Biological water striders have advantages such as fexible movement, low disturbance to the water surface, and low noise. Researchers have developed a large number of biomimetic water strider robots based on their movement mechanism, which have broad application prospects in water quality testing, water surface reconnaissance, and search. This article mainly reviews the research progress of biomimetic water strider robots. First, the biological and kinematic characteristics of water striders are outlined, and some mechanical parameters of biological water striders are summarized. The basic equations of water strider movement are then described. Next, an overview is given of the past and current work on skating and jumping movements of biomimetic water strider robots based on surface tension and water pressure dominance. Based on the current research status of biomimetic water strider robots, the shortcomings of current research on biomimetic water striders are summarized, and the future development of biomimetic water strider robots is discussed. This article provides new insights for the design of biomimetic water strider robots.

Cartilage regeneration and repair are considered clinical challenges since cartilage has limited capability for reconstruction. Although tissue-engineered materials have the ability to repair cartilage, they have weak mechanical characteristics and cannot resist long-term overload. On the other hand, surgery to replace the joint is frequently done to treat signifcant cartilage deterioration these days. However, the materials that are being used for replacement have high friction coefcients, lack shock absorption functions, and lack cushioning. Further research on natural articular cartilage structure and function may lead to bionic hydrogels, which have suitable physicochemical and biological characteristics (e.g., tribological and mechanical properties and the ability to support loadbearing capability), but need improvements. Based on their tribological and mechanical characteristics, the current review highlights the most recent advancements of bionic hydrogels used for articular cartilage, highlighting both the feld's recent progress and its potential for future research. For this reason, frstly, some important property improvement methods of bionic hydrogels are discussed and then, the recent fndings of various research on the making of those bionic materials are provided and compared. It seems that by using some modifcations such as product design, surface treatments, animal tests, controlling the isoelectric point of hydrogels, and computer simulation, the intended mechanical and tribological characteristics of natural articular cartilage may be attained by the bionic hydrogels.

eature Subset Selection (FSS) is an NP-hard problem to remove redundant and irrelevant features particularly from medical data, and it can be efectively addressed by metaheuristic algorithms. However, existing binary versions of metaheuristic algorithms have issues with convergence and lack an efective binarization method, resulting in suboptimal solutions that hinder diagnosis and prediction accuracy. This paper aims to propose an Improved Binary Quantum-based Avian Navigation Optimizer Algorithm (IBQANA) for FSS in medical data preprocessing to address the suboptimal solutions arising from binary versions of metaheuristic algorithms. The proposed IBQANA’s contributions include the Hybrid Binary Operator (HBO) and the Distance-based Binary Search Strategy (DBSS). HBO is designed to convert continuous values into binary solutions, even for values outside the [0, 1] range, ensuring accurate binary mapping. On the other hand, DBSS is a twophase search strategy that enhances the performance of inferior search agents and accelerates convergence. By combining exploration and exploitation phases based on an adaptive probability function, DBSS efectively avoids local optima. The efectiveness of applying HBO is compared with fve transfer function families and thresholding on 12 medical datasets, with feature numbers ranging from 8 to 10,509. IBQANA's efectiveness is evaluated regarding the accuracy, ftness, and selected features and compared with seven binary metaheuristic algorithms. Furthermore, IBQANA is utilized to detect COVID-19. The results reveal that the proposed IBQANA outperforms all comparative algorithms on COVID-19 and 11 other medical datasets. The proposed method presents a promising solution to the FSS problem in medical data preprocessing.

Some living organisms with hierarchical structures in nature have received extensive attention in various fields. The hierarchical structure with multiple pores, a large number of solid–gas interfaces and tortuous conduction paths provide a new direction for the development of thermal insulation materials, making the living creatures under these extreme conditions become the bionic objects of scientific researchers. In this review, the research progress of bionic hierarchical structure in the field of heat insulation is highlighted. Polar bears, cocoons, penguin feathers and wool are typical examples of heat preservation hierarchy in nature to introduce their morphological characteristics. At the same time, the thermal insulation mechanism, fractal model and several preparation methods of bionic hierarchical structures are emphatically discussed. The application of hierarchical structures in various fields, especially in thermal insulation and infrared thermal stealth, is summarised. Finally, the hierarchical structure is prospected.

Bamboo is a typical biological material widely growing in nature with excellent physical and mechanical properties. It is lightweight with high strength and toughness. The naturally optimized bamboo structure, which has inspired global material scientists and engineers for decades, is significantly important for the bionic design of novel structural materials with ultra-light, ultra-strong, or ultra-tough and comprehensive properties. Typical literature on innovative composite materials and structural members inspired by bamboo are reviewed in this paper, and the research progress and prospects in this field are expounded in three parts. First, the structural characteristics of the bamboo wall layer along the thickness and height directions are described in terms of chemical composition, gradient structure, pore structure, and hollow structure with variable cross-section. Second, this paper summarizes the research progress on new composite materials and structural components by applying bamboo’s structural features from the perspective of sustainability, designability, and customization. Finally, given the limitations of current research, the biomimetic scientific research on bamboo’s structural characteristics is prospected from the interpretation of bamboo structure, new bamboo-like materials, and structural design optimization perspectives, providing a reference for future research on biomimetic aspects of biomass.

With the development of camera technology, high-speed cameras have greatly contributed to capturing the movement and posture of animals, which has dramatically promoted experimental biology research. At the same time, with the concept of bionics gradually gaining popularity among researchers, the design of robots is absorbing more and more biological features, where the interest in the bio-inspired robot is hewed out. Compared with the traditional robot, the bio-inspired robot imitates the motion pattern to achieve similar propulsion features, which may be more effective and reasonable. In this paper, the motion patterns of aquatic animals are divided into four categories according to their propulsion mechanisms: drag-based, lift-based, jet-based, and interface-based. And bio-inspired robots imitating aquatic prototypes are introduced and reviewed. Finally, the prospect of aquatic bio-inspired robots is discussed.

By imitating the body structure and movement mode of the crab in nature, a novel stick–slip piezo-driven positioning platform was proposed by employing the bionic flexible hinge mechanism with a symmetrical structure and two piezoelectric stacks. The structural design and bionic motion principle were discussed, followed by analyzing the feasibility, safety, and output magnification ratio of the bionic flexible hinge mechanism via the stiffness matrix method and finite element simulation. To investigate the output performances of the positioning platform, a prototype was fabricated and an experiment system was established. Stepping characteristics of the positioning platform under various driving voltages were characterized, and the results indicated that the positioning platform could move steadily under various driving voltages. Within 1 s, the differences between the forward and reverse output displacement were less than 3% under different driving frequencies, proving the high bidirectional motion symmetry. The maximum driving speed of 5.44 mm/s was obtained under the driving voltage of 120 V and driving frequency of 5 Hz. In addition, the carrying load capacity of the positioning platform was tested by standard weights, and the results showed that when the carrying load reached 10 N, the driving speed could still reach 60 μm/s.

Mechanoreceptors play a vital role for animals to sense and monitor environmental parameters, like flow speed, tactile resistance, and pressure. The hairy-structured trichoid sensillum, a common type of mechanoreceptor in insects, is generally non-motile, embedded in a socket connected with cuticular substrate. However, we discover that the trichoid sensilla on the tongue of western bees (Apis mellifera L.) is rotatable and can be actively maneuvered by bees. The trichoid sensilla together with the socket base are mounted on the origami-like sheath of the tongue, and can rotate outwards along with the deformation of the tongue sheath. We illustrate that the rotation of the tongue sensilla hairs can locally generate shear force in the liquid to sense the viscosity, which may facilitate bees to adjust their feeding strategies. The viscosity sensitivity of the rotatable trichoid sensilla based on the origami-like mechanism, according to our mechanical model, is 13 times greater than that of the fixed sensilla. In addition, our finite element analysis shows that strain would concentrate on the trichoid sensilla base when rotating in the liquid, which may structurally enhance its perception sensitivity. This study reports a new mechanism of active mechanoreceptors and may have implications for origami mechanisms with correlative functional components, especially for micro-robotic systems used in underwater viscosity sensing.

Water-lubricated bearings have great advantages in the application of ship tail bearings due to the characteristics of green, pollution-free, and sustainable. However, the poor wettability of water-lubricated materials, as well as the low viscosity and poor load-carrying capacity of water, resulting in poor lubricating film integrity and short material service life under low-speed, heavy-load, start-stop conditions, which limits its application. To study the relationship between wettability and lubrication state and improve the lubrication performance of Si3N4 under water lubrication conditions, the characteristic parameters that determine the hydrophilicity of Sphagnum were detected and extracted, and the bionic Si3N4 model was established using Material Studio. Then, the molecular dynamic behavior and tribological properties of different Si3N4 models were simulated and analyzed. Pore structure affects the spreading and storage of water on the material surface and changes the wettability of the material. Under the condition of water lubrication, better wettability and water storage promote the formation of water film, effectively improve the lubrication state of the material, and improve its bearing performance

Four novel chiral honeycomb structures inspired by the biological arrangement shape are designed. The functional principle is raised to solve the large deformation of bio-inspired structures and the structural constitutive model is proposed to explain the quasi-static mechanical properties of chiral honeycomb array structures and honeycomb structures. Simulation and experiment results verify the accuracy of theoretical analysis results and the errors are all within 15%. In structural mechanical properties, Equidimensional Chiral Honeycomb Array Structure (ECHS) has excellent mechanical properties. Among ECHS, Small-sized Column Chiral Honeycomb Array Structure (SCHCS) has the best properties. The bearing capacity, specific energy absorption, and specific strength of SCHCS are more than twice as much as the others in this paper. The chiral honeycomb array structure has the best mechanical properties at a certain size. In the structural design, the optimal size model should be obtained first in combination with the optimization algorithm for the protection design.

The Firefly Algorithm (FA) is a highly efficient population-based optimization technique developed by mimicking the flashing behavior of fireflies when mating. This article proposes a method based on Differential Evolution (DE)/current-to-best/1 for enhancing the FA's movement process. The proposed modification increases the global search ability and the convergence rates while maintaining a balance between exploration and exploitation by deploying the global best solution. However, employing the best solution can lead to premature algorithm convergence, but this study handles this issue using a loop adjacent to the algorithm's main loop. Additionally, the suggested algorithm’s sensitivity to the alpha parameter is reduced compared to the original FA. The GbFA surpasses both the original and five-version of enhanced FAs in finding the optimal solution to 30 CEC2014 real parameter benchmark problems with all selected alpha values. Additionally, the CEC 2017 benchmark functions and the eight engineering optimization challenges are also utilized to evaluate GbFA’s efficacy and robustness on real-world problems against several enhanced algorithms. In all cases, GbFA provides the optimal result compared to other methods. Note that the source code of the GbFA algorithm is publicly available at https://www.optim-app.com/projects/gbfa.

Pacinian corpuscle is a tactile receptor that responds to high-frequency (20–1000 Hz) vibration and has high-pass filtering and mechanical signal amplification functions. It is the main receptor of vibration tactility closely related to fine touch sensation, which is the ability to perceive and localize objects’ shape, texture, and size. Currently, it is still difficult to measure and calculate the friction generated by robots grasping objects. The resolution of touch and vibration sensors cannot satisfy the demand for understanding tribological behavior. The simulation of Pacinian corpuscles’ structure and replication of its key functions will bring richer touch information to robots. In this review article, the structure and functions of Pacinian corpuscles are summarized from the internal structure of a single Pacinian corpuscle and the spatial distribution of multiple Pacinian corpuscles. Then, theoretical models and research on the bionics design of Pacinian corpuscles are introduced based on the three reception processes of Pacinian corpuscles: mechanical transmission, electromechanical transduction, and neural excitation. Finally, the bottlenecks of current research on the simulation of Pacinian corpuscles are summarized, followed by the proposal of research ideas on the simulation of Pacinian corpuscles.

Bilateral rehabilitation systems with bilateral or unilateral assistive robots have been developed for hemiplegia patients to recover their one-side paralysis. However, the compliant robotic assistance to promote bilateral inter-limb coordination remains a challenge that should be addressed. In this paper, a biomimetic variable stiffness modulation strategy for the Variable Stiffness Actuator (VSA) integrated robotic is proposed to improve bilateral limb coordination and promote bilateral motor skills relearning. An Electromyography (EMG)-driven synergy reference stiffness estimation model of the upper limb elbow joint is developed to reproduce the muscle synergy effect on the affected side limb by independent real-time stiffness control. Additionally, the bilateral impedance control is incorporated for realizing compliant patient–robot interaction. Preliminary experiments were carried out to evaluate the tracking performance and investigate the multiple task intensities’ influence on bilateral motor skills relearning. Experimental results evidence the proposed method could enable bilateral motor task skills relearning with wide-range task intensities and further promote bilateral inter-limb coordination.

In this work, we propose a real proportional-integral-derivative plus second-order derivative (PIDD2) controller as an efficient controller for vehicle cruise control systems to address the challenging issues related to efficient operation. In this regard, this paper is the first report in the literature demonstrating the implementation of a real PIDD2 controller for controlling the respective system. We construct a novel and efficient metaheuristic algorithm by improving the performance of the Aquila Optimizer via chaotic local search and modified opposition-based learning strategies and use it as an excellently performing tuning mechanism. We also propose a simple yet effective objective function to increase the performance of the proposed algorithm (CmOBL-AO) to adjust the real PIDD2 controller's parameters effectively. We show the CmOBL-AO algorithm to perform better than the differential evolution algorithm, gravitational search algorithm, African vultures optimization, and the Aquila Optimizer using well-known unimodal, multimodal benchmark functions. CEC2019 test suite is also used to perform ablation experiments to reveal the separate contributions of chaotic local search and modified opposition-based learning strategies to the CmOBL-AO algorithm. For the vehicle cruise control system, we confirm the more excellent performance of the proposed method against particle swarm, gray wolf, salp swarm, and original Aquila optimizers using statistical, Wilcoxon signed-rank, time response, robustness, and disturbance rejection analyses. We also use fourteen reported methods in the literature for the vehicle cruise control system to further verify the more promising performance of the CmOBL-AO-based real PIDD2 controller from a wider perspective. The excellent performance of the proposed method is also illustrated through different quality indicators and different operating speeds. Lastly, we also demonstrate the good performing capability of the CmOBL-AO algorithm for real traffic cases. We show the CmOBL-AO-based real PIDD2 controller as the most efficient method to control a vehicle cruise control system.

The structural evolutions of the organisms during the development of billions of years endow them with remarkable thermal-regulation properties, which have significance to their survival against the outer versatile environment. Inspired by the nature, there have been extensive researches to develop thermoregulating materials by mimicking and utilizing the advantages from the natural organisms. In this review, the latest advances in thermal regulation of bioinspired microstructures are summarized, classifying the researches from dimension. The representative materials are described with emphasis on the relationship between the structural features and the corresponding thermal-regulation functions. For one-dimensional materials, wild silkworm cocoon fibers have been involved, and the reasons for unique optical phenomena have been discussed. Pyramid cone structure, grating and multilayer film structure are chosen as typical examples of two-dimensional bionics. The excellent thermal performance of the three-dimensional network frame structures is the focus. Finally, a summary and outlook are given.

Morphing botanical tissues and animal muscles are all fiber-mediated composites, in which fibers play a passive and active role, respectively. Herein, inspired by the mechanism of fibers functioning in morphing botanical tissues and animal muscles, we propose two sorts of fiber-dominated composite actuators. First, inspired by the deformation of awned seeds in response to humidity change, we fabricate passive fiber-dominated actuators using non-active aligned carbon fibers via 4D printing method. The effects of process parameters, structural parameters, and fiber angles on the deformation of the printed actuators are examined. The experimental results show that the orientation degree is enhanced, resulting in a better swelling effect as the printing speed increases. Then, motivated by the actuation mechanism of skeletal muscle, we prepare active fiber-dominated actuators using active polyurethane fibers via 4D printing and pre-stretching method. The effect of fiber angle and loading on the actuation mode is experimentally analyzed. The experimental results show that the rotation angle of the actuator gradually decreases with the angle from 45° to 60°. When the fiber angle is 0° and 90°, the driver basically stops rotating while shrinking along the loading direction. Based on the above actuation mechanisms, identical contraction behaviors are realized both in passive and active fiber-dominated soft actuators. This work provides a validation method for biologically actuation mechanisms via 4D printing technique and smart materials and adds further insights to the design of bioinspired soft actuators.

Hybrid metaheuristic algorithms play a prominent role in improving algorithms' searchability by combining each algorithm's advantages and minimizing any substantial shortcomings. The Quantum-based Avian Navigation Optimizer Algorithm (QANA) is a recent metaheuristic algorithm inspired by the navigation behavior of migratory birds. Different experimental results show that QANA is a competitive and applicable algorithm in different optimization fields. However, it suffers from shortcomings such as low solution quality and premature convergence when tackling some complex problems. Therefore, instead of proposing a new algorithm to solve these weaknesses, we use the advantages of the bonobo optimizer to improve global search capability and mitigate premature convergence of the original QANA. The effectiveness of the proposed Hybrid Quantum-based Avian Navigation Optimizer Algorithm (HQANA) is assessed on 29 test functions of the CEC 2018 benchmark test suite with different dimensions, 30, 50, and 100. The results are then statistically investigated by the Friedman test and compared with the results of eight well-known optimization algorithms, including PSO, KH, GWO, WOA, CSA, HOA, BO, and QANA. Ultimately, five constrained engineering optimization problems from the latest test suite, CEC 2020 are used to assess the applicability of HQANA to solve complex real-world engineering optimization problems. The experimental and statistical findings prove that the proposed HQANA algorithm is superior to the comparative algorithms.

With the growing demand for miniaturized workspaces, the demand for microrobots has been increasing in robotics research. Compared to traditional rigid robots, soft robots have better robustness and safety. With a flexible structure, soft robots can undergo large deformations and achieve a variety of motion states. Researchers are working to design and fabricate flexible robots based on biomimetic principles, using magnetic fields for cable-free actuation. In this study, we propose an inchworm-shaped soft robot driven by a magnetic field. First, a robot is designed and fabricated and force analysis is performed. Then, factors affecting the soft robot’s motion speed are examined, including the spacing between the magnets and the strength and frequency of the magnetic field. On this basis, the motion characteristics of the robot in different shapes are explored, and its motion modes such as climbing are experimentally investigated. The results show that the motion of the robot can be controlled in a two-dimensional plane, and its movement speed can be controlled by adjusting the strength of the magnetic field and other factors. Our proposed soft robot is expected to find extensive applications in various fields.

Wall climbing robots can be used to undertake missions in many unstructured environments. However, current wall climbing robots have mobility difficulties such as in the turning or accelarating. One of the main reasons for the limitations is the poor flexibility of the spines. Soft robotic technology can actively enable structure deformation and stiffness varations, which provides a solution for the design of active flexible spines. This research utilizes pneumatic soft actuators to design a flexible spine with the abilities of actively bending and twisting by each joint. Using bending and torsion moment equilibriums, respectively, from air pressure to material deformations, the bending and twisting models for a single actuator with respect to different pressure are obtained. The theoretical models are verified by finite-element method simulations and experimental tests. In addition, the bending and twisiting motions of single joint and whole spine are analytically modeled. The results show that the bionic spine can perform desired deformations in accordance with the applied pressure on specified chambers. The variations of the stiffness are also numerically assessed. Finally, the effectiveness of the bionic flexible spine for actively producing sequenced motions as biological spine is experimentally validated. This work demonstrated that the peneumatic spine is potential to improve the spine flexibility of wall climbing robot.

In this paper, a bionic mantis shrimp amphibious soft robot based on a dielectric elastomer is proposed to realize highly adaptive underwater multimodal motion. Under the action of an independent actuator, it is not only able to complete forward/backwards motion on land but also has the ability of cyclically controllable transition motion from land to water surface, from water surface to water bottom and from water bottom to land. The fastest speed of the soft robot on land is 170 mm/s, and it can crawl while carrying up to 4.6 times its own weight. The maximum speeds on the water surface and the water bottom are 30 mm/s and 14.4 mm/s, respectively. Furthermore, the soft robot can climb from the water bottom with a 9° slope transition to land. Compared with other similar soft robots, this soft robot has outstanding advantages, such as agile speed, large load-carrying capacity, strong body flexibility, multiple motion modes and strong underwater adaptability. Finally, nonlinear motion models of land crawling and water swimming are proposed to improve the environmental adaptability under multiple modalities, and the correctness of the theoretical model is verified by experiments.

Soft climbing/crawling robots have been attracting increasing attention in the soft robotics community, and many prototypes with basic locomotion have been implemented. Most existing soft robots achieve locomotion by planar bending deformation and lack sufficient mobility. Enhancing the mobility of soft climbing/crawling robots is still an open and challenging issue. To this end, we present a novel pneumatic leech-like soft robot, Leechbot, with both bending and stretching deformation for locomotion. With a morphological structure, the robot consists of a three-chambered actuator in the middle for the main motion, two chamber-net actuators that act as ankles, and two suckers at the ends for anchoring on surfaces. The peristaltic motion for locomotion is implemented by body stretching, and direction changing is achieved by body bending. Due to the novel design and two deformation modes, the robot can make turns and transit between different surfaces; the robot, hence, has excellent mobility. The development of the robot prototype is presented in detail in this paper. To control its motion, tests were carried out to determine the relationship between step length and air pressure as well as the relationship between motion speed and periodic delay time. A kinematic model was established, and the kinematic mobility and surface transitionability were analyzed. Gait planning based on the inflating sequence of the actuating chambers is presented for straight crawling, turn making, and transiting between surfaces and was verified by a series of experiments with the prototype. The results show that a high mobility in soft climbing/crawling robots can be achieved by a novel design and by proper gait planning.

The aim of this study is to systematically reveal the differences in the biomechanics of 16 hand regions related to bionic picking of tomatoes. The biomechanical properties (peak loading force, elastic coefficient, maximum percentage deformation and interaction contact mechanics between human hand and tomato fruit) of each hand region were experimentally measured and covariance analyzed. The results revealed that there were significant variations in the assessed biomechanical properties between the 16 hand regions (p?<?0.05). The maximum pain force threshold (peak loading force in I2 region) was 5.11 times higher than the minimum pain force threshold (in Th1 region). It was found that each hand region in its normal direction can elastically deform by at least 15.30%. The elastic coefficient of the 16 hand regions ranged from 0.22 to 2.29 N mm?1. The interaction contact force acting on the fruit surface was affected by the selected human factors and fruit features. The obtained covariance models can quantitatively predict all of the above biomechanical properties of 16 hand regions. The findings were closely related to hand grasping performance during tomato picking, such as soft contact, surface interaction, stable and dexterous grasping, provided a foundation for developing a high-performance tomato-picking bionic robotic hand.

The underactuated fingers used in prosthetic hands account for a large part of design consideration in anthropomorphic prosthetic hand design. There are considerable numbers of designs available for underactuated prosthetic fingers in literature but, emulating the anthropomorphic flexion movement is still a challenge due to the complex nature of the motion. To address this challenge, a hybrid mechanism using both linkage-based mechanism and tendon-driven actuation has been proposed in this paper. The presented mechanism includes a novel offset slider-crank-based finger that has been designed using a combination of different lengths of cranks and connecting rods. The prototypes of both the new mechanism and the conventional tendon-driven mechanism are constructed and compared experimentally based on interphalangeal joint angle trajectory during flexion. The angles achieved through the new hybrid mechanism are compared with the conventional tendon-driven mechanism and the Root Mean Square Error (RMSE) values have been calculated by comparing to the anthropomorphic flexion angles of the published literature. The RMSE values calculated for three interphalangeal joints of the hybrid mechanism are found to be less than their counter-parts of the conventional tendon-driven mechanism. In addition to achieving resemblance to anthropomorphic flexion angles, the mechanism is designed within the anthropometric human finger dimensions.

Bioinspired Multi-Metal Structures (MMSs) combine distinct properties of multiple materials, benefiting from improved properties and providing superior designs. Additive Manufacturing (AM) exhibits enormous advantages in applying different materials and geometries according to the desired functions at specific locations of the structure, having great potential in fabricating multi-materials structures. However, current AM techniques have difficulty manufacturing 3D MMSs without material cross-contamination flexibly and reliably. This study demonstrates a reliable, fast, and flexible direct ink writing method to fabricate 3D MMSs. The in-situ material-switching system enables the deposition of multiple metallic materials across different layers and within the same layer. 3D Fe–Cu MMSs with complex geometries and fine details are fabricated as proof of concept. The microstructures, chemical and phase compositions, and tensile fracture surfaces of the Fe–Cu interfaces indicate a well-bonded interface without cracks, delamination, or material cross-contamination. We envision this novel method making other metallic combinations and even metal-ceramic components. It paves the way for manufacturing 3D MMSs using AM and establishes the possibilities of numerous MMSs applications in engineering fields.

Both thermochromic and photochromic coating have attracted many attentions due to their widely applications, but the low stability is a big obstacle. Inspired by the lotus leaf, to endow the chromic coating with superhydrophobicity is a possible solution. In this research, a dual response coating was prepared by adding photochromic and thermochromic particles simultaneously. The prepared sample demonstrated at least four-state color switching, which can be successfully used in tactile imaging, multi-color fabric, erasable record, and security labels. The superhydrophobicity was achieved by introducing vinyl-terminated polydimethylsiloxane, which not only offers low surface energy but also can cross-link with the particles to increase the adhesion. Thus, the prepared sample maintained superhydrophobicity after various kinds of destruction (such as sandpaper abrasion, corrosive liquid attack, ultrasonic treatment, UV irradiation, and high-speed drops/turbulent jets impact). Even though the superhydrophobicity can be destroyed by plasma etching, it can be recovered after 12 h at room temperature.

McKibben muscles are increasingly used in many robotic applications due to their advantages of lightweight, compliant, and skeletal muscles-like behaviours. However, there are still huge challenges in the motion control of McKibben muscles due to the system nonlinearity (e.g., hysteresis) and model uncertainties. To investigate the control issues, a soft artificial arm actuated by an antagonistic pair of McKibben muscles, mimicking the biological structure of skeleton-muscle systems, is developed. Inspired by the biological motor control capability that humans can control and coordinate a group of muscles to achieve complex motions, a cerebellum-like controller based on Spiking Neural Networks (SNNs) is employed for the motion control of the developed artificial arm. Benefit from the employment of the SNN-based cerebellar model, the proposed control scheme provides online adaptive learning capability, good computational efficiency, fast response, and strong robustness. Finally, several simulations and experiments are conducted subject to different environmental disturbances. Both simulation and experimental results verify that the proposed method can achieve good tracking performance, adaptability, and strong robustness.

Developing high-performance composite materials is of great significance as a strong support for high-end manufacturing. However, the design and optimization of composite materials lack a theoretical basis and guidance scheme. Compared with traditional composite materials, natural materials are composed of relatively limited components but exhibit better mechanical properties through ingenious and reasonable synthetic strategies. Based on this, learning from nature is considered to be an effective way to break through the bottleneck of composite design and preparation. In this review, the recent progress of natural composites with excellent properties is presented. Multiple factors, including structures, components and interfaces, are first summarized to reveal the strategies of natural materials to achieve outstanding mechanical properties. In addition, the manufacturing technologies and engineering applications of bioinspired composite materials are introduced. Finally, some scientific challenges and outlooks are also proposed to promote next-generation bioinspired composite materials.

Inspired by the simple yet amazing morphology of the Octopus, we propose the design, fabrication, and characterization of multi-material bio-inspired soft Octopus robot (Octobot). 3D printed molds for tentacles and head were used. The tentacles of the Octobot were casted using Ecoflex-0030 while head was fabricated using relatively flexible material, i.e., OOMOO-25. The head is attached to the functionally responsive tentacles (each tentacle is of 79.12 mm length and 7 void space diameter), whereas Shape Memory Alloy (SMA) muscle wires of 0.5 mm thickness are used in Octobot tentacles for dual thrust generation and actuation of Octobot. The tentacles were separated in two groups and were synchronously actuated. Each tentacle of the developed Octobot contains a pair of SMA muscles (SMA-α and SMA-β). SMA-α muscles being the main actuator, was powered by 9 V, 350 mA power supply, whereas SMA-β was used to provide back thrust and thus helps to increase the actuation frequency. Simulation work of the proposed model was performed in the SolidWorks environment to verify the vertical velocity using the octopus tentacle actuation. The design morphology of Octobot was optimized using simulation and TRACKER software by analyzing the experimental data of angle, displacement, and velocity of real octopus. The as-developed Octobot can swim at variable frequencies (0.5–2 Hz) with the average speed of 25 mm/s (0.5 BLS). Therefore, the proposed soft Octopus robot showed an excellent capability of mimicking the gait pattern of its natural counterpart.

With the fast development of Internet of Things, flexible and extensible sensors have undergone a great revolution. Because of the limited functions of traditional flexible sensors, more and more researchers begin to develop biomimetic sensors inspired by nature, which introduce unique structures of various natural creatures into sensors through a simple and low-cost process, endowing them with excellent comprehensive properties. By imitating structures, compositions, biological mechanisms of natural organisms, these flaws can be overcome, making sensors have a variety of functions, such as hydrophobicity, discoloration and so on. In this paper, biomimetic objects used in sensors are summarized from three perspectives, plants (lotus leaves), animals (butterfly wings) and components (enzymes). And then, the common preparation methods of biomimetic materials are described in detail, such as template method, hydrothermal method, lithography. Furthermore, the current applications of biomimetic sensors in wearable fields like electronic skin, human health detection and human motion detection, are also generalized. Finally, the difficulties and limitations of sensors, efforts to improve properties of materials, as well as likely future developments were discussed. Hence, it is highly promising to provide readers with a quick glimpse into the research landscape of this field.

Once working at heights is dangerous, it is a significant accident. These accidents brought substantial economic losses and caused a large number of casualties. Therefore, it is essential to use wall-climbing robots to replace manual work at heights. The design of the wall-climbing robot is inspired by the climbing action of insects or animals. An intelligent bionic robot device can carry special equipment to operate on the wall and perform some dangerous operations instead of firefighters or inspection personnel more efficiently. The scope of application is vast. This paper firstly summarizes the research progress of wall-climbing robots with three different moving methods: wheel-climbing, crawler-based, and leg-footed robots; summarizes the applications and breakthroughs of four adsorption technologies: negative pressure, magnetic force, bionic and electrostatic; discusses the application of motion control algorithms in wall-climbing robots. Secondly, the advantages and disadvantages of different migration modes and adsorption methods are pointed out. The distribution and advantages of the combined application of different migration modes and adsorption methods are analyzed. In addition, the future development trend of wall-climbing robots and the promoting effect of bionic technology development on wall-climbing robots are proposed. The content of this paper will provide helpful guidance for the research of wall-climbing robots.

Water-lubricated bearing has become the development trend in the future because of its economy and environmental friendliness. The poor friction performance under low speed and heavy load seriously limits the popularization and application of water-lubricated bearings. Learning from nature, the phenomenon of low friction and wear in nature has aroused great interest of scientists, and a lot of research has been carried out from mechanism analysis to bionic application. In this review, our purpose is to provide guiding methods and analysis basis for the bionic design and theoretical research of anti-friction and anti-wear of water-lubricated bearings. The development of water-lubricated bearing materials are described. Some typical examples of natural friction reduction and drag reduction are introduced in detail, and several representative preparation methods are listed. Finally, the application status of bionic tribology in water-lubricated bearings is summarized, and the future development direction of water-lubricated bearings is prospected.

Over the past 5 years, many works have been performed to reveal the potentials of Zinc (Zn)-based materials as temporary bone scaffolds with the expectation that their emergence could address some of the main concerns associated with magnesium- and iron-based materials. Thanks to the emerging Additive Manufacturing (AM) technology, it facilitates the optimization of the design and production of topological porous Zn-based materials suited for bone scaffolds. Since the studies on the porous Zn-based scaffolds are on the rise, we provide the most current progress in the development of porous Zn-based scaffolds for bone applications. The impacts of recently developed topological design from the AM as well as the advanced dynamic-flow corrosion on their corrosion, mechanical properties, and in vitro biocompatibility are also presented. Plus, we identify a number of research gaps and the challenges encountered in adopting porous Zn-based scaffolds for orthopedic applications and suggest some promising areas for future research.

Eclosion is a rapid process of morphological changes in insects, especially for the wings of butterflies. The orange oakleaf butterfly (Kallima inachus) transits from pupae to adults with a 9.3 fold instant increase in the surface area of their wings. To explore the mechanism for the rapid morphological changes in butterfly wings, we analyzed changes in microstructures in the wings of K. inachus. We found that there were lots of micron-sized foldable units in the wings at the pupal stage. The foldable units could provide as much as 31.35 times of increase in wing surface area. During eclosion, foldable units were flattened sequentially and resulted in a rapid increase in wing surface areas. The unfolding process was regulated by the structures and layouts of wing veins. Based on our observation, foldable units play important roles in both deformation and stretching of wings. The foldable units of microstructures may provide mimics for simulating entities of large-deformational bionic structures with practical application.

Recently, researchers have concentrated on studying ionic polymer metal composite (IPMC) artificial muscle, which has numerous advantages including a relatively large strain under low input voltage, flexibility, high response, low noise, light weight, and high driving energy density. This paper reports recent developments in IPMC artificial muscle, including improvement methods, modeling, and applications. Different types of IPMCs are described, along with various methods for overcoming some shortcomings, including improvement of Nafion matrix membranes, surface preparation of Nafion membranes, the choice of high-performing electrodes, and new electro-active polymers for enhancing the properties of IPMCs. IPMC models are also reviewed, providing theoretical guidance for studying the performance and applications of IPMCs. Successful applications such as bio-inspired robots, opto-mechatronic systems, and medical engineering are discussed.

This paper presents an efficient and versatile OpenFOAM (Open-source Field Operation And Manipulation)-based numerical solver for fully resolved simulations that can handle any rigid and deforming bodies moving in the fluid. The algorithm used for solving Fluid–Structure Interactions (FSI) involving the immersed structure with changeable shapes is based on the momentum redistribution method. The present approach excludes the need to solve elastic equations, obtain high-accuracy predictions of the flow field and provide a rigorous basis for implementing the Immersed Boundary Method (IBM). The OpenFOAM implementation of the algorithm is discussed along with the design methodology for developing bio-inspired underwater vehicles using the present solver. The computational results are validated with the experimental observations of the two-dimensional and three-dimensional anguilliform swimmer case studies. The study further extended to the three-dimensional hydrodynamics of a bioinspired, self-propelling manta bot. The motion of the body is specified a priori according to the reported experimental observations. The results quantify the vortex formation and shedding processes and enable the identification of the portions of the body responsible for the majority of thrust. The body accelerates from rest to an asymptotic mean forward velocity of 0.2 ms?1 in almost 5 s, consistent with experimental observations. It is observed that the developed computational model is capable of performing any motion simulation and manoeuvrability analysis, which are critical for the designers to develop novel unmanned underwater vehicles.

Dragonflies have naturally high flying ability and flight maneuverability, making them more adaptable to harsh ecological environments. In this paper, a flapping wing bionic air vehicle with three-degrees-of-freedom is designed and manufactured by simulating the flight mode of dragonfly. Firstly, the body structure of dragonfly was analyzed, and then the design scheme of flapping wing micro air vehicle was proposed based on the flight motion characteristics and musculoskeletal system of dragonfly. By optimizing the configuration and using Adams to do kinematic simulation, it is shown that the designed structure can make the wings move in an “8” shape trajectory, and the motion in three directions can maintain good consistency, with good dynamic performance. Based on CFD simulation method, we analyzed that the wing has the conditions to achieve flight with good aerodynamic performance at the incoming flow speed of 5 m s?1 and frequency of 4 Hz, and studied the effects of angle of attack and flutter frequency on the aerodynamic performance of the aircraft. Finally, the force measurement test of the aircraft prototype is carried out using a force balance and a small wind tunnel. The test results show that the prototype can provide the average lift of 3.62 N and the average thrust of 2.54 N, which are in good agreement with the simulation results.

For centuries, researchers have been fascinated by how simple-minded arthropods pick up definite cues and locate a potential target in an instant. Contrary to the active echolocation of classical creatures, arthropods exhibit passive characteristics. They use spatially separated sensilla to cooperatively pinpoint target-generated signal sources such as sound, light, ground vibration, air disturbance, and thermal radiation. The paper introduces the localization mechanisms of typical terrestrial arthropods with diverse survival habits. Focusing on these special mechanisms, a series of theoretical models and advanced bionic equipment have been reviewed, and some key challenges and future directions are proposed. We believe that intensive study on arthropods can promote innovative development of miniaturized, low power-dissipation, and high-performance localization equipment, thereby enhancing and expanding current localization techniques.

The Salp Swarm Algorithm (SSA) may have trouble in dropping into stagnation as a kind of swarm intelligence method. This paper developed an adaptive barebones salp swarm algorithm with quasi-oppositional-based learning to compensate for the above weakness called QBSSA. In the proposed QBSSA, an adaptive barebones strategy can help to reach both accurate convergence speed and high solution quality; quasi-oppositional-based learning can make the population away from traping into local optimal and expand the search space. To estimate the performance of the presented method, a series of tests are performed. Firstly, CEC 2017 benchmark test suit is used to test the ability to solve the high dimensional and multimodal problems; then, based on QBSSA, an improved Kernel Extreme Learning Machine (KELM) model, named QBSSA–KELM, is built to handle medical disease diagnosis problems. All the test results and discussions state clearly that the QBSSA is superior to and very competitive to all the compared algorithms on both convergence speed and solutions accuracy.

Wingtip slots, where the outer primary feathers of birds split and spread vertically, are regarded as an evolved favorable feature that could eff ectively improve their aerodynamic performance. They have inspired many to perform experiments and simulations as well as to relate their results to aircraft design. This paper aims to provide guidance for the research on the aerodynamic mechanism of wingtip slots. Following a review of previous wingtip slot research, four imperfections are put forward: vacancies in research content, inconsistencies in research conclusions, limitations of early research methods, and shortage of the aerodynamic mechanism analysis. On this basis, further explorations and expansion of the infl uence factors for steady state are needed; more attention should be poured into the application of fl ow fi eld integration method to decompose drag, and evaluation of variation in induced drag seems a more rational choice. Geometric and kinematic parameters of wingtip slot structure in the unsteady state, as well as the fl exibility of wingtips, should be taken into account. As for the aerodynamic mechanism of wingtip slots, the emphasis can be placed on the study of the formation, development, and evolution of wingtip vortices on slotted wings. Besides, some research strategies and feasibility analyses are proposed for each part of the research.

Energy consumption and acoustic noise can be signifi cantly reduced through perching in the sustained fl ights of small Unmanned Aerial Vehicles (UAVs). However, the existing fl ying perching robots lack good adaptability or loading capacity in unstructured environments. Aiming at solving these problems, a deformable UAV perching mechanism with strong adaptability and high loading capacity, which is inspired by the structure and movements of birds' feet, is presented in this paper. Three elastic toes, an inverted crank slider mechanism used to realize the opening and closing movements, and a gear mechanism used to deform between two confi gurations are included in this mechanism. With experiments on its performance towards diff erent objects, Results show that it can perch on various objects reliably, and its payload is more than 15 times its weight. By integrating it with a quadcopter, it can perch on diff erent types of targets in outdoor environments, such as tree branches, cables, eaves, and spherical lamps. In addition, the energy consumption of the UAV perching system when perching on objects can be reduced to 0.015 times that of hovering.