Nature is a huge gallery of art involving nearly perfect structures and properties over the millions of years of development. Many plants and animals show water-repellent properties with fine micro-structures, such as lotus leaf, water skipper and wings of butterfly. Inspired by these special surfaces, the artificial superhydrophobic surfaces have attracted wide attention in both basic research and industrial applications. The wetting properties of superhydrophobic surfaces in nature are affected by the chemical compositions and the surface topographies. So it is possible to realize the biomimetic superhydrophobic surfaces by tuning their surface roughness and surface free energy correspondingly. This review briefly introduces the physical-chemical basis of superhydrophobic plant surfaces in nature to explain how the superhydrophobicity of plant surfaces can be applied to different biomimetic functional materials with relevance to technological applications. Then, three classical effects of natural surfaces are classified: lotus effect, salvinia effect, and petal effect, and the promising strategies to fabricate biomimetic su-perhydrophobic materials are highlighted. Finally, the prospects and challenges of this area in the future are proposed.

The topography and wettability of the underside of English weed (Oxalis pes-caprae) leaves and of their biomimetic rep-licas are investigated. Polyvinyl siloxane molds were cast from the leaves and then filled with an epoxy pre-polymer to produce replicas. The particular topographical structures of leaves and replicas were evaluated by optical microscopy and Scanning Electron Microscopy (SEM) analysis. The static wettability of leaves and replicas was assessed by contact angle measurements, while the dynamic wettability was characterized by estimating contact angle hysteresis and studying the dynamic behavior of impacting water droplets. A smooth glass slip and its replica were used as control surfaces. The replica moulding method used was able to transfer the characteristic pattern of irregular 100 µm – 200 µm × 60 µm convex papillae interspersed with stomata of the original leaf to the epoxy replicas. The static contact angle of 143? ± 3? and the contact angle hysteresis of 2? indicate that the underside of the English weed leaf is close to superhydrophobic. The lower contact angles (130? ± 4?) and higher hysteresis (31?) observed for the replica when compared with the original leaves were associated to an inaccurate replication of the chemistry and structures of the three-dimensional wax projections covering the plant surface. Also, trichomes in the original leaves could not be accurately reproduced due to their flexibility and fragility. Differences in wetting behavior were also evident from droplet impact experiments, with rebound regimes prevailing in the original leaves and regimes characterized by higher adhesion and larger dissipation predominating in the replicas. Nevertheless, the morphological features of the leaf transferred to the replica were sufficient to promote a clear hydrophobic behavior of the replica when compared with the smooth epoxy ref-erence surface.

This investigation reports the nanomechanical properties of shallow water shrimp exoskeleton at temperatures ranging from 30 ?C to 80 ?C measured using nanoindentation experiments. Scanning Electron Microscopy (SEM) measurements suggest that the shrimp exoskeleton has the Bouligand structure in its layers, a key characteristic of the crustaceans. The thickness of the layers and packing density are found to be different from that of lobsters and crabs reported earlier in the literature. Mechanical properties at high temperatures are determined using micro materials nanoindentation test set up combined with the hot stage. The properties measured during nanoindentation test are corrected for the creep and thermal drift during the experiments. The reduced modulus values are found to be around 28 GPa at 30 ?C that reduces to approximately 24 GPa at 80 ?C. The hardness values also decrease from 1.6 GPa at 30 ?C to around 1.2 GPa at 80 ?C. The indentation size effect is found to be absent at all temperatures. Creep mechanisms of polymers like materials and its temperature dependence are discussed to give more insight into the deformation mechanism.

Materials with appropriate adhesive properties are suitable for the fabrication of bionic adhesive pads. In this study, a novel polydimethylsiloxane (PDMS) material enhanced with two types of crosslinkers, carbon nanotubes and graphene sheets, was fabricated. The Contact Angle (CA) and cross-sectional morphology of the new material were investigated and observed using a CA meter and Scanning Electron Microscopy (SEM), respectively. CA measurements indicate that the surface energy of the novel material is twice that of the common PDMS material. SEM observations show that carbon nanotubes and graphene sheets are well dispersed in the polymer, a feature that improves the mechanical properties of the new material. The adhesive per-formance of this novel composite was tested on an in-house fabricated friction machine. Results show that at a preload of only 50 mN, the adhesion of the novel PDMS material is up to ~3.7 times that of common PDMS. The maximum macroscale shear strength and normal adhesion reach 4 N•cm−2 and 1 N•cm−2, respectively. The adhesive capability of the material is maintained even after hundreds of times of repeated use. This novel material exhibits excellent adhesion, sufficiently high elastic modulus and high repeatability at low preloads.

Hydrogel has been extensively studied as an articular cartilage repair and replacement material. PVA-HA-Silk composite hydrogel was prepared by freezing-thawing method in this paper. Mechanical properties were determined by experiments and the friction coefficient of PVA-HA-Silk composite hydrogel against steel ball was verified using micro-tribometer. Finite Element Method (FEM) was used to study the lubrication mechanism of PVA-HA-Silk composite hydrogel and the relation between the interstitial fluid load support and the start-up friction resistance. The results show that the elastic modulus and the permeability are 2.07 MPa and 10−15m4N−1s−1, respectively, and the start-up friction coefficients of PVA-HA-Silk composite hydrogel are in the range of 0.15–0.2 at different contact loads, contact time and sliding speeds. The start-up friction resistance of PVA-HA-Silk composite hydrogel increases with the contact load and contact time. With the increase in sliding speed, the start-up friction resistance of PVA-HA-Silk composite hydrogel decreases. There is an inverse relation between the start-up friction resistance and the interstitial fluid load support. The change of fluid flow with the increase in sliding displacement has an important effect on the interstitial fluid load support and friction resistance. The interstitial fluid load support decreases with the increase in contact load and contact time, while the interstitial fluid load support reinforces with the increase in sliding speed. Moreover, PVA-HA-Silk composite hydrogel has mechanical properties of recovery and self-lubricating.

Animals’ free movement in natural environments has attracted many researchers to explore control methods for bio-inspired robots. This paper presents a novel reflex mechanism based on a Central Pattern Generator (CPG) for adaptive locomotion of limbless robots. First, inspired by the concept of reflex arc, the reflex mechanism is designed on a connectionist CPG model. Since the CPG model inspired by the spinal cord of lampreys is developed at the neuron level, it provides a possible natural solution for sensory reflex integration. Therefore, sensory neurons that bridge the external stimuli and the CPG model, together with the concept of reflex arc, are utilized for designing the sensory reflex mechanism. Then, a border reflex and a body reflex are further developed and applied on the ends and the middle part of a limbless robot, respectively. Finally, a ball hitting scenario and a corridor passing scenario are designed to verify the proposed method. Results of simulations and on-site ex-periments show the feasibility and effectiveness of the reflex mechanism in realizing fast response and adaptive limbless lo-comotion.

This paper presents the design and development of a starfish-like soft robot with flexible rays and the implementation of multi-gait locomotion using Shape Memory Alloy (SMA) actuators. The design principle was inspired by the starfish, which possesses a remarkable symmetrical structure and soft internal skeleton. A soft robot body was constructed by using 3D printing technology. A kinematic model of the SMA spring was built and developed for motion control according to displacement and force requirements. The locomotion inspired from starfish was applied to the implementation of the multi-ray robot through the flexible actuation induced multi-gait movements in various environments. By virtue of the proposed ray control patterns in gait transition, the soft robot was able to cross over an obstacle approximately twice of its body height. Results also showed that the speed of the soft robot was 6.5 times faster on sand than on a clammy rough terrain. These experiments demonstrated that the bionic soft robot with flexible rays actuated by SMAs and multi-gait locomotion in proposed patterns can perform successfully and smoothly in various terrains.

The cuttlefish have higher swimming speed and more maneuverability than most of the fish mainly benefiting from their unique jet propulsion mechanism, which is realized by the contraction and expansion of their flexible mantle. However it is difficult to mimic this jet propulsion mechanism using conventional electro-mechanical structures. In this paper, the musculature of the cuttlefish mantle and how the mantle flexibly contracts and expands were analyzed first. Then the Shape Memory Al-loy(SMA) wires were chosen as the actuators and the soft silica gel was chosen as the body materials to develop a biomimetic mantle jet propeller. The SMA wires were embedded within the soft silica gel formed with cuttlefish mantle shape along the annular direction to mimic the circular muscles of cuttlefish mantle. The water was squeezed out the mantle cavity to form rear jets when the biomimetic mantle was contracted by SMA wires. A mechanical model and a thermal model were established to analyze the jet thrust and the jetting frequency. Theoretical analysis shows that the jet thrust is proportional to the square of the rate of change of SMA strain. Increasing the driving voltage can improve the rate of change of SMA strain, thus can improve both the jet thrust and the jetting frequency. However the jetting frequency is mainly restricted by the cooling of SMA wires. To maximize the jetting frequency, the optimal driving parameters for different driving voltage were calculated. The propulsion performance was tested and the results show that the jet thrust can increase with the driving voltage as predicted and the maximum average jet thrust is 0.14 N when the driving voltage is 25 V. The swimming test was carried out to verify the feasi-bility of the novel design. It is shown that the biomimetic jet propeller can swim with higher speed as the jet thrust and jetting frequency increase and the maximum speed can reach 8.76 cm•s−1 (0.35 BL•s−1) at a jetting frequency of 0.83 Hz.

High-resolution Particle-Image Velocimetry (PIV) and time-resolved force measurements were performed to analyze the impact of the comb-like structure on the leading edge of barn owl wings on the flow field and overall aerodynamic performance. The Reynolds number was varied in the range of 40,000 to 120,000 and the range of angle of attack was 0? to 6? for the PIV and −15? to +20? for the force measurements to cover the full flight envelope of the owl. As a reference, a wind-tunnel model which possessed a geometry based on the shape of a typical barn owl wing without any owl-specific adaptations was built, and measurements were performed in the aforementioned Reynolds number and angle of attack range. This clean wing model shows a separation bubble in the distal part of the wing at higher angles of attack. Two types of comb-like structures, i.e., artificial serrations, were manufactured to model the owl’s leading edge with respect to its length, thickness, and material properties. The artificial structures were able to reduce the size of the separation region and additionally cause a more uniform size of the vortical structures shed by the separation bubble within the Reynolds number range investigated, resulting in stable gliding flight independent of the flight velocity. However, due to increased drag coefficients in conjunction with similar lift coefficients, the overall aerodynamic performance, i.e., lift-to-drag ratio is reduced for the serrated models. Nevertheless, especially at lower Reynolds numbers the stabilizing effect of the uniform vortex size outperforms the lower aerodynamic performance.

The longitudinal disturbance motion of different insects at hovering flight has the same modal structure. Here, we consider the case of lateral motion. The lateral dynamic flight stability of two model insects, hoverfly and honeybee, at hovering flight is studied. The method of computational fluid dynamics is applied to compute the stability derivatives. The techniques of eigen-value and eigenvector analysis are used to solve the equations of motion. Results show that the lateral disturbance motion of the hoverfly has three natural modes of motion: an unstable divergence mode, a stable oscillatory mode and a stable subsidence mode, and the flight is unstable; while the honeybee has a different modal structure (a stable slow subsidence mode, a stable fast subsidence mode, and a nearly neutrally stable oscillatory mode) and the flight is nearly neutrally stable. The change in modal structure between the two insects is due to their roll-moment/side-velocity derivative having different sign, and the sign dif-ference is because that the hoverfly has a relatively small, but the honeybee has a relatively large, distance between the wing roots and the center of mass. Thus, unlike the case of longitudinal motion, for lateral motion, some insects have different modal structures and stability properties from others.

In this work, we develop an artificial foldable wing that mimics the hind wing of a beetle (Allomyrina dichotoma). In real flight, the beetle unfolds forewings and hind wings, and maintains the unfolded configuration unless it is exhausted. The arti-ficial wing has to be able to maintain a fully unfolded configuration while flapping at a desirable flapping frequency. The arti-ficial foldable hind wing developed in this work is based on two four-bar linkages which adapt the behaviors of the beetle’s hind wing. The four-bar-linkages are designed to mimic rotational motion of the wing base and the vein folding/unfolding motion of the beetle’s hind wing. The behavior of the artificial wings, which are installed in a flapping-wing system, is observed using a high-speed camera. The observation shows that the wing could maintain a fully unfolded configuration during flapping motion. A series of thrust measurements are also conducted to estimate the force generated by the flapping-wing system with foldable artificial wings. Although the artificial foldable wings give added burden to the flapping-wing system because of its weight, the thrust measurement results show that the flapping-wing system could still generate reasonable thrust.

Locust has the capacity to maintain a righting posture and glide through attitude adjustment after leaping. A prototype inspired by the dynamic mechanism of attitude adjustment of locusts was developed. The prototype consists of a pair of wings driven by a four-bar mechanism, and a 2 Degree of Freedom (DOF) tail to imitate the movement of the locust abdomen. The power source, microcontroller, wireless data transmission module, and attitude sensors are contained in the fuselage. Experi-ments imitating the flight of locust were conducted to determine the mechanism of locust Subsequent Attitude Adjustment (SAA). The tethered prototype was driven by the movement of the tail and the flapping of the wings. Results show that the pitch and yaw of the tail, and the asymmetric action of the flapping wings significantly influence the posture of the prototype. These findings suggest that both the wiggling abdomen and flapping wings contribute to the locust SAA in the air. This research lays the groundwork and technical support for the probable design and development of practical jumping robots with attitude ad-justment function.

The possibility of mimicking desirable properties from nature accelerates material improvement and generates commercial interests. For heat pipe development, many attempts have been made in heat pipe wicks to enhance its capillary performance by mimicking biology. Constructing biporous, composite, or nanopillar wicks with aim of achieving hierarchical structure has been found in many studies. Mimicking beetle shell surface to obtain hybrid wettability shows biomimetic potential in heat pipe wicks. This paper firstly reviews some fundamental studies in biomimetics, establishing a general idea of surface wetting and capillary effect. MRI scanning of two live plants (Musa X Paradisiaca and Salix Flamingo) provides the possibility of visual-ising internal structures in vivo and obtaining rates of water transport in xylem vessels. In addition, by investigating the work inspired directly or indirectly from biomimetics, the role that biomimetics plays in modern heat pipe technology is revealed. Our innovation which syntheses a low level of hierarchical structure and integrates integral wicks for different heat pipe sections including evaporator, adiabatic, and condenser is introduced. Mathematical modelling in terms of capillary pressure and cap-illary rise rate to characterise such new structure is provided.

In video sequence-based iris recognition system, the problem of making full use of relationship and correlation among frames still remains to be solved. A brand new template level multimodal fusion algorithm inspired by human cognition manner is proposed. In that a non-isolated geometrical manifold, named Hyper Sausage Chain due to its sausage shape, is trained using the frames from a pattern class for representing an iris class in feature space. We can classify any input iris by observing which manifold it locates in. This process is closer to the function of human being, which takes ‘matter cognition’ instead of ‘matter classification’ as its basic principle. The experiments on self-developed JLUBR-IRIS dataset with several video sequences per person demonstrate the effectiveness and usability of the proposed algorithm for video sequence-based iris recognition. Fur-thermore, the comparative experiments on public CASIA-I and CASIA-V4-Interval datasets show that our method can also achieve improved performance of image-based iris recognition system, provided enough samples are involved in training stage.

This paper proposes a route optimization method to improve the performance of route selection in Vehicle Ad-hoc Network (VANET). A novel bionic swarm intelligence algorithm, which is called ant colony algorithm, was introduced into a traditional ad-hoc route algorithm named AODV. Based on the analysis of movement characteristics of vehicles and according to the spatial relationship between the vehicles and the roadside units, the parameters in ant colony system were modified to enhance the performance of the route selection probability rules. When the vehicle moves into the range of several different roadsides, it could build the route by sending some route testing packets as ants, so that the route table can be built by the reply information of test ants, and then the node can establish the optimization path to send the application packets. The simulation results indicate that the proposed algorithm has better performance than the traditional AODV algorithm, especially when the vehicle is in higher speed or the number of nodes increases.