SECM imaging of micropatterned organic films on carbon surfaces

Micropatterned carbon surfaces were prepared by electrochemical soft-lithography and imaged with scanning electrochemical microscopy. The technique allows the characterization of the surface in terms of resistance to molecules permeating the layer. Two types of electrogenerated organic layers were tested: sub-monolayers of tetraethyleneglycol diamine (TGD) and methylphenyl (MP) layers of variable thickness. TGD surfaces were found to provide little isolation and molecules can freely diffuse inside the layer to reach the surface. MP covered surfaces offer a much better resistance to organic molecules and can be almost insulating in the case of multilayer deposits. The blocking was found to be slightly better in water in agreement with the poor affinity of the aromatic layer with water.     

Fluorescence biosensing micropatterned surfaces based on immobilized human acetylcholinesterase

Human acetylcholinesterase (AChE) is a widely studied target enzyme in drug discovery for Alzheimer’s disease (AD). In this paper we report evaluation of the optimum structure and chemistry of the supporting material for a new AChE-based fluorescence sensing surface. To achieve this objective, multilayered silicon wafers with spatially controlled geometry and chemical diversity were fabricated. Specifically, silicon wafers with silicon oxide patterns (SiO₂/Si wafers), platinum-coated silicon wafers with SiO₂ patterns (SiO₂/Pt/Ti/Si wafers), and Pt-coated wafers coated with different thicknesses of TiO₂ and SiO₂ (SiO₂/TiO₂/Pt/Ti/Si wafers) were labelled with the fluorescent conjugation agent HiLyte Fluor 555. Selection of a suitable material and the optimum pattern thickness required to maximize the fluorescence signal and maintain chemical stability was performed by confocal laser-scanning microscopy (CLSM). Results showed that the highest signal-to-background ratio was always obtained on wafers with 100 nm thick SiO₂ features. Hence, these wafers were selected for covalent binding of human AChE. Batch-wise kinetic studies revealed that enzyme activity was retained after immobilization. Combined use of atomic-force microscopy and CLSM revealed that AChE was homogeneously and selectively distributed on the SiO₂ microstructures at a suitable distance from the reflective surface. In the optimum design, efficient fluorescence emission was obtained from the AChE-based biosensing surface after labelling with propidium, a selective fluorescent probe of the peripheral binding site of AChE.

Effect of viscoelasticity on adhesion of bioinspired micropatterned epoxy surfaces

The effect of viscoelasticity on adhesion was investigated for micropatterned epoxy surfaces and compared to nonpatterned surfaces. A two-component epoxy system was used to produce epoxy compositions with different viscoelastic properties. Pillar arrays with flat punch tip geometries were fabricated with a two-step soft lithography process. Adhesion properties were measured with a home-built adhesion tester using a spherical sapphire probe as a counter-surface. Compared to flat controls, micropatterned epoxy samples with low viscoelasticity (i.e., low damping factors) showed at least a 20-fold reduction in pull-off force per actual contact area for both low (E' = 2.3 MPa) and high (E' = 2.3 GPa) storage moduli. This antiadhesive behavior may result from poor contact formation and indicates that the adhesion performance of commonly used elastomers for dry adhesives (e.g., polydimethylsiloxane) is governed by the interfacial viscoelasticity. Adhesion significantly increased with increasing viscoelasticity. Micropatterned samples with high viscoelasticity showed a 4-fold reduction in adhesion for aspect ratio (AR) 1.1 patterns but a 2-fold enhancement in adhesion for AR 2.2 patterns. These results indicate that viscoelasticity can enhance the effect of surface patterning on adhesion and should be considered as a significant parameter in the design of artificial patterned adhesives.     

Colloidal deposition on remotely controlled charged micropatterned surfaces in a parallel-plate flow chamber

This article describes a method to influence colloid deposition by varying the zeta potential at microelectrodes with remotely applied electric potentials. Deposition experiments were conducted in a parallel-plate flow chamber for bulk substrates of glass, indium tin oxide (ITO), and ITO-coated glass microelectrodes in 10 and 60 mM potassium chloride solutions. Colloid deposition was found to be a function of solution chemistry and the small locally delivered electric surface potentials. Electric fields and physical surface heterogeneity can be ruled out as cause of the observed deposition. Results are reported using experimentally determined Sherwood numbers and compared to the predictions of a previously developed patch model. Minor deviations between predicted and experimental Sherwood numbers imply that physical and chemical interactions occur. Specifically, we propose that colloidal particles respond to local variations in surface potential through electrostatic interactions, altering particle streamlines flowing along the surface and ultimately the extent of deposition.     

Superhydrophobic effects of self-assembled monolayers on micropatterned surfaces: 3-D arrays mimicking the lotus leaf

The contact angle of water has been measured on a series of self-assembled monolayers (SAM) on thermally evaporated and sputter coated silver surfaces. It is found that micropatterning the surface using nanosphere lithography leads to large increases in the contact angle and generates superhydrophobic surfaces with contact angles >150 degrees. The type of functional groups on the SAMs, the metal island size, and the metal island thickness all contribute to the measured contact angle. The maximum contact angle found was 161 degrees for a fluorinated alkanethiol on 80 nm thick silver islands.     

Influence of the structure of nanoscopic building blocks on the assembly of micropatterned surfaces

The effect of solution-state nanoscale structures on the assembly of micropatterns by solvent evaporation was explored with a novel amphiphilic diblock copolymer synthesized by reversible addition–fragmentation chain transfer polymerization. A copolymer of the structure poly(styrene-alt-maleic anhydride)₇₅-b-isoprene₈₄ was assembled into inverse micelles in toluene, and covalently stabilized in the core by reactive amidation of maleic anhydride residues with 2,2′-(ethylenedioxy)bis(ethylamine) to create core-crosslinked nanoparticles (CCNPs) or in the shell by the photoinitiated radical crosslinking reactions of isoprene units to create large crosslinked aggregates (LCAs) of heterogeneous sizes and shapes. Micropatterned films were prepared by the deposition of the diblock copolymer as a solution in acetone and the nanoscale structures (inverse micelle, crosslinked aggregate, and CCNP) as solutions in toluene onto trimethylysilyl chloride treated glass microscope slides under ambient conditions. An analysis by optical microscopy and tapping-mode atomic force microscopy (AFM) indicated that the nanoscale surface topology could be controlled by the pre-establishment of the block copolymer phase segregation into well-defined core–shell nanoassemblies in solution. The most interesting films resulted from the evaporative deposition of inverse micelle and CCNP solutions, which afforded uniform, straplike micropatterns of similar dimensions on the microscale and low surface roughness on the nanoscale (roughness = 4 ± 1 and 6± 1 nm by AFM). © 2006 Wiley Periodicals, Inc. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5218–5228, 2006     

Adhesion of bioinspired micropatterned surfaces: effects of pillar radius, aspect ratio, and preload

Inspired by biological attachment systems, micropatterned elastomeric surfaces with pillars of different heights (between 2.5 and 80 microm) and radii (between 2.5 and 25 microm) were fabricated. Their adhesion properties were systematically tested and compared with flat controls. Micropatterned surfaces with aspect ratios above 0.5 were found to be more compliant than flat surfaces. The adhesion significantly increases with decreasing pillar radius and increasing aspect ratio of the patterned features. A preload dependence of the adhesion force has been identified and demonstrated to be crucial for obtaining adhesives with tunable adherence.     

Direct visualization of reversible switching of micropatterned polyelectrolyte brushes on gold surfaces using laser scanning confocal microscopy

We apply confocal fluorescence microscopy for real time studies of reversible conformational changes of poly(methacryloyloxyethyl phosphate) (PMEP) brushes chemically grafted onto gold substrates. Oregon green 488 fluorophores chemically attached onto the PMEP polymers were used as reporters for probing the conformational changes. Use of a specially designed liquid flow microchamber allowed dynamic imaging of the brushes under varying environmental conditions. The fluorescence intensities exhibited fully reversible brightness changes on alternation of the solution in the chamber between water and KCl. This reversible quenching behavior is consistent with a conformational change between an extended and a collapsed brush configuration. The fluorescence quenching behavior of the brushes was found to be dependent on ion concentration as well as polymer grafting density and was caused by nonradiative energy transfer to the polymer scaffold and the gold substrate.     

Shock absorption properties of synthetic sports surfaces: A review

Repeated impact loading during running is a risk factor in the etiology of overuse injuries. Shock absorption can reflect the degree of force attenuation when the heel lands first during movement. This study summarizes the major achievements in the existing literature regarding shock absorption from the engineering perspective and then suggests directions for further investigation. Studies have explained the influencing factors related to shock absorption from the synthetic sports surface itself. Some special measurement methods that can be used to assess vertical and horizontal shock absorption simultaneously are discussed. Numerical simulations related to shock absorption are reviewed, including how to acquire a constitutive model of the sports surface and simulate the manner of loading. Future work should aim to build “player movement‐surface structure and material‐player performance” relationship systems, with more accurate measurements of shock absorption properties in the vertical and horizontal directions and numerical models that can truly reflect actual movements. Solving these problems can strengthen the theoretical and practical understanding of the relationship between synthetic sports surfaces and injury, and athletes can develop more expert performance with fewer injuries.     

Cooperative self-assembly: producing synthetic polymers with precise and concise primary structures

The quest to construct mechanically interlocked polymers, which present precise monodisperse primary structures that are produced both consistently and with high efficiencies, has been a daunting goal for synthetic chemists for many years. Our ability to realise this goal has been limited, until recently, by the need to develop synthetic strategies that can direct the formation of the desired covalent bonds in a precise and concise fashion while avoiding the formation of unwanted kinetic by-products. The challenge, however, is a timely and welcome one, as a consequence of, primarily, the potential for mechanically interlocked polymers to act as dynamic (noncovalent) yet robust (covalent) new materials for a wide array of applications. One such strategy which has been employed widely in recent years to address this issue, known as Dynamic Covalent Chemistry (DCC), is a strategy in which reactions operate under equilibrium and so offer elements of "proof-reading" and "error-checking" to the bond forming and breaking processes such that the final product distribution always reflects the thermodynamically most favourable compound. By coupling DCC with template-directed protocols, which utilise multiple weak noncovalent interactions to pre-organise and self-assemble simpler small molecular precursors into their desired geometries prior to covalent bond formation, we are able to produce compounds with highly symmetric, robust and complex topologies that are otherwise simply unobtainable by more traditional methods. Harnessing these strategies in an iterative, step-wise fashion brings us ever so much closer towards perfecting the controlled synthesis of high order main-chain mechanically interlocked polymers. This tutorial review focuses (i) on the development of DCC-namely, the formation of dynamic imine bonds-used in conjunction with template-directed protocols to afford a variety of mechanically interlocked molecules (MIMs) and ultimately (ii) on the synthesis of highly ordered poly[n]rotaxanes with high conversion efficiencies.     

Functional group analysis on oxidized surfaces of synthetic textile polymers

A comprehensive collection of wet-chemical analyses of functional groups on oxidatively treated surfaces of hydrophobic polymers like poly(ethylene terephthalate) or polyolefine is presented. New methods are introduced. Textiles and foils have been subjected to advanced oxidation processes and the different oxygen functions have been quantified. Analysis of surface functional groups includes radical site determination with radical scavengers like diphenylpicrylhydrazyl, reduction of peroxides determined iodometrically, cationic dyestuff adsorption, carbonyl binding to Girard reagent P and surface hydroxyl group determination by surface nitrosation and subsequent azo-dye formation photometrically determinable. Use of potential surface swelling agents has been excluded except for addition of wetting agent. Wet-chemical analyses on textile surfaces bear the benefit of integrating over (relatively) large sample areas, a point which is interesting when regarding inhomogenities of textile or other surface constructions. In addition examples for visualisation for the existence of surface groups are described.     

Lipid barrier layers on surfaces of synthetic water permeable membranes

Barrier layers (area 0.79 cm²) from oxidized cholesterol or mixtures of oxidized cholesterol with phosphatidyl serine or phosphatidyl ethanol amine were formed on surfaces of different water-permeable synthetic membranes in 0.1 M NaCl as models of biological membranes. Ionic conductivity across the membranes decreased from 10⁻²-10⁻³ to 10⁻⁷-10⁻⁸ Ω⁻¹ cm⁻² when the barrier layers were formed on their surfaces. Average thicknesses of barrier layers 4.5–11 nm were estimated from electric capacitance. The layers were unstable with lifetimes ranging from several minutes to 50 hr according to the support membrane used. The interfacial tension between synthetic membrane surface and either water or lipid solution was calculated from contact angle measurement. The relation between barrier layer stability and hydrophobic and polar interaction of lipids with support surface was studied. The most stable barrier layers (lifetimes 30–50 hr) were formed on cellophane and gelatin membranes with surfaces hydrophobized by reaction with palmytoyl chloride.     

Stepwise deposition of metal organic frameworks on flexible synthetic polymer surfaces

Thin films of [Cu(3)(btc)(2)](n) (btc = 1,3,5-benzenetricarboxylate) metal organic framework were deposited in a stepwise manner on surfaces of flexible organic polymers. The thickness of films can be precisely controlled. The deposition of the first cycles was monitored by UV-vis spectroscopy. The porosity was proven by the adsorption of pyrazine, which was monitored by FT-IR and thermogravimetric analysis. The deposition of MOF thin films on flexible polymer surfaces might be a new path for the fabrication of functional materials for different applications, such as protection layers for working clothes and gas separation materials in the textile industry.     

Noncovalent cell surface engineering: incorporation of bioactive synthetic glycopolymers into cellular membranes

The controlled addition of structurally defined components to live cell membranes can facilitate the molecular level analysis of cell surface phenomena. Here we demonstrate that cell surfaces can be engineered to display synthetic bioactive polymers at defined densities by exogenous membrane insertion. The polymers were designed to mimic native cell-surface mucin glycoproteins, which are defined by their dense glycosylation patterns and rod-like structures. End-functionalization with a hydrophobic anchor permitted incorporation into the membranes of live cultured cells. We probed the dynamic behavior of cell-bound glycopolymers bearing various hydrophobic anchors and glycan structures using fluorescence correlation spectroscopy (FCS). Their diffusion properties mirrored those of many natural membrane-associated biomolecules. Furthermore, the membrane-bound glycopolymers were internalized into early endosomes similarly to endogenous membrane components and were capable of specific interactions with protein receptors. This system provides a platform to study cell-surface phenomena with a degree of chemical control that cannot be achieved using conventional biological tools.     

A simple strategy for detecting synthetic polymers on solid surfaces using liquid crystal

In this study, we developed a liquid crystal (LC)-based detection method for polymer films synthesized on solid surfaces. A dark to bright transition in the optical appearance of nematic 4-cyano-4′-pentylbiphenyl (5CB) was observed after transferring a poly(methyl methacrylate) (PMMA) film onto a glass substrate functionalized with n-octyltrichlorosilane (OTS). This phenomenon indicates an orientational transition of 5CB from a homeotropic to a planar-random state. The optical response of 5CB was then evaluated directly through polymerization reactions on the OTS-functionalized glass substrate. Polymer films of PMMA, poly(glycidyl methacrylate) (PGMA), and poly(dimethylsiloxane) (PDMS) were synthesized on OTS surfaces covered with their reaction mixtures. All polymer films displayed bright signals of 5CB, which corresponded to the planar-random orientation of LCs. However, no change in orientation was observed for the control experiments. We confirmed the formation of polymer films on the OTS surface using atomic force microscopy. Overall, our results suggest that LCs can be used to construct optical monitoring systems for the product of polymerization reactions.

Gold glyconanoparticles: synthetic polyvalent ligands mimicking glycocalyx-like surfaces as tools for glycobiological studies

A simple and versatile methodology is described for tailoring sugar-functionalised gold nanoclusters (glyconanoparticles) that have 3D polyvalent carbohydrate display and globular shapes. This methodology allows the preparation of glyconanoparticles with biologically significant oligosaccharides as well as with differing carbohydrate density. Fluorescent glyconanoparticles have been also prepared for labelling cells in biological tests. The materials are water soluble, stable under physiological conditions and present an exceptional small core size. All of them have been characterised by (1)H NMR, UV and IR spectroscopy, TEM and elemental analysis. Their highly polyvalent network can mimic glycosphingolipid clustering and interactions at the plasma membrane, providing an controlled system for glycobiological studies. Furthermore, they are useful building blocks for the design of nanomaterials.     

Post-grafting of silica surfaces with pre-functionalized organosilanes: new synthetic equivalents of conventional trialkoxysilanes

This article describes recent advances that have been made in the development of methods for post-grafting of silica surfaces using functionalized organosilanes. While procedures employing conventional trialkoxysilane precursors have been utilized to immobilize organic and biological molecules onto inorganic supports, such as silica and glass, they have intrinsic limitations including sensitivity to hydrolysis and slow reaction rates. In this context, new synthetic equivalents to conventional trialkoxysilanes and new grafting methods have been devised to overcome these drawbacks and improve post-grafting processes. A key feature of the new strategies is the stability of the immobilizing groups that enables the silane precursors to be functionalized and purified without decomposition before immobilization. Recent developments made in the design of immobilization methods, which employ non-catalytic and catalytic approaches, are described.     

Cell sheet engineering: intelligent polymer patterned surfaces for tissue engineered liver

We describe a new culture system utilizing the temperature-responsive polymer grafted surface for designing of cell position and layered tissue reconstruction. Organizing of the hepatic tissue structure by controlling the culture system, that is patterned co-culture and layered cell sheet co-culture achieved by moving the cultured cells from the culture surface, resulted in regulation of the hepatocyte function. The technique for cell sheet manipulation would promote the liver tissue engineering in quality.     

Effect of divalent cations on the adhesion rate of cellular surfaces with ionizable groups

The adhesion rate of cells under charge regulation onto a rotating disc with constant potential is investigated theoretically in this paper. In particular, the effect of the presence of divalent carions in the suspension medium on adhesion rate of cells is discussed. By using sheep leucocytes as an illustrative example, it is shown that the presence of divalent cations in the suspension medium has the effect of decreasing the adhesion rate of cells. At a fixed level of ionic strength, the adhesion rate decreases with the increase of the concentration of divalent cations in the suspension medium for the various values of Peclet number andAd parameter given in this paper. For a fixed concentration of cations, the adhesion rate increases with the increase of ionic strength. At high ionic strength, the effect of increasing the concentration of cations on decreasing the adhesion rate of cells is not as high as that at low ionic strength. Applying the concept of Donnan potential, it is found that the magnitude of the electrostatic force between an ion-penetrable cell membrane and a solid surface is much smaller than that for the ion-impenetrable cell membrane.Nomenclature a cell radius (cm) - A Hamaker's constant (erg) - Ad A/kT - C dimensionless cell concentration - D cell diffusion coefficient (cm²/s) - e magnitude of electron charge (statcoul) - F dimensionless interaction force between cell and rotating disc pernkT - h minimum separation distance between cell surface and disc surface (cm) - H dimensionless separation distance between cell surface and disc surfaceh/a - [H ⁺] _r hydrogen ion concentration in the suspension medium (mole dm^–3) - [H ⁺] _s hydrogen ion concentration on the cell surface (mole dm^–3) - Boltzmann's constant (erg K^–1) - K _a dissociation equilibrium constant for acid groups on cell surface (mole dm^–3) - K _b dissociation equilibrium constant for base groups on cell surface (mole dm^–3) - n ionic strength in the suspension medium (ions cm^–3 - Pe Peclet number - q valence of cations - Sa the reciprocal of acidic density on the cell surface (cm²/group) - S _b the reciprocal of basic density on the cell surface (cm²/group) - Sh Sherwood number - T absolute temperature (K) - the fraction of cationic electrolyte in the suspension medium, 01 - reciprocal of Debye length, (cm^–1) - fluid kinematic viscosity (cm²/s) - ×a - l distance between two plate surfaces in Derjuguin's model (cm) - dimensionless total interaction energy between cell surface and disc surface - _vdw dimensionless unretarded van der Waals potential between cell surface and disc surface - _DL dimensionless double-layer interaction potential between cell surface and disc surface - dimensionless electrostatic potential between cell surface and disc surface - rotating speed of the disc (rad/s)     

Adsorption of Thermomonospora fusca E5 and Trichoderma reesei cellobiohydrolase I cellulases on synthetic surfaces

The interfacial behavior of Thermomonosporafusca E5 and Trichoderma reesei cellobiohydrolase I (CBHI) cellulases were studied at synthetic surfaces. For this purpose, colloidal silica and polystyrene particles were used to prepare cellulase-particle suspensions that could be analyzed by solution-phase techniques. Circular dichroism spectroscopy of each cellulase, alone as well as in suspension with silica, was used to determine whether structural changes occurred on adsorption. Changes in spectra were observed for CBHI, but not for E5. Gel-permeation chromatography of the cellulase-particle suspensions showed that neither cellulase binds to silica, suggesting that changes in spectra for CBHI were a result of solution-phase phenomena. Microfiltration of cellulase-polystyrene suspensions showed that both cellulases bind to polystyrene. However, circular dichroism experiments with polysterene proved unworkable, owing to excessive light absorption by the polystyrene. Adsorption kinetics of each cellulase were recorded, in situ, at hydrophilic and silanized, hydrophobic silica surfaces using ellipsometry. Ellipsometric data recorded for each cellulase at hydrophilic silica showed insignificant adsorption. Binding did occur between each cellulase and silanized silica, most likely mediated through hydrophobic associations. Adsorption in this case was irreversible to dilution.