The slippery liquid-infused porous surfaces inspired by the microstructure of carnivorous nepenthes have aroused widespread attention, which show stable liquid repellency, glorious self-repairing powers and effective anti-fouling properties. The surfaces are manufactured via the infusion of lubricant oil into porous structures, a process which allows other fluids to slide off the interfaces readily. However, the practical applications of slippery liquid-infused surfaces are limited to the complicated preparation processes and poor oil lock ability. We aim to, in this review, present the fundamental theories of the slippery liquid-infused porous surface. Some typical natural examples are clarified while representative fabricating methods such as liquid flame spray, layer-by-layer assembly, lithography and so on are listed. The slippery surface can facilitate the manufacture of transparent and multi-functional slippery materials by means of straightforward procedures. The slippery liquid-infused porous surfaces were applied in hot water repellency, anti-fouling, ice-phobic, water condensation, control of underwater bubble transport and drag reduction. This article discusses all these issues along with emerging applications as well as future challenges.

This work is focused on the development of a facile strategy to fabricate superhydrophobic coatings, which are characterized with lower water freezing temperature and lower ice adhesion. First, a kind of polyacrylic acid (PAA) based resin material is synthesized as the coat-ing-matrix. Then the functionally-modified SiO2 nanoparticles are added to regulate the surface morphology for obtaining the ideal superhydrophobicity. The as-synthesized resin coatings possess strong bonding strength with metal substrate, and the surface hierarchical morphologies (10 wt% SiO2 nanoparticles) induce the robust superhydrophobicity with a high water contact angle of 152?. Also, the superhydrophobic coatings are endowed with high icephobicity, and the freezing temperature of reference water droplet is reduced to ?20.33 ?C comparing with that (?13.83 ?C) on the coatings without additive nanoparticles. Furthermore, the ice adhesion strength on the superhydrophobic coatings is only 250 kPa, exhibiting the great ability of ice repellence.

Hierarchical structures significantly influence the development of metal surface wettability. In this study, three kinds of hierarchical structures formed by the superimposition of different nanoscale (quasi-) periodic structures on micro-column arrays were fabricated on 304 stainless steel surfaces via picosecond laser irradiation. Scanning Electron Microscope (SEM) and Confocal Laser Scanning Microscope (CLSM) were used to characterize the created hierarchical structures. An optical contact angle meter was used to analyse the wetting performances. The results show that the surfaces of these fabricated samples have superhydrophobic properties and strong adhesion per-formances, which can be attributed to the formation of hierarchical structure that causes a reduction in the liquid-solid contact area and the change in the direction of surface tension. By controlling the dimensionof the nanotextures on the micro-column arrays, the hydrophobic property of 304 stainless steel surfaces can be greatly improved.

In skull bone tissue engineering, cells do not easily survive and proliferate in the scaffold because of the lack of nutrient transport channels. To address these problems, a vascular design and fabrication method based on human skull diploic vein characteristics was proposed. The skull sample was scanned by micro-CT, and the 3D model was constructed by Avizo. By analyzing the characteristics of the diploic vein, the vascular centerline model, path model, taper model and bifurcation model were proposed. Two vascular network examples were constructed by iteration of the bifurcation unit. The mold method of constructing vascular scaffolds embedded within the bionic channels was proposed. The scaffold material is PDMS, and the surface was coated with collagen. The Human Umbilical Vein Endothelial Cells (HUVECs) were planted into the lumen of the channels for 7 days in vitro and found to be able to proliferate. The cells cultured for three days were fluorescently stained, and it was found that the cells were well attached to the surfaces of the lumen. This vascular design and fabrication process can lay a foundation for vascularization in bone tissue engineering.

With the rapid development of photoelectric products, their miniaturization and high integration have intensified the problem of heat dissipation. Vapor chamber is a special type of heat pipe that is a particularly effective heat spreader for electronics. In this paper, a novel Leaf-vein-inspired Gradient Porous (LGP) wick structure is designed macroscopically and the LGP design is verified using a general model. After that, the gradient porous design Model 1G is selected for the subsequent mesoscopic modeling. Then a connected 2D random LGP wick model presenting porosity gradient is generated by the expanded quartet structure generation set method. Using the mesoscopic Lattice Boltzmann Method (LBM), the flow and heat transfer in the LGP wick model is analyzed. For verification, FLUENT based on the macroscopic finite volume method is used as a benchmark. Finally, the microscopic flow behaviors in the 2D random LGP wick model are analyzed using the LBM developed. Observing the entire flowing process from the inlet to outlet, it is possible to explain the mesoscopic and macroscopic phenomena well based on the microscopic flow behaviors.

Tissue engineering has been a subject of extensive scientific exploration in the last two decades making gradual inroads into clinical studies as well. Along with regenerative cells and growth factors, biomaterial scaffolds are integral to the development of a tissue engineered construct. It is now appreciated that scaffolds should mimic the target tissue properties intimately in order to provide a 
micro-environment milieu that allows the seeded cells to differentiate into the desired tissue. Even from a structural viewpoint, mismatch between scaffold and native matrix properties can cause cell necrosis through mechanisms such as stress shielding. One of the key properties of most body tissues is that they exhibit anisotropy. However, most fabrication methods generate isotropic scaffolds and require specific modifications to produce anisotropic scaffolds. In the last decade, the advent of additive manufacturing and bioprinting has provided facile tools to fabricate scaffolds with desired anisotropy. On the other hand, a biomimetic scaffold can be designed only when target tissue anisotropy is well known to the tissue engineer. This review presents an overview of the anisotropic properties of different tissues, which will be critical for developing biomimetic engineered constructs. The traditional anatomical records do not adequately present these properties from the perspective of designing tissue engineering scaffolds. Subsequently, present state-of-the art in development of anisotropic scaffolds as well as tissue constructs using different conventional and emerging fabrication techniques is discussed. It is expected that the readers will obtain a comprehensive reference on the research area by examining these two aspects juxtaposed to each other and gain key trends for fabrication of anisotropic scaffolds, plausibly with improved regenerative outcomes.

In nature, shells exhibit remarkable high toughness and impact resistance to the external load despite their brittle main constituent and simple hierarchical structure. In this work, the structure of the mussel shell Hyriopsis cumingii is analyzed by scanning electron microscope and atomic force microscope, and the macro/micro compression and impact tests are performed. Results show that the shell has a three-layer structure: an outer cuticle layer, a prismatic layer, and a nacreous layer. The stiffer and load-dependent prismatic layer is conducive to improve the impact resistance of shell structure. Fracture morphology after failure proves that cracks are transgranularly propagated inside the prism and aragonite platelet, and the crack deflection and platelet pullout can effectively lock the stress, thereby eventually improving the impact-resistance and toughness of the shell.

The scales of body surface of Laudakia stoliczkana have the morphology of convex hulls, which are arranged in groove structure in macroscopic scale. Its body surface skin is mainly composed of the “soft” layer of keratin and the “hard” layer of the cuticle covering on the “soft” layer. The coupling effect of the scale morphology and skin’s structure gives Laudakia stoliczkana the excellent ability to resist the sand erosion in desert environment. Inspired by the convex surface morphology and the composite structure of the “soft” and “hard” layers of the skin of Laudakia stoliczkana, the coupling bionic samples are fabricated and the erosion resistance performance is tested. The test results show that the coupling bionic samples have good erosion resistance performance and the samples with spherical convex hull exhibit the best erosion resistance performance. Moreover, based on the theory of stress wave propagation in solid the numerical simulations of particles impacting to the coupling bionic samples and bionic layered structure are done respectively and the anti-erosion mechanism of the bionic layered structure is analyzed. The simulation results are consistent with the experimental results, which show that the coupling bionic samples can effectively reduce the amplitude of the incident stress wave, and thus can prevent the failure of samples.

The current research is aimed towards the development of dragonfly inspired nanocomposite flapping wing for micro air vehicles (MAVs). The wing is designed by taking inspiration from the hind wing of dragonfly (Anax Parthenope Julius). Carbon nanotubes (CNTs)/polypropylene nanocomposite and low-density polyethylene are used as the wing materials. The nanocomposites are developed with varying CNTs’ weight percentage (0% – 1%) and characterized for dynamic mechanical properties, which revealed that the 0.1 weight percentage case produces highest storage modulus values throughout the frequency range (1 Hz – 90 Hz). It is also observed that the storage modulus values are in the range of Young’s modulus of veins and membrane of natural insect wings. This is useful to achieve true biomimicking. Advanced manufacturing technique such as photolithography is used for wing fabrication. The length, weight and average thickness of the fabricated wing are ~44 mm, 26.22 mg and 187 μm, respectively. The structural dynamic properties of the fabricated wing are obtained experimentally and computationally using DIC and ANSYS, respectively. The developed dragonfly inspired wing showed a natural frequency of 29.4 Hz with a bending mode shape which is close to the characteristic frequency of its natural counterpart.

This paper presents the application of an artificial neural network to develop an approach to determine and study the energy-optimal wing kinematics of a hovering bionic hawkmoth model. A three-layered artificial neural network is used for the rapid prediction of the unsteady aerodynamic force acting on the wings and the required power. When this artificial network is integrated into genetic and simplex algorithms, the running time of the optimization process is reduced considerably. The validity of this new approach is confirmed in a comparison with a conventional method using an aerodynamic model based on an extended unsteady vortex-lattice method for a sinusoidal wing kinematics problem. When studying the obtained results, it is found that actual hawkmoths do not hover under an energy-
optimal condition. Instead, by tilting the stroke plane and lowering the wing positions, they can compromise and expend some energy to enhance their maneuverability and the stability of their flight.

This paper presents the design of a bionic pectoral fin with fin rays driven by multi-joint mechanism. Inspired by the cownose ray, the bionic pectoral fin is modeled and simplified based on the key structure and movement parameters of the cownose ray’s pectoral fin. A novel bionic propulsion fin ray composed of a synchronous belt mechanism and a slider-rocker mechanism is designed and optimized in order to minimize the movement errors between the designed fin rays and the spanwise curves observed from the cownose ray, and thereby reproducing an actively controllable flapping deformation. A bionic flapping pectoral fin prototype is developed accordingly. Observations verify that the bionic pectoral fin flaps consistently with the design rule extracted from the cownose ray. Experiments in a towing tank are set up to test its capability of generating the lift force and the propulsion force. The movement parameters within the usual propulsion capabilities of the bionic pectoral fin are utilized: The flapping frequency of 0.2 Hz – 0.6 Hz, the flapping amplitude of 3? – 18?, and the phase difference of 10? – 60?. The results show that the bionic pectoral fin with actively controllable spatial deformation has expected propulsion performance, which supports that the natural features of the cownose ray play an important role in designing and developing a bionic prototype.

One of the most important topics in neuroscience is the issue of brain electrical stimulation and its widespread use. Based on this issue, rat robot, a rat navigation system was introduced in 2002, which has utilized brain electric stimulations as a guide and a reward for driving rats. Recently systems have been designed which are automatically navigated by a computer. One of the obstacles in the way of these systems is to select the stimulation frequency of the somatosensory cortex for the rotation action. In this paper, the stimulation parameters of the somatosensory cortex for rotation in the T-shaped maze were examined for the first time with applying only one pulse train. Then, the optimized parameters have been utilized in a complex maze. The results show that the performance is directly related to the pulse width and it has an inverse relationship with the pulse intervals. With optimal parameters, correctly controlling the animal in 90% of the trials in the T-maze, were managed, and in the complex maze, about 70% of the stimuli with optimized parameters were with only applying one pulse train. The results show that the stimulation parameters for navigation with only one pulse train are well optimized, and the results of this paper can be a trigger for an automatic navigation and reduce the computational costs and automatic system errors.Neuroscience & Neuroengineering Research Lab., Biomedical Engineering Department, School of Electrical Engineering, Iran University of Science and Technology (IUST), Narmak, 16846-13114, Tehran, Iran

The electromagnetic field (EMF) is one of many environmental factors, which earth creatures are exposed to. There are many reports on the effects of EMF on living organisms. However, since the mechanism has not yet been fully understood, the biological effects of EMF are still controversial. In order to explore the effects of bio-inspired EMF (BIEMF) on normal and cancer cells, various cultured cells have been exposed to BIEMF of different directions, i.e. vertical, parallel and inclined. Significantly reduced ATP production in Hela and A549 cancer cells is found for the parallel and vertical BIEMF. More careful examination on Hela cells has revealed a cell density dependent inhibition on colony formation. The morphological observation of BIEMF-exposed Hela cells has suggested that the retarded cell proliferation is probably caused by cell death via apoptosis. Together these results may afford new insights for cancer prevention and treatment.

Multilevel thresholding is a simple and effective method in numerous image segmentation applications. In this paper, we propose a new multilevel thresholding method that uses cooperative pigeon-inspired optimization algorithm with dynamic distance threshold (CPIOD) for boosting applicability and the practicality of the optimum thresholding techniques. Firstly, we employ the cooperative behavior in the map and compass operator of the pigeon-inspired optimization algorithm to overcome the “curse of dimensionality” and help the algorithm converge fast. Then, a distance threshold is added to maintain the diversity of the pigeon population and increase the vitality to avoid local optimization. Tsallis entropy is used as the objective function to evaluate the optimum thresholds for the considered gray scale images. Four benchmark images are applied to test the property and the stability of the proposed CPIOD algorithm and three other optimization algorithms in multilevel thresholding problems. Segmentation results of four optimization algorithms show that CPIOD algorithm can not only get higher quality segmentation results, but also has better stability.