Bionic Surface Research Articles

Femtosecond laser-induced superwetting surfaces

The materials with various superwettabilities have attracted increasing interests because of their broad applications, such as water/oil-repellent coating, self-cleaning coating, anti-ice/fog/snow, manipulation of droplets, oil/water separation, antifouling, anti-corrosion, underwater drag reduction, lab chip, cell engineering, fog collection, microfluidic systems, and so on. After millions of years of evolution, natural organisms have evolved perfect structures and multifunctional surfaces. The surfaces of many plants and animals are endowed with special wettability, which inspire scientists to design and fabricate bionic surfaces with superwettability. It is found that the surface wettability is mainly determined by the chemical composition and surface microstructure. Inspired by nature (e.g., lotus leaf, fish scale, pitcher plant, red rose petal, rice leaf, butterfly wings), a large number of superwetting surfaces have been developed by various microfabrication technologies. However, those methods, more or less, are suffered from some inherent limitations, e.g., tight restriction on special materials, lack flexibility, and complex fabrication process. The development of a widely applicable and simple tool that can easily achieve various superwettabilities is still the major trend in this research field. Femtosecond laser has been proven to be a strong tool in advanced micro/nanofabrication. Recently, this tool is also successfully applied to design and change the surface wettability of different solid substrates. The femtosecond laser microfabrication has many advantages, such as small heat-affected zone, precise ablation threshold, non-contact process, and high resolution. In addition, the femtosecond laser can ablate almost all of the materials, including semiconductors, metals, polymers, glasses, and ceramics. By the simple one-step scanning manner, micro/nanoscale hierarchical structures can be directly created on the surfaces of different materials via the femtosecond laser treatment. Taking advantages of these features, femtosecond laser microfabrication have also been a great success in preparing superwetting surfaces. In this review, we summarize the recent developments in femtosecond laser-structured surfaces with special wettability. The article starts with the introduction related to the theoretical basis of wettability and the features of femtosecond laser microfabrication, as the background. Then, different superwettabilities achieved by femtosecond laser treatment are summarized, grouped by the characteristic of wettability. Inspired by nature, those laser-induced surface microstructures have superhydrophobicity, underwater superoleophobicity, underwater superaerophobicity, slippery liquid-infused porous surface, controllable adhesion, and anisotropic wettability, respectively. In each class of properties, the biological surface with such superwettability is introduced in advance. Then, how to use a femtosecond laser to design and fabricate these special superwetting microstructures was discussed, i.e., the preparation principle. According to the formation mechanism of these superwetting states, the internal relation between the femtosecond laser-induced surface microstructure and the macroscopic wettability is revealed; that is, surface microstructure determines the surface wettability. Next, some examples about the practical applications of the femtosecond laser-designed superwetting surfaces are also introduced following various superwettabilities, such as self-cleaning, manipulation of liquid droplets, oil/water separation, cell engineering, fog harvesting, buoyancy enhancement, liquid patterning, underwater gas capture, and detection analysis. Finally, the existing challenges and future prospects of this fast-growing field are discussed. The technology of femtosecond laser-controlled surface wettability is still irreplaceable by other microfabrication methods because of its special advantages. Such technology is better at designing and preparing fine microstructures and complex and heterogeneous wettability. This technology will have superiority in some special applications, such as cell engineering, military facilities, etc. With more and more scientists and engineers getting into this research field and being devoted to fabricating various superwetting surfaces, this research direction will have a bright and exciting future.

Fabrication of biomimetic graphene films on fabric base by two-beam laser interference

Through millions of years of evolution and natural selection, various biological species own unique physiological structure and amazing functionality. Biomimetic fabrication demonstrate remarkable trend of development, artificial biomimetic materials and intelligent functional surfaces have been extensively studied by scientists both theoretically and experimentally. In general, traditional biomimetic materials consisting of metal, metal oxides, carbon materials and some other polymer materials, which make outstanding contribution to the generation and development of engineering bionics science and interface chemistry analysis. However, simpleminded traditional materials are not capable to deal with the presence of intelligent driving control and micro nano device applications in artificial biomimetic science. It is well established that the combination of novel materials and novel biomimetic technology may lead to promote progress and development of fabrication with smart integration of multifunctional biomimetic devices. More recently, a kind of carbon nanomaterials with an atomic layer thickness which named graphene has attracted most widely attention due to its excellent properties, for instance ultrahigh carrier mobility, good electrical conductivity, high transmittance and biocompatibility since it has been founded by mechanical stripping adhesive tape, it becomes a new star of materials scientific fields. Its stable physical/chemical properties make it widely applied in electronic devices, optical devices, biochips, and even intelligent robots. Based on graphenes distinctive material properties, micronano-structured graphene surfaces with special wettability may be fabricated in a biomimetic manner that not only contribute to the experimental research but also bring about a new revolution of graphene-devices. A method of fabrication of biomimetic graphene surface with multilevel-structures by two-beam laser interference system has been proposed. Graphene oxide films on different fabric bases have been reduced and ablated by Nd:YAG laser interference system. Periodic graphene micronano-structures with grating-like micro structures and additional nanoscale structures have been produced during laser processing process with appropriate laser power (0.4 W), which resulted in deoxidization of abundant hydrophilic oxygen containing groups (OCGs) on GO sheets. To original GO film, the reduced GO (RGO) surface not only exhibited more rough geometry, but also owned lower surface energy. Raman spectroscopy has been characteristiced, the result of the D and G band peaks of RGO show neglectable changes contrast GO. The reason is that the laser cutting and ablation can bring additional new defects on the edges of graphene sheets, which leads to the increase of D band peak. As a result, the spectra show unobvious changes. Roughness of the fabric surface (silk, cotton, nylon) further increased the surface roughness of biomimetic graphene surface. Graphene biomimetic surface with multi-structures has been formed by the double action of rough fabric base and graphene micronano-structure. The graphene bionic surface with nylon substrate has the largest hydrophobic angle, ~156°. The biomimetic graphene surface not only possesses superhydrophobic wettability, but also exhibits rainbow structural color due to the existence of periodic graphene micronano-structures. We believe that the biomimetic graphene surface on fabric substrate will not only have important application prospects in the field of bionics, but also be a major exploration and breakthrough in the future research of optoelectronic and wearable devices.

An Optimal Wet Friction Plate Inspired by Biological Surface Patterns

It is found that many biological organisms exhibit superior adhesion characteristics in wet environments. It has been observed that the foot pads of tree frogs and katydids are consist of a number of closely arranged polygons, most of them are hexagonal. In this paper, the common structure of two kinds of biological foot pad was extracted to model the bionic surface structure of friction plates. The friction plate prototypes were also prepared. Through the multivariate orthogonal regression design, the optimum parameter combination of the friction performances of the prototypes of the bionic plates has been obtained. The hexagonal circumcircle size is 10 mm, the groove width is 1 mm, and the hexagonal diagonal angle is 90°. Then the maximum static friction coefficient, dynamic friction coefficient and wear amount of the optimal friction plate were tested and compared with the control group friction plates. The comparative analysis of the experiment findings demonstrated that the bionic structure with hexagonal ring grooves can significantly improve the friction performance of the friction plates.

Numerical prediction on abrasive wear reduction of bulk solids handling equipment using bionic design

Abrasive wear can cause surface damage of bulk solids handling equipment. Reducing the abrasive wear is beneficial to lower the maintenance cost. Previous research elaborated on the bionic design methodology to reduce surface wear of bulk solids handling equipment. To facilitate the application of the bionic design methodology in bulk solids handling, this research examines the effectiveness of a bionic model using discrete element method (DEM) simulations. A reference case of an abrasive wear scenario in bulk solids handling is simulated, and the wear volume of a smooth chute surface is predicted. By applying a bionic model to the chute surface and using the same simulation model, the wear volume of a bionic surface is predicted. By comparisons, it is identified that the bionic surfaces produce less wear than the smooth surface. In addition, the sensitivities of the geometrical parameters for the wear reduction are predicted. Therefore, the abrasive wear reduction effectiveness of the bionic model is demonstrated.

Experimental investigations on drag-reduction characteristics of bionic surface with water-trapping microstructures of fish scales

Biological surfaces with unique wettability in nature have provided an enormous innovation for scientists and engineers. More specifically, materials possessing various wetting properties have drawn considerable attention owing to their promising application prospects. Recently, great efforts have been concentrated on the researches on wetting-induced drag-reduction materials inspired by biology because of their ability to save energy. In this work, the drag-reduction characteristics of the bionic surface with delicate water-trapping microstructures of fish Ctenopharyngodon idellus scales were explored by experimental method. Firstly, the resistance of smooth surface and bionic surface experimental sample at different speeds was carefully tested through the testing system for operation resistance. Then, the contact angle (CA) of fish scale surface was measured by means of the contact angle measuring instrument. It was discovered that the bionic surface created a rewarding drag-reduction effect at a low speed, and the drag-reduction rate significantly displayed a downward trend with the increase in flow speed. Thus, when the rate was 0.66 m/s, the drag-reduction effect was at the optimum level, and the maximum drag reduction rate was 2.805%, which was in concordance with the simulated one. Furthermore, a contact angle (CA) of 11.5° appeared on the fish scale surface, exhibiting fine hydrophilic property. It further manifested the spreading-wetting phenomenon and the higher surface energy for the area of apical of fish scales, which played an important role in drag-reduction performance. This work will have a great potential in the engineering and transportation field.

Bionic PDMS film with hybrid superhydrophilic/superhydrophobic arrays for water harvest

This paper presents a cheap and facile strategy for fabricating hybrid superhydrophilic/superhydrophobic arrays on a flexible polydimethylsiloxane (PDMS) film to harvest water from fog efficiently. The hydrophobic PDMS film, which mimics the micro-/nanostructures on a beetle’s back, was selected as the substrate, on which a hydrophilic silicon dioxide (SiO2) colloidal monolayer was fabricated through self-assembly. After reactive ion etching, the silicon dioxide microsphere arrangement changed from pristine hexagonal close packed into hexagonal non-close packed. The silicon dioxide microspheres demonstrated superhydrophilicity and functioned as masks. Patterned grooves were also formed on the PDMS film and displayed superhydrophobicity. The fabricated hybrid superhydrophilic/superhydrophobic array films exhibited extreme wettability contrast and excellent water-harvesting performance of 3660·5 mg/(cm2 h), which is much better than that of bionic surfaces of the Namib Desert beetles’ back reported by others. The bionic flexible films can be reproduced with low cost and can be applied in water-trapping tents, building coverings, water or organic vapor condensers and microfluidic channels.

Heat Transfer Designed for Bionic Surfaces with Rib Turbulators Inspired by Alopias Branchial Arch in a Simplified Gas Turbine Transition Piece

The energy needed for highly efficient heat transfer has shown a continuous growth, as the energy reduction. For highly efficient power convection, gas turbine is an important device at present. But, the design of highly efficient gas turbine is limited by the temperature and the material’s temperature resistance around the inlet. One part of the inlet need to be protected from burning out is transition piece. A bionic thermal surface with rib turbulators is designed according to the turbulence function of alopias’ branchial arches and is evaluated for thermo-protection enhancement in a simplified gas turbine transition piece using computational fluid dynamics (CFD) simulation. With the given diameter (Φ = 10.26 mm) of the impinging hole, three different horizontal distances (S) from impinging holes to the front of first-row rib were solved, which were S1 = 20 mm, S2 = 40 mm, and S3 = 60 mm, respectively, in case 1. But, the results revealed that S is not a significant influence factor on heat transfer efficiency. The cooling coefficient increases from 0.194 to 0.198 when the distance varies from S1 to S3. In case 2, rib turbulator width (W) and height (H) have been studied in ranges from 0.5 × Φ to 1.5 × Φ. All of the numerical results indicated that the best size of the rib turbulators could improve the heat transfer efficiency to 32.5%, when comparing with the smooth surface. All of the comparisons will benefit the structural design of heat transfer, which could be used for solving more severe problems in thermo-protection.

Coupling Effect of Morphology and Mechanical Properties Contributes to the Tribological Behaviors of Snake Scales

It is known that the tribological behaviors of snake skins are contributed by the synergistic action of multiple factors, such as surface morphology and mechanical properties, which has inspired fabrication of scale-like surface textures in recent years. However, the coupling effect and mechanism remain to be elucidated. In this work, the morphology and mechanical properties of the scales from different body sections (leading body half, middle trunk and tailing body half) and positions (dorsal, lateral and ventral) of Boa constrictor and Eryx tataricus were characterized and compared to investigate the corresponding effects on the tribological behaviors and to probe the possible coupling mechanism. The morphological characterizations of scanning electron microscopy and atomic force microscopy revealed significant differences between the two species that the scales from Boa constrictor are rougher in general. The mechanical properties measured by nanoindentation corroboratively demonstrated substantial differences in elastic modulus and hardness. Interestingly, the ventral scales with lower surface roughness, together with relatively larger elastic modulus and hardness, manifest higher friction coefficients. A “double-crossed” hypothesis was proposed to explain the observed coupling effect of morphology and mechanical properties on friction, which may afford valuable insights for the design of bionic surface with desirable tribological performance.

Enhanced properties of PES membrane with bionic surface of self-assembled core-shell micelles

Herein, self-assembled core-shell micelles of amphiphilic comb copolymer imitating the structure of fish scales was employed to tune the surface structure and surface properties of PES membrane. Numerous papillae with a diameter of 100–200 nm were fabricated on membrane surface, which effectively improved the performances of the resultant membrane. Upon modification, water contact angle of the membrane was decreased from 78.3° to as low as 43.8°, while the flux recovery ratio was increased from 61.2% to as high as 97.4%. This study provided a facile way for the fabrication of composite membranes with regular surface structure.

仿生鲨鱼皮滚压成型表面减阻数值模拟研究

仿生鲨鱼皮滚压成型表面减阻数值模拟研究

Preparation of Robust Superhydrophobic Halloysite Clay Nanotubes via Mussel-Inspired Surface Modification

In this study, a novel and convenient bio-inspired modification strategy was used to create stable superhydrophobic structures on halloysite clay nanotubes (HNTs) surfaces. The polydopamine (PDA) nanoparticles can firmly adhere on HNTs surfaces in a mail environment of pH 8.5 via the oxidative self-polymerization of dopamine and synthesize a rough nano-layer assisted with vitamin M, which provides a catechol functional platform for the secondary reaction to graft hydrophobic long-chain alkylamine for preparation of hierarchical micro/nano structures with superhydrophobic properties. The micromorphology, crystal structure, and surface chemical composition of the resultant superhydrophobic HNTs were characterized by field emission scanning electron (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The as-formed surfaces exhibited outstanding superhydrophobicity with a water contact angle (CA) of 156.3 ± 2.3°, while having little effect on the crystal structures of HNTs. Meanwhile, the resultant HNTs also showed robust stability that can conquer various harsh conditions including strong acidic/alkaline solutions, organic solvents, water boiling, ultrasonic cleaning, and outdoor solar radiation. In addition, the novel HNTs exhibited excellent packaged capabilities of phase change materials (PCMs) for practical application in thermal energy storage, which improved the mass fractions by 22.94% for stearic acid and showed good recyclability. These HNTs also exhibited good oil/water separation ability. Consequently, due to the superior merits of high efficiency, easy operation, and non-toxicity, this bionic surface modification approach may make HNTs have great potentials for extensive applications.

Adsorption and Wetting of Protein Affected by Bionic Surface Texture Desig Nfor Artificial Organs Application

Background Surface texture has been widely used in functional surface design. Protein adsorption on the surface plays an impmtant role in improving biocompatibility of materials for aitificial organs development. Methods Anay of bionic surface texture was fabricated on the surface of titanium alloy to imitate the surface of artificial organs. Experiments of BSA protein adso rption were perfonned on the different surface textures under stead body temperature of 38 degree centigrade for 4 hours. Property of absorption and wetting were characterized by polarizing microscope, scanning electron microscope and contact angle meter. Results Results showed that BSA adsorption decreased with the increasing of surface texture depths and ratios, and tended to be stable finally. The wetting property became poorer as the surface texture depths and ratios increased. There was a remarkab le conelation between them. However, High levels of texture depths and density may lead to the negative influence on the tribo logical property of the surface. Conclusion Bionic surface texture has obvious influence on the adsorption and wetting of protein. Proper parameters of bionic surface texture may be of importance for the surface design in the real specific application. Acknowledgment Supported by a project grant from the Science and Technology Innovation Fund (Grand No. 2014kct-03).

Review of mechanical research and aerodynamic drag reduction of bionic surface micro-structures

Review of mechanical research and aerodynamic drag reduction of bionic surface micro-structures

Influence of PVD-duplex-treated, Bionic Surface Structures on the Wetting Behavior for Sheet-Bulk Metal Forming Tools

Bionic surface structures, inspired by the flora, were developed for Sheet-Bulk Metal Forming (SBMF) in order to locally control the friction condition by adjusting the wetting behavior. Five bionic structures were micromilled on ASP®2023 in annealed as well as hardened and tempered conditions. Subsequently, the structured surfaces were plasma-nitrided and coated with a CrAlN thin film. The influence of the treatment method on the structural geometry was investigated with the aid of a scanning electron microscope and 3D-profilometer. The wetting behaviors of water and deep drawing oil (Berufluid ST6007) on bionic surfaces were evaluated using contact angle measurements. The resulting micro-milled structures exhibit an almost identical shape as their bionic models. However, the roughness of the structured surfaces is influenced by the microstructure. The combination of plasma-nitriding and Physical Vapor Deposition (PVD) leads to an increase in roughness. All bionic structures possess higher contact angles than that of the unstructured surfaces when wetted by water. This can be explained by the fact that the structural elevations block the spreading. When the bionic surfaces are wetted by deep drawing oil, the lubricant spreads in the structural cavities, leading to smaller contact angles. Furthermore, the anisotropy of the structure has an influence on the wetting behavior.

The effect of the micro-structures on the scorpion surface for improving the anti-erosion performance

New bionic function surface inspired from desert scorpion was developed for erosion resistance application in this research. Three elements, bump, groove-shape and curvature, were applied on the surface. Using of Stereo Microscope, the micro-structures of the scorpion (Androctonus australis) were analyzed. According to information, bionic samples were manufactured. Solid particle erosion behavior is investigated using a blasting jet machine at particle impact angle (30°) and stress of air compressor is 0.5MPa. The experimental results of bionic samples were compared with traditional smooth sample and each other, respectively. Results of erosion test and Scanning Electron Microscope (SEM) were selected as evaluation standard and explored anti-erosion mechanisms of these micro-structures which were on the bionic surface. The experimental results show that bionic samples have superior solid particle erosion resistance than traditional smooth sample, owing to the micro-structures on the surface. Referring to the analysis, both the bump and curvature can improve the anti-erosion performance by changing the relative impact angle which is compared to the surface of sample.

Water-trapping and drag-reduction effects of fish Ctenopharyngodon idellus scales and their simulations

In the last decades, surface drag reduction has been re-emphasized because of its practical values in engineering applications, including vehicles, aircrafts, ships, and fuel pipelines. The bionic study of drag reduction has been attracting scholars’ attentions. Here, it was determined that the delicate microstructures on the scales of the fish Ctenopharyngodon idellu s exhibit remarkable drag-reduction effect. In addition, the underlying drag-reduction mechanism was carefully investigated. First, exceptional morphologies and structures of the scales were observed and measured using a scanning electron microscope and 3-dimensional (3D) microscope. Then, based on the acquired data, optimized 3D models were created. Next, the mechanism of the water-trapping effect of these structures was analyzed through numerical simulations and theoretical calculations. It was determined that there are many microcrescent units with certain distributions on its surface. In fact, these crescents are effective in generating the “water-trapping” effect and forming a fluid-lubrication film, thus reducing the skin friction drag effectively. Contrasting to a smooth surface, the dynamics finite-element analysis indicated that the maximum drag-reduction rate of a bionic surface is 3.014% at 0.66 m/s flow rate. This study can be used as a reference for an in-depth analysis on the bionic drag reduction of boats, underwater vehicles, and so forth.

Effects of Bionic Units in Different Scales on the Wear Behavior of Bionic Impregnated Diamond Bits

Based on anti-wear theory of soil animals, the samples of impregnated diamond bit with bionic self-regenerated non-smooth surface were designed and fabricated. Such a bionic surface was characterized by concave-shape units of different scales that continuously maintained their shape and function during the whole working process. Abrasion tests were carried out to investigate the performance of samples. Results showed that the bionic samples exhibit excellent wear resistance and drilling performance under the action of bionic self-regenerated units, especially those with units of 2 mm – 3 mm diameter. The particle-trapping mechanism coming from the self-regenerated concaves and the lubricating mechanism coming from the continuously self-supplying of solid lubricant are important reasons for reducing or even avoiding the severe abrasions. The improved drilling performance of bionic samples derives from, on the one hand, the back edge of bionic unit that contributes to exposing new diamond and supplying additional shear stresses to increase the cutting ability, on the other hand, the enhanced load per unit area due to the decreased contact area at the frictional interface. The relationship between the wear behavior and the scale of bionic unit was revealed. The unit of smaller scale on the bionic samples can enhance the shear stress level. Further reducing the scale to a contain extent will diminish the wear resistance of sample. While increasing the scale can lead to the poor lubricating effect.

Influence of Cycle Temperature on the Wear Resistance of Vermicular Iron Derivatized with Bionic Surfaces

Depending on their applications, such as in brake discs, camshafts, etc., the wear behavior of vermicular iron is influenced by the thermal cycling regime. The failure of a working part during its service life is a consequence of both thermal fatigue and wear. Previously, the wear and thermal fatigue resistance properties of vermicular iron were separately investigated by researchers, rather than a study combining these two factors. In the present work, the effect of cycle temperature on the wear resistance of specimens with bionic units processed by laser has been investigated experimentally. The wear behavior pre- and post-thermal cycling has also been investigated, and the influence of different cycle temperatures on the wear resistance is discussed. The results indicate that the thermal cycling regime brought about negative influences with varying degrees, on the material properties, such as the microstructures, micro-hardness, cracks, and oxidation resistance properties. All these factors synergistically reduced the wear resistance of vermicular iron. In particular, the negative influence apparently increased with an increase in cycle temperature. Nevertheless, the post-thermal-cycle wear resistance of the specimens with bionic units was superior to those without bionic units. Hence, the laser bionic process is an effective way to improve the performance of vermicular iron in combined thermal cycling and wear service conditions.

Biomimetic cardiovascular stents for invivo re-endothelialization.

The use of cardiovascular stents for rapid invivo re-endothelialization is a promising strategy for reducing cardiovascular implantation or preventing local thrombus formation and restenosis. Surface-patterned intravascular endoprosthetic stents have been developed to prevent life-threatening complications. In this study, vascular smooth muscle cell (VSMC)-biomimetic surface patterns were fabricated on 316L cardiovascular stents using a femtosecond laser and then implanted into the iliac artery of rabbit. The invitro data revealed that the bionic surface patterns matched the morphology of the VSMCs well, which promotes the adhesion, proliferation, and migration of human umbilical vein endothelial cells. In addition, the patterned surfaces can significantly enhance re-endothelialization. Consequently, the surface biomimetic stent with the VSMC surface pattern is likely an effective approach to ensure rapid re-endothelialization and possibly reduce the incidence of in-stent restenosis.

Constructing bio-layer of heparin and type IV collagen on titanium surface for improving its endothelialization and blood compatibility.

The modification of cardiovascular stent surface for a better micro-environment has gradually changed to multi-molecule, multi-functional designation. In this study, heparin (Hep) and type IV collagen (IVCol) were used as the functional molecule to construct a bifunctional micro-environment of anticoagulation and promoting endothelialization on titanium (Ti). The surface characterization results (AFM, Alcian Blue 8GX Staining and fluorescence staining of IVCol) indicated that the bio-layer of Hep and IVCol were successfully fabricated on the Ti surface through electrostatic self-assembly. The APTT and platelet adhesion test demonstrated that the bionic layer possessed better blood compatibility compared with Ti surface. The adhesion, proliferation, migration and apoptosis tests of endothelial cells proved that the Hep/IVCol layer was able to enhance the endothelialization of the Ti surface. The in vivo animal implantation results manifested that the bionic surface could encourage new endothelialization. This work provides an important reference for the construction of multifunction micro-environment on the cardiovascular scaffold surface.