was found that walking with additional 50% body weight (BW + 50%) resulted in a greater dispersion of instantaneous axes of rotation in the talocrural and subtalar joints during the stance phase of gait. The talocrural joint is more plantarflexed and anteriorly translated during the early and late stance phases than during the midstance phases, which suggests that additional weight-bearing affects the stability of the AJC. Moreover, walking with BW + 50% showed that the center of rotation of the talocrural joint was positioned more superiorly and posteriorly during the foot flat to heel-off phase. This, accordingly, increases the ankle-foot gear ratio and the force of the dorsiflexors.

The 7075 Al alloy fabricated using laser powder bed fusion (L-PBF) technology exhibits coarse columnar grains and significant thermal cracking, which hinders it from meeting mechanical and corrosion resistance standards. In this study, 2 wt% micron-sized the Ti6Al4V (TC4) powder was mechanically mixed into 7075 Al alloy powder, resulting in the fabrication of an Al alloy characterized by fine equiaxed grains through the L-PBF process. The resulting alloy sample exhibited no cracks, with an average grain size of 2.016 nm. During solidification, Al3Ti cubic particles formed in situ, serving as heterogeneous nucleation sites, while the Ti element, which possesses a high growth limiting factor (Q value), further facilitates the heterogeneous nucleation of grains. The mechanical properties of the alloy were significantly improved, achieving an ultimate tensile strength of 369.204 MPa and an elongation at break of 9.371%, which is more than nine times greater than that of the L-PBF 7075 Al alloy. Furthermore, the corrosion current density decreased from 9.096E-06 to 2.089E-06, indicating a marked enhancement in the alloy's corrosion resistance. This method has the potential to be applied to the L-PBF of other low-weldability, high-strength Al alloys, thereby laying the groundwork for expanding the industrial applications of L-PBF.

Abstract The current primary treatment approach for malignant pelvic tumors involves hemipelvic prosthesis reconstruction following tumor resection. In cases of Enneking type II + III pelvic tumors, the prosthesis necessitates fixation to the remaining iliac bone. Prevailing methods for prosthesis fixation include the saddle prosthesis, ice cream prosthesis, modular hemipelvic prosthesis, and personalized prosthetics using three-dimensional printing. To prevent failure of hemipelvic arthroplasty protheses, a novel fixation method was designed and finite element analysis was conducted. In clinical cases, the third and fourth sacral screws broke, a phenomenon also observed in the results of finite element analysis. Based on the original surgical model, designs were created for auxiliary dorsal iliac, auxiliary iliac bottom, auxiliary sacral screw, and auxiliary pubic ramus fixation. A nonlinear quasi-static finite element analysis was then performed under the maximum load of the gait cycle, and the results indicated that assisted sacral dorsal fixation significantly reduces stress on the sacral screws and relative micromotion exceeding 28 μm. The fixation of the pubic ramus further increased the initial stability of the prosthesis and its interface osseointegration ability. Therefore, for hemipelvic prostheses, incorporating pubic ramus support and iliac back fixation is advisable, as it provides new options for the application of hemipelvic tumor prostheses.

Abstract Because nickel-titanium (NiTi) alloys have unique functions, such as superelasticity, shape memory, and hysteresis similar to bone in the loading-unloading cycles of their recoverable deformations. They likely offer good bone integration, a low loosening rate, individual customization, and ease of insertion. Due to the poor processability of NITI, traditional methods cannot manufacture NiTi products with complex shapes. Orthopedic NiTi implants need to show an adequate fracture elongation of at least 8%. Additive manufacturing can be used to prepare NiTi implants with complex structures and tunable porosity. However, as previously reported, additively manufactured NiTi alloys could only exhibit a maximum tensile fracture strain of 7%. In new reports, a selective laser melting (SLM)–NiTi alloy has shown greater tensile strain (15.6%). Nevertheless, due to the unique microstructure of additive manufacturing NiTi that differs from traditional NITI, the biocompatibility of SLM-NITI manufactured by this new process requires further evaluation In this study, the effects of the improved NiTi alloy on bone marrow mesenchymal stem cell (BMSC) proliferation, adhesion, and cell viability were investigated via in vitro studies. A commercial Ti-6Al-4V alloy was studied side-by-side for comparison. Like the Ti-6Al-4V alloy, the SLM-NiTi alloy exhibited low cytotoxicity toward BMSCs and similar effect on cell adhesion or cell viability. This study demonstrates that the new SLM-NiTi alloy, which has exhibited improved mechanical properties, also displays excellent biocompatibility. Therefore, this alloy may be a superior implant material in biomedical implantation. Graphical Abstract

Laser powder bed fusion of 316 L (LPBF-316 L) has been known to exhibit high ductility but low strength, along with strong corrosion resistance and weak anti-friction properties. Graphene is commonly utilized as a reinforcement phase in metals fabricated through LPBF, as this process helps reduce the tendency of graphene to agglomerate. Therefore, it is crucial to investigate the impact of incorporating graphene into the LPBF-316 L alloy, aiming to enhance toughening and anti-friction properties while maintaining the original corrosion resistance. Various concentrations of graphene were incorporated into 316 L powder and processed using LPBF. The study examined the impact of graphene concentration on the electrochemical, mechanical, and friction properties of the resulting composites. The study revealed a significant reduction in corrosion current from 8.05 ± 0.6 × 10−7 A/cm2 to 6.61 ± 0.8 × 10−8 A/cm2. The 15-day immersion experiment further validated that the incorporation of graphene contributed to enhancing the stability of corrosion resistance. Additionally, the presence of graphene led to improved strength and ductility in LPBF-316 L through grain refinement and precipitation. Notably, samples containing 0.2 wt% graphene exhibited a tensile fracture strength of 927.4 MPa and ductility of 54.75%. In addition, the compressive fracture strength of 2342.8 MPa, both surpassing that of LPBF-316 L. Furthermore, the study investigated the impact of graphene content on the friction of LPBF-316 L, revealing that graphene addition increased matrix hardness, reduced COF, and enhanced wear resistance. Overall, the findings suggest that graphene serves as an effective reinforcing agent for 316 L stainless steel matrix composites, enhancing mechanical properties, friction resistance, and wear resistance while preserving original corrosion resistance.

The laser powder bed fused NiTi alloys (LPBF-NiTi) demonstrate shape memory functionality and superelasticity as a result of their distinctive phase transition characteristics. Nevertheless, achieving precise control and regulation of the phase transition temperature poses a challenge, influenced by factors like powder composition and process parameter. In this study, a feature screening strategy and machine learning (ML) method were employed to predict and regulate the phase transition temperature of LPBF-NiTi alloy, offering a more efficient and cost-effective alternative to traditional experimental methods of regulation and control. Specifically, accuracy analysis was performed on LPBF-NiTi phase transition datasets with varying compositions and process conditions utilizing generalized regression neural network (GRNN), and other methods. The findings indicate that the interpretable features extracted through the selection strategy outlined in this study when combined with the GRNN model, demonstrate a high level of prediction accuracy (R2 = 0.97). To investigate the accuracy of the model, this study utilized various process parameters to fabricate NiTi alloys with different compositions from Ni50.8Ti49.2 alloy powder. Using this model, the study identified a novel, larger window of optimal LPBF processing that allows for controllable complex phase transitions.

High entropy alloys exhibit excellent performance under different-temperature conditions. In order to investigate the effect of temperature on the mechanical-thermal coupling fatigue failure of classical CoCrFeMnNi high entropy alloy to accelerate the application of high entropy alloys, the uniaxial tensile and fatigue tests at temperatures ranging from RT to 500 °C were conducted, and statics simulation analysis of fatigue specimens under fatigue loading conditions was conducted. The results of the uniaxial tensile tests illustrated that the yield stress and tensile strength of the alloy decreased with increasing temperature. In contrast, the elongation after the fracture of the alloy increased with temperature. The fatigue test results revealed that the fatigue life decreased as the temperature increased. The fracture morphology of the fatigue specimens and the flank morphology and dislocation distribution near the crack nucleation zone were collected to support the investigation. Accordingly, the reasons for the high-temperature-induced decrease in fatigue crack nucleation and propagation lives were systematically investigated. The main reasons for the higher-temperature-induced decrease in crack nucleation lives were a decrease in the yield stress of the alloy, more easily triggered dislocation motion and stress homogenization. The reasons for the decrease in fatigue crack propagation lives induced by higher temperatures were the more prone occurrence of dislocation motion, a decrease in yield stress, and a decrease in the area of the crack propagation region.

The number of layers and ply orientations determined the service performance of carbon fiber-reinforced polymer (CFRP) materials. Under low-temperature service conditions, the unclear weakening mechanism of mechanical properties of CFRP aggravates the failure risks of aerospace structures. In present work, the unclear correlation between layers with alternating orientations and the tensile-failure mechanisms of CFRP, the low temperature-mechanical coupling micromechanical behavior, and the failure mechanism of CFRP was experimentally revealed by using a horizontal testing instrument integrated with a low-temperature loading module and real-time optical imaging function. Based on various temperatures in a range from −40 °C to room temperature (RT) and two strain rates, the gradually decreasing trends of tensile strength, Young's modulus, and elongation after fracture with decreasing temperature are obtained. Three failure modes including fiber brittle fracture, fiber pull-out, and interface debonding are proposed to reveal the low temperature-mechanical coupling failure mechanism. Low-temperature asynchronous shrinkage of carbon fiber and epoxy resin promoted the transition from fiber brittle fracture to delamination at the interface. The proposed instrument could establish the approximatively actual service conditions involving low temperature and mechanical load.

NiTi alloys exhibit significant potential for biological applications, and the fabrication of customized NiTi geometries is greatly facilitated by the use of laser powder bed fusion (LPBF) processing. However, there are several challenges with post-processing NiTi specimens processed via LPBF, such as uneven, loosely packed, weakly corrosive surfaces, and low dimensional precision. Therefore, solving the surface problem of metals prepared by LPBF has become the key to the application. In this paper, the influence of the solution and parameters on surface roughness, surface shape and size, composition, and corrosion resistance was studied by adjusting the composition of the polishing solution and polishing parameters. The results show that polishing for 2 h in S2 solution (HNO3: HF: H2O = 40:10:50) produces the smoothest surface with the roughness characteristics Sa is 10.41 ± 0.63 μm and Ra is 0.39 ± 0.30 μm. At the same time, the corrosion resistance of polished samples has been significantly improved in simulated body fluids (SBF), and the corrosion current density (Icorr) reduced by up to one order of magnitude, reaching 5.38 ± 0.24 × 10−8. By altering the polishing process duration, it is possible to achieve a micron-level roughness surface while maintaining dimensional accuracy, making LPBF-NiTi more suitable for implant applications. Ultimately, we conclude with a brief discussion of how chemical polishing affects the handling of materials with complex structures. Between 30 and 1 h, LPBF-NiTi scaffolds were polished in S2 solution to provide porosities and dimensional accuracy that best matched the design parameters.

To overcome the challenges posed by the complex structure and large parameter requirements of existing classification models, the authors propose an improved extreme learning machine (ELM) classifier for human locomotion intent recognition in this study, resulting in enhanced classification accuracy. The structure of the ELM algorithm is enhanced using the logistic regression (LR) algorithm, significantly reducing the number of hidden layer nodes. Hence, this algorithm can be adopted for real-time human locomotion intent recognition on portable devices with only 234 parameters to store. Additionally, a hybrid grey wolf optimization and slime mould algorithm (GWO-SMA) is proposed to optimize the hidden layer bias of the improved ELM classifier. Numerical results demonstrate that the proposed model successfully recognizes nine daily motion modes including low-, mid-, and fast-speed level ground walking, ramp ascent/descent, sit/stand, and stair ascent/descent. Specifically, it achieves 96.75% accuracy with 5-fold cross-validation while maintaining a real-time prediction time of only 2 ms. These promising findings highlight the potential of onboard real-time recognition of continuous locomotion modes based on our model for the high-level control of powered knee prostheses.

To investigate the effect of temperature on the compressive strength of CoCrFeMnNi high entropy alloy with lattice structures prepared by powder bed fusion, the mechanical properties of the lattice structures at a temperature in a range from 20 °C to 900 °C were obtained through a self-developed in-situ mechanical-thermal coupling compressive system. The real-time deformation behaviors of the lattice structures were observed by an optical-infrared dual-spectrum imaging system. The experimental results indicated that the compressive strength, structural stiffness, and energy absorption of the specimens increased with the increasing temperature ranging from 20 °C to 600 °C during the load-bearing stage, accompanied by a fracture mode from cleavage step to dimple. At an elevated temperature of 900 °C, the specimens exhibited the worst compressive strength and structural stiffness but the highest densification strain. Significantly, the temperature-dependent deformation behaviors were revealed, as the gradually increased temperature promoted the deformation failure behavior transforming from “layer by layer” to “45° shear band”. The improved plasticity at elevated temperatures enhanced the deformation capacity of lattice structures, released the local concentrated load and effectively weakened the stress concentration.

Dung beetle leg joints exhibit a remarkable capacity to support substantial loads, which is a capability significantly influenced by their surface microstructure. The exploration of biomimetic designs inspired by the surface microstructure of these joints holds potential for the development of efficient self-locking structures. However, there is a notable absence of research focused on the surface microstructure of dung beetle leg joints. In this study, we investigated the structural characteristics of the surface microstructures present in dung beetle leg joints, identifying the presence of fish-scale-like, brush-like, and spike-like microstructures on the tibia and femur. Utilizing these surface microstructural characteristics, we designed a self-locking structure that successfully demonstrated functionality in both the rotational direction of the structure and self-locking in the reverse direction. At a temperature of 20 °C, the biomimetic closure featuring a self-locking mechanism was capable of generating a self-locking force of 18 N. The bionic intelligent joint, characterized by its unique surface microstructure, presents significant potential applications in aerospace and various engineering domains, particularly as a critical component in folding mechanisms. This research offers innovative design concepts for folding mechanisms, such as those utilized in satellite solar panels and solar panels for asteroid probes.

Beetle femur–tibial joints can bear large loads, and the joint structure plays a crucial role. Differences in living habits will lead to differences in femur–tibial joint structure, resulting in different mechanical properties. Here, we determined the structural characteristics of the femur–tibial joints of three species of beetles with different living habits. The tibia of Scarabaeidae Protaetia brevitarsis and Cetoniidae Torynorrhina fulvopilosa slide through cashew-shaped bumps on both sides of the femur in a guide rail consisting of a ring and a cone bump. The femur–tibial joint of Buprestidae Chrysodema radians is composed of a conical convex tibia and a circular concave femur. A bionic structure design was developed out based on the characteristics of the structure of the femur–tibial joints. Differences in the failure of different joint models were obtained through experiments and finite element analysis. The experimental results show that although the spherical connection model can bear low loads, it can maintain partial integrity of the structure and avoid complete failure. The cuboid connection model shows a higher load-bearing capacity, but its failure mode is irreversible deformation. As key parts of rotatable mechanisms, the bionic models have the potential for wide application in the high-load engineering field.

Snakes can move freely on land, in lakes, and in other environments. During movement, the scales are in long-term contact with the external environment, providing protection to the body. In this study, we evaluated the mechanical properties and scratching performance of the ventral and dorsal scales from Dinodon rufozonatum, a generalist species that moves on both land and in streams under wet and dry conditions. The results showed that the elastic modulus and hardness of the dry scales were greater than those of the wet scales. The average scale friction coefficient under wet conditions (0.1588) was 9.3% greater than that under dry conditions (0.1453). The scales exhibit brittle damage in dry environments, while in wet environments, ductile damage is observed. This adaptation mechanism allows the scales to protect the body by dissipating energy and reducing stress concentration, ensuring efficient locomotion and durability in both terrestrial and aquatic environments. Understanding how this biomaterial adapts to environmental changes can inspire the development of bionic materials.

Inspired by “crimped” collagen fiber, which induce a low-level load region within the hierarchical structures of ligaments and tendons, this study introduces a braiding technology aiming at characterizing nonlinear mechanical behavior. Samples of the developed artificial ligament with a multilayer braided structure were fabricated and tested. Alterations in the number of braiding layers, wales, and courses significantly affect the mechanical properties of the artificial ligaments. Specifically, the toe length exhibited an increase of up to 104.58 %, while the linear stiffness exhibited variations concomitant with changes in these parameters. Additionally, a mathematical model to describe the relationship between the toe length and linear stiffness was developed based on the braiding parameters and material properties of the fibers. Alternative fibers were employed and tested to demonstrate a consistency with the mathematical model. The correlation coefficients were calculated as 0.9644 for the toe length and 0.9203 for the linear stiffness. Lastly, this study mimics the mechanical behavior of the human medial collateral ligament (MCL) by integrating the artificial ligament into a bio-fidelity knee model with a joint stiffness of 1.77 Nm/deg, resulting in a high degree of similarity with human knee in valgus-varus, further affirming the utility and applicability of this study.

The current literature studied the median nerve (MN) at specific locations during joint motions. As only a few particular parts of the nerve are depicted, the relevant information available is limited. This experiment investigated the morphological and biomechanical properties of the MN. The effects of the shoulder and wrist motions on MN were explored as well. Eight young healthy female individuals were tested with two-dimensional ultrasound and shear wave elastography (SWE). The morphological and biomechanical properties were examined in limb position 1, with the wrist at the neutral position, the elbow extended at 180°, and the shoulder abducted at 60°. In addition, the experiment assessed the differences among the wrist, forearm, elbow, and upper arm with Friedman’s test and Bonferroni post hoc analysis. Two groups of limb positions were designed to explore the effects of shoulder movements (shoulder abducted at 90° and 120°) and wrist movements (wrist extended at 45° and flexed at 45°) on the thickness and Young’s modulus. Differences among the distributions of five limb positions were tested as well. The ICC3, 1 values for thickness and Young’s modulus were 0.976 and 0.996, respectively. There were differences among the MN thicknesses of four arm locations in limb position 1, while Young’s modulus was higher at the elbow and wrist than at the forearm and upper arm. Compared to limb position 1, only limb position 4 had an effect on MN thickness at the wrist. Both shoulder and wrist motions affected MN Young’s modulus, and the stiffness variations at typical locations all showed a downward trend proximally in all. The distributions of MN thickness and Young’s modulus showed fold line patterns but differed at the wrist and the pronator teres. The MN in the wrist is more susceptible to limb positions, and Young’s modulus is sensitive to nerve changes and is more promising for the early diagnosis of neuropathy.

Highlights A bio-inspired flexible strain sensor with hypersensitivity and highly selective frequency response is prepared by styrene–isoprene–styrene combined with monolayer graphene. Benefiting from the structural design inspired by nature and hysteresis of viscoelastic materials, bio-inspired structures, and original materials' properties complement each other. The frequency recognition resolution of bio-inspired flexible strain sensor reaches 0.2 Hz, making it ideal for human–computer interaction and mechanical equipment health inspection.

Abstract Clarifying the consecutive droplet rebound mechanisms can provide scientific inspirations to regulate dynamic wettability of superhydrophobic surface, which facilitates the practical applications on efficient heat control and active anti-icing. Generally, droplet rebound behaviors are directly affected by surface structure and Weber number. Here, we report a novel “golden section” design criterion to regulate the droplet rebound number determined by the structure spacing, subverting conventional knowledge. Especially, the droplet can continuously rebound for 17 times on the metal-based surface, exhibiting an amazing phenomenon of “droplet trampoline”. The droplet rebound number has been experimentally revealed to be closely related to Weber number. We propose novel quantitative formulas to predict droplet rebound number and clarify the coupling effect of the structure spacing and the Weber number on the rebound mechanisms, which can be utilized to establish the regulation criteria of rebound numbers and develop novel metal-based superhydrophobic materials.

In this study, based on the principles of bionics, we fabricated a bionic non-smooth concave pit structure on the shoulders of friction stir welding tools and detected the thermal cycling curve, downforce, and torque of the tool in the welding process. We tested the wear loss weight and analyzed the surface morphology of the shoulder surfaces after welding for 200 m. This study found that as the distance between the concave pits decreased and the number of concave pits increased, the maximum downforce, torque, and temperature in the welding process showed a decreasing trend. As the speed increased, no matter how the tool structure changed, the downforce and torque decreased, while the peak thermal cycle temperature increased. The experimental welding results show that the wear loss weight of the non-smooth structure tool significantly reduced. The lowest wear loss weight of the tool with a concave pit interval of 1.125 mm was only 0.1529 g, which is 27% lower than that of the conventional tool. Our observations of the surface morphology of the tool shoulder after welding showed that the amount of aluminum swarf on the tool shoulder of the welding tool gradually declined with the increasing density of the uneven pits. The lowest number of aluminum chips adhered to a welding tool with a pit distance of 1.125 mm. Therefore, friction stir welding tools with biomimetic structures have better wear resistance and adhesion resistance.

Additive manufactured bimetallic structures provide site-specific functions by joining two metallic materials in the designed area, offering customized solutions for biomedical and engineering applications. However, cracking, delamination, or cross-contamination frequently occurs at the joint between two dissimilar metallic materials due to their different thermal properties. In the paper, porous bimetallic structures made of biomedical materials (Fe, Ti6Al4V, and Inconel 718) for bone implants are fabricated via direct ink writing (DIW) with a dual syringe system. After subsequent heat treatment, the original shapes of the bimetallic structures are well-preserved, and the shrinkages of the two materials are equalized by adjusting the sintering temperature. All joints are free of cracks and delamination, and the material deposition sequence has no impact on them, according to microstructural analyses of the interface. The pores created by binder pyrolysis and metallic powder sintering are necessary for bone growth, cell migration, body fluid flow, etc. The Fe–Ti6Al4V and Fe-Inconel 718 bimetallic structures have better mechanical properties than the Fe structures and can perform multiple functions that are challenging for monometallic implants.

Existing research suggested 300∼600 μm as the optimal pore size range for metallic bone implants. The human bones, however, have numerous pores smaller than 300 μm for bone ingrowth, cell growth and migration, fluid flow, and so forth. The bone implant with such small-sized pores has been rarely manufactured and its property is unclear. In the paper, biodegradable Fe scaffolds of different pore sizes (50 μm, 100 μm, 150 μm, 200 μm, and 300 μm) were fabricated by direct ink writing (DIW) with subsequent sintering. The interconnected pores of all scaffolds are highly precise and have no residual powders. The in-vitro degradation and compression tests were conducted on the scaffolds to evaluate the effect of pore size on degradation and mechanical behaviors, respectively. The results indicate that a decrease in pore size leads to an increase in degradation rate, from 0.0423 ± 0.0014 to 0.0433 ± 0.0035 mm/year, with the exception of the 50 μm scaffolds which exhibit the lowest value of 0.0052 ± 0.0018 mm/year due to clogging by degradation products; meanwhile, both elastic modulus and yield strength rise from 344.8 ± 18.6 MPa to 625.0 ± 52.5 MPa and from 9.5 ± 0.9 MPa to 15.1 ± 0.8 MPa, respectively. The pore size of 100 μm shows the most significant potential for use in Fe bone implants regarding its good degradation and mechanical behaviors. Our work provides new insight into the preferable pore size of metallic bone implants produced by additive manufacturing.

Abstract Impacts occur everywhere, and they pose a serious threat to human health and production safety. Flexible materials with efficient cushioning and energy absorption are ideal candidates to provide protection from impacts. Despite the high demand, the cushioning capacity of protective materials is still limited. In this study, an integrated bionic strategy is proposed, and a bioinspired structural composite material with highly cushioning performance is developed on the basis of this strategy. The results demonstrated that the integrated bionic material, an S‐spider web‐foam, has excellent energy storage and dissipation as well as cushioning performance. Under impact loading, S‐spider web‐foam can reduce peak impact forces by a factor of 3.5 times better than silicone foam, achieving unprecedented cushioning performance. The results of this study deepen the understanding of flexible cushioning materials and may provide new strategies and inspiration for the preparation of high‐performance flexible cushioning materials.

The dome shaped structures of natural organisms can provide design inspiration for impact resistant structural materials. Most of the existing biomimetic dome shaped impact resistant materials are directly formed using 3D printing technology, and the samples cannot dynamically adjust the impact resistance properties in the various applications. Herein, 4D printing of fused filament fabrication is employed to form flat structures with different structural patterns via programming the printing process parameters, which can be deformed into biomimetic dome structures with dynamic thermal stimulation treatment. The thermal stimulation treatment can drive the dynamic transformation of 2D planar structures into 3D structures, and the higher the thermal stimulation temperature, the greater the degree of eminence and the denser the structure under the same experimental conditions. The thermal stimulation temperature and the mechanical properties of the structural samples show a certain positive correlation. In addition, different design structural patterns have different compressive mechanical properties. The more the number of circular units, the more obvious the energy absorption characteristics. The impact-resistant biomimetic structures can be applied to the surface strengthening and cushioning of various weapons, vehicles, heavy equipment, and launch structure.

Hyperspectral remote sensing (RS) has rapidly developed in recent years and has been widely used in the military field. This technology not only brings huge opportunities for military reconnaissance but also poses unprecedented challenges to military camouflage, severely complicating the development of plant hyperspectral camouflage materials and technology. In this review, the spectral reflectance characteristics of plants and the application of hyperspectral RS in plant RS and military operations are reviewed. The development status of bionic camouflage materials that simulate the spectral reflection characteristics of plants is analyzed. With the existing hyperspectral camouflage materials and technology, bionic camouflage technology is limited by the inability of bionic materials to accurately imitate the characteristic absorption peaks of green vegetation, low stability and durability, and the large overall material thickness, which complicate actual large-scale application. On this basis, a future development direction and a trend of plant hyperspectral bionic camouflage materials and technology are proposed.

Human heel pads commonly undergo cyclic loading during daily activities. Low cyclic loadings such as daily human walking tend to have less effect on the mechanical properties of heel pads. However, the impact of cyclic loading on cushion performance, a vital biomechanical property of heel pads, under engineering test condition remains unexplored. Herein, dynamic mechanical measurements and finite element (FE) simulations were employed to explore this phenomenon. It was found that the wavy collagen fibers in the heel pad will be straightened under cycle compression loading, which resulted in increased stiffness of the heel pad. The stiffness of the heel pads demonstrated an inclination to escalate over a span of 50,000 loading cycles, consequently resulting in a corresponding increase in peak impact force over the same loading cycles. Sustained cyclic loading has the potential to result in the fracturing of the straightened collagen fibers, this collagen breakage may diminish the stiffness of the heel pad, leading to a reduction in peak impact force. This work enhances understanding of the biomechanical functions of human heel pad and may provide potential inspirations for the innovative development of healthcare devices for foot complex.

Responsive photonic crystals (PCs) with bio-inspired microstructures and tailorable functionalities are of critical importance for their potential applications in diverse fields such as biological detection, sensing, decoration, anti-counterfeiting, etc. However, limited by preparation technologies and design theories, it is still a challenge to accurately and uniformly deposit smart responsive materials on natural PC structures and achieve dual stimulus response. Herein, a simple and rapid in situ polymerization method is presented for preparing dual-responsive PCs with ultra-precise micro-/nanoscale hierarchical structures. Exposure of the reaction site by deacetylation of Morpho butterfly wings allows in situ polymerisation of poly (N-isopropylacrylamide-co-acrylic acid) (P(NIPAAM-co-AAc)) on the surface of the natural photonic structure. The obtained P(NIPAAM-co-AAc) photonic crystals (P(NIPAAM-co-AAc)-PCs) exhibited a dual response to pH and temperature reversibility. In addition, the synergistic effect of the structures and materials on the optical response of the natural PCs is revealed. This work allows the combination of natural hierarchical PC structures with smart hydrogel to achieve an optical response to pH and temperature, thus opening up the channels for responsive PC to multiple stimulus responses.

Both oxyhydrogen and butanol are renewable alternative fuels. Based on gasoline/butanol compound injection mode, although the introduction of oxyhydrogen can effectually enhance the optimal BDIr (butanol direct injection ratio), it also leads to an increase in NO emission. Therefore, this paper further studies the influence of lean-burn on the combustion and emission of ternary-fuel combined supply engine with oxyhydrogen/butanol/gasoline. In this paper, three variables are set, namely five BDIr (0–80%), five ONPIv (oxyhydrogen negative pressure inhalation volume) (0–16 L/min) and five λ (1.0–1.4). The results show that the larger the λ, the more significant the impact of oxyhydrogen on improving combustion and thermal transfer inside the cylinder. With the increase of ONPIv, CoVIMEP, CA 10–90 and CA 0-10 decrease, IMEP increases. Under all lean-burn conditions, ONPI can reduce CO and HC emissions. Under the condition of λ = 1.4, when ONPIv = 16 L/min, NO emission is 49.98% lower than the value of the original engine. Moreover, based on BDIr = 40%, 16 L/min ONPIv can elevate the λ limit from 1.41 to 1.83. In summary, “1.1 = λ ≤ 1.2+ONPIv = 16 L/min+60%≤BDIr≤80%” is the excellent control strategy of ONPI + BDI + GPI engine. The synergistic influence of lean-burn and larger BDIr can greatly reduce gasoline consumption and NOx emission caused by oxyhydrogen, but also worsen the mixture combustion atmosphere. ONPI can effectively improve this problem, and further increase energy efficiency. The coupling technology of ternary-fuel combined supply and lean-burn has a positive impact on improving thermal transfer efficiency, optimizing mixture combustion and decreasing gaseous emission.

Understanding the distinct functions of human muscles could not only help professionals obtain insights into the underlying mechanisms that we accommodate compromised neuromuscular system, but also assist engineers in developing rehabilitation devices. This study aims to determine the contribution of major muscle and the energy flow in the human musculoskeletal system at four sub-phases (collision, rebound, preload, push-off) during the stance of walking at different speeds. Gait experiments were performed with three self-selected speeds: slow, normal, and fast. Muscle forces and mechanical work were calculated by using a subject-specified musculoskeletal model. The functions of individual muscles were characterized as four functional behaviors (strut, spring, motor, damper), which were determined based on the mechanical energy. The results showed that during collision, hip flexors (iliacus and psoas major) and ankle dorsiflexors (anterior tibialis) were the most dominant muscles in buffering the stride with energy absorption; during rebound, the posterior muscles (gluteus maximus, gastrocnemius, posterior tibialis, soleus) contributed the most to energy generation; during preload, energy for preparing push-off was mainly absorbed by the muscles surrounding knee (vastus, semimembranosus, semitendinosus); during push-off, ankle plantar flexors (gastrocnemius, soleus, posterior tibialis, peroneus muscles, flexor digitorum, flexor hallucis) mainly behaved to generate energy for forward propulsion. With increased walking speed, additional energy (almost 400%) from harder stride was mainly absorbed by the flexor muscles. Hip extensors and adductors transferred more energy (around 150%) to the distal segments during rebound. Soleus and gastrocnemius muscles generated more energy (about 75%) to the proximal segments for propulsion. Along with our previous study of joint-level energy analysis, these findings could assist better understanding of human musculoskeletal behaviors during locomotion and provide principles for the bio-design of related assistive devices from motors performance enhancement to rehabilitation such as exoskeleton and prosthesis.

The frosting processes on the wing surface before and after removing the scale of the Catocala electa Borkhauson were observed by using a self-assembled experiment device. The results showed that the formation process of frosting on the wing surface with or without scales was similar. However, the scale could affect the attachment shape of water vapour on the wing surface and the time when frost began to form. The formation time of frosting on the wing surface without scales was earlier than that on the wing surface with scales, which was about 614 s. The influence mechanism of the scales on the frosting process was analyzed from the wettability and morphology of the scales on the wing surface Catocala electa Borkhauson. The scale on the wing surface of Catocala electa Borkhauson showed superhydrophobic properties, and the scale surface had criss-cross ribs, which formed many special micro-nano spaces. Superhydrophobicity could promote the rolling of water on the scales and reduce the adhesion area between water and scale surface. The special space structure could delay the cooling of droplets on the scale surface of Catocala electa Borkhauson. The study might be helpful to design or optimize the functional surfaces with anti-frosting properties based on the structure of the scale surface.

Water loss and surface defects of articular cartilage extremely aggravate the risk of osteoarticular diseases. The effects of water content and surface defects on the mechanical properties of cartilage need to be taken into further account. By using a self-developed in-situ tensile tester, the tensile stress-strain relationship and real-time morphological changes under conditions of different water contents are obtained with and without a micro void. It is confirmed that tissue structure and permeability are the main factors affecting the strength and ductility of cartilage. The less water content contributes to the lower permeability, inducing higher strength but poorer plasticity. Raman spectroscopy analysis results directly reveal the transition from the bonding water with stronger hydrogen bonds to the free water with weaker hydrogen bonds in cartilage layer caused by both drying treatment and tensile deformation, which results in decreased permeability and enhanced resistance to deformation. Raman-based organic matrix content is negatively correlated with permeability but positively correlated with the strength of cartilage. The obtained experimental data may facilitate to predict cartilage damage and develop artificial cartilage materials.

In this work, we show that selective laser surface remelting, apart from modifying the microstructure, can also act as a design method to treat the surface of AZ91D magnesium alloy with varying treatment patterns, thus providing a feasible approach to tailor the electrochemical behaviour and to improve its corrosion resistance. Two treatment patterns, spots and stripes, are designed, in which cases, the boundary ratio and geometrical complexity are analyzed and compared. Besides microstructure, Hydrogen evolution, and potentiodynamic polarization curves are studied. It is found that in the central treated area, corrosion is hindered by formation of the greatly refined β-Mg17Al12 continuous network, together with the uniform distribution of surface potential. As a comparison, in the boundary region, extensive micro/galvanic couples are detrimental to the corrosion resistance, due to the oriented dendritic microstructure. As a result, good corrosion resistance, 3–5 times higher than the as-received material, is obtained despite of the variation of treatment patterns and presence of extensive micro/galvanic couples in the boundary region, indicating that selective laser surface remelting could act as a feasible way to tailor the corrosion behaviour of AZ91D. It is suggested that this technique provides not only a metallurgical approach, and also a design one to improve the corrosion resistance of AZ91D, which may lead to numerous applications of both AZ91D and laser surface treatment.

In this work, wall-shaped NiTi components were fabricated by cold metal transfer (CMT) based wire arc additive manufacturing (WAAM) with optimized depositing speed. The microstructure, mechanical properties, and wear performance of the as-fabricated specimens along the building direction, together with their correlations were investigated in-depth. Coarse columnar grains were refined gradually with the increase of wall height. An equiaxed microstructure was obtained in the upper region. The Ni4Ti3 precipitates were distributed in the matrix. The microhardness, critical stress, and elongation increase monotonously with the increase of wall height. Plastic deformation, together with wear-induced work hardening is the main form of wear, which is mainly hindered by the superelasticity of NiTi alloys. Good homogeneity of the microstructure, mechanical properties, and wear resistance is obtained due to the CMT process with optimized depositing speed, indicating that this technique provides great potential to make novel NiTi flexible structures.

In this paper, the directional characteristics of wind noise emitted by different bionic rods were studied based on a hybrid computational aeroacoustics method. The noise reduction mechanism of surface grooves, pits, and bumps was analyzed, respectively. The basic principle of noise reduction is to reduce the influence of the vortex shedding on the rod by changing the shape of the rod or passive control technology to reduce the dipole sound source. The unsmooth transverse surface will increase the loss of flow on the leading edge of the rod and reduce the vertical effect of vortex shedding on the rod. The convex leading edge of the rod can help to transfer the vertical noise from low frequency to high frequency and reduce the vertical effect of wake vortex shedding to reduce the peak sound pressure level. The cost of those was the increase in the aerodynamic drag and the increase in noise in the flow direction (the increase in the amplitude of drag fluctuation). In particular, the longitudinal v-groove structure on the surface of the elliptical rod can reduce the circumferential aerodynamic noise while keeping the aerodynamic drag coefficient unchanged.

Scaling is a universal issue encountered in pipeline steel during offshore oil extraction. In this paper, a synergic anti-scaling Cu-Zn-CeO2 coating on the pipeline steel substrate was fabricated by one-step composite electrodeposition and magnetic stirring. It shows the wettability transition from superhydrophilic to superhydrophobic of the multi-scale structured Cu-Zn-CeO2 coating without low-surface-energy modification after heating at 60℃ for 60 min and stored in air for ∼ 35 days. The wettability transition is owing to the hydrocarbons adsorption. The heating treatment and the multi-scale structure improve the hydrocarbons adsorption and reduce the transition time. The inherent hydrophobic CeO2 is beneficial for the superhydrophobic property and reduces the transition time. Compared with the steel substrate and previous superhydrophobic Cu and Cu-Zn coatings, it indicates the superhydrophobic Cu-Zn-CeO2 coating shows the promising synergic anti-scaling property due to its superhydrophobicity and the anti-scaling property of Cu-Zn alloys. This eco-friendly synergic anti-scaling Cu-Zn-CeO2 coating also shows excellent self-cleaning and anti-fouling properties. Moreover, the stability of the superhydrophobic Cu-Zn-CeO2 coating was enhanced compared with our previous superhydrophobic Cu-Zn coating due to CeO2 nanoparticles. This research enriches the theory and the technology of the wetting field, which also provides a technical basis for solving scaling problems of pipelines.

Abstract Intelligent wearable devices are essential for telemedicine healthcare as they enable real‐time monitoring of physiological information. Elaborately constructing synapse‐inspired materials provides a crucial guidance for designing high‐performance sensors toward multiplex stimuli response. However, a realistic mimesis both in the “structure and sense” of biological synapses to obtain advanced multi‐functions is still challenging but essential for simplifying subsequent circuit and logic programs. Herein, an ionic artificial synapse integrated with Ti3CNTx nanosheets in situ grown with zeolitic imidazolate framework flowers (ZIF‐L@Ti3CNTx composite) is constructed to concurrently mimic the structure and working mechanism of the synapse. The flexible sensor of the bio‐inspired ZIF‐L@Ti3CNTx composite exhibits excellent dual‐mode dimethylamine (DMA) and strain‐sensitive response with non‐overlapping resistance variations. The specific ions conduction working principle triggered by DMA gas or strain with the assistance of humidity is confirmed by the density functional theory simulation. Last, an intelligent wearable system is self‐developed by integrating the dual‐mode sensor into flexible printed circuits. This device is successfully applied in pluralistic monitoring of abnormal physiological signals of Parkinson's sufferers, including real‐time and accurate assessment of simulated DMA expiration and kinematic tremor signals. This work provides a feasible routine to develop intelligent multifunctional devices for upsurging telemedicine diagnosis.

Over millions of years of natural evolution, organisms have developed nearly perfect structures and functions. The self-fabrication of organisms serves as a valuable source of inspiration for designing the next-generation of structural materials, and is driving the future paradigm shift of modern materials science and engineering. However, the complex structures and multifunctional integrated optimization of organisms far exceed the capability of artificial design and fabrication technology, and new manufacturing methods are urgently needed to achieve efficient reproduction of biological functions. As one of the most valuable advanced manufacturing technologies of the 21st century, laser processing technology provides an efficient solution to the critical challenges of bionic manufacturing. This review outlines the processing principles, manufacturing strategies, potential applications, challenges, and future development outlook of laser processing in bionic manufacturing domains. Three primary manufacturing strategies for laser-based bionic manufacturing are elucidated: subtractive manufacturing, equivalent manufacturing, and additive manufacturing. The progress and trends in bionic subtractive manufacturing applied to micro/nano structural surfaces, bionic equivalent manufacturing for surface strengthening, and bionic additive manufacturing aiming to achieve bionic spatial structures, are reported. Finally, the key problems faced by laser-based bionic manufacturing, its limitations, and the development trends of its existing technologies are discussed.

It remains an extreme challenge to fabricate artificial joint materials with applicability of mechanical properties compared with bones, superior biocompatibility, anti-friction and wear resistance performances. Here, we report an effective strategy to simultaneously enhance the anti-friction and wear resistance performance of Ti6Al4V substrate through optimizing the porosity and sputtering a high-entropy alloy (HEA) coating. The progressive scratch experiments are carried out to equivalently imitate the scratch deformation process induced by hard particles and evaluate the anti-friction and wear resistance performances, which directly reveal the significantly decreased coefficient of friction (COF) of porous substrate based on suitable pore diameter covered with HEA coating compared with pure Ti6Al4V substrate. The porous design is verified to effectively weaken the stress shielding effect and simultaneously improve the hydrodynamic lubrication. Attributed to the coupling effects of pore structure-induced “flexibility” and HEA coating-induced surface hardening, the composite structure exhibits low COF value, wear volume and enhanced scratch resistance. The design concept would facilitate the development of novel medical implant materials with requirements of anti-friction and wear resistance.

Abstract 4D printing of metallic shape‐morphing systems can be applied in many fields, including aerospace, smart manufacturing, naval equipment, and biomedical engineering. The existing forming materials for metallic 4D printing are still very limited except shape memory alloys. Herein, a 4D printing method to endow non‐shape‐memory metallic materials with active properties is presented, which could overcome the shape‐forming limitation of traditional material processing technologies. The thermal stress spatial control of 316L stainless steel forming parts is achieved by programming the processing parameters during a laser powder bed fusion (LPBF) process. The printed parts can realize the shape changing of selected areas during or after forming process owing to stress release generated. It is demonstrated that complex metallic shape‐morphing structures can be manufactured by this method. The principles of printing parameters programmed and thermal stress pre‐set are also applicable to other thermoforming materials and additive manufacturing processes, which can expand not only the materials used for 4D printing but also the applications of 4D printing technologies.

Abstract With the characteristics of low driving voltage, light weight, and flexibility, ionic polymer‐metal composites (IPMCs) have attracted much attention as excellent candidates for artificial muscle materials in the fields of biomedical devices, flexible robots, and microelectromechanical systems. Under small voltage excitation, ions inside the IPMC proton exchange membrane migrate directionally, leading to differences in the expansion rate of the cathode and the anode, which in turn deform. This behavior is caused by the synergistic action of a three‐layer structure consisting of an external electrode layer and an internal proton exchange membrane, but the electrode layer is more dominant in this process due to the migration and storage of ions. The exploration of modifications and alternatives for proton exchange membranes and recent advances in the fabrication and characterization of conductive materials, especially carbon‐based materials and conductive polymers, have contributed significantly to the development of IPMCs. This paper reviews the progress in the application of proton exchange membranes and electrode materials for IPMCs, discusses various processes currently applied to IPMCs preparation, and introduces various promising applications of cutting‐edge IPMCs with high performance to provide new ideas and approaches for the research of new generation of low‐voltage ionic soft actuators.

Through the synergy of nervous system and the self-regulation of muscle stiffness, living organisms are capable of quickly adjusting movements and actively adapting to dynamic environments. Likewise, the stiffness-changing and self-sensing functionalities are critical to empower soft robots with adjustable load capacity and agile movement. This work presents a paradigm for the design and fabrication of soft actuators with stiffness tunability and intrinsic self-sensing feedback through 4D printing method. The integration of 4D printed conductive composite into soft actuator body allows for stiffness adjustment within three orders of magnitude and ensures real-time stiffness-sensing, bending-sensing and pressure-sensing feedback. By constructing the theoretical deformation models and decoupling the resistance signals by machine learning methods, information on the stiffness, deformation and pressure of the material at different temperatures can be obtained. Cardiac-mimicking actuator and active therapeutic insoles are fabricated as proof-of-concept demonstrations, among which the active therapeutic insoles can perceive plantar pressure changes and conduct pressure-releasing actuation to ease the pain of patient at walk. It demonstrates the potential of this design approach for versatile applications such as medical assistive devices, artificial muscles, soft robotics, etc.

Diving beetle, an excellent biological prototype for bionic underwater vehicles, can achieve forward swimming, backward swimming, and flexible cornering by swinging its two powerful hind legs. An in-depth study of the propulsion performance of them will contribute to the micro underwater vehicles. In this paper, the kinematic and dynamic parameters, and the hydrodynamic efficiency of the diving beetle are studied by analysis of swimming videos using Motion Capture Technology, combined with CFD simulations. The results show that the hind legs of diving beetle can achieve high propulsion force and low return resistance during one propulsion cycle at both forward and backward swimming modes. The propulsion efficiencies of forward and backward swimming are 0.47 and 0.30, respectively. Although the efficiency of backward swimming is lower, the diving beetle can reach a higher speed in a short time at this mode, which can help it avoid natural enemies. At backward swimming mode, there is a long period of passive swing of hind legs, larger drag exists at higher speed during the recovery stroke, which reduces the propulsion efficiency to a certain extent. Reasonable planning of the swing speed of the hind legs during the power stroke and the recovery stroke can obtain the highest propulsion efficiency of this propulsion method. This work will be useful for the development of a bionic propulsion system of micro underwater vehicle.

Recently, laser powder bed fusion of nitinol alloys (LPBF-NiTi) has attracted much attention due to its ability to precisely form complex parts. However, the wear and corrosion resistance is crucial for practical applications of LPBF-NiTi alloys. Rare earth oxides are common additives used to improve the surface properties of alloys. In this work, nano-sized cerium oxide (CeO2) is selected as the additive, and the influence rule and mechanism of different addition amounts of CeO2 on the surface properties of LPBF-NiTi alloy are deeply studied. The results showed that the addition of an appropriate amount of CeO2 (0.03 wt% CeO2 addition) could effectively refine the grains and improve the grain order, which achieved the improvement of the mechanical properties (tensile strength and toughness) of the LPBF-NiTi alloy. Furthermore, the reduction in friction coefficient and wear scar depth/width proved that the addition of CeO2 effectively improves the wear resistance of LPBF-NiTi alloys, which were mainly attributed to the synergistic action of the precipitation of the secondary hard phase (NiCe), the grain refinement strengthening, and stable phase transformation brought about by high latent heat of transformation. In addition, the improvement of anti-corrosion was reflected in the reduction of corrosion current density Icorr and pitting pits, mainly due to the formation of NiCe precipitates and grain refinement, which effectively hindered the propagation and extension of pitting corrosion. Most significantly, the 0.03% CeO2 sample achieved the simultaneous improvement of mechanical properties and surfaced functional properties, which greatly expanded the application prospects of NiTi–CeO2 alloys.

Mechanical properties at small scale of mixed-phase Fe24Co25Ni24Cr23Al4 high-entropy alloy (HEA) were examined by micro-pillar compression tests in nano-indentation system. The micro-pillars with diameter of 400 nm were fabricated in the individual face centered cubic (FCC), body centered cubic (BCC) and their interfacial region employing a focused ion beam (FIB) technology. A combination of scanning electron microscope and transmission electron microscopy was performed on the deformed micro-pillars to determine the micro/nano structures. The interfacial pillars exhibited higher strength as compared with single BCC and FCC pillars according to the stress–strain responses during compression, which was attributed to the synergetic strengthening of FCC/BCC incoherent interface and A2/B2 coherent interface in mixed-phase pillar. The observed B2 particles inside BCC were induced by the spinodal decomposition. Moreover, a large number of dislocations pile-up against interface, indicative of the strengthening of the interface.

Selective laser melting (SLM)-fabricated NiTi alloys have attracted widespread interest because they can achieve high-precision preparation of implant materials with complex structures. However, as an implant material, SLM-NiTi alloy exhibits poor osteogenic and excessive release of Ni ions. In this investigation, a bioactive dicalcium phosphate dihydrate (DCPD) coating was prepared on the surface of SLM-NiTi alloy by electrodeposition for the first time to improve the biocompatibility and corrosion resistance of the SLM-NiTi alloys. The influence of coating preparation parameters (deposition current and deposition time) on morphology and corrosion resistance had been studied by SEM, electrochemical and immersion tests. The DCPD coating obtained when the deposition current was 3 mA and the deposition time was 30 min showed a uniform and dense morphology and had the best corrosion resistance, which the corrosion current density Icorr was three orders of magnitude lower than that of SLM-NiTi alloy. Moreover, as the precursor of hydroxyapatite (HA), DCPD effectively promoted the deposition of HA, thus improving the biomineralization property of the SLM-NiTi alloy. The in vitro cell experiments showed that the DCPD coating provided a good interface and microenvironment for the growth and adhesion of osteoblasts. Good corrosion resistance, biocompatibility and biomineralization properties render the DCPD coated SLM-NiTi alloys have great clinical application prospects as biomedical implants.

As a layered complicated porous elastic–plastic material, articular cartilages undertake the tasks of buffering stress, lubricating joint, and preventing wear. Nevertheless, the irregular articular cartilage shape indicates potential differences in properties at various regions. The lack of full domain surface micromechanical properties restricts the revelation of cartilage structure failure mechanism and impedes the design of biomimetic cartilage compatible with the actual working conditions. In the present work, the full domain knee articular cartilage surface was reasonably divided into microregions based on the approximate curvature principle. Through depth-sensing indentation array, the region-dependent differences in mechanical properties were revealed, and the hardness and Young's modulus distributions of full domain cartilage structure surface were experimentally obtained for the first time. The microstructure-property correlation was established and the microstructure-dependent load adaptability was also verified, as the region (concave side of condylar surface) with maximum hardness and Young's modulus exhibited a striped pattern with approximately consistent orientation, and the regions adjacent to the suprapatellar synovial bursa with lowest bearing capacity exhibited peeling collagen fibers.

In nature, some fish can adhere tightly to the surface of stones, aquatic plants, and even other fish bodies. This adhesion behavior allows these fish to fix, eat, hide, and migrate in complex and variable aquatic environments. The adhesion function is realized by the special mouth and sucker tissue of fish. Inspired by adhesion fish, extensive research has recently been carried out. Therefore, this paper presents a brief overview to better explore underwater adhesion mechanisms and provide bionic applications. Firstly, the adhesion organs and structures of biological prototypes (e.g., clingfish, remora, Garra, suckermouth catfish, hill stream loach, and goby) are presented separately, and the underwater adhesion mechanisms are analyzed. Then, based on bionics, it is explained that the adhesion structures and components are designed and created for applications (e.g., flexible gripping adhesive discs and adhesive motion devices). Furthermore, we offer our perspectives on the limitations and future directions.

The level of joint laxity, which is an indicator of accurate diagnosis for musculoskeletal conditions is manually determined by a physician. Studying joint laxity via artificial joints is an efficient and economical way to improve patient experience and joint proficiency. However, most of study focus on the joint geometry but are inadequate with regard to the tailored mechanical properties of soft tissues. On the basis of collagen fibril deformation, this study proposes bioinspired 3D fibers braided from polyethene multifilament for the reproduction of the controlled nonlinear behavior of ligaments and tendons. Four braided bands are designed, all showing biological behaviors. Two knot-based bands exhibit large toe strains of 10.98% and 5.33% but low linear modulus of 239.84 MPa and 826.05 MPa. The other two bands without knots exhibit lower toe strains of 1.61% and 1.52% but high linear modulus of 2605.27 MPa and 2050.74 MPa. Empirical formulas for braiding parameters (wales and courses) and mechanical properties are expressed to provide a theoretical basis for the mimicry of different tissues in the human body by artificial joints. All parameters have significant effects on the linear region of the load-displacement curve of a fiber due to braided structure, while changing the number of wales facilitates a major contribution to the toe region. A biofidelic human knee has been successfully reconstructed by using bioinspired 3D braided fibers. This study demonstrates that the nonlinear mechanical properties of soft tissues can be replicated by bioinspired 3D braided fibers, further yielding the design of more biomechanically realistic artificial joints.

Nanoindentation creep behavior and underlying mechanisms of nanocrystalline (NC) Ni and NC Ni-20 wt% Fe (Ni-Fe) alloy were investigated at room temperature by a new testing method. The continuous creep strain rate versus creep stress data and hence the continuous apparent activation volume versus creep stress data in the entire holding stage on each single sample were achieved under a loading rate-controlled mode by a cooperative use of the continuous stiffness measurement (CSM) technique. Furthermore, the dependence of the apparent activation volume on the creep stress was interpreted by performing a theoretical analysis. Based on the above experimental and theoretical results and the high-resolution transmission electron microscope observation of the microstructures, the effects of the loading rate and stacking fault energy on the nanoindentation creep behavior of NC Ni and NC Ni-Fe alloy and the underlying mechanisms were analyzed. It was demonstrated that NC Ni-Fe alloy shows higher creep resistance in the transient regime, but lower creep resistance in the steady-state regime compared to NC Ni. The contact stiffness data obtained by the CSM technique in a strain rate-controlled mode can be used to determine the creep stress data from the creep displacement data obtained in a loading rate-controlled mode.