Substrate Withdrawal Research Articles

Continuous protein-density gradients: A new approach to correlate physical cues with cell response.

To assess cellular behavior within heterogeneous tissues, such as bone, skin, and nerves, scaffolds with biophysical gradients are required to adequately replicate the in vivo interaction between cells and their native microenvironment. In this study, we introduce a strategy for depositing ultrathin films comprised of laminin-111 with precisely controlled biophysical gradients onto planar substrates using the Langmuir-Blodgett (LB) technique. The gradient is created by controlled desynchronization of the barrier compression and substrate withdrawal speed during the LB deposition process. Characterization of the films was performed using techniques such as atomic force microscopy and confocal fluorescence microscopy, enabling the comprehensive analysis of biophysical parameters along the gradient direction. Furthermore, human adipose-derived stem cells were seeded onto the gradient films to investigate the influence of protein density on cell attachment, showing that the distribution of the cells can be modulated by the arrangement of the laminin at the air-water interface. The presented approach not only allowed us to gain insights into the intricate interplay between biophysical cues and cell behavior within complex tissue environments, but it is also suited as a screening approach to determine optimal protein concentrations to achieve a target cellular output.

Silane‐Modified Mesoporous Silica Nanocoatings for Selective Mid‐Infrared Waveguide‐Based Gas Sensing

AbstractThis paper reports the use of silane monolayers of different polarities to enable recognition and selective interfacial enrichment of nonpolar versus polar gases for spectroscopic mid‐infrared (MIR) on‐chip sensing. However, detection of gases using on‐chip waveguides (WGs) is challenging because of the low concentrations of gas molecules within the evanescent field surrounding the WGs. To solve this issue, high‐surface‐area, precisely‐controlled‐thickness nanocoatings are introduced whose surface modification with strategically selected silanes enables control of preferential adsorption and concentration of polar versus nonpolar gas analytes. Conformal nanocoatings are constructed using layer‐by‐layer deposition of mesoporous silica nanoparticles (MSNs) at substrate withdrawal speeds controlled within the capillary regime. Surface modification of the WG‐immobilized MSNs with hydrophobic triethoxy(octyl)silane enables, for the first time, enhanced sensitivity and selectivity towards nonpolar methane gas as compared to its polar counterpart acetone. On the other hand, modification of the nanocoatings with (3‐aminopropyl)triethoxysilane leads to preferential binding of polar acetone vapors. This work demonstrates the capability of interfacial modification for controlling the selection and enhancement of the spectroscopic features of gas analytes with different polarities. The developed interfacial assemblies can enable diverse spectroscopic gas sensing platforms for applications in health diagnostics, environmental monitoring, and process control.

Surface Functionalization Utilizing Mesoporous Silica Nanoparticles for Enhanced Evanescent-Field Mid-Infrared Waveguide Gas Sensing

This work focuses on the development of nanoparticle-based layer-by-layer (LbL) coatings for enhancing the detection sensitivity and selectivity of volatile organic compounds (VOCs) using on-chip mid-infrared (MIR) waveguides (WGs). First, we demonstrate construction of conformal coatings of polymer/mesoporous silica nanoparticles (MSNs) on the surface of Si-based WGs using the LbL technique and evaluate the coating deposition conditions, such as pH and substrate withdrawal speed, on the thickness and homogeneity of the assemblies. We then use the modified WGs to achieve enhanced sensitivity and selectivity of polar organic compounds, such as ethanol, versus non-polar ones, such as methane, in the MIR region. In addition, using density functional theory calculations, we show that such an improvement in sensing performance is achieved due to preferential adsorption of ethanol molecules within MSNs in the vicinity of the WG evanescent field.

All-nanoparticle layer-by-layer coatings for Mid-IR on-chip gas sensing.

Functionalization of optical waveguides with submicron coatings of zinc peroxide (ZnO2) and silica (SiO2) nanoparticles (NPs) is reported that enabled selective concentration of acetone vapors in the vicinity of the waveguide, boosting the sensitivity of a mid infrared (MIR) on-chip detector. Controlled thickness was achieved by introducing precise control of the substrate withdrawal speed to the layer-by-layer (LbL) deposition technique.

Self-organized dip-coating patterns of simple, partially wetting, nonvolatile liquids

When a solid substrate is withdrawn from a bath of simple, partially wetting, nonvolatile liquid, one typically distinguishes two regimes, namely, after withdrawal the substrate is macroscopically dry or homogeneously coated by a liquid film. In the latter case, the coating is called a Landau-Levich film. Its thickness depends on the angle and velocity of substrate withdrawal. We predict by means of a numerical and analytical investigation of a hydrodynamic thin-film model the existence of a third regime. It consists of the deposition of a regular pattern of liquid ridges oriented parallel to the meniscus. We establish that the mechanism of the underlying meniscus instability originates from competing film dewetting and Landau-Levich film deposition. Our analysis combines a marginal stability analysis, numerical time simulations and a numerical bifurcation study via path-continuation.

Monolayer Arrays of Nanoparticles on Block Copolymer Brush Films.

Two-dimensional arrays of nanoparticles (NPs) have widespread applications in optical coatings, plasmonic sensors, and nanocomposites. Current bottom-up approaches that use homogeneous NP templates, such as silane self-assembled monolayers or homopolymers, are typically plagued by NP aggregation, whereas patterned block copolymer (BCP) films require specific compositions for specific NP distributions. Here, we show, using polystyrene- b-poly(4-vinylpyridine) (PS- b-P4VP) and gold NPs (AuNPs) of various sizes, that a nanothin PS- b-P4VP brushlike coating (comprised of a P4VP wetting layer and a PS overlayer), which is adsorbed onto flat substrates during their immersion in very dilute PS- b-P4VP tetrahydrofuran solutions, provides an excellent template for obtaining dense and well-dispersed AuNPs with little aggregation. These non-close-packed arrays have similar characteristics regardless of immersion time in solution (about 10-120 s studied), solution concentration below a critical value (0.1 and 0.05 mg/mL studied), and AuNP diameter (10-90 nm studied). Very dilute BCP solutions are necessary to avoid deposition, during substrate withdrawal, of additional material onto the adsorbed BCP layer, which typically leads to patterned surfaces. The PS brush coverage depends on immersion time (adsorption kinetics), but full coverage does not inhibit AuNP adsorption, which is attributed to PS molecular rearrangement during exposure to the aqueous AuNP colloidal solution. The simplicity, versatility and robustness of the method will enable applications in materials science requiring dense, unaggregated NP arrays.

Critical Role of the Atmosphere in Dip-Coating Process

Dip-coating is a common liquid deposition technique employed in research, but also for industrial production, to obtain polymer, hybrid and inorganic thin layers of controlled thickness. During liquid deposition, the substrate withdrawal speed allows in principle an easy tuning of deposited film thickness (first modeled by Landau and Levich). Yet, experimentally, unexplained thickness irreproducibility or strong fluctuations of the sol-gel films are often observed when coating large substrates, which is a critical issue for optical coatings such as anti-reflective/reflective coatings. In this study, we pointed out for the first time that uncontrolled solvent relative pressure gradients (coming from solvent evaporation) are responsible for these thickness fluctuation issues. We investigated and quantified their impact for various solutions (of sol-gel or polymer), and pointed out that the solvent evaporation rate is not constant but strongly depends on the geometric configuration of the dip-coating experiment. From this understanding, we demonstrated how an accurate tuning of processing atmosphere can provide a very good control on layer thickness in the practical case of the deposition of anti-reflective water repellent coating. In a second example, we used this phenomenon for developing a very easy synthesis strategy leading to giant and controlled thickness gradient profiles.

Evaporation-Driven Deposition of ITO Thin Films from Aqueous Solutions with Low-Speed Dip-Coating Technique.

We suggest a novel wet coating process for preparing indium tin oxide (ITO) films from simple solutions containing only metal salts and water via evaporation-driven film deposition during low-speed dip coating. Homogeneous ITO precursor films were deposited on silica glass substrates from the aqueous solutions containing In(NO3)3·3H2O and SnCl4·5H2O by dip coating at substrate withdrawal speeds of 0.20-0.50 cm min-1 and then crystallized by the heat treatment at 500-800 °C for 10-60 min under N2 gas flow of 0.5 L min-1. The ITO films heated at 600 °C for 30 min had a high optical transparency in the visible range and a good electrical conductivity. Multiple-coating ITO films obtained with five-times dip coating exhibited the lowest sheet (ρS) and volume (ρV) resistivities of 188 Ω sq-1 and 4.23 × 10-3 Ω cm, respectively.

Stationary contact line formation and particle deposition in dip coating

ABSTRACTThe stationary contact line formation and particle deposition in the evaporation regime of dip coating is investigated numerically by solving the conservation equations of mass, momentum, energy, vapor mass fraction, and particle concentration. A sharp-interface level-set method for tracking the liquid–gas interface is extended to include the effect of phase change and to treat the particle deposition as well as the liquid–gas–solid contact line on a moving substrate. The computations demonstrate that the particle deposition occurs spontaneously near the stationary contact line and the deposition thickness depends on the deposition rate constant and the substrate withdrawal velocity.

Experimental study on film thickness and the problem of free surface film flow in dip coating

AbstractDip coating is widely applied in industries for coating a solid substrate with a fluid because of its simplicity and applicability to substrates with different shapes. An experimental study was reported with dip coater on the film coating of solid plates by withdrawal from a tank filled with silicone oil fluids or polyacrylic acid (PAA) solutions with different rheological properties, the liquid film thickness deposited on the plate substrate was measured using capacitance method, and the evolution of free surface morphology was recorded with photographs. The purpose was to investigate the effects of plate substrate roughness, withdrawal speed, rest time, and fluid viscosity on the liquid film thickness and free surface morphology in detail. Results showed that the increases in coating fluid viscosity, withdrawal speed, and substrate roughness are beneficial to film thickening. The influence of rest time on liquid film thickness could be neglected when it was greater than 3 min. For silicone oil fluids, the free surface exhibited a depression, which gradually deepened, with the increasing in withdrawal speed and viscosities. By contrast, PAA solutions showed a bump on the free surface, exhibiting a curvature that increased with the increasing in withdrawal speed and concentrations. © 2016 Curtin University of Technology and John Wiley & Sons, Ltd.

Numerical simulation of stick-slip contact line motion and particle line formation in dip coating

Numerical simulation is performed for stick-slip contact line motion and particle line formation in dip coating. The liquid–gas interface as well as the liquid–gas–solid contact line is tracked by a sharp-interface level-set method, which is extended to include the effect of phase change, to implement the contact angle model for the stick-slip contact line motion, and to treat the particle deposition on a moving substrate. The computations demonstrate that the particle line formation is directly related to the stick-slip contact line motion. The effects of initial particle concentration, substrate withdrawal velocity, substrate temperature and contact angle on the particle line formation in dip coating are investigated.

Spontaneous Pattern Formation Induced by Bénard-Marangoni Convection for Sol-Gel-Derived Titania Dip-Coating Films: Effect of Co-solvents with a High Surface Tension and Low Volatility.

Evaporation-driven surface tension gradient in the liquid layer often causes the convective flow, i.e., Bénard-Marangoni convection, resulting in the formation of cell-like patterns on the surface. Here, we prepared sol-gel-derived titania films from Ti(OC3H7(i))4 solutions by dip coating and discussed the effect of the addition of co-solvents with a high surface tension and low volatility on the spontaneous pattern formation induced by Bénard-Marangoni convection. Propylene glycol (PG, with a surface tension of 38.6 mN m(-1)) and dipropylene glycol (DPG, with a surface tension of 33.9 mN m(-1)) were added to the coating solutions containing 2-propanol (2-Pr, with a surface tension of 22.9 mN m(-1)) for controlling the evaporation-driven surface tension gradient in the coating layer on a substrate. During dip coating at a substrate withdrawal speed of 50 cm min(-1) in a thermostatic oven at 60 °C, linearly arranged cell-like patterns on a micrometer scale were spontaneously formed on the titania gel films, irrespective of the composition of coating solutions. Such surface patterns remained even after the heat treatment at 200 and 600 °C, where the densification and crystallization of the titania films progressed. The width and height of the cell-like patterns increased with increasing PG and DPG contents in the coating solutions, where the addition of PG resulted in the formation of cells with a larger height than DPG.

Linking Precursor Alterations to Nanoscale Structure and Optical Transparency in Polymer Assisted Fast-Rate Dip-Coating of Vanadium Oxide Thin Films.

Solution processed metal oxide thin films are important for modern optoelectronic devices ranging from thin film transistors to photovoltaics and for functional optical coatings. Solution processed techniques such as dip-coating, allow thin films to be rapidly deposited over a large range of surfaces including curved, flexible or plastic substrates without extensive processing of comparative vapour or physical deposition methods. To increase the effectiveness and versatility of dip-coated thin films, alterations to commonly used precursors can be made that facilitate controlled thin film deposition. The effects of polymer assisted deposition and changes in solvent-alkoxide dilution on the morphology, structure, optoelectronic properties and crystallinity of vanadium pentoxide thin films was studied using a dip-coating method using a substrate withdrawal speed within the fast-rate draining regime. The formation of sub-100 nm thin films could be achieved rapidly from dilute alkoxide based precursor solutions with high optical transmission in the visible, linked to the phase and film structure. The effects of the polymer addition was shown to change the crystallized vanadium pentoxide thin films from a granular surface structure to a polycrystalline structure composed of a high density of smaller in-plane grains, resulting in a uniform surface morphology with lower thickness and roughness.

Titanium dioxide sol–gel-coated expanded clay granules for use in photocatalytic fluidized-bed reactor

An experimental research into the titania coatings on granulated expanded clay to be used in fluidized-bed photocatalytic reactor was undertaken. The preparation procedures were performed via sol–gel method using dip coating techniques. Two sol–gel compositions based on tetrabutyl orthotitanate and titanium tetraisopropoxide as well as two commercial TiO2 sols were examined. The impacts of titania precursor concentration, modification of sol–gel by industrially available TiO2 nanoparticles, the substrate withdrawal speed and thermal treatment conditions on the coatings’ properties were studied. The photocatalytic activity of expanded clay-supported titania was evaluated by the degradation of an emerging micropollutant, tetracycline family antibiotic doxycycline. Mechanically stable and active coatings with properties dependent on sol–gel processing parameters were obtained. The application of porous titania sol–gel-coated expanded clays could combine pollutants’ adsorption and their photocatalytic degradation. The compromise between coatings’ improved photocatalytic performance, on the one hand, and their adhesion and attrition properties, significant for fluidized-bed operation, on the other hand, lead to the determination of appropriate processing parameters.

Spontaneous formation of nanopatterns in velocity-dependent dip-coated organic films: from dragonflies to stripes.

We present an experimental study of the micro- and mesoscopic structure of thin films of medium length n-alkane molecules on the native oxide layer of a silicon surface, prepared by dip-coating in a n-C32H66/n-heptane solution. Electron micrographs reveal two distinct adsorption morphologies depending on the substrate withdrawal speed v. For small v, dragonfly-shaped molecular islands are observed. For a large v, stripes parallel to the withdrawal direction are observed. These have lengths of a few hundred micrometers and a few micrometer lateral separation. For a constant v, the stripes' quality and separation increase with the solution concentration. Grazing incidence X-ray diffraction and atomic force microscopy show that both patterns are 4.2 nm thick monolayers of fully extended, surface-normal-aligned alkane molecules. With increasing v, the surface coverage first decreases then increases for v > v(cr) ∼ 0.15 mm/s. The critical v(cr) marks a transition between the evaporation regime, where the solvent's meniscus remains at the bulk's surface, and the entrainment (Landau-Levich-Deryaguin) regime, where the solution is partially dragged by the substrate, covering the withdrawn substrate by a homogeneous film. The dragonflies are single crystals with habits determined by dendritic growth in prominent 2D crystalline directions of randomly seeded nuclei assumed to be quasi-hexagonal. The stripes' strong crystalline texture and the well-defined separation are due to an anisotropic 2D crystallization in narrow liquid fingers, which result from a Marangoni flow driven hydrodynamic instability in the evaporating dip-coated films, akin to the tears of wine phenomenology.

Evaporation-driven self-organization of photoluminescent organic dye-doped silica-poly(vinylpyrrolidone) hybrid films prepared by low-speed dip-coating

We prepared silica-poly(vinylpyrrolidone) (PVP) hybrid films containing a photoluminescent organic dye, rhordamine 6G (R6G), by low-speed dip-coating, where the spontaneous pattern formation was induced in the films. Stripe patterns arranged perpendicular to the substrate withdrawal direction were spontaneously formed by stick-slip motion at the meniscus during dip-coating, and the film structure (i.e., the film thickness, and the height, width and spacing of stripe patterns) was changed with increasing amounts of volatile solvent (C2H5OH) in solutions (C2H5OH/Si(OCH3)4 mole ratio (x)=20–150). As a result of the optimization of the film structure, localized photoluminescence at the stripe patterns was achieved over x=120.

Two-Dimensional Patterns of Poly(N-isopropylacrylamide) Microgels to Spatially Control Fibroblast Adhesion and Temperature-Responsive Detachment

Thermoresponsive poly(N-isopropyl acrylamide) (PNIPAM) microgels were patterned on polystyrene substrates via dip coating, creating cytocompatible substrates that provided spatial control over cell adhesion. This simple dip-coating method, which exploits variable substrate withdrawal speeds forming particle suspension stripes of densely packed PNIPAM microgels, while spacings between the stripes contained sparsely distributed PNIPAM microgels. The assembly of three different PNIPAM microgel patterns, namely, patterns composed of 50 μm stripe/50 μm spacing, 50 μm stripe/100 μm spacing, and 100 μm stripe/100 μm spacing, was verified using high-resolution optical micrographs and ImageJ analysis. PNIPAM microgels existed as monolayers within stripes and spacings, as revealed by atomic force microscopy (AFM). Upon cell seeding on PNIPAM micropatterned substrates, NIH3T3 fibroblast cells preferentially adhered within spacings to form cell patterns. Three days after cell seeding, cells proliferated to form confluent cell layers. The thermoresponsiveness of the underlying PNIPAM microgels was then utilized to recover fibroblast cell sheets from substrates simply by lowering the temperature without disrupting the underlying PNIPAM microgel patterns. Harvested cell sheets similar to these have been used for multiple tissue engineering applications. Also, this simple, low-cost, template-free dip-coating technique can be utilized to micropattern multifunctional PNIPAM microgels, generating complex stimuli-responsive substrates to study cell-material interactions and allow drug delivery to cells in a spatially and temporally controlled manner.

THREE-DIMENSIONAL MATHEMATICAL SHAPE MODEL AND PROCESS RESEARCH OF SPRAY-FORMED BILLET

Spray forming is an advanced technology that is used to produce a variety of high- performance materials with the characteristics of rapid solidification. By properly controlling of spray forming parameters, it is possible to fabricate near-net-shaped preforms, such as rod-billets, strips, and tubes. During the billet spray forming process, the shape of deposit strongly influences the solidification and consequently end-product quality. Therefore, it is necessary to reveal the shape forming mechanism in spray forming process. In the present work, a three-dimensional (3D) model, tracing the coordinates of the moving surface of a growing spray-formed billet, has been formulated to predict the shape evolution of the general deposit. This geometric model takes into account geometrical process parameters in the whole spray forming process: mass flux and mass distribution, position of the atomizer, distance between atomizer and the preform, substrate withdrawal velocity and rotation speed. This makes it possible to model not only the growth of a Gaussian shaped deposit in which case the spray axis and the rotation axis coincide, but also the profile evolution as there is a spray angle between these two axes. For this purpose, must be taken into account as a core part of the surface evolution algorithm. On the basis of this 3D model, a timesaving and accurate methodology is established to determine the shadowing effect coefficient, using the triangular element checking algorithm coupled with back face culling (BFC). The transient shape modeling has been validated by numerical algorithms and experimental investigation, and has proved that the simulated billet profiles are in good agreement with the experimental data. The effect of spray forming parameters, such as spray distribution parameters, withdrawal velocity, initial eccentric distance, spray angle and angular velocity of rotation, are analyzed. According to the obtained simulation results, the most dominant parameters affecting the shape evolution of deposit are the spray distribution parameters, withdrawal velocity, and initial eccentric distance. It is also found that the spray angle mainly affects the profile

Antigen and substrate withdrawal in the management of autoimmune thrombotic disorders

AbstractPrevailing approaches to manage autoimmune thrombotic disorders, such as heparin-induced thrombocytopenia, antiphospholipid syndrome and thrombotic thrombocytopenic purpura, include immunosuppression and systemic anticoagulation, though neither provides optimal outcome for many patients. A different approach is suggested by the concurrence of autoantibodies and their antigenic targets in the absence of clinical disease, such as platelet factor 4 in heparin-induced thrombocytopenia and β2-glycoprotein-I (β2GPI) in antiphospholipid syndrome. The presence of autoantibodies in the absence of disease suggests that conformational changes or other alterations in endogenous protein autoantigens are required for recognition by pathogenic autoantibodies. In thrombotic thrombocytopenic purpura, the clinical impact of ADAMTS13 deficiency caused by autoantibodies likely depends on the balance between residual antigen, that is, enzyme activity, and demand imposed by local genesis of ultralarge multimers of von Willebrand factor. A corollary of these concepts is that disrupting platelet factor 4 and β2GPI conformation (or ultralarge multimer of von Willebrand factor oligomerization or function) might provide a disease-targeted approach to prevent thrombosis without systemic anticoagulation or immunosuppression. Validation of this approach requires a deeper understanding of how seemingly normal host proteins become antigenic or undergo changes that increase antibody avidity, and how they can be altered to retain adaptive functions while shedding epitopes prone to elicit harmful autoimmunity.

Spontaneous Formation of Linearly Arranged Microcraters on Sol–Gel-Derived Silica–Poly(vinylpyrrolidone) Hybrid Films Induced by Bénard–Marangoni Convection

Complex, sophisticated surface patterns on micrometer and nanometer scales are obtained when solvent evaporates from solutions containing nonvolatile solutes dropped on a solid substrate. Such evaporation-driven pattern formation has been utilized as a fabrication process of highly ordered patterns in thin films. Here, we suggested the spontaneous pattern formation induced by Bénard-Marangoni convection triggered by solvent evaporation as a novel patterning process of sol-gel-derived organic-inorganic hybrid films. Microcraters of 1.0-1.5 μm in height and of 100-200 μm in width were spontaneously formed on the surface of silica-poly(vinylpyrrolidone) hybrid films prepared via temperature-controlled dip-coating process, where the surface patterns were linearly arranged parallel to the substrate withdrawal direction. Such highly ordered micropatterns were achieved by Bénard-Marangoni convection activated at high temperatures and the unidirectional flow of the coating solution on the substrate during dip-coating.