Thanks to its excellent mechanical properties, magnesium alloys have many potential applications in the aerospace and other fields. However, failure to adequately solve corrosion problems of magnesium alloy becomes one of the factors restricting its wide use in many industrial fields. Inspired by nature, researchers designed and fabricated bio-inspired water-repellent (superhydrophobic and slippery liquid-infused porous surface) surfaces with special wetting properties by exploring the surface microstructures of plants and animals such as lotus leaf and nepenthes pitcher, exhibiting excellent corrosion-resistant performance. This article summarizes the research progress on corrosion resistance of magnesium alloys with bio-inspired water-repellent properties in recent years. It mainly introduces the corrosion reasons, types of corrosion of magnesium alloys, and the preparation of magnesium alloys with bio-inspired water-repellent properties to improve corrosion resistance. In particular, it is widely used and effective to construct water-repellent and anti-corrosion coating on the surface of magnesium alloy by surface treatment. It is hoped that the research in this review can broaden the application range of magnesium alloys and provide a powerful reference for the future research on corrosion resistance of magnesium alloys.

As the essential technology of human-robotics interactive wearable devices, the robotic knee prosthesis can provide above-knee amputations with functional knee compensations to realize their physical and psychological social regression. With the development of mechanical and mechatronic science and technology, the fully active knee prosthesis that can provide subjects with actuating torques has demonstrated a better wearing performance in slope walking and stair ascent when compared with the passive and the semi-active ones. Additionally, with intelligent human-robotics control strategies and algorithms, the wearing effect of the knee prosthesis has been greatly enhanced in terms of stance stability and swing mobility. Therefore, to help readers to obtain an overview of recent progress in robotic knee prosthesis, this paper systematically categorized knee prostheses according to their integrated functions and introduced related research in the past ten years (2010?2020) regarding (1) mechanical design, including uniaxial, four-bar, and multi-bar knee structures, (2) actuating technology, including rigid and elastic actuation, and (3) control method, including mode identification, motion prediction, and automatic control. Quantitative and qualitative analysis and comparison of robotic knee prosthesis-related techniques are conducted. The development trends are concluded as follows: (1) bionic and lightweight structures with better mechanical performance, (2) bionic elastic actuation with energy-saving effect, (3) artificial intelligence-based bionic prosthetic control. Besides, challenges and innovative insights of customized lightweight bionic knee joint structure, highly efficient compact bionic actuation, and personalized daily multi-mode gait adaptation are also discussed in-depth to facilitate the future development of the robotic knee prosthesis.

This paper proposes a system for stable ladder climbing of the human-sized four-limbed robot “WAREC-1”, including the following 3 components: (a) Whole-body motion planning; (b) Rung recognition system and (c) Reaction force adjustment. These 3 components guarantee appropriate ladder climbing motion, successful rung grub and proper reaction force distribution at contact points throughout the climbing motion, respectively. With this system, (1) Stable ladder climbing in 2-point contact gait by a human-sized robot and (2) Successful and stable climbing of an irregular ladder (with a higher or inclined rung) in both 3-point and 2-point contact gait with the capability of recognizing the target rung and the corresponding motion planning are realized, which have rarely been realized by former studies. Finally, experiment results and data of the robot ladder climbing are also presented to evaluate the proposed system. 

Inspired by bacterial flagella in nature, magnetic helical microswimmer is an ideal model to perform complex task in a low Reynolds number environments. Shape Memory Polymers (SMPs) with desirable properties are considered as one of the most preferred options for the development of small-scale robots. However, fabricating and programming strategies are still challenging. Here, we report an approach to fabricate helical microswimmers based on thermoplastic SMP (polylactic acid). Melt-spun polylactic acid fibers containing magnetic particles were enwound to form helical microstructures. Their shape recovery behaviors were programmed by annealing and pre-deformation. Three forms of helical microswimmers (constant-helix-angle conical helix, constant-pitch conical helix, and straight helix) with controlled morphological parameters were tailored. The obtained microswimmers showed 3D locomotion capability under rotating magnetic fields. The maximum swimming velocity of microswimmers was nearly six body lengths per second, and the near-wall swimming of conical helixes along their sharp end exhibited a smaller drift. Moreover, we demonstrated programmed shape-switching processes (spring-like contraction and elongation, coiling and uncoiling) and self-repairing of the microswimmers. As demonstrations of potential applications, tasks of mobile microstent, cargo delivery, and minimally invasive injection were carried out. The multifunctional shape-memory microswimmers have immense potential in a variety of applications.

Stingrays can undulate their wide pectoral fins to thrust themselves and swim freely underwater. Many researchers have used bionics to directly imitate their undulating mechanism and manufacture undulatory underwater robots. Based on the limitations of the existing undulatory underwater robots, this paper proposes a novel undulatory propulsion strategy, which aims to use the stingray undulating mechanism more thoroughly. First, the mathematical models of both traditional and novel structures are established to accurately describe their undulating mechanism. Then, based on the dynamic mesh technology, the flow field vortex structure they generated is analyzed through fluid-structure interaction simulation, and the thrust force and lateral force generated by them are calculated, which verified that this novel propulsion strategy is indeed more effective. Finally, a prototype robot based on the improved propulsion strategy is manufactured. Compared with the existing stingray robots, the prototype has obvious advantages, thus verifying the accuracy of the simulation results. 

Motivated by optimal combination of paired wings configuration and stroke-plane inclination in biological flapping flights that can achieve high aerodynamic performance, we propose a biomimetic rotor-configuration design to explore optimal aerodynamic performance in multirotor drones. While aerodynamic interactions among propellers in multirotor Unmanned Aerial Vehicles (UAVs) play a crucial role in lift force production and Figure of Merit (FM) efficiency, the rotor-configuration effect remains poorly understood. Here we address a Computational Fluid Dynamics (CFD)-based study on optimal aerodynamic performance of the rotor-configuration in hovering quadrotor drones with a specific focus on the aerodynamic effects of tip distance, height difference and tilt angle of propellers. Our results indicate that the tip distance-induced interactions can most alter lift force production and hence lead to remarked improvement in FM, and the height difference also plays a key role in improving aerodynamic performance, while the tilt angle effect is less important. Furthermore, we carried out an extensive analysis to explore the optimal aerodynamic performance of the rotor-configuration over a broad parameter space, by combining the CFD-based simulations and a novel surrogate model. We find that a rotor-configuration with a large tip distance and some height difference with zero tilt angle is capable of optimizing both lift force production and FM, which could offer a novel optimal design as well as maneuver strategy for multirotor UAVs.

As the basis of flight behavior, the initiation process of insect flight is accompanied by a transition from crawling mode to flight mode, and is clearly important and complex. Insects take flight from a vertical surface, which is more difficult than takeoff from a horizontal plane, but greatly expands the space of activity and provides us with an excellent bionic model. In this study, the entire process of a butterfly alighting from a vertical surface was captured by a high-speed camera system, and the movements of its body and wings were accurately measured for the first time. After analyzing the movement of the center of mass, it was found that before initiation, the acceleration perpendicular to the wall was much greater than the acceleration parallel to the wall, reflecting the positive effects of the legs during the initiation process. However, the angular velocity of the body showed that this process was unstable, and was further destabilized as the flight speed increased. Comparing the angles between the body and the vertical direction before and after leaving the wall, a significant change in body posture was found, evidencing the action of aerodynamic forces on the body. The movement of the wings was further analyzed to obtain the laws of the three Euler angles, thus revealing the locomotory mechanism of the butterfly taking off from the vertical surface. 

This paper addresses the design of a novel bionic robotic device for upper limb rehabilitation tasks at home. The main goal of the design process has been to obtain a rehabilitation device, which can be easily portable and can be managed remotely by a professional therapist. This allows to treat people also in regions that are not easily reachable with a significant cost reduction. Other potential benefits can be envisaged, for instance, in the possibility to keep social distancing while allowing rehabilitation treatments even during a pandemic spread. Specific attention has been devoted to design the main mechatronic components by developing specific kinematics and dynamics models. The design process includes the implementation of a specific control hardware and software. Preliminary experimental tests are reported to show the effectiveness and feasibility of the proposed design solution.

A subsystem impactor test for pedestrian lower limb injury evaluation has been brought in China New Car Assessment Protocol (CNCAP). Concerning large anthropometric differences of the people from different countries, the present study aims to establish and validate a finite element lower limb model representing 50th Chinese male size for pedestrian safety research, then compare its biomechanical responses with the general models currently in wide use in the world for pedestrian safety evaluation. Concerning the vehicle-pedestrian impact loading environment, the previously developed lower limb model with three-dimensional muscles was adjusted and validated through the related experiments. Then, the biomechanical responses of the validated model were compared with the Total Human Model for Safety (THUMS) and Advanced Pedestrian Legform Impactor (aPLI) models by combing with four typical vehicles. The results showed that both consistency and significant differences of biomechanical responses existed between the present model and the other two models. The injury measurements of the thigh region of the present model showed extremely large differences with the other two models, while the tibia and Medial Collateral Ligament (MCL) injury measurements show similar values. Thus, it can be concluded that directly using the aPLI or THUMS models for Chinese pedestrian safety evaluation is not robust concerning both kinematic responses and injury measurements.

Reckless discharge of industrial wastewater and domestic sewage as well as frequent leakage of crude oil have caused serious environmental problems and posed severe threat to human survival. Various nature inspired superhy-drophobic surfaces have been successfully applied in oily water remediation. However, further improvements are still urgently needed for practical application in terms of facile synthesis process and long-term durability towards harsh environment. Herein, we propose a simple one-step dodecyl mercaptan functionalization method to fabricate Super-hydrophobic-Superoleophilic Copper Mesh (SSCM). The prepared SSCM possesses excellent water repellence and oil affinity, enabling it to successfully separate various oil-water mixtures with high separation efficiency (e.g., > 99% for hexadecane-water mixture). The SSCM retains high separating ability when hot water and strong corrosive aqueous solutions are used to simulate oil-water mixtures, indicating remarkable chemical durability of the dodecyl mercaptan functionalized copper mesh. Additionally, the efficiency can be well maintained during 50 cycles of separation, and the water repellence is even stable after storage in air for 120 days, demonstrating the reusability and long-term stability of the SSCM. Furthermore, the functionalized mesh also shows good mechanical robustness towards abrasion by sandpaper, and oil-water separation efficiency of > 96% can be obtained after 10 cycles of abrasion. The reported one-step dodecyl mercaptan functionalization could be a simple method for increasing the water repellence of copper mesh, and thereby be a great candidate for treating large-scale oily wastewater in harsh environments.

The shortage of skin for grafting continues to be a major problem in the treatment of serious skin injuries. 3D bioprinting provides a new way to solve this problem. However, current 3D printed skin is less effective in treatment of large wounds because of severe shrinkage and scarring. In this study, bionically designed bilayer skin was fabricated using an extrusion-based bioprinter and a gelatin/sodium alginate/gelatin methacrylate hydrogel with excellent physical and biological properties. Full-thickness skin wounds were created in the back of nude mice and treated with bioprinted skin or hydrogel. Bioprinted skin accelerated wound healing, reduced wound contraction and scarring, and facilitated wound skin epithelialization compared with the bioprinted hydrogel or untreated wound. The skin from the wound was collected 28 days after grafting for histology and immunofluorescence analysis. The thickness of the dermis and epidermis of the bioprinted skin was similar to that of nude mice. Microvascular formation in the dermis and dense keratinocytes in the epidermis of the bioprinted skin were observed. This study provides a potential treatment strategy for reducing skin contraction and scar in large skin wounds.

In the past decades, many materials have been studied as carriers for targeted drug delivery. However, there is a need for utilizable and selective carrier materials with few side effects.  Here, the magnetic Ganoderma Lucidum Spores (mGLS) as a highly efficient targeted drug delivery carrier were explored. Then the regulatable targeted drug delivery system was verified by loading and releasing of the 5-Fluorouracil (5-FU). The results showed that the maximum of the loaded 5-FU reached 250.23 mg·g?1 in the mGLS. The cumulative release of the 5-FU for the drug delivery system could reach 80.11% and 67.14% in the PBS and HCl after 48 h, respectively. In addition, this system showed the good pharmacokinetic properties in vivo. After 12 h, the blood concentration in the 5-FU@mGLS group kept at 5.3 μg·mL?1 and was four times higher than that in the 5-FU group. In summary, the GLS as a natural microscale core-shell structures appears the striking application in carrier material for oral drug delivery.

The aim of this study was to reconstruct surface porous structure with hundreds of micrometers and then bio-mineralize Sr-doped Calcium Phosphate (Sr-doped CaP) on Polyetheretherketone (PEEK) profile to enhance its bioactivity. A surface porous structure was prepared on PEEK profile by embedding and acid-etching of SiO2 particles as porogen (SP-PEEK). Then the Sr-doped CaP was further decorated on the porous surface after sulfonation, introduction of Sr-doped CaP crystal seeds and bio-mineralization in 1.5 times simulated body fluid (BSSP-PEEK-CaP/Sr). It was feasible to reconstruct the surface porous structure with hundreds of micrometers on PEEK profile by the present method without damaging its mechanical properties. The Sr-doped CaP crystal seeds effectively promoted the bio-mineralization of bio-inertness PEEK. All as-prepared PEEK did not inhibit the proliferation of cells. ALP of bio-mineralized groups was significantly increased than that of the other groups. The BSSP-PEEK-CaP/Sr obviously affected the morphology and promoted the adhesion and spreading of cells. As a result, the cyto-biocompatibity and bioactivity of PEEK were improved after bio-mineralization. Sr-doped CaP on PEEK most likely was beneficial for cells, which was associated with the increasing of the hydrophilicity on PEEK. This study provided a candidate method to improve the osteogenesis of PEEK implants. 

Selective Laser Melting (SLM), one of the metal additive manufacturing methods in the powder bed, is frequently used in the production of 316L stainless steel biomaterial. In this study, the effect of duplex surface modification (metal additive manufacturing and plasma oxidizing) on the corrosion resistance of 316L was investigated. Ti6Al4V layer was formed by additive manufacturing on 316L produced by selective laser melting method. The obtained layered Ti6Al4V/316L samples were oxidized by plasma at 650 ?C – 750 ?C and 1 h – 4 h parameter conditions. TiO2 ceramic layer was formed on the Ti6Al4V/316L structure by plasma oxidation process in several layer thicknesses. Corrosion properties of the TiO2 layer were determined by Open Circuit Potential (OCP), potentiodynamic polarization, and Electrochemical Impedance Spectroscopy (EIS) tests in Simulated Body Fluid (SBF) solution. Also, the surface characterizations of the samples were determined by the Vickers micro-hardness tester, Scanning Electron Microscopy (SEM), and X-Ray Diffractometer (XRD) analysis. From the results, it was obtained that the corrosion resistance of the plasma oxidized was higher than the untreated 316L and layered Ti6Al4V/316L samples. The best corrosion resistance was obtained under the 750 ?C and 4 h parameter conditions because of the increasing plasma oxidizing time and temperature.

This paper proposes a down-stroke abrasive belt grinding under micro feeding for noise reduction surface. Firstly, a physical model of processing under micro feeding for noise reduction structure was established. Based on the flexible contact characteristics of abrasive belt grinding and Hertz contact theory, a mathematical model suitable for this method was established, considering vibration and abrasive belt wear. Secondly, a simulation analysis was carried out. Then, an experimental platform was built to analyze the influence of process parameters on surface roughness and surface microstructure, with the model verified. Finally, the propeller with pit structure was simulated, and the noise reduction performance of the propeller under this method and general abrasive belt grinding was compared and analyzed. The results show that the maximum error of the model based on proposed method does not exceed 10%, and the coincidence degree of the minimum error point can reach 90% at lower feed speed and higher linear velocity of the abrasive belt. The noise reduction effect of the propeller with pit-shaped surfaces can reach 35%. Through the above analysis, the proposed method can be used for the processing of noise reduction surfaces. 

Micro-textured surfaces have improved the tribological performance of contact surfaces under lubricated conditions; however, not practiced due to manufacturing challenges. In addition to simpler micro-pits or straight-trench type textures, sophisticated bioinspired textures on commercial radial ball bearings have been scarcely studied. In this work, Dendroaspis polylepis (Mamba snake) skin-type textures were fabricated on the inner race of FAG radial ball bearings using a nanosecond fiber laser machine. Though the snake textures were primarily meant to enhance friction, the dimensions of the texture have been carefully chosen to improve the tribological performance under lubricated condition. The textured bearings were assembled and experimented at various rotational speeds and lightly loaded conditions to measure vibrational amplitude, frictional torque, and temperature rise. Compared to untextured (conventional) bearing, the snake-skin type textured bearings resulted in improved tribo-dynamic performance.

In the original Moth-Flame Optimization (MFO), the search behavior of the moth depends on the corresponding flame and the interaction between the moth and its corresponding flame, so it will get stuck in the local optimum easily when facing the multi-dimensional and high-dimensional optimization problems. Therefore, in this work, a generalized oppositional MFO with crossover strategy, named GCMFO, is presented to overcome the mentioned defects. In the proposed GCMFO, GOBL is employed to increase the population diversity and expand the search range in the initialization and iteration jump phase based on the jump rate; crisscross search (CC) is adopted to promote the exploitation and/or exploration ability of MFO. The proposed algorithm’s performance is estimated by organizing a series of experiments; firstly, the CEC2017 benchmark set is adopted to evaluate the performance of GCMFO in tackling high-dimensional and multimodal problems. Secondly, GCMFO is applied to handle multilevel thresholding image segmentation problems. At last, GCMFO is integrated into kernel extreme learning machine classifier to deal with three medical diagnosis cases, including the appendicitis diagnosis, overweight statuses diagnosis, and thyroid cancer diagnosis. Experimental results and discussions show that the proposed approach outperforms the original MFO and other state-of-the-art algorithms on both convergence speed and accuracy. It also indicates that the presented GCMFO has a promising potential for application.