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PubMed2002

Formation of a self-assembled phenylboronic acid monolayer and its application toward developing a surface plasmon resonance-based monosaccharide sensor.

For the surface-optoelectronic study of sugar sensing, we synthesized and characterized dithiobis(4-butyrylamino-m-phenylboronic acid) (DTBA-PBA) as a recognition molecule. DTBA-PBA has a boronic acid group that has been known to form covalently bonded complexes with the 1,2- or 1,3-diol of sugars. A self-assembled monolayer (SAM) of DTBA-PBA was formed on a gold surface and characterized by atomic-force microscopy, Fourier transform infrared reflection absorption spectroscopy, and surface electrochemical measurements. An interaction study between monosaccharides and DTBA-PBA SAM was performed using surface plasmon resonance spectroscopy. The increase in molecular interactions between DTBA-PBA SAM and monosaccharides resulted in an optically induced electron excitation change on the Au surface through a refractive index change of the interfacial recognition layer. This correlation between electron excitation and molecular interaction was measurable at very low monosaccharide concentrations (1.0 x 10(-12)M). DTBA-PBA SAM shows a selective fructose sensing among four kinds of monosaccharides, even in a low concentration range.

Biosensing Techniques↗
PubMed2006

Abrading increases oxygen and hardness of titanium surface.

CP Ti was mirror-polished and then abraded with waterproof SiC papers of two different grit sizes: 16 and 3 microm. As-polished and abraded surfaces were characterized by means of EPMA, XPS, XRD, and hardness test. Oxygen in the mirror-polished surface was uniformly distributed at the lowest level. Comparatively, abrading with SiC papers increased the surface oxygen amount and hardness. Owing to its excellent abrasivity, the coarse grit efficiently scratched the surface and hindered the regenerated oxide film from growing thick, but allowed only the metal-oxide interfacial gradient zone to extend. But, the fine grit merely rubbed the surface and allowed both the oxide film and interfacial zone to extend. Further, the surface appeared to be lightly yellow-colored, suggesting that the oxide film was thicker, probably within 10 nm, than the nominal one. When compared with the bulk, the interfacial zone was rich in oxygen and therefore subjected to high coherency strain, which was introduced to relieve the great lattice mismatch between the outer and inner layers of titanium substrate. Effects of solute oxygen hardening and strain hardening were speculated to be responsible for the surface hardening of both SiC-abraded surfaces. In conclusion, abrading with a coarse grit led to accumulation of a high, non-uniform strain in the titanium substrate, thereby hardening the surface further.

Analysis of Variance↗
PubMed2001

Dissolution Kinetics, Selective Leaching, and Interfacial Reactions of a Bioglass Coating Enriched in Alumina.

Bioglass coatings are interesting for developing a direct bond between prostheses and bone. But the high solubility of these materials limits their application. The addition of alumina can be used to control their solubility, but may inhibit the bonding mechanisms. In this paper, we study a bioglass in the SiO(2)-Na(2)O-CaO-P(2)O(5)-K(2)O-Al(2)O(3)-MgO system. After delays of implantation from 2 to 12 months, the bioglass/bone interface is characterized by energy-dispersive X-ray spectroscopy coupled with scanning transmission electron microscopy. Bioglass dissolution can be decomposed into three steps with selective leaching. Results show that, at 2 months after implantation, the bioglass is composed of Al, Si, Ca, and P. Alumina addition increases the coating stability without inhibiting the bonding process. Complex physicochemical reactions take place at the bioglass periphery. The coating bonds to bone through a Ca-P layer on top of a pure Si-rich layer. These phenomena are associated with bioactivity properties, which occur for up to 6 months. After 12 months, the bioglass is composed of silicon. Copyright 2001 Academic Press.

Journal Article↗
PubMed1989

Properties and biological interactions of polyurethane anionomers: effect of sulfonate incorporation.

In order to investigate the factors affecting the interaction of polyurethanes and blood, a series of poly(tetramethylene oxide)-based polyurethane block copolymers was synthesized with systematically varying levels of ion incorporation in the hard segment block. A bimolecular nucleophilic substitution reaction was used to replace up to 20% of the urethane hydrogens with propyl sulfonate groups. Bulk and surface characterization was performed, and a canine ex vivo arteriovenous shunt was used to monitor initial platelet and fibrinogen deposition on these surfaces. The microphase separation and bulk physical properties were found to vary with ionic content. Surface analysis using both in vacuo (ESCA) and water-equilibrated (contact angle) methods indicated that these polymers, and especially the highly sulfonated materials, could rearrange to minimize their interfacial tension, depending on the contacting environment. Platelet deposition onto these materials decreased as the level of sulfonation increased, with the highly sulfonated polymer showing substantially less platelet spreading and activation than previously seen in the same experiment with other polymers.

Anions↗
PubMed2006

Probing interfacial chemistry of single droplets with field-induced droplet ionization mass spectrometry: physical adsorption of polycyclic aromatic hydrocarbons and ozonolysis of oleic acid and related compounds.

The recently developed technique of field-induced droplet ionization (FIDI) is applied to study interfacial chemistry of a single droplet. In a new variation of the FIDI method, 1-2-mm-diameter droplets hang from a capillary and undergo heterogeneous reactions between solution-phase analytes and gas-phase species. Following a specified reaction time, the application of a high electric field induces FIDI in the droplet, generating fine jets of highly charged progeny droplets that are characterized by mass spectrometry. Sampling over a range of delay times following exposure of the droplet to gas-phase reactants, the spectra yield the temporal variation of reactant and product concentrations. We illustrate the technique with three examples: the adsorption of the polycyclic aromatic hydrocarbon naphthalene into a water-methanol droplet, the ozonolysis of oleic acid, and localization of the carbon-carbon double bond within a lysophosphatidic acid. Gas-phase naphthalene reacts with 80% methanol-20% water droplets containing 100 microM silver nitrate. Positive ion mass spectra show increasing concentrations of silver ion-naphthalene adducts as exposure times increase. To examine the ozonolysis of organic molecules, gas-phase ozone generated by a mercury pencil-style lamp reacts with either 10 microM oleic acid or 100 microM oleoyl-L-alpha-lysophosphatidic acid (LPA; 18:1). Negative ion spectra from the ozonolysis of oleic acid show azelaic acid and 9-oxononanoic acid as the principle reaction products. Ozonolysis products from LPA (18:1) unambiguously demonstrate the double bond position in the original phospholipid.

Journal Article↗
PubMed2004

The epitaxial growth of cholesterol crystals from bile solutions on calcite substrates.

Epitaxial relationships between the surfaces of inorganic and bioorganic crystals can be an important factor in crystal nucleation and growth processes in a variety of biological environments. Crystalline cholesterol monohydrate (ChM), a constituent of both gallstone and atherosclerotic plaques, is often found in association with assorted mineral phases. Using in situ atomic force microscopy (AFM) and well-characterized model bile solutions, the nucleation and epitaxial growth of ChM on calcite (104) surfaces in real-time is demonstrated. The growth rates of individual cholesterol islands formed on calcite substrates were determined at physiological temperatures. Evidence of Ostwald's ripening was also observed under these experimental conditions. The energetics of various (104) calcite/(001) ChM interfaces were calculated to determine the most stable interfacial structure. These simulations suggest that the interface is fully hydrated and that cholesterol hydroxyl groups are preferentially positioned above carbonate ions in the calcite surface. This combination of experimental and theoretical work provides a clearer picture of how preexisting mineral seeds might provide a viable growth template that can reduce the energetic barrier to cholesterol nucleation under some physiological conditions.

Arteriosclerosis↗
PubMed2007

Hydrolysis characterization of phospholipid monolayers catalyzed by different phospholipases at the air-water interface.

Combination of some newly developed microscopic and spectroscopic techniques with conventional Langmuir monolayer method can provide more quantitative information with the molecular orientation and reorganization process of spread amphiphilic molecules at the air/water interface. These techniques are extended to investigate the hydrolysis process of spreading lipid monolayer catalyzed by different enzymes, phospholipases A2, C and D, respectively. Synchrotron X-ray diffraction and infrared reflection absorption spectroscopy are able directly to give the structural information of the assembled monolayer, interfacial activity of amphiphiles and their components at the interface. Microscopic technique such as Brewster angle microscopy (BAM), fluorescence microscopy (FM) can be used to trace the morphological changes dynamically as the spreading lipid monolayer is hydrolyzed at the air/water interface. We summary here some latest progress in this filed and give a brief review over the hydrolysis features of phospholipid monolayer catalyzed by different enzymes. It is attempted to establish a model of membrane hydrolysis process in order to better understand the mechanism of membrane metabolism and signal transduction in a living system.

Air↗
PubMed2005

Electrokinetics at high ionic strength and hypothesis of the double layer with zero surface charge.

A growing number of publications in the last two decades have suggested that the structure and other properties of the interfacial water layer can significantly affect the double layer (DL) because of changes in ion solvatation energy. Most interesting is the possibility that a double layer might in fact exist, even when there is no electric surface charge at all, solely because of the difference in cation and anion concentrations within this interfacial water layer. Dukhin, Derjaguin, and Yaroschuk suggested this possibility 20 years ago and developed a phenomenological theory. Recently, Mancui and Ruckenstein created more sophisticated microscopic model. In this article, we present our first experimental result regarding the verification of this "zero surface charge" DL model. The electroacoustic technique allows testing at high ionic strength (up to 2 M). As a first step, we confirm the surprising result of Johnson, Scales, and Healy regarding large zeta potential of alumina (8 +/- 1 mV) in 1 M KCl. As a second step, we suggest using nonionic surfactant Tween 80 for probing and modifying the structure of the interfacial layer at high ionic strength. The application of surfactant at moderate ionic strength (i.e., <0.1 mol/dm3), as might be expected, reduces the zeta potential simply by shifting the slipping plane. However, there is no influence of surfactant on the zeta potential observed at high ionic strength. It turns out that a high concentration of KCl simply eliminates surfactant adsorption. We develop a new technique for characterizing the adsorption of nonionic surfactant using an acoustic attenuation measurement. We hope that these methods in combination with a proper surfactant and electrolyte selection would allow us to gain more detailed information on the interface structure at high ionic strength.

Journal Article↗
PubMed2001

Saddle-splay elasticity and interfacial nematostatics.

This Brief Report drives the generalized force balance equations of interfacial statics between nematic liquid crystals (NLC) and isotropic fluids (I), using the classical equations of liquid crystal physics, taking into account an important class of gradient surface elasticity, known as saddle-splay elasticity. The objective is to identify the exact nature of the saddle-splay contributions to the fundamental interfacial force balance equations, known as the Laplace-Young equation and the Marangoni force equation. General expressions for the dynamic generalization of these two equations were given by Shih, Mann, and Brown [Mol. Cryst. Liq. Cryst. 98, 47 (1983)], but the specific form of the static terms appearing in these two equations were missing in the literature, and are now given in this paper. It is found that the tensorial order and functional form of the contributions of saddle-splay elasticity to the two force balance equations are congruent with those arising from the interfacial tension. Therefore, to generalize the interfacial equations of nematostatics by including saddle-splay energy, the interfacial tension must be renormalized with the saddle-splay energy contribution. In addition, saddle splay gives rise to distortion stresses, the two-dimensional analog to the bulk Ericksen stresses, which contribute to the tangential Marangoni force. Exact expressions for pressure jumps across NLC/I interfaces and for the tangential Marangoni force are derived and analyzed. These generalized results are expected to be useful in the characterization of nematocapillarity phenomena, such as wetting, spreading, and the mechanics of thin nematic films.

Journal Article↗
PubMed2004

Morphological and chemical characterizations of the interface of a hydroxyapatite-coated implant.

The present study aimed at morphological and chemical characterization of the coating-substrate interface of a commercially available dental implant coated with plasma-sprayed hydroxyapatite (HA). For this purpose, elements in the chemically and mechanically exposed substrate surfaces were analyzed by EPMA and XPS. A thin titanium oxide film containing Ca and P was found at the interface. When the implant was subjected to mechanical stress, a mixed mode of cohesive and interfacial fractures occurred. The cohesive fracture was due to separation of the oxide film from the substrate, while the interfacial fracture was due to exfoliation of the coating from the oxide film bonded to the substrate. Analysis showed diffusion of Ca into the metal substrate, hence indicating the presence of chemical bond at the interface. However, mechanical interlocking seemed to play the major role in the interfacial bond.

Calcium↗
PubMed2006

Fabrication and characterization of titanium-matrix composite with 20 vol% hydroxyapatite for use as heavy load-bearing hard tissue replacement.

Titanium-matrix composite with 20 vol% HA ceramic was fabricated by hot pressing technique and the microstructure of the composite was studied by transmission electron microscope (TEM). The mechanical and biological properties of the composite were investigated by mechanical and in vivo studies. The experimental results by TEM observation show the bonding state of Ti/HA interface in Ti-20 vol% HA composite with the relative density of 97.86% is good, however, there exists an interfacial transition zone between Ti and HA. In Ti matrix of the composite and pure Ti metal, an interesting substructure comprised of screw dislocations with Burgers vectors b of 1/3 < 11 20> was found. Screw dislocations are straight and regularly distributed, and cross slip can be observed. The subgrain boundaries consist of dislocation network walls with equidistant dislocation lines in the same direction. Elastic modulus and Vicker's hardness of Ti-20 vol%HA composite are 102.6 GPa and 3.41 GPa respectively. Owing to the existence of 20 vol% HA ceramic, bending strength and fracture toughness of the composite decrease sharply to 170.1 MPa and 3.57 MPa.m(1/2) respectively, which are only about 17.5 and 12% of those of pure Ti metal. In vivo studies indicate Ti-20 vol% HA composite has good biocompatibility, and even better osteointegration ability than pure titanium, especially in the early stage after the implantation. In conclusion, Ti-20 vol% HA composite is suitable for heavy load-bearing hard tissue replacement from the point of view of both mechanical properties and biocompatibility.

Animals↗
PubMed1999

Critical Condensate Saturation in Porous Media.

The understanding of gas and condensate flow in porous media is critical to the optimum exploitation of gas-condensate reservoirs. Critical condensate saturation and relative permeabilities are the key parameters for the evaluation of possible recovery strategies. This work is aimed at developing a mechanistic network model for the critical condensate saturation in which phase trapping and connectivity in the pore corners are critically examined. Porous media are modeled by networks of pore bodies interconnected by pore throats. Bodies and throats are characterized by their connectivity, shapes, and radii distributions. Pore-level laws are identified from micromodel experiments with near-critical fluids. A nonzero critical condensate saturation can be obtained in the absence of contact angle hysteresis due to the converging-diverging nature of the throats. The critical saturation at which the condensate flows is found to be a function of pore geometry, water saturation, and interfacial tension (or the Bond number). The modified sphere-pack model underpredicts the critical condensate saturation of typical sandstones. The cubic model adequately predicts the critical saturation and its experimentally observed trends. Copyright 1999 Academic Press.

Journal Article↗
PubMed2000

Geometry-dominated fluid adsorption on sculpted solid substrates.

The shape and chemical composition of solid surfaces can be controlled at a mesoscopic scale. Exposing such structured substrates to a gas that is close to coexistence with its liquid phase can produce quite distinct adsorption characteristics compared to those of planar systems, which may be important for technologies such as super-repellent surfaces or micro-fluidics. Recent studies have concentrated on the adsorption of liquids on rough and heterogeneous substrates, and the characterization of nanoscopic liquid films. But the fundamental effect of geometry on the adsorption of a fluid from the gas phase has hardly been addressed. Here we present a simple theoretical model which shows that varying the shape of the substrate can exert a profound influence on the adsorption isotherms of liquids. The model smoothly connects wetting and capillary condensation through a number of examples of fluid interfacial phenomena, and opens the possibility of tailoring the adsorption properties of solid substrates by sculpting their surface shape.

Journal Article↗
PubMed2005

Phase and interface behaviors in type-I and type-V Lennard-Jones mixtures: theory and simulations.

Density gradient theory (DGT) and molecular-dynamics (MD) simulations have been used to predict subcritical phase and interface behaviors in type-I and type-V equal-size Lennard-Jones mixtures. Type-I mixtures exhibit a continuum critical line connecting their pure critical components, which implies that their subcritical phase equilibria are gas liquid. Type-V mixtures are characterized by two critical lines and a heteroazeotropic line. One of the two critical lines begins at the more volatile pure component critical point up to an upper critical end point and the other one comes from the less volatile pure component critical point ending at a lower critical end point. The heteroazeotropic line connects both critical end points and is characterized by gas-liquid-liquid equilibria. Therefore, subcritical states of this type exhibit gas-liquid and gas-liquid-liquid equilibria. In order to obtain a correct characterization of the phase and interface behaviors of these types of mixtures and to directly compare DGT and MD results, the global phase diagram of equal-size Lennard-Jones mixtures has been used to define the molecular parameters of these mixtures. According to our results, DGT and MD are two complementary methodologies able to obtain a complete and simultaneous prediction of phase equilibria and their interfacial properties. For the type of mixtures analyzed here, both approaches have shown excellent agreement in their phase equilibrium and interface properties in the full concentration range.

Journal Article↗
PubMed2005

A novel esterase from Bacillus subtilis (RRL 1789): purification and characterization of the enzyme.

An esterase (EC 3.1.1.1) produced by an isolated strain of Bacillus subtilis RRL 1789 exhibited moderate to high enantioselectivity in the kinetic resolution of several substrates like aryl carbinols, hydroxy esters, and halo esters. The enzyme named as B. subtilis esterase (BSE), was purified to >95% purity with a specific activity of 944 U/mg protein and 12% overall yield. The purified enzyme is approximately 52 kDa monomer, maximally activity at 37 degrees C and pH 8.0 and fairly stable up to 55 degrees C. The enzyme does not exhibit the phenomenon of interfacial activation with tributyrin and p-nitrophenyl butyrate beyond the saturation concentration. The enzyme showed preference for triacyglycerols and esters of p-nitrophenol with short chain fatty acid. Presence of Ca2+ ions increases the activity of enzyme by approximately 20% but its presence does not have any influence on the thermostability of the enzyme. The enzyme is not a metalloprotein and belongs to the family of serine proteases. The N-terminal amino acid sequence of BSE determined, as Met-Thr-Pro-Glu-Iso-Val-Thr-Thr-Glu-Tyr-Gly- revealed similarity with the N-terminal amino acid sequence of p-nitrobenzylesterase of B. subtilis.

Amino Acid Sequence↗
PubMed2001

Nanoscale clustering of RGD peptides at surfaces using comb polymers. 2. Surface segregation of comb polymers in polylactide.

Part 1 of these studies described poly(methyl methacrylate-r-polyoxyethylene methacrylate) P(MMA-r-POEM) comb polymers that present Arg-Gly-Asp (RGD) peptides at a surface in nanoscale clusters on a protein-resistant background for control of cell adhesion. Here in part 2, we examine surface segregation of these peptide-modified and unmodified comb polymers blended with polylactide (PLA) as a self-assembly approach suitable for surface modification of porous tissue engineering scaffolds. Multiple thermodynamic driving forces for surface enrichment of the comb polymer are exploited by annealing PLA/P(MMA-r-POEM) blends above the glass transition of the blend components but below the melting point of PLA, while in contact with water. Predictions of the interfacial composition profiles of annealed blends were made using a self-consistent field (SCF) lattice model. The calculations predict strong enrichment of the comb in the top approximately 50 A of blends, and organization of comb molecules in quasi-2D conformations at the interface, similar to the apparent structure of pure comb surfaces in contact with water described in part 1. Experimentally, PLA/comb blend surfaces were characterized by contact angle measurements, XPS, quantification of ligand-cluster surface density and stability by AFM and fluorescent nanosphere labeling, and cell attachment assays. These data were consistent with SCF predictions, showing significant enrichment of the comb at water-annealed surfaces and RGD cluster densities consistent with 2D conformations for comb molecules in the surface layer. Bulk miscibility of the blends was verified by dynamic rheometry, small-angle neutron scattering, DSC and X-ray diffraction studies. Surface segregation of combs provided tunable cell adhesion on PLA through surface-localized nanoclusters of RGD atop a cell-resistant background.

Cell Adhesion↗
PubMed2004

Physicochemical parameters associated with nanoparticle formation in the salting-out, emulsification-diffusion, and nanoprecipitation methods.

PURPOSE: The aim of this work was to relate the physicochemical properties of the aqueous and organic phases used for nanoparticle (NP) preparation to the formation of NP produced by salting-out, emulsification-diffusion, and nanoprecipitation. METHODS: Methacrylic acid copolymer and poly(vinyl alcohol) (PVAL) were selected as NP polymer and emulsifying agent, respectively. Salting-out and emulsification-diffusion NP batches were prepared modifying the PVAL content in the aqueous phase. For nanoprecipitation, NP were produced with variation of the polymer content and type of solvent in the organic phase. RESULTS: For salting-out and emulsification-diffusion, NP formation was discussed in terms of the emulsification theory. The nanoemulsion obtained during NP preparation was visualized by scanning electron microscopy. Aqueous and organic phases used for NP preparation were characterized by their viscosity and surface tension. NP characteristics such as particle mean size, residual surfactant, suspendability in water after freeze-drying, and morphology were explained in terms of these properties. For nanoprecipitation, NP formation was analyzed considering the diffusion-stranding phenomenon. CONCLUSIONS: NP formation by salting-out and emulsification-diffusion was related to PVAL chain interactions at the droplet interface (e.g., reduction in the interfacial tension, mechanical stabilization, and steric stabilization) and in the bulk solution (hydrodynamic stabilization). For nanoprecipitation, chi(solvent-water) and delta(delta solvent-water) of the organic phase solvents were well related to the NP characteristics.

Diffusion↗
PubMed2003

An off-normal fibre-like texture in thin films on single-crystal substrates.

In the context of materials science, texture describes the statistical distribution of grain orientations. It is an important characteristic of the microstructure of polycrystalline films, determining various electrical, magnetic and mechanical properties. Three types of texture component are usually distinguished in thin films: random texture, when grains have no preferred orientation; fibre texture, for which one crystallographic axis of the film is parallel to the substrate normal, while there is a rotational degree of freedom around the fibre axis; and epitaxial alignment (or in-plane texture) on single-crystal substrates, where an in-plane alignment fixes all three axes of the grain with respect to the substrate. Here we report a fourth type of texture--which we call axiotaxy--identified from complex but symmetrical patterns of lines on diffraction pole figures for thin films formed by solid-state reactions. The texture is characterized by the alignment of planes in the film and substrate that share the same d-spacing. This preferred alignment of planes across the interface manifests itself as a fibre texture lying off-normal to the sample surface, with the fibre axis perpendicular to certain planes in the substrate. This texture forms because it results in an interface, which is periodic in one dimension, preserved independently of interfacial curvature. This new type of preferred orientation may be the dominant type of texture for a wide class of materials and crystal structures.

Journal Article↗