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Journal of Bionic Engineering

ISSN 1672-6529

CN 22-1355/TB

Editor-in-Chief : Luquan Ren Published by Science Press and Springer

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10 March 2023, Volume 20 Issue 2
Previous Issue   

Optimal Variable Stiffness Control and Its Applications in Bionic Robotic Joints: A Review

Yuanxi Sun, Yuntao Tang, Jia Zheng, Dianbiao Dong & Long Bai
Journal of Bionic Engineering. 2023, 20 (2):  417-435.  DOI: 10.1007/s42235-022-00278-x
Abstract ( 188 )  
Variable Stiffness Actuation (VSA) is an efficient, safe, and robust actuation technology for bionic robotic joints that have emerged in recent decades. By introducing a variable stiffness elastomer in the actuation system, the mechanical-electric energy conversion between the motor and the load could be adjusted on-demand, thereby improving the performance of the actuator, such as the peak power reduction, energy saving, bionic actuation, etc. At present, the VSA technology has achieved fruitful research results in designing the actuator mechanism and the stiffness adjustment servo, which has been widely applied in articulated robots, exoskeletons, prostheses, etc. However, how to optimally control the stiffness of VSAs in different application scenarios for better actuator performance is still challenging, where there is still a lack of unified cognition and viewpoints. Therefore, from the perspective of optimal VSA performance, this paper first introduces some typical structural design and servo control techniques of common VSAs and then explains the methods and applications of the Optimal Variable Stiffness Control (OVSC) approaches by theoretically introducing different types of OVSC mathematical models and summarizing OVSC methods with varying optimization goals and application scenarios or cases. In addition, the current research challenges of OVSC methods and possible innovative insights are also presented and discussed in-depth to facilitate the future development of VSA control.
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Systematic Review on Wearable Lower Extremity Robotic Exoskeletons for Assisted Locomotion

Shuang Qiu, Zhongcai Pei, Chen Wang & Zhiyong Tang
Journal of Bionic Engineering. 2023, 20 (2):  436-469.  DOI: 10.1007/s42235-022-00289-8
Abstract ( 133 )  
Lower extremity robotic exoskeletons (LEEX) can not only improve the ability of the human body but also provide healing treatment for people with lower extremity dysfunction. There are a wide range of application needs and development prospects in the military, industry, medical treatment, consumption and other fields, which has aroused widespread concern in society. This paper attempts to review LEEX technical development. First, the history of LEEX is briefly traced. Second, based on existing research, LEEX is classified according to auxiliary body parts, structural forms, functions and fields, and typical LEEX prototypes and products are introduced. Then, the latest key technologies are analyzed and summarized, and the research contents, such as bionic structure and driving characteristics, human–robot interaction (HRI) and intent-awareness, intelligent control strategy, and evaluation method of power-assisted walking efficiency, are described in detail. Finally, existing LEEX problems and challenges are analyzed, a future development trend is proposed, and a multidisciplinary development direction of the key technology is provided.
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Progress on Medical Implant: A Review and Prospects

Ankur Pandey & Swagatadeb Sahoo
Journal of Bionic Engineering. 2023, 20 (2):  470-494.  DOI: 10.1007/s42235-022-00284-z
Abstract ( 108 )  
Medical implant from different materials such as metals, ceramics, polymers and composites have gained a lot of research attraction due to wide applications in medical industry for treatment, surgical operations and preparing artificial body parts. In this work, we highlight a comprehensive review of medical implant mechanism, various types of implant materials, factors affecting the performance of implant and different characterization techniques. This review provides an overall summary of the state-of-the-art progress on various interesting and promising material-based medical implant. Finally, few new prospects are explained from the established theoretical and experimental results for real-life applications. This study is expected to promote extended interest of scientists and engineers in recent trend of modern biomaterials based medical implant.
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The Novel Variable Stiffness Composite Systems with Characteristics of Repeatable High Load Bearing and Response Rate

Zhiwei Tuo, Zhaohua Lin, Qian Zhao, Yunhong Liang, Han Wu, Chang Liu & ZhiWu Han
Journal of Bionic Engineering. 2023, 20 (2):  495.  DOI: 10.1007/s42235-022-00281-2
Abstract ( 126 )  
On the base of controllable variable stiffness property, variable stiffness composites were the main components of functional materials in aerospace. However, the relatively low mechanical strength, stiffness range, and response rate restricted the application of variable stiffness composite. In this work, the novel variable stiffness composite system with characteristics of repeatable high load bearing and response rate was successfully prepared via the double-layer anisotropic structure to solve the bottlenecks of variable stiffness composites. The novel variable stiffness composite systems were composed of variable stiffness layer of polycaprolactone (PCL) and the driven layer of silicone elastomer with alcohol, which continuously changed Young’s modulus from 0.1 to 7.263 MPa (72.63 times variation) in 200 s and maintained maximum weight of 11.52 times its own weight (8.5 g). Attributed to the relatively high variable stiffness range and load bearing value of variable stiffness composite system, the repeatable response process led to the efficient high load driven as “muscle” and diversified precise grab of objects with different shapes as “gripper”, owning widespread application prospects in the field of bionics.
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A Programmable Inchworm-Inspired Soft Robot Powered by a Rotating Magnetic Field

Honglin Shen, Shuxiang Cai, Zhen Wang, Zheng Yuan, Haibo Yu & Wenguang Yang
Journal of Bionic Engineering. 2023, 20 (2):  506-514.  DOI: 10.1007/s42235-022-00296-9
Abstract ( 206 )  
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.
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Design and Experimental Validation of a Worm-Like Tensegrity Robot for In-Pipe Locomotion

Xiaolin Dai, Yixiang Liu, Wei Wang, Rui Song, Yibin Li & Jie Zhao
Journal of Bionic Engineering. 2023, 20 (2):  515-529.  DOI: 10.1007/s42235-022-00301-1
Abstract ( 171 )  
Traditional rigid-body in-pipe robots usually have complex and heavy structures with limited flexibility and adaptability. Although soft in-pipe robots have great improvements in flexibility, they still have manufacturing difficulties due to their reliance on high-performance soft materials. Tensegrity structure is a kind of self-stressed spatial structure consisting discrete rigid struts connected by a continuous net of tensional flexible strings, which combines the advantages of both rigid structures and soft structures. By applying tensegrity structures into robotics, this paper proposes a novel worm-like tensegrity robot for moving inside pipes. First, a robot module capable of body deformation is designed based on the concept of tensegrity and its deformation performance is analyzed. Then, the optimal parameters of the module are obtained based on the tensegrity form-finding. The deformation ability of the tensegrity module is tested experimentally. Finally, the worm-like tensegrity robot that can crawl inside pipes is developed by connecting three modules in series. Motion performance and load capacity are tested on the prototype of the worm-like tensegrity robot by experiments of moving in horizontal pipe, vertical pipe, and elbow pipe. Experimental results demonstrate the effectiveness of the proposed design and suggest that the robot has high compliance, mobility, and adaptability although with simple structure and low cost.
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Design of an Active Flexible Spine for Wall Climbing Robot Using Pneumatic Soft Actuators

Guangming Chen, Tao Lin, Gabriel Lodewijks & Aihong Ji
Journal of Bionic Engineering. 2023, 20 (2):  530-542.  DOI: 10.1007/s42235-022-00273-2
Abstract ( 130 )  
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.
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Design and Realization of a Novel Hybrid-Drive Robotic Fish for Aquaculture Water Quality Monitoring

Yiting Ji, Yaoguang Wei, Jincun Liu & Dong An
Journal of Bionic Engineering. 2023, 20 (2):  543-557.  DOI: 10.1007/s42235-022-00282-1
Abstract ( 162 )  
Thunniform swimmers (tuna) have a swinging narrow sequence stalk and a moon-shaped tail fin, which performs poorly at slow speed, higher acceleration and turning maneuverability. In most cases, faster speed and higher maneuverability are mutually rejection for most marine creatures and their robotic opponents. This paper presents a novel hybrid tuna-like swimming robot for aquaculture water quality monitoring, which interleaves faster speed and higher maneuverability. The robotic prototype emphasizes on streamlining and enhanced maneuverability mechanism designs in conjunction with a narrow caudal propeller to the tail. The innovative design endows the robot to easily execute the multi-mode swimming gait, including forward swimming, turning, diving/surfacing. The capabilities of our robot are validated through a series of indoor swimming pool and field breeding ponds. The robotic fish can achieve a maximum speed up to about 1.16 m/s and a minimum turning radius less than 0.46 Body Lengths (BL) and its maximum turning speed can reach 78.6 °°/s. Due to its high speed, maneuverability and relatively small size, the robotic fish shed light on intelligent monitoring in complex aquatic environments.
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CPG Modulates the Omnidirectional Motion of a Hexapod Robot in Unstructured Terrain

Wei Zhang, Qingshuo Gong, Haoyu Yang & Yejing Tang
Journal of Bionic Engineering. 2023, 20 (2):  558-567.  DOI: 10.1007/s42235-022-00290-1
Abstract ( 142 )  
Freely shuttling in complex terrain is a basic skill of multi-legged animals. To make the hexapod robot have omnidirectional motion ability by controlling only one parameter, this paper uses the motion control method based on Central Pattern Generator (CPG), maps the output signal of CPG to the foot end trajectory space of the hexapod robot, and proposes an omnidirectional gait controller strategy. In addition, to enable the hexapod robot to adapt to unstructured terrain, an adaptive method based on Dynamic Threshold (DT) is proposed to enable the hexapod robot move in all directions without changing the heading angle in unstructured terrain. Finally, the feasibility of the proposed method is verified by virtual simulation and hexapod robot prototype experiment. Results show that the hexapod robot can omnidirectional motion without changing the heading angle and has good stability in unstructured terrain.
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A Hybrid Territorial Aquatic Bionic Soft Robot with Controllable Transition Capability

Qingzhong Li, Fukang Zhang, Zeying Jing, Fujie Yu & Yuan Chen
Journal of Bionic Engineering. 2023, 20 (2):  568-583.  DOI: 10.1007/s42235-022-00294-x
Abstract ( 166 )  
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.
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Study on Control Technology of Tendon Bionic Driving Robot System

Ke Xu, Wenzhuo Li, Chenghao Ji & Bing Liu
Journal of Bionic Engineering. 2023, 20 (2):  584-597.  DOI: 10.1007/s42235-022-00283-0
Abstract ( 158 )  
Although traditional position-controlled industrial robots can be competent for most assembly tasks, they cannot complete complex tasks that frequently interact with the external environment. The current research on exoskeleton robots also has problems such as excessive inertia of exoskeleton robots, poor system integration and difficult human–computer interaction control. To solve these problems, this paper independently develops a tendon driving robotic system composed of a tendon driving robotic arm and an upper limb exoskeleton, and studies its control technology. First, the robot system is selected, configured, and constructed. Second, the kinematics of the robot is analyzed, and then the dynamics are studied, and the parameter identification experiment of single degree of freedom is completed. Finally, the research on zero-force control and impedance control of the robot has effectively improved the robot’s human–machine integration ability, ensured the flexibility and compliance in the process of human–computer interaction. The compliant control problem expands the usage scenarios and application scope of robots and contributes to the realization of complex operations of this group of robots in unstructured environments.
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Bionic Muscle Control with Adaptive Stiffness for Bionic Parallel Mechanism

Yaguang Zhu, Ruyue Li & Zhipeng Song
Journal of Bionic Engineering. 2023, 20 (2):  598-611.  DOI: 10.1007/s42235-022-00279-w
Abstract ( 148 )  
As the torso is critical to the coordinated movement and flexibility of vertebrates, a 6-(Degree of Freedom) DOF bionic parallel torso with noteworthy motion space was designed in our previous work. To improve the compliance of the parallel mechanism, a pair of virtual muscle models is constructed on both sides of the rotating joints of each link of the mechanism, and a bionic muscle control algorithm is introduced. By analyzing the control parameters of the muscle model, dynamic characteristics similar to those of biological muscle are obtained. An adaptive stiffness control is proposed to adaptively adjust the stiffness coefficient with the change in the external load of the parallel mechanism. The attitude closed-loop control can effectively keep the attitude angle unchanged when the position of the moving platform changes. The simulations and experiments are undertaken to validate compliant movements and the flexibility and adaptability of the parallel mechanism.
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sEMG-Based Lower Limb Motion Prediction Using CNN-LSTM with Improved PCA Optimization Algorithm

Meng Zhu, Xiaorong Guan, Zhong Li, Long He, Zheng Wang & Keshu Cai
Journal of Bionic Engineering. 2023, 20 (2):  612-627.  DOI: 10.1007/s42235-022-00280-3
Abstract ( 189 )  
In recent years, sEMG (surface electromyography) signals have been increasingly used to operate wearable devices. The development of mechanical lower limbs or exoskeletons controlled by the nervous system requires greater accuracy in recognizing lower limb activity. There is less research on devices to assist the human body in uphill movements. However, developing controllers that can accurately predict and control human upward movements in real-time requires the employment of appropriate signal pre-processing methods and prediction algorithms. For this purpose, this paper investigates the effects of various sEMG pre-processing methods and algorithms on the prediction results. This investigation involved ten subjects (five males and five females) with normal knee joints. The relevant data of the subjects were collected on a constructed ramp. To obtain feature values that reflect the gait characteristics, an improved PCA algorithm based on the kernel method is proposed for dimensionality reduction to remove redundant information. Then, a new model (CNN?+?LSTM) was proposed to predict the knee joint angle. Multiple approaches were utilized to validate the superiority of the improved PCA method and CNN-LSTM model. The feasibility of the method was verified by analyzing the gait prediction results of different subjects. Overall, the prediction time of the method was 25 ms, and the prediction error was 1.34?±?0.25 deg. By comparing with traditional machine learning methods such as BP (backpropagation) neural network, RF (random forest), and SVR (support vector machine), the improved PCA algorithm processed data performed the best in terms of convergence time and prediction accuracy in CNN-LSTM model. The experimental results demonstrate that the proposed method (improved PCA?+?CNN-LSTM) effectively recognizes lower limb activity from sEMG signals. For the same data input, the EMG signal processed using the improved PCA method performed better in terms of prediction results. This is the first step toward myoelectric control of aided exoskeleton robots using discrete decoding. The study results will lead to the future development of neuro-controlled mechanical exoskeletons that will allow troops or disabled individuals to engage in a greater variety of activities.
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The Fabrication of Gas-driven Bionic Soft Flytrap Blade and Related Feasibility Tests

Yangwei Wang, Jie Yan, Jian Li, Meizhen Huang & Zhibo Luan
Journal of Bionic Engineering. 2023, 20 (2):  628-644.  DOI: 10.1007/s42235-022-00285-y
Abstract ( 126 )  
Unlike most animals, plants fail to move bodily at will. However, movements also occur in every single part of plants out of energy and nutrients needs, spanning from milliseconds to hours on a time scale. And with the growing understanding of plant movement in the academic community, bionic soft robots based on plant movement principles are increasingly studied and are considered by scientists as a source of inspiration for innovative engineering solutions. In this paper, through the study of the biological morphology, microstructure, and motion mechanism of the flytrap, we developed chambered design rules, and designed and fabricated a gas-driven bionic flytrap blade, intending to investigate its feasibility of performing complex bending deformation. The experimental result shows that the bionic flytrap blade can achieve multi-dimensional bending deformation, and complete the bending and closing action within 2 s. The performance of the bionic flytrap blade fabricated is in high agreement with the real flytrap blade in terms of bending and deformation, achieving an excellent bionic design effect. In this study, the chambered design rules of the bionic flytrap blade were proposed and developed, and the possibility of its deformation was investigated. The effects of different chamber types and different flow channel design precepts on the bending deformation of the bionic flytrap blade were revealed, together with the relationship between the response time and flow rate of the bionic flytrap blade. At last, this study provides new ideas for the study of plant blade motion mechanism in a hope to expand the application fields of bionic robots, especially hope to offer solutions for plant-type robotics.
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Fuzzy Logic Control of a Head-movement Based Semi-autonomous Human–machine Interface

Yasir Özlük & Eda Akman Aydin
Journal of Bionic Engineering. 2023, 20 (2):  645-655.  DOI: 10.1007/s42235-022-00272-3
Abstract ( 164 )  
Quadriplegia is a neuromuscular disease that may cause varying degrees of functional loss in trunk and limbs. In such cases, head movements can be used as an alternative communication channel. In this study, a human–machine interface which is controlled by human head movements is designed and implemented. The proposed system enables users to steer the desired movement direction and to control the speed of an output device by using head movements. Head movements of the users are detected using a 6 DOF IMUs measuring three-axis accelerometer and three-axis gyroscope. The head movement axes and the Euler angles have been associated with movement direction and speed, respectively. To ensure driving safety, the speed of the system is determined by considering the speed requested by the user and the obstacle distance on the route. In this context, fuzzy logic algorithm is employed for closed-loop speed control according to distance sensors and reference speed data. A car model was used as the output device on the machine interface. However, the wireless communication between human and machine interfaces provides to adapt this system to any remote device or systems. The implemented system was tested by five subjects. Performance of the system was evaluated in terms of task completion times and feedback from the subjects about their experience with the system. Results indicate that the proposed system is easy to use; and the control capability and usage speed increase with user experience. The control speed is improved with the increase in user experience.
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Investigate the Wake Flow on Houseflies with Particle-Tracking-Velocimetry and Schlieren Photography

Yun Liu & Angel David Lozano
Journal of Bionic Engineering. 2023, 20 (2):  656-667.  DOI: 10.1007/s42235-022-00277-y
Abstract ( 130 )  
Utilizing high-speed schlieren photography and particle-tracking-velocimetry, the wake flow of tethered houseflies is investigated. The high-speed schlieren photography is implemented on tethered houseflies inside an air container with a stable vertical temperature gradient to visualize the disturbed wake flow from the insects. The resulting photography images were then processed with the physics based optical flow method to derive the light-path averaged flow velocity. Additionally, the state of the art: Shake-the-Box system is implemented on a tethered housefly to measure the volumetric flow field in the wake of the insect, revealing interesting flow behavior and structures that can also be observed and correlated to the schlieren photography images. Comparing the dimensionless velocity magnitude of the wake flow from the two experiments, a good qualitative agreement is reached, suggesting the viability of high-speed schlieren photography in investigating the wake flow of small insects. Furthermore, the high-speed schlieren photography is successfully applied on a housefly that is taking off from the ground, visualizing the disturbed wake flow on the freely flying insect that is challenging to visualize with other methods.
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Complementary Methods to Acquire the Kinematics of Swimming Snakes: A Basis to Design Bio-inspired Robots

Elie Gautreau, Xavier Bonnet, Tom Fox, Guillaume Fosseries, Valéry Valle, Anthony Herrel & Med Amine Laribi
Journal of Bionic Engineering. 2023, 20 (2):  668-682.  DOI: 10.1007/s42235-022-00291-0
Abstract ( 105 )  
The vast diversity of morphologies, body size, and lifestyles of snakes represents an important source of information that can be used to derive bio-inspired robots through a biology-push and pull process. An understanding of the detailed kinematics of swimming snakes is a fundamental prerequisite to conceive and design bio-inspired aquatic snake robots. However, only limited information is available on the kinematics of swimming snake. Fast and accurate methods are needed to fill this knowledge gap. In the present paper, three existing methods were compared to test their capacity to characterize the kinematics of swimming snakes. (1) Marker tracking (Deftac), (2) Markerless pose estimation (DeepLabCut), and (3) Motion capture were considered. (4) We also designed and tested an automatic video processing method. All methods provided different albeit complementary data sets; they also involved different technical issues in terms of experimental conditions, snake manipulation, or processing resources. Marker tracking provided accurate data that can be used to calibrate other methods. Motion capture posed technical difficulties but can provide limited 3D data. Markerless pose estimation required deep learning (thus time) but was efficient to extract the data under various experimental conditions. Finally, automatic video processing was particularly efficient to extract a wide range of data useful for both biology and robotics but required a specific experimental setting.
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Effects of Avian Wings Color Patterns on Their Flight Performance: Experimental and Computational Studies

Ahmed Aboelezz, Brenden Herkenhoff & Mostafa Hassanalian
Journal of Bionic Engineering. 2023, 20 (2):  683-710.  DOI: 10.1007/s42235-022-00275-0
Abstract ( 139 )  
There are many theories behind the colors of a bird’s feathers. Many of these theories point to the color’s purpose to attract mates and hide from predators. Some recent investigations concluded that the dark colors of birds help in reducing the drag force during flight. A new theory is presented in the current research, which states that a bird's dark color not only reduces the drag, but the color pattern also improves the overall flight performance, and each color pattern has a different type of flight performance improvement. This difference in improvement is a result of variation in hot and cold surfaces on the bird skin as a result of the variation between light and dark feather colors. To prove this new theory, thermal images were captured of real bird wings under the effect of infrared waves. Also, a novel wind tunnel wing with the ability to adjust the temperature in desired locations and patterns on the wing’s surface was manufactured and tested to evaluate the effect of aerodynamics forces as a function in the surface temperature and the hot–cold regions. The collected data from this wing showed potential flight efficiency improvements of 20%, comparing the lift-to-drag ratio for specific heating cases, which could increase the flight range. Individually considering lift and drag, there were specific heating cases with corresponding angles of attack in which these parameters improved by up to 20% and 7%, respectively. Some heating cases could increase the lift at a low angle of attack, which is helpful in cruise flight performance, while some cases could increase the maximum lift coefficient by 6%. This is very helpful in lowering stall and the minimum flight speeds. Furthermore, some cases could increase the lift-to-drag ratio, which led to an increase in the flight range. To better understand the effect of the various patterns, computational fluid dynamics (CFD) simulations were conducted on the wing. The new theory was proved based on the CFD results and verified through the successful results from the wind tunnel experiments.
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Wing Modulation and Aerodynamics of Hoverflies in Gust Perturbations

Yanlai Zhang, Mancang Gu & Jianghao Wu
Journal of Bionic Engineering. 2023, 20 (2):  711-721.  DOI: 10.1007/s42235-022-00274-1
Abstract ( 122 )  
Flapping-Wing Micro-Air Vehicles are likely to suffer from airflow perturbations. They can mimic the wing modulation of insects in airflow perturbations. However, our knowledge of wing modulation of insects to airflow perturbations remains limited. Here, we subjected hoverflies to headwind and lateral gust perturbations and filmed their wing motions. Then, computational fluid dynamics was employed to estimate the effects of hoverflies’ wing kinematic modulations. We also clipped off the antennae of hoverflies to test whether the wing kinematic modulations were different. Results show that hoverflies increase the mean positional angle and modulate the deviation angle to make the wing tip paths of upstroke and downstroke close to compensate for the pitch moment perturbations in the headwind gust. Hoverflies employ asymmetric responses in positional angle in the lateral gust. The stroke amplitude of the left (right) wing increases (decreases) and the mean positional angle of the left (right) wing decreases (increases) during the right lateral gust. Antennae have little effect on the wing kinematic modulations in the lateral gust. These asymmetric responses produce a roll moment, tilting the body to resist the side force generated by the gust. This is a typical helicopter model employed by hoverflies to alleviate the gust. These results provide insight into the remarkable capacity of hoverflies to contend with gusts and can also inspire the design of flapping-wing micro-air vehicles.
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Heat Transfer Characteristics of the Microfluidic Biomimetic Chameleon Skin with Active Thermal Camouflage

Lujia Li, Huanhuan Li, Jian Cao & Songjing Li
Journal of Bionic Engineering. 2023, 20 (2):  722-733.  DOI: 10.1007/s42235-022-00286-x
Abstract ( 147 )  
Natural organisms have different techniques to avoid enemies, such as chameleon skin with innate camouflage ability to change with the surrounding environment. Inspired by this, a microfluidic biomimetic chameleon skin based on infrared (IR) information processing is proposed for active thermal camouflage in a dynamic infrared background. Microfluidic circulation in microcavities distributed under the skin is controlled by a thermal camouflage system. The structure and working principle of the biomimetic skin are introduced, and the thermal camouflage system is established and tested to explore the heat transfer characteristics between the skin and the fluid. The mechanism of collecting the background infrared information and regulating the skin temperature through the control signal generated by the infrared information processing system is illustrated. Furthermore, the dynamic thermal response of the skin is tested when transitioning between different temperature backgrounds, modeling the ambient temperature of the sand, woodland and lakes where chameleons live. The performance of the skin is evaluated by measuring the camouflage responding time of the skin to an external heat source. The results show that the chameleon biomimetic skin is naturally transitioned and matched by infrared information processing and microfluidics. The limitation that the conventional thermal camouflage technology cannot adapt to the dynamic combat environment is overcome and the weaknesses of a small camouflage band range and a single form of camouflage are resolved in this study, thus effectively improving the target’s survivability in combat.
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Evaporation Characteristics and Morphological Evolutions of Fuel Droplets After Hitting Different Wettability Surfaces

Yanling Chen, Liang Guo, Ningning Cai, Wanchen Sun, Yuying Yan, Degang Li, Han Wang & Rong Xuan
Journal of Bionic Engineering. 2023, 20 (2):  734-747.  DOI: 10.1007/s42235-022-00293-y
Abstract ( 124 )  
To solve the wall-wetting problem in internal combustion engines, the physical and chemical etching methods are used to prepare different wettability surfaces with various microstructures. The evaporation characteristics and morphological evolution processes of diesel and n-butanol droplets after hitting the various surfaces are investigated. The results show that the surface microstructures increase the surface roughness (Ra), enhancing the oleophilic property of the oleophilic surfaces. Compared with n-butanol droplets, the same surface shows stronger oleophobicity to diesel droplets. When a droplet hits an oleophilic property surface with a lower temperature, the stronger the oleophilicity, the shorter the evaporation time. For oleophilic surfaces, larger Ra leads to a higher Leidenfrost temperature (TLeid?Leid). The low TLeid?Leid caused by enhanced oleophobicity, dense microstructures and increased convex dome height facilitates droplet rebound and promotes the evaporation of the wall-impinging droplets into the cylinder. The evaporation rate of the droplets is not only related to the characteristics of the solid surfaces and the fuel droplets but also affected by the heat transfer rate to the droplets in different boiling regimes. The spreading diameter of a droplet on an oleophobic surface varies significantly less with time than that on an oleophilic surface under the same surface temperature.
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Hydrothermal Desulfurization on Porous Sulfonated CFR-PEEK Surface Structure Used for Implant Application

Jingdan Li, Wen Qin, Patrick Osei Lartey, Yulong Fu & Jing Ma
Journal of Bionic Engineering. 2023, 20 (2):  748-761.  DOI: 10.1007/s42235-022-00276-z
Abstract ( 121 )  
The poor wear resistance and bio-inertness surface of polyetheretherketone (PEEK) limits the implant applications of PEEK and its composites. Carbon fiber (CFR) was used to boost the wear resistance of PEEK; however, the bioactivity of carbon fiber-reinforced polyetheretherketone (CFR-PEEK) composites is even worse. The bioactivity of CFR-PEEK can be enhanced by constructing 3D porous structure. Nevertheless, large number of sulfur component introduced by sulfonation shows cytotoxicity and can cause damage to human cells. Besides, the sulfur component affects the cytotoxicity and bioactivity of sulfonated CFR-PEEK (SCFR-PEEK). Hydrothermal treatment can sweep away the sulfur component in the 3D porous structure of SCFR-PEEK. Meanwhile, the changes in crystallinity and hardness after hydrothermal treatment may also affect the wear resistance. Therefore, the effect of hydrothermal temperature on wear resistance, cytotoxicity and bioactivity of SCFR-PEEK were studied. In this work, the samples with hydrothermal temperature 90–120 ℃ exhibited high wear resistance. The 3D pore structure of SCFR-PEEK unchanged after hydrothermal treatment, and the sulfur component in the 3D pore structure gradually decreased with increasing hydrothermal temperature by SEM images and EDS analysis. In addition, SCFR-PEEK treated in 90–120 ℃. Exhibited low cytotoxicity and high bioactivity, which is beneficial for the implant materials.
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Identification of Pulmonary Hypertension Animal Models Using a New Evolutionary Machine Learning Framework Based on Blood Routine Indicators

Jiao Hu, Shushu Lv, Tao Zhou, Huiling Chen, Lei Xiao, Xiaoying Huang, Liangxing Wang & Peiliang Wu
Journal of Bionic Engineering. 2023, 20 (2):  762-781.  DOI: 10.1007/s42235-022-00292-z
Abstract ( 123 )  
Pulmonary Hypertension (PH) is a global health problem that affects about 1% of the global population. Animal models of PH play a vital role in unraveling the pathophysiological mechanisms of the disease. The present study proposes a Kernel Extreme Learning Machine (KELM) model based on an improved Whale Optimization Algorithm (WOA) for predicting PH mouse models. The experimental results showed that the selected blood indicators, including Haemoglobin (HGB), Hematocrit (HCT), Mean, Platelet Volume (MPV), Platelet distribution width (PDW), and Platelet–Large Cell Ratio (P-LCR), were essential for identifying PH mouse models using the feature selection method proposed in this paper. Remarkably, the method achieved 100.0% accuracy and 100.0% specificity in classification, demonstrating that our method has great potential to be used for evaluating and identifying mouse PH models.
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Distributed Flocking Algorithm for Multi-UAV System Based on Behavior Method and Topological Communication

Yifei Feng, Jingshi Dong, Jianlin Wang & Hang Zhu
Journal of Bionic Engineering. 2023, 20 (2):  782-796.  DOI: 10.1007/s42235-022-00287-w
Abstract ( 151 )  
There are many interesting flocking phenomena in nature, such as joint predation and group migration, and the intrinsic communication patterns of flocking are essential for studying group behavior. Traditional models of communication such as the pigeon flock model and the wolf pack model define all agents within a perceptual distance as the neighborhoods, and some models have fixed communicating numbers. There is a significant impact on the quality of the flocking formation when encountering poor initial state of the flocking, multiple obstacles, or loss of certain agents. To solve this problem, this paper proposes a local communication model with nearest agents in four directions. Based on this model and behavioral method, two distributed flocking formation algorithms are designed in this paper for different scenarios, namely the flocking algorithm and the circular formation algorithm. Numerical simulation results show that the flocking can pass through the obstacle area and re-formation smoothly, and also the formation quality of the flocking is better compared with the traditional communication model.
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Boosting Whale Optimizer with Quasi-Oppositional Learning and Gaussian Barebone for Feature Selection and COVID-19 Image Segmentation

Jie Xing, Hanli Zhao, Huiling Chen, Ruoxi Deng & Lei Xiao
Journal of Bionic Engineering. 2023, 20 (2):  797-818.  DOI: 10.1007/s42235-022-00297-8
Abstract ( 140 )  
Whale optimization algorithm (WOA) tends to fall into the local optimum and fails to converge quickly in solving complex problems. To address the shortcomings, an improved WOA (QGBWOA) is proposed in this work. First, quasi-opposition-based learning is introduced to enhance the ability of WOA to search for optimal solutions. Second, a Gaussian barebone mechanism is embedded to promote diversity and expand the scope of the solution space in WOA. To verify the advantages of QGBWOA, comparison experiments between QGBWOA and its comparison peers were carried out on CEC 2014 with dimensions 10, 30, 50, and 100 and on CEC 2020 test with dimension 30. Furthermore, the performance results were tested using Wilcoxon signed-rank (WS), Friedman test, and post hoc statistical tests for statistical analysis. Convergence accuracy and speed are remarkably improved, as shown by experimental results. Finally, feature selection and multi-threshold image segmentation applications are demonstrated to validate the ability of QGBWOA to solve complex real-world problems. QGBWOA proves its superiority over compared algorithms in feature selection and multi-threshold image segmentation by performing several evaluation metrics.
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Non-dominated Sorting Advanced Butterfly Optimization Algorithm for Multi-objective Problems

Sushmita Sharma, Nima Khodadadi, Apu Kumar Saha, Farhad Soleimanian Gharehchopogh & Seyedali Mirjalili
Journal of Bionic Engineering. 2023, 20 (2):  819-843.  DOI: 10.1007/s42235-022-00288-9
Abstract ( 169 )  
This paper uses the Butterfly Optimization Algorithm (BOA) with dominated sorting and crowding distance mechanisms to solve multi-objective optimization problems. There is also an improvement to the original version of BOA to alleviate its drawbacks before extending it into a multi-objective version. Due to better coverage and a well-distributed Pareto front, non-dominant rankings are applied to the modified BOA using the crowding distance strategy. Seven benchmark functions and eight real-world problems have been used to test the performance of multi-objective non-dominated advanced BOA (MONSBOA), including unconstrained, constrained, and real-world design multiple-objective, highly nonlinear constraint problems. Various performance metrics, such as Generational Distance (GD), Inverted Generational Distance (IGD), Maximum Spread (MS), and Spacing (S), have been used for performance comparison. It is demonstrated that the new MONSBOA algorithm is better than the compared algorithms in more than 80% occasions in solving problems with a variety of linear, nonlinear, continuous, and discrete characteristics based on the Pareto front when compared quantitatively. From all the analysis, it may be concluded that the suggested MONSBOA is capable of producing high-quality Pareto fronts with very competitive results with rapid convergence.
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