Fish’s outstanding motion and coordination performance make it an excellent source of inspiration for scientists and engineers aiming to design and control next-generation autonomous underwater vehicles within the framework of bionics. This paper offers a general review of the current status of bionic robotic fish, with particular emphasis on the hydrodynamic modeling and testing, kinematic modeling and control, learning and optimization, as well as motion coordination control. Among these aspects, representative studies based on ideas and concepts inspired from fish motion and coordination are discussed. At last, the major challenges and the future research directions are addressed in the context of integration of various research streams from ichthyologic, hydrodynamic, mechanical, electronic, control, and artificial intelligence. Further development of bionic robotic fish can be utilized to execute some specific missions in complex underwater environments, where operations are unsafe or impractical for divers or conventional underwater vehicles.

A Body and/or Caudal Fin (BCF) fish modulate its body stiffness by mechanisms consisting of antagonistic muscles. The mecha-nisms can be considered as Redundant Planar Rotational Parallel Mechanisms (RPRPM) with antagonistic flexible elements. For a typical RPRPM, its stiffness consists of the adjustable stiffness resulting from internal forces and the inherent stiffness caused by inherent com-pliances of flexible elements. In order to decouple the adjustable stiffness from the inherent stiffness and expand the range of stiffness variation, a variable-stiffness decoupled mechanism based on the Mechanically Adjustable Compliance and Controllable Equilibrium Position Actuator (MACCEPA) is presented and used to construct a soft robotic fish with large stiffness variation. According to the analysis of the evolution from RPRPM to MACCEPA, it can be found that MACCEPA is just a special type of RPRPM with only an adjustable stiffness. In addition, MACCEPA existed before RPRPM mechanism. The prototype of the soft robotic fish with variable-
stiffness decoupled mechanisms is built to explore the relationships between the body stiffness and the swimming performance. It is validated experimentally that the stiffness variation multiple of the robotic fish is raised, the swimming performance of the robotic fish is improved when the stiffness is modulated to match the driving frequency.

This paper presents a new Center of Gravity (COG) trajectory planning algorithm for a quadruped robot with redundant Degrees of Freedom (DOFs). Each leg has 7 DOFs, which allow the robot to exploit its kinematic redundancy for various locomotion and manipu-lation tasks. Also, the robot can suitably adapt to different environment (e.g., passing through a narrow gap) by simply changing the body posture. However, the robot has significant COG movement during the leg swinging phase due to the heavy leg weights; the weight of all the four legs takes up 80% of the robot’s total weight. To achieve stable walking in the presence of undesired COG movements, a new COG trajectory planning algorithm was proposed by using a combined Jacobian of COG and centroid of a support polygon including a foot contact constraint. Additionally, the inverse kinematics of each leg was solved by modified improved Jacobian pseudoinverse (mIJP) algorithm. The mIJP algorithm could generate desired trajectories for the joints even when the robot’s leg is in a singular posture. Owing to these proposed methods, the robot was able to perform various modes of locomotion both in simulations and experiments with improved stability.

In the emerging area of humanoid robotics, path planning and autonomous navigation have evolved as one of the most promising area of research. This paper deals with the design and development of a novel navigational controller to guide humanoids in cluttered envi-ronments. The basic parameters of the ant colony optimization technique have been modified to have enhanced control as Adaptive Ant Colony Optimization (AACO). The controller that has been implemented in the humanoids receives sensory information about obstacle distances as inputs and provides required turning angle as output to reach the specified target position. The proposed controller has been tested in both simulated and experimental environments created under laboratory conditions, and a good agreement has been observed between the simulation and experiment results. Here, both static and dynamic path planning have been attempted. Finally, the proposed controller has also been tested against other existing techniques to validate the efficiency of the AACO in path planning
problems.

The effect of asymmetric heaving motion on the aerodynamic performance of a two-dimensional flapping foil near a wall is studied numerically. The foil executes the heaving and pitching motion simultaneously. When the heaving motion is symmetric, the mean thrust coefficient monotonically increases with the decrease in mean distance between foil and wall. Meanwhile, the mean lift coefficient first increases and then decreases sharply. In addition, the negative mean lift coefficient appears when the foil is very close to the wall. After the introduction of asymmetric heaving motion, the influence of wall effect on the force behavior becomes complicated. The mean thrust coefficient is enhanced when the duration of upstroke is reduced. Moreover, more and more enhancement can be achieved when the foil approaches the wall gradually. On the other hand, the positive mean lift coefficient can be observed when the duration of downstroke is shortened. By checking the flow patterns around the foil, it is shown that the interaction between the vortex shed from the foil and the wall can greatly modify the pressure distribution along the foil surface. The results obtained here might be utilized to optimize the kinematics of the Micro Aerial Vehicles (MAVs) flying near a solid wall.

Every year more than 5 million people worldwide become hemiplegic as a direct consequence of stroke. This neurological deficiency, often leads to a partial or a total loss of standing up abilities and /or ambulation skills. In order to propose new supporting solutions lying between the wheelchair and the walker, this paper presents a technological strategy for designing an assistive device for a biomechanical study of the Sit-To-Stand movement (STS). The control algorithms are implemented in TwinCAT runtime environment. The communi-cation between the component and the control computer is ensured via the EtherCAT fieldbus. The aim of this architecture lies in the fact that it allows a quick development of a research prototype with the same safety issues found on an industrial machine. An experimental test of the STS strategy is presented and discussed in order to evaluate the strategy.

While the leading-edge serration in owls’ wing is known to be responsible for low noise gliding and flapping flights, the findings on its aero-acoustic role have been diverse or even controversial. Here we present an experimental study of the morphological effects of leading-edge serrations on aerodynamic force production by utilizing owl-inspired, single-feather, clean and serrated wing models with different serration lengths and spacing, and by combining Particle Image Velocimetry (PIV) and force measurements. Force measurements show that an increase in the length and density of the leading-edge serrations leads to a reduction in the lift coefficient and lift-to-drag ratio at Angles of Attack (AoAs) < 15? whereas the clean and serrated wings achieve comparable aerodynamic performance at higher AoAs > 15?, which owl wings often reach in flight. Furthermore PIV visualization of the flow fluctuations demonstrates that the leading-edge serration-based mechanism is consistent in all serrated wing models in terms of passive control of the laminar-turbulent transition while at AoAs > 15? similar suction flow is present at leading edge resulting in a comparable aerodynamic performance to that of the clean wing. Our results indicate the robustness and usefulness of leading-edge serration-inspired devices for aero-acoustic control in biomimetic rotor designs.

Loss of function of large tissues is an urgent clinical problem. Although the artificial microfluidic network fabricated in large tis-sue-engineered constructs has great promise, it is still difficult to develop an efficient vessel-like design to meet the requirements of the biomimetic vascular network for tissue engineering applications. In this study, we used a facile approach to fabricate a branched and multi-level vessel-like network in a large muscle scaffolds by combining stereolithography (SL) technology and enzymatic crosslinking mechanism. The morphology of microchannel cross-sections was characterized using micro-computed tomography. The square cross-sections were gradually changed to a seamless circular microfluidic network, which is similar to the natural blood vessel. In the different micro-channels, the velocity greatly affected the attachment and spread of Human Umbilical Vein Endothelial Cell (HUVEC)-Green Fluorescent Protein (GFP). Our study demonstrated that the branched and multi-level microchannel network simulates biomimetic microenvironments to promote endothelialization. The gelatin scaffolds in the circular vessel-like networks will likely support myoblast and surrounding tissue for clinical use.

The physical environment plays a critical role in modulating stem cell differentiation into specific lineages. In this study, we designed and synthesized a series of low-molecular-weight gels (LMWGs) with different moduli based on phenylboronic acid derivatives. The moduli of the LMWGs were readily tuned by varying the alkyl chain without any chemical crosslinker. The cell responses to the gels were evaluated with mesenchymal stem cell (MSCs), in respect of cell morphology, proliferation and differentiation. The prepared gels were non-toxic to MSCs, suggesting good biocompatibility. The hydrogel stiffness exerted a striking modulation effect on MSC fate decisions, where MSCs were inclined to differentiate into osteoblasts in stiff LMWGs and into chondrocytes in soft LMWGs. The pivotal elastic modulus of the LMWGs to drive MSC differentiation into osteoblastic lineage and chondrocytic lineage were approximately
20 kPa – 40 kPa and 1 kPa – 10 kPa, respectively. Overall, our results demonstrated that the modification of hydrogel stiffness via tuning the alkyl chain was a simple but effective approach to regulate MSC differentiation into specific lineage, which might have important implications in the design of LMWGs for tissue engineering applications.

Long-term loosening is the major cause of failure of arthroplasty. One of the major causes is stress shielding, initiated by the large stiffness difference between prosthesis and bone tissue. Therefore, prosthesis with reduced stiffness properties to match those of the bone tissue may be able to minimize such a problem. Design with porous structure is believed to reduce the stiffness of the prosthesis, however at the cost of decreased strength. In this study, a patient-specific bone-implant finite element model was developed for contact mechanics study of hip joint, and algorithms were developed to adjust the elastic modulus of elements in certain regions of the femoral stem, until optimal properties were achieved according to the pre-defined criterions of the strength and stability of the system. The global safety factor of the optimized femoral stem was 11.3, and 26.4% of elements were designed as solid. The bone volume with density loss was reduced by 40% compared to the solid stem. The methodology developed in this study provides a universal method to design a patient-specific prosthesis with a gradient modulus distribution for the purposes of minimizing the stress shielding effect and extending the lifespan of the implant.

The tribological behavior of the CoCr28Mo/CoCr28Mo pair was studied using pin-on-disc tribometer. Four bio-lubricants were re-tained including pure sesame oil, nigella oil, physiological solution (0.9% NaCl) and Hyalgan®. Hyalgan® is a sodium hyaluronate
(20 mg/2 mL) pharmaceutical intra-articular injection used, in this study, as a reference. The Coefficient of Friction (CoF) and wear rate (K) of CoCr28Mo were computed after tribological tests. The tribological efficiency of vegetable oils with regard to their chemical compo-sition and structure was compared to Hyalgan. It is found that, the use of vegetable oils enhanced significantly the tribological behavior of CoCr28Mo/CoCr28Mo pair. The obtained results were correlated to the chemical structure of vegetable oils namely the Unsaturations Number (UN) of fatty acids constituting the oil. Microscopic and chemical characterization of CoCr28Mo pins and discs were conducted and the wear mechanism was discussed.

Self-assembly technology of sub-micrometer-sized colloidal particles is the most promising approach for the preparation of large-area Photonic Crystals (PCs). However, PCs obtained by this method are facile to be destroyed by external factors such as friction, impact, and pollutants. The highly keratinized epidermis of chameleon skin acts as a protective role for the dermis with photon cells of the tunable band-gap structure. Inspired by the epidermis structure of chameleon, we use whey protein to develop a sort of protective film on the surface of artificially synthesized PCs. The film possesses positive mechanical properties that make the PCs friction and impact re-sistant. In addition, favorable resistance to water and CO2 could prevent PCs from being destroyed by pollutants. Consequently, PCs with protective film are well preserved when subjected to external factors (such as friction) and the optical properties of the PCs are successfully maintained, that may significantly promote the utilization of PCs in optical devices.

The ultrasonic scalpel has a number of excellent properties; however, its use in in vivo surgery is limited since the scalpel is not flexible enough. Changing the mechanism of ultrasonic vibration can allow the ultrasonic scalpel to bend. This paper reveals the mecha-nism of vibration generation of leaf-cutting ants, which is based on the microstructural and mechanical properties of special organs that produce the vibrations. Microstructural characteristics of cross-sections of the vibratory organ of Atta cephalotes were observed using scanning electron microscopy. It was found that the scraper perfectly matches the file plate dorsoventrally; however, the file teeth cannot catch the scraper. An exploration of the kinematics of the file-scraper device was subsequently carried out to reveal a face-to-face contact mode, facilitating a gentler engagement process. For the first time, the mechanism of vibration generation of leaf-cutting ants was inves-tigated using a laser micrometer and high-speed camera. Results reveal the file-scraper device significantly amplifies the input frequency by 125 times, and magnification depends mainly on the tooth spacing and speed of engagement. Finally, nanoindentation tests were performed on file and scraper samples. The results show that they have similar mechanical properties, which greatly reduces friction and wear. This paper may provide theoretical guidance for the development of bionic vibration generators.

We experimentally studied droplet impact dynamics onto wing feathers of kingfishers. Distilled water droplets with a fixed diameter of 2.06 mm were used as drop liquid and the initial impact velocities of droplets varied from 0.28 m•s−1 to 1.60 m•s−1. Two high-speed cameras were utilized to capture the impact process of water droplets onto the wing feather surface from both horizontal and vertical directions. Two states of the feathers (elastic and inelastic) were considered to study the influence of elasticity. At the entire impact ve-locity range we studied, regular rebound, bubble trapping and jetting, partial pinning and partial rebound of droplets on inelastic wing feather surface were observed as the initial impact velocity increased. However, only one dynamic behavior (regular rebound) was found on the elastic wing feather surface. The elasticity plays a more important role in the direction difference of droplet spreading than wing feather microstructure. The contact time of water droplets on the elastic wing feather surface was less than that on the inelastic surface within the range of Web numbers from 1.06 to 36 under test conditions.

To counter the threat of hyperspectral detection, it is necessary to develop biomimetic materials to simulate the solar spectral re-flection characteristics of plant leaf accurately. Two kinds of membranaceous yellow biomimetic materials were prepared by dispersing the particles of chrome titanium yellow and iron oxide yellow as fillers in polyvinyl alcohol films respectively. Reflectance and transmittance of the biomimetic materials were measured, and absorption and scattering coefficients of the biomimetic materials were inverted with a four-flux model. Results indicate that the biomimetic material adopting chrome titanium yellow particles can simulate the solar spectrum reflection characteristics of yellow leaf because of the similar absorption and scattering characteristics. The biomimetic material adopting iron oxide yellow particles cannot simulate the spectrum reflection characteristics of yellow leaf near the wavelength of 900 nm due to the characteristic absorption of the iron oxide. When the volume fraction of the chrome titanium yellow particles is lower than 2.12%, the absorption and scattering coefficients both increase approximately linearly with the volume fraction, indicating that the particles can scatter radiation independently. Therefore, the reflectance of the biomimetic material can be regulated through linearly changing of the volume fraction of the chrome titanium yellow particles.

This paper presents an Enhanced Moth-Flame Optimization (EMFO) technique based on Cultural Learning (CL) and Gaussian Mutation (GM). The mechanism of CL and the operator of GM are incorporated to the original algorithm of Moth-Flame Optimization (MFO). CL plays an important role in the inheritance of historical experiences and stimulates moths to obtain information from flames more effectively, which helps MFO enhance its searching ability. Furthermore, in order to overcome the disadvantage of trapping into local optima, the operator of GM is introduced to MFO. This operator acts on the best flame in order to generate several variant ones, which can increase the diversity. The proposed algorithm of EMFO has been comprehensively evaluated on 13 benchmark functions, in comparison with MFO. Simulation results verify that EMFO shows a significant improvement on MFO, in terms of solution quality and algorithmic reliability.