In order to satisfy the needs of different applications and more complex intelligent devices, smart control of surface wettability will be necessary and desirable, which gradually become a hot spot and focus in the field of interface wetting. Herein, we review interfacial wetting states related to switchable wettability on superwettable materials, including several classical wetting models and liquid adhesive behaviors based on the surface of natural creatures with special wettability. This review mainly focuses on the recent developments of the smart surfaces with switchable wettability and the corresponding regulatory mechanisms under external stimuli, which is mainly governed by the transformation of surface chemical composition and geometrical structures. Among that, various external stimuli such as physical stimulation (temperature, light, electric, magnetic, mechanical stress), chemical stimulation (pH, ion, solvent) and dual or multi-triggered stimulation have been sought out to realize the regulation of surface wettability. Moreover, we also summarize the applications of smart surfaces in different fields, such as oil/water separation, programmable transportation, anti-biofouling, detection and delivery, smart soft robotic etc. Furthermore, current limitations and future perspective in the development of smart wetting surfaces are also given. This review aims to offer deep insights into the recent developments and responsive mechanisms in smart biomimetic surfaces with switchable wettability under external various stimuli, so as to provide a guidance for the design of smart surfaces and expand the scope of both fundamental research and practical applications.

With the explosive growth of the world’s population and the rapid increase in industrial water consumption, the world’s water supply has fallen into crisis. The shortage of fresh water resources has become a global problem, especially in arid regions. In nature, many organisms can collect water from foggy water under harsh conditions, which provides us with inspiration for the development of new functional fog harvesting materials. A large number of bionic special wettable synthetic surfaces are synthesized for water mist collection. In this review, we introduce some water collection phenomena in nature, outline the basic theories of biological water harvesting, and summarize six mechanisms of biological water collection: increased surface wettability, increased water transmission area, long-distance water delivery, water accumulation and storage, condensation promotion, and gravity-driven. Then, the water collection mechanisms of three typical organisms and their synthesis are discussed. And their function, water collection efficiency, new developments in their biomimetic materials are narrated, which are cactus, spider and desert beetles. The study of multiple bionics was inspired by the discovery of Nepenthes’ moist and smooth peristome. The excellent characteristics of a variety of biological water collection structures, combined with each other, are far superior to other single synthetic surfaces. Furthermore, the main problems in the preparation and application of biomimetic fog harvesting materials and the future development trend of materials fog harvesting are prospected.

In a biomimetic approach the feasibility of liquid flow actuation by vibrating protruding structures excited via guided acoustic waves is investigated. Inspired by periodically beating cilia the loop part of a punched metallic hook-and-loop tape with tilted protruding loops was used as a waveguide for plate waves in water. Such waves were excited in the frequency range of 110 Hz to 220 Hz by directly coupling the tape to a loudspeaker membrane. A flow generated in the tilt direction of the loops with velocities up to 
60 mm·s?1 was visualized by ink droplets deposited on the tape. The phenomenon persisted, when the protruding length of the loops was reduced by decreasing the protrusion angle. However, after closing the punch holes near the loops with sticking tape streaming could not be observed any longer. The same happened with open punch holes when the ink was replaced by glycerol. Low-frequency acoustic streaming around vibrating sharp edges is proposed as an explanation for the observed phenomena. Applications are expected with respect to the modification of flow profiles and the enhancement of transport processes along and across liquid-solid boundaries.

Ice accumulation is a safety and operational threat in power lines, wind turbines, and transportations. Surfaces having both passive anti-icing and active deicing functionalities are very rare. Here, we report a self-cleaning slippery photothermal trap, which is icephobic passively and deice the surfaces actively by converting sun light to heat at the ice-substrate interface. The photothermal trap consists of three layers: a candle soot layer act as solar radiation absorber, a magnetic iron oxide Fe3O4 nanoparticles layer act as heat spreader for lateral dispersal of sun light, and Room Temperature Vulcanized (RTV) insulation to reduce the transverse heat loss. Upon illumination under microsolar 300, the temperature of the surface increased by 40 ?C within 200 s. The heat confinement at the magnetic Fe3O4 nanoparticles layer leads to rapid increase of the surface temperature, ice start to melt and silicone lubricant facilitates the ice removal. The slippery photothermal trap removed the frozen droplet (10 μL) within 40 s upon the illumination of sun light and the frozen droplet was completely converted into water after 7 min illumination of solar light at ?20 ?C. The developed slippery photothermal trap also melted the fully frost covered layer within 100 s at ?20 ?C under sunlamp. The average defrosted length (25 mm) was also observed by irradiation of laser light for 45 s. The self-cleaning slippery photothermal coating showed outstanding deicing performance at subzero temperature for long term due to the infusion of silicone oil into the nanostructures and same chemical composition with binder.

Mimicry of nature drives the development of bionic materials. Bionic superhydrophobic materials are a kind of high-efficiency materials to handle oil spills and water pollution. However, the stability of surface coatings of the superhydrophobic materials remains a challenge. Herein, a new category of self-assembly bionic superhydrophobic surface coating was prepared via one-step condensation/copolymerization of vinyltriethoxysilane (VTES) and divinylbenzene (DVB), which realized the close combination of covalent bonds between organic (e.g. DVB) and inorganic matter (e.g. VTES), and avoided the swelling of polydivinylbenzene (PDVB) in the process of collection of oil from water. This organic-inorganic hybrid polymer could self-assembly deposit on the surface of sponge even other substrates. For example, P(VTES-DVB)-SiO2/MS obtained by assembling P(VTES-DVB)-SiO2 on the surface of Melamine Sponge (MS) exhibited superhydrophobicity with a Water Contact Angle (WCA) of 157.3?, the optimal adsorption capacity of 77 g·g?1 – 136 g·g?1 for diverse oils, and an excellent separation efficiency of 99.3%. Besides, the excellent acid and alkali resistance of P(VTES-DVB)-SiO2/MS suggested the potential value in practical oil-water separation. P(VTES-DVB)-SiO2 showed the outstanding hydrophobic performance by using as coating on different substrates. This work provided a new idea about the stable combination of organic and inorganic matter in the surface modification.

3D printing has made remarkable progress in soft tissue reconstruction enabling the custom design of complex material implants with patient specific geometry. The aim of this study was to inkjet print mechanically reinforced biocompatible hydrogels. Here, we developed a double crosslinked ink by optimizing the rheological properties of solutions of sodium alginate (NaAlg), NaAlg/transglutaminase (TG), CaCl2 and gelatin/CaCl2. The results showed that a two-component ink system comprising NaAlg (4% w/v)/TG (0.8% w/v) and gelatin (4% w/v)/CaCl2 (3% w/v) gave optimum printability. The mechanical and biological properties of printed alginate/gelatin hydrogels prepared from inks with different gelatin contents, and incorporated fibroblasts, were characterized by Scanning Electron Microscope (SEM), mechanical testing and laser confocal microscopy. The compressive moduli of alginate/gelatin hydrogels could be adjusted from 19.2 kPa ± 1.2 kPa to 65.9 kPa ± 3.3 kPa by increasing the content of gelatin. After incubation for 7 d, fibroblasts had permeated all printed hydrogels and the rate of proliferation increased with increasing gelatin content. The highest cell proliferation rate (497%) was obtained in a hydrogel containing 4.5% (w/v) gelatin. This study offers a new strategy for the fabrication of 3D structures used to mimic the function of native tissues.

Entangled Porous Titanium Alloy Metal Rubber (EPTA-MR) was used as a nucleus pulposus material in the design of non-fusion intervertebral disc prosthesis for the first time. A novel artificial lumbar intervertebral disc prosthesis was designed by reconstructing the lumbar model with reverse engineering technology, and the biomechanical behavior of the prosthesis was simulated under varied working conditions. The nucleus pulposus size was determined by the actual size of human prosthesis. EPTA-MR samples with different densities were prepared by medical titanium alloy wire experimental studies were conducted on static stiffness, damping energy consumption, and fatigue life. The results indicated that the static stiffness of EPTA-MR could reach approximately 1500 N·mm?1, and its loss factor remained higher than 0.2, and the variation range was relatively small, with excellent vibration damping capacity and bearing capacity. Among them, the overall performance of EPTA-MR with a density of 2.5 g·cm?3 was closer to that of the physiologic intervertebral disc. A macro experiment of five million fatigue vibration tests combined with microstructure observation exhibited a wear rate of only 0.9396 g·MC?1, with no noticeable change in the internal micro-morphology. Therefore, the EPTA-MR has a broad application prospect as the nucleus pulposus material of artificial intervertebral disc prosthesis.

The replacement of synthetic foam materials using natural biological ones is of great significance for saving energy/resources and reducing environmental pollutions. Here we characterized the microstructure and mechanical properties of natural cornstalk pith, which has a large annual output yet lacks an effective exploitation, and evaluated its feasibility for applications as a substitute for synthetic foam materials. The cornstalk pith was revealed to be a cellular material composed of closed cells elongated along the growth direction of corn plant and reinforced by well-aligned vascular bundles penetrating the foam matrix. The compressive behavior is featured by a stable stress plateau which is favorable for energy absorption with its mechanical properties largely dependent on the hydration state and loading configuration. In particular, the initial dimension and mechanical properties of cornstalk pith can be effectively recovered after deformation simply by hydration treatment owing to swelling effect caused by the turgor pressure from osmosis. The cornstalk pith demonstrates an outstanding combination of low density and high energy absorption efficiency among various foam materials, specifically with its plateau stress and energy absorption comparable or even superior to those of some typical synthetic foam materials. These along with the huge resources and good biodegradability make it a promising natural energy absorbing cellular material for replacing synthetic counterparts.

Research on the mechanical properties of brain tissue has received extensive attention. However, most of the current studies have been conducted at the phenomenological level. In this study, the indentation method was used to explore the difference in local mechanical properties among different regions of the porcine cerebral cortex. Further, hematoxylin–eosin and immunofluorescence staining methods were used to determine the correlation between the cellular density at different test points and mechanical properties of the porcine cerebral cortex. The frontal lobe exhibited the strongest viscosity. The temporal lobe displayed the lowest sensitivity to changes in the indentation speed, and the occipital lobe exhibited the highest shear modulus. Additionally, the shear modulus of different areas of the cerebral cortex was negatively correlated with the total number of local cells per unit area and positively correlated with the number of neuronal cell bodies per unit area. Exploration of the mechanical properties of the local brain tissue can provide basic data for the establishment of a finite element model of the brain and mechanical referential information for the implantation position of brain chips.

Mimicking compositional and constructional features of the extracellular matrix (ECM) is an effective parameter in improving the biological response of biomaterials. In this regard, carbon nanotube (CNT) and gelatin were added to magnesium-calcium phosphate cement (CNG) to mimic fibrillar construction and organic composition of ECM, respectively, besides the CNG performance was compared with the plain and CNT-reinforced cement. Cementation behavior of the cements was investigated by evaluating their setting time, cement composition variation during setting, and viscosity fluctuation. Furthermore, compressive strength, degradation, and cell response of the cements were compared. Adding 5 wt.% gelatin reduced setting time about 60%, because of gel formation, not due to struvite precipitation. Moreover, the gelatin decreased compressive strength by about 20%. Although gelatin decreased compressive strength, the strength remained in the range attributed to trabecular bone. All the types of cement indicated shear thinning behavior that made their injectability feasible. Compared to other types of cement, CNG enhanced proliferation and differentiation of mesenchymal stem cells besides faster degradation, nontoxicity and suitable cell adhesion. Hence, mimicking features of CNG enhanced osteoconductivity and osteoinductivity of the cement compared to the plain one.

As a result of frequent food waste and environmental pollution, there has been an increasing demand for the development of packaging materials that intrinsically inhibit and reduce likelihood of non-Newtonian liquids adherence. In this work, inspired from ciliary structures on the leg of water strider, the hierarchical conical array was formed by magnetic field control and laser etching without any mask. Due to the tapered geometry of the cones and the multiscale surface roughness of the array, the droplets would bounce many times after impacting with the superhydrophobic surface (SHS) and roll off. By changing the spaces and apex angles of conical microcolumns the SHS has controlled adhesion, superior self-cleaning property and droplets bounce performance for a variety of non-Newtonian viscous liquids. After suffering from various types of damage including repeated tape tearing, finger touch and folding test, the SHS still maintained excellent superhydrophobic property, which may have potential application as all kinds of packaging interface materials. We demonstrate that the excellent droplets bounce behavior of the hierarchical array enables the efficient and robust prevention of food liquids adhesion.

Hovering ability forms the basis for space operations of Micro Aerial Vehicles (MAVs). The problem of uneven load puts high demands on the wing design. In this paper, a new hovering-mode for MAVs, inspired by flapping flight in bees and hummingbirds but using high-aspect-ratio and low-stress wings, is proposed. Different from the flapping actuations that occur at the wing roots, the two wings are driven back and forth in a straight line. To simplify the design and control the angle of attack, passive wing rotation is employed. The numerical results and analysis show that the maximum stress of the oscillating wing is approximately 1/6 of that of the flapping wing when the lift of the oscillating wing is twice that of the flapping wing. A theoretical aerodynamic model of the kinematics of the vehicle’s driving mechanism was developed to fulfill its design. Force measurements indicate that the vehicle generates a sufficiently high cycle-averaged vertical thrust (71 g) for liftoff at a maximum frequency of 5.56 Hz, thereby validating the proposed aerodynamic model. Moreover, liftoff performance is presented to visually demonstrate the vertical take-off capabilities and hovering potential of the aeromechanical solution.

This paper presents the moving mechanism of a high-speed insect-scale microrobot via electromagnetically induced vibration of two simply supported beams. The microrobot, which has a body length of 12.3 mm and a total mass of 137 mg, can achieve reciprocating lift motion of forelegs without any intermediate linkage mechanisms due to the design of an obliquely upward body tilt angle. The gait study shows that the body tilt angle prevents the forelegs from swinging backward when the feet contact the ground, which results in a forward friction force applied on the feet. During forward movement, the microrobot utilizes the elastic deformation of the simply supported beams as driving force to slide forward and its forelegs and rear legs work as pivots alternatively in a way similar to the movement of soft worms. The gait analysis also indicates that the moving direction of the microrobot is determined by whether its body tilt angle is obliquely upward or downward, and its moving speed is also related to the body tilt angle and as well as the body height. Under an applied AC voltage of 4 V, the microrobot can achieve a moving speed at 23.2 cm·s?1 (18.9 body lengths per second), which is comparable to the fastest speed (20 cm·s?1 or 20 body lengths per second) among the published insect-scale microrobots. The high-speed locomotion performance of the microrobot validates the feasibility of the presented actuation scheme and moving mechanism.

This paper proposes a new stochastic optimizer called the Colony Predation Algorithm (CPA) based on the corporate predation of animals in nature. CPA utilizes a mathematical mapping following the strategies used by animal hunting groups, such as dispersing prey, encircling prey, supporting the most likely successful hunter, and seeking another target. Moreover, the proposed CPA introduces new features of a unique mathematical model that uses a success rate to adjust the strategy and simulate hunting animals’ selective abandonment behavior. This paper also presents a new way to deal with cross-border situations, whereby the optimal position value of a cross-border situation replaces the cross-border value to improve the algorithm’s exploitation ability. The proposed CPA was compared with state-of-the-art metaheuristics on a comprehensive set of benchmark functions for performance verification and on five classical engineering design problems to evaluate the algorithm’s efficacy in optimizing engineering problems. The results show that the proposed algorithm exhibits competitive, superior performance in different search landscapes over the other algorithms. Moreover, the source code of the CPA will be publicly available after publication. 

Medical image segmentation is a challenging task especially in multimodality medical image analysis. In this paper, an improved pulse coupled neural network based on multiple hybrid features grey wolf optimizer (MFGWO-PCNN) is proposed for multimodality medical image segmentation. Specifically, a two-stage medical image segmentation method based on bionic algorithm is presented, including image fusion and image segmentation. The image fusion stage fuses rich information from different modalities by utilizing a multimodality medical image fusion model based on maximum energy region. In the stage of image segmentation, an improved PCNN model based on MFGWO is proposed, which can adaptively set the parameters of PCNN according to the features of the image. Two modalities of FLAIR and T1C brain MRIs are applied to verify the effectiveness of the proposed MFGWO-PCNN algorithm. The experimental results demonstrate that the proposed method outperforms the other seven algorithms in subjective vision and objective evaluation indicators.

The current Whale Optimization Algorithm (WOA) has several drawbacks, such as slow convergence, low solution accuracy and easy to fall into the local optimal solution. To overcome these drawbacks, an improved Whale Optimization Algorithm (IWOA) is proposed in this study. IWOA can enhance the global search capability by two measures. First, the crossover and mutation operations in Differential Evolutionary algorithm (DE) are combined with the whale optimization algorithm. Second, the cloud adaptive inertia weight is introduced in the position update phase of WOA to divide the population into two subgroups, so as to balance the global search ability and local development ability. ANSYS and Matlab are used to establish the structure model. To demonstrate the application of the IWOA, truss structural optimizations on 52-bar plane truss and 25-bar space truss were performed, and the results were are compared with that obtained by other optimization algorithm. It is verified that, compared with WOA, the IWOA has higher efficiency, fast convergence speed, better solution accuracy and stability. So IWOA can be used in the optimization design of large truss structures.