Advanced Nanostructured Surfaces for the Control of Biofouling: Cell Adhesions to Three-Dimensional Nanostructures

In this paper, the interaction mechanism between the solid–liquid–gas interface phenomenon caused by nanostructure and surface wettability and boiling heat transfer is described, and the heat transfer theory of single wettable nanostructure surface and mixed wettable nanostructure surface is proposed. Through molecular dynamics simulation, the thermodynamic model of the wettable surface of nanostructures is established. The nanostructures are set as four rectangular lattice structures with a height of 18 Å. The solid atoms are platinum atoms, and the liquid atoms are argon atoms. The simulation results show that with the increase of surface hydrophilicity of nanostructures, the fluid temperature increases significantly, and the heat transfer at the interface is enhanced. With the increase in surface hydrophobicity of nanostructures, the atoms staying on the surface of nanostructures are affected by the hydrophobicity, showing a phenomenon of exclusion, and the evaporation rate in the evaporation area of nanostructures is significantly increased. In addition, the mixed wettable surface is influenced by the atomic potential energy and kinetic energy of the solid surface, and when compared with the pure wettable surface under the nanostructure, it changes the diffusion behavior of argon atoms on the nanostructure surface, enhances the heat transfer phenomenon compared with the pure hydrophobic surface, and enhances the evaporation phenomenon compared with the pure hydrophilic surface. This study provides insights into the relationship between the vapor film and the heating surface with mixed wettability and nanostructures.

Effects of surface nanostructure and wettability on CO2 nucleation boiling: A molecular dynamics study

Recent nanotechnology revolutions have cast increased challenges to biotechnology including bio-adhesion of cells. Surface topography and chemistry tailored by the nanotechnology exert significant effects on such applications so that it is necessary to understand how cells migrate and adhere on three-dimensional micro- and nanostructures. However, the effects of the surface topography and chemistry on cell adhesions have not been studied systematically and interactively yet mostly due to the inability to create well-controlled nanostructures over a relatively large surface area. In this paper, we report on the bio-adhesions of varying cell types on well-ordered (post and grate patterns), dense-array (230 nm in pattern periodicity), and sharp-tip (less than 10 nm in tip radius) nanostructures with varying three-dimensionalities (50- 500 nm in structural height). Significantly lower cell proliferation and smaller cell size were measured on tall nanostructures. On a grate pattern, significant cell elongation and alignment along the grate pattern were observed. On tall nanostructures, it was shown that cells were levitated by sharp tips and easily peeled off, suggesting that cell adherence to the tall and sharp-tip nanostructures was relatively weak. The control of cell growth and adherence by the nanoscale surface topographies can benefit the micro- and nanotechnogies-based materials, devices, and systems, such as for anti-biofouling and anti-microbial surfaces. The obtained knowledge by this investigation will also be useful to deal with engineering problems associated with the contact with biological substances such as biomaterials and biosensors.

Displacement efficiency and displacement pattern of multiphase flow in porous media have a profound influence on many geo-energy applications such as geologic CO$_{2}$ sequestration and enhanced oil recovery. Wettability is one of the most important factors affecting the displacement pattern and displacement efficiency of multiphase flow in porous media. Here, we combined the glass microfluidics, inverted microscope and high speed CMOS camera to set up a visualization experimental system and modified the surface wettability of the glass microfluidics using the silanization treatment and piranha solution. Pore-scale visualization displacement experiments were conducted on five flow rates and two wetting conditions (hydrophilic and hydrophobic conditions) in glass microfluidics which are fabricated from the pore structure of natural sandstone. Experimental results show that the displacement pattern shifts from capillary fingering to compact displacement pattern both in the hydrophilic and hydrophobic media as the flow rate increases. Under lower flow rates, the capillary force plays the dominant role in the fluid invasion processes. The invasion finger width and the number of air clusters in hydrophilic media are both smaller than those in the hydrophobic media, but the maximum air cluster radius, the average cluster radius and the standard deviation of cluster radius are all greater under hydrophilic conditions. The results also demonstrate that the displacement efficiency under hydrophilic condition is significantly lower than that of hydrophobic conditions due to single-channel flow and by pass flow phenomena which both only occur in hydrophilic media. Finally, a modified capillary number was introduced in order to consider the role of wettability (contact angle) under favourable displacement. Then, a relationship between the displacement efficiency and the modified capillary number was proposed, which provides a potential and useful method for the prediction of displacement efficiency under different wetting conditions during favourable displacement.

Droplet impact and LFP on wettability and nanostructured surface

Understanding the fundamental mechanisms of vapor condensation on rough surfaces is crucial to a wide range of industrial applications. A hybrid thermal lattice Boltzmann model of the condensation heat transfer process on downward-facing rough surfaces characterized by the Cantor fractal is developed and numerically analyzed to investigate the condensation phase change behaviors on rough hydrophobic and hydrophilic surfaces. The dynamic behaviors of vapor condensation, including the evolutions of vapor–liquid interface, heat flux, condensate mass, and temperature distribution, on the hydrophilic and hydrophobic rough surfaces are presented and compared with corresponding smooth surfaces. The results indicate that the rough surface preferred a filmwise condensation under hydrophilic conditions but a hybrid dropwise–filmwise condensation under hydrophobic conditions. On the rough hydrophobic surface, the liquid film can rapidly adsorb droplets, maintaining a high-efficiency dropwise condensation. The absorption of droplets accelerates the liquid film growth and detachment process on the rough hydrophobic surface, which reduces the time-averaged thermal resistance of the filmwise region. These two behaviors together enhance condensation heat transfer on the downward-facing rough hydrophobic surface. Besides, stable dropwise condensation could also be formed on smooth hydrophilic surfaces and has better heat transfer performance than corresponding hydrophobic surfaces under the same heat transfer condition.

Investigation of thermal transport characteristics of thin-film liquid evaporation over nanostructured surface has been conducted using molecular dynamics simulation with particular importance on the effects of the nanostructure configuration for different wall–fluid interaction strengths. The nanostructured surface considered herein comprises wall-through rectangular nanoposts placed over a flat wall. Both the substrate and the nanostructure are of platinum while argon is used as the evaporating liquid. Two different wall–fluid interaction strengths have been considered that essentially emulate both hydrophilic and hydrophobic wetting conditions for three different nanostructure configurations. The argon–platinum molecular system is first equilibrated at 90 K and then followed by a sudden increase in the wall temperature at 130 K that induces evaporation of argon laid over it. Comparative effectiveness of heat and mass transfer for different surface wetting conditions has been studied by calculating the wall heat flux and evaporative mass flux. The results obtained in this study show that heat transfer occurs more easily in cases of nanostructured surfaces than in case of flat surface. Difference in behavior of argon molecules during and after the evaporation process, that is, wall adsorption characteristics, has been found to depend on the surface wetting condition as well as on presence and configuration of nanostructure. A thermodynamic approach of energy balance shows reasonable agreement with the present molecular dynamics study.

The adhesion behavior and bactericidal properties of the nanostructured surface of Si nanopillar array, which mimicked a cicada wing surface, were evaluated using Escherichia coli. Wettability of the nanostructured surface was controlled by using self-assembled monolayer (SAM). The adhesion behavior was strongly dependent on the wettability of the surface and whether it was a nanostructured or a flat surface. The number of adhered cells on the nanostructured surface was higher than that on the flat Au surface. In addition, the cell membrane was more strongly damaged at a higher contact angle than at a lower contact angle on the nanostructured surface. Time-lapse imaging was used to analyze the changes in fluorescence intensity caused by the effusion of an intercellular fluid, including fluorescent protein (mCherry), at the single cell level on the cicada wing surface and the artificial nanostructured surface. We found that there were three stages of changes in the fluorescence intensity gradient.

Effects of bubble coalescence on pool boiling heat transfer and critical heat flux – A parametric study based on artificial cavity geometry and surface wettability

Non-equilibrium molecular dynamics simulations have been conducted to understand the effect of solid-liquid interfacial wettability and surface material on the phase change phenomena of the thin liquid argon film placed over flat substrate at high wall superheat. The molecular system consists of a three phase simulation domain involving solid wall, liquid argon and argon vapor. After the system is thermally equilibrated at 90K and kept in equilibrium for a while, a high wall superheat (250K that is far above the critical temperature of argon) is induced at the liquid boundary so that the liquid undergoes ultrafast heating. Both hydrophilic and hydrophobic surfaces were considered in the present study in order to observe the effect of surface wettability on phase change characteristics for three different solid substrate materials namely, Platinum (Pt), Silver (Ag) and Aluminium (Al). Results obtained in the present study are discussed in terms of transient atomic distribution inside system domain, heat flux characteristics across the solid-liquid interface together with evaporative mass flux from liquid argon. Simulation results show that, depending on the surface wetting condition, the phase change process appears to be very different (explosive/ diffusive) for all three substrate materials under consideration. Among three materials considered herein, Al is found to offer the least favourable condition for phase change process while Pt and Ag show similar heat and mass transfer characteristics for both hydrophilic and hydrophobic wetting conditions. Surface wettability effect is found to be more prominent than the effect of substrate material in thin film liquid phase change phenomena.Journal of Chemical Engineering, Vol. 29, No. 1, 2017: 49-55

Appropriate surface wettability and roughness of biomaterials is an important factor in cell attachment and proliferation. In this study, we investigated the correlation between surface wettability and roughness, and biological response in human adipose-derived stem cells (hADSCs). We prepared wettable and rough gradient polyethylene (PE) surfaces by increasing the power of a radio frequency corona discharge apparatus with knife-type electrodes over a moving sample bed. The PE changed gradually from hydrophobic and smooth surfaces to hydrophilic (water contact angle, 90º to ~50º) and rough (80 to ~120 nm) surfaces as the power increased. We found that hADSCs adhered better to highly hydrophilic and rough surfaces and showed broadly stretched morphology compared with that on hydrophobic and smooth surfaces. The proliferation of hADSCs on hydrophilic and rough surfaces was also higher than that on hydrophobic and smooth surfaces. Furthermore, integrin beta 1 gene expression, an indicator of attachment, and heat shock protein 70 gene expression were high on hydrophobic and smooth surfaces. These results indicate that the cellular behavior of hADSCs on gradient surface depends on surface properties, wettability and roughness.

Many technological processes occurred upon the extraction and primary processing of coal (dust suppression, grouting, hydraulic fracturing, wet enrichment, etc.) depend on the wettability of the coal surface, determined by the physicochemical properties of the interacting media. The filtration properties of a fractured-porous coal massif significantly depend on the wettability of the surface. We present the results of studying the wettability of the coal surface with water and its filtration through a layer of coal powder. It is shown that the increased humidity of coal contributes to an increase in the wetting and filtration properties of the coal layer in relation to water due to the creation of a hydrate shell at the contact surface. It is revealed that the method of coal sample preparation significantly affects the functional composition and hydrophilicity of the outer surface of coal particles. Grinding coal in the presence of oxygen in air contributes to the formation of polar oxygen groups (hydroxyl, carboxyl) on the surface of coal particles, which leads to an increase in the hydrophilicity and filtration properties of coal. The results obtained can be used to predict the wettability of coals with process fluids, to improve technologies for mining, enrichment and processing of coals.

In order to study the effects of working conditions and solid surface topography on the wettability of material, a series of No. 45 steel specimens with the same surface arithmetic average height Sa and different surface microstructures is designed and manufactured by laser surface texturing. All the surfaces are measured by a non-contact three-dimensional (3D) optical profiler Talysulf CCI Lite and characterized by the ISO25178. A series of wetting experiments is carried out with the No. 32 turbine oil on an optical contact angle and surface tension meter SL200 KS. The effects of temperature, droplet volume and surface structure on the wettability are analyzed. Meanwhile, quantitative research of the relationship between the random characteristics of topography and wettability of the solid surface is conducted with parameters obtained from the ISO25178. Based on the fact that the contact angle is an acute angle, the results show that the contact angle of the droplet on the solid surface decreases rapidly to a stable value in the wetting process. The stable value decreases with the increase of the temperature, while it first increases and then decreases with the increase of the droplet volume. The surface wettability can be affected by the laser micro-texturing. Surfaces with similar values of Sa show different wettabilities for different micro-textures with different shapes and directions. Textured surfaces with grooves along the spreading direction of the droplet perform the best wettability in our research. Results also predicate that the wettability of surface is greatly influenced by the amplitude parameters (Sku, Ssk), spatial parameters (Str, Sal), hybrid parameters (Sdq, Sdr), and feature parameters (Sda, Sdv), which are all obtained from the ISO25178. The wettability of hydrophilic surface becomes better with increasing Sku, Sal, and Sdr and reducing Ssk, Str, and Sdq.

Tantalum is a promising orthopaedic implant coating material due to its robust mechanical properties, corrosion resistance, and excellent biocompatibility. Previous studies have demonstrated improved biocompatibility and tissue integration of surface-treated tantalum coatings compared to untreated tantalum. Surface modification of tantalum coatings with biologically inspired microscale and nanoscale features may be used to evoke optimal tissue responses. The goal of this study was to evaluate commercial tantalum coatings with nanoscale, sub-microscale, and microscale surface topographies for orthopaedic and dental applications using human bone marrow-derived mesenchymal stem cells (hBMSCs). Tantalum coatings with different microscale and nanoscale surface topographies were fabricated using a diffusion process or chemical vapor deposition. Biological evaluation of the tantalum coatings using hBMSCs showed that tantalum coatings promote cellular adhesion and growth. Furthermore, hBMSC adhesion to the tantalum coatings was dependent on surface feature characteristics, with enhanced cell adhesion on sub-micrometer- and micrometer-sized surface topographies compared to hybrid nano-/microstructures. Nanostructured and microstructured tantalum coatings should be further evaluated to optimize the surface coating features to promote osteogenesis and enhance osseointegration of tantalum-based orthopaedic implants.

Materials surface wettability is a fundamental property of a solid. Wettability plays a paramount role in the everyday applications of solid materials in many fields of science and technology. Numerous examples include advanced membranes (from water purification to biopharmaceuticals), energy storage devices, windows, raincoats, roofs, disposable diapers, microfluidics, bandages, tissue scaffolds, and bio-implants. With the continuous development of modern society, the demand for advanced functional materials with the desirable surface wettability is increasing faster than ever before. This is why precise control over surface wettability is expected to provide materials with superior properties for unprecedented applications in diverse fields.Over the past decade, conventional wet chemistry approaches have been among the most frequently used methods for surface wettability control. However, they are often energy-inefficient, pollute the environment, and rely on harsh synthesis conditions. Recently, low-temperature plasma processing has attracted major attention in surface wettability control. The reason for this particular interest is because plasma processing is highly-selective, environmentally friendly, and low-cost. Plasma processing can uniquely modify both the surface chemistry and surface topography for a wide range of materials. Moreover, it can be operated at very mild conditions such as room temperature, atmospheric pressure, and open-air environments.Plasma can be used as a controlled reactive physicochemical environment for surface activation, coating deposition, and nanostructuring of diverse materials. The unique plasma-specific conditions and effects allow precise control over microscopic surface chemical composition and surface nanostructures by adjusting the macroscopical energy input. Accordingly, effective control over surface wettability can be achieved for a broad range of hard and soft materials. An environmentally friendly, large scale and low-cost wetting control method that does not result in bulk damage, would result in improvement of industrial applications. A possible solution to this wetting control problem is atmospheric-pressure plasma (APP), especially the plasma generated in open-air due to the benefits of solvent-free treatment, requiring no vacuum systems and suitable for in-line processes. In the current work, we will give a comprehensive overview of different atmospheric pressure plasma processes capable to change the surface properties of the polymers with little or no change of the bulk. Two main approaches: (i) plasma activation introducing oxygen-containing groups into the material surface; (ii) plasma polymerization directed to the change of the surface composition will be highlighted and background will be explained.Recently our team developed a new approach based on the use of a combination of plasma activation and plasma polymerization, two different plasma techniques in a single process to achieve different surface wetting properties from hydrophilic to hydrophobic, with the high long-term stability of the coatings in water. Such a type of research approach realized in one plasma source was not yet applied for wettability control and has very promising application potential in the industrial processing of polymers. For surface engineering, and easy to scale-up the radio frequency (RF) plasma system was adopted to perform both plasma activation and plasma polymerization on PET substrate in the atmospheric pressure in the open air. Different characterization methods including WCA measurements, Fourier-transform infrared spectroscopy (FT-IR), XPS, and atomic force microscopy (AFM) were applied to get an insight into surface chemistry and morphology and the effect of the combination of the plasma activation with plasma polymerization.The developed approach has shown the capability of stable coatings deposition with the use of acrylic acid, HMDSO or fluorine-containing precursors PFDA. We demonstrate a single-step, fast, green, cheap, and universal plasma-based approach with potential for large-scale production of oil/water separation membranes, namely aerosol-assisted plasma deposition (AAPD). A hydrophobic polyester membrane is exposed to an in-line atmospheric pressure plasma coupled with an aerosol of a 2-hydroxyethyl methacrylate (HEMA) monomer. A plasma polymerized HEMA thin film is thus successfully coated on the membrane, resulting in an superhydrophilic/underwater superoleophobic surface. With created coating, the water pre-wetted plasma-functionalized polyester membrane shows an ultrahigh separation efficiency above 97.8% towards various oil/water mixtures and a superb water flux above 35.6 L m-2 s-1. Importantly, it also exhibits excellent performance in anti-oil-fouling, recyclability, and durability, indicating its high potential in real-life usage. To further examine the universality of the proposed approach, another hydrophilic monomer (acrylic acid) is also used to functionalize the polyester membranes. The obtained functionalized membranes can also efficiently separate diversified oil/water mixtures. Therefore, this study demonstrates the capability of plasma-based surface engineering methods to manipulate surface properties of materials in a very wide range from superhydrophobic to hydrophilic and even super-hydrophilic which opens new areas of applications.