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At least 325 records · Page 18Linked to original sources
PubMed2004

Production and characterization of O/W emulsions containing droplets stabilized by lecithin-chitosan-pectin mutilayered membranes.

The possibility of producing stable oil-in-water (O/W) emulsions containing oil droplets surrounded by multiple layer interfacial membranes from food grade ingredients has been demonstrated. These emulsions were produced using a three stage process that relies on the adsorption of charged biopolymers to oppositely charged surfaces. Emulsions (0.5 wt % corn oil, 0.1 wt % lecithin, 0.0078 wt % chitosan, 0.02 wt % pectin, and 100 mM acetic acid, pH 3.0) containing oil droplets stabilized by lecithin-chitosan-pectin membranes were formed using this interfacial layer-by-layer deposition process. The droplets in these emulsions had good stability to aggregation over a wide range of pH values and salt concentrations (pH 4-8 at 0 mM NaCl and pH 3-8 at 100 mM NaCl). This technology could be extremely useful to the food industry for the creation of O/W emulsions with improved properties or novel applications, e.g., improved stability to environmental stresses, protection of labile substances, controlled release, and triggered release.

Adsorption↗
PubMed2006

Solution pH alters mechanical and electrical properties of phosphatidylcholine membranes: relation between interfacial electrostatics, intramembrane potential, and bending elasticity.

Solution pH affects numerous biological processes and some biological membranes are exposed to extreme pH environments. We utilized micropipette aspiration of giant unilamellar vesicles composed of 1-stearoyl-2-oleoyl-phosphatidylcholine to characterize the effect of solution pH (2-9) on membrane mechanical properties. The elastic area compressibility modulus was unaffected between pH 3 and 9 but was reduced by approximately 30% at pH 2. Fluorescence experiments utilizing the phase-sensitive probe Laurdan confirmed gel-phase characteristics at pH 2, explaining the reduction of membrane elasticity. The membrane bending stiffness, kc, increased by approximately 40% at pH 4 and pH 9 over the control value at pH 6.5. Electrophoretic mobility measurements indicate that these changes are qualitatively consistent with theoretical models that predict the effect of membrane surface charge density and Debye length on kc, substantiating a coupling between the mechanical and interfacial electrical properties of the membrane. The effect of pH on intramembrane electrical properties was examined by studying the spectral shifts of the potentiometric probe di-8 ANEPPS. The intramembrane (dipole) potential (Psid) increased linearly as the solution pH decreased in a manner consistent with the partitioning of hydroxide ions into the membrane. However, changes in Psid did not correlate with changes in kc. These mechanical and electrical studies lead to the conclusion that the effect of pH on membrane bending stiffness results from alterations in interfacial, as opposed to intramembrane, electrostatics.

Computer Simulation↗
PubMed2006

Characterization of the kinetics of phospholipase C activity toward mixed micelles of sodium deoxycholate and dimyristoylphosphatidylcholine.

Phospholipase C catalyzed hydrolysis of dimyristoyl phosphatidylcholine (DMPC) in phospholipid-bile salt mixed micelles was studied with particular attention on the relationship between interfacial enzyme activity and the physicochemical properties of substrate aggregates. Steady state kinetics is observed and it is argued that conditions for steady state exist because the enzyme encounters a steady supply of substrate by hopping between micelles at a rate faster than the chemical reaction rate. An existing kinetic model is reformulated to a more usable form. This presents a new approach to treating the kinetic data and allows extraction of the kinetic parameters of the model from the activity dependence on micellar lipid substrate surface concentration. The kinetic parameters were found to depend on the physicochemical properties of substrate aggregates, but remain constant over a range of lipid and bile salt concentrations. The substrate aggregates were characterized by time-resolved fluorescence quenching (TRFQ). The activity values and the micelle sizes group into two sets: (i) larger micelles for bile salt/lipid 5 with lower activity and longer steady state ( approximately 10 min). At least two sets of parameters, for bile salt/lipid 5, characterize the kinetics. Higher enzyme-micelle dissociation constant and lower catalytic rate are found for the group of smaller micelles. An explanation supporting our finding is that as micelles become smaller the overlap area for enzyme-micelle binding decreases, leading to weaker binding. Consequently the enzyme dissociation constant increases. Extension of the present approach to other phospholipases and substrates to establish its generality and correlation between micelle size and the catalytic rate are areas for future investigations.

Catalysis↗
PubMed2001

In vitro mechanical integrity of hydroxyapatite coatings on Ti-6Al-4V implants under shear loading.

A new test method for the mechanical behavior of coatings on metal substrates under shear loading has been developed. Finite element simulations show that this new test method provides an almost identical shear load on the coatings to that of the conventional test. Using the new method, the static and fatigue behavior of plasma-sprayed hydroxyapatite (HA) coatings on Ti-6Al-4V substrates were studied at room temperature as a function of processing conditions. The results of the static tests show that the nominal interface shear strength is in the range of 25 approximately 40 MPa. The fatigue resistance to cyclic shear loading was characterized by shear stress amplitude versus cycle-to-failure for the samples that failed within 1010(7)cycles, and by residual nominal interfacial shear strength for the samples that survived 1010(7)cycles. The experimental results indicate that a threshold level of shear stress amplitude exists for introducing fatigue damage to HA coatings. AES and XPS studies indicated that bonding between the coating and substrate does not occur over about 12 percent of the area of the interface while bonding in the contact area of the interface is mainly mechanical interlocking. A failure mechanism of interfacial microflaw coalescence is suggested.

Alloys↗
PubMed2002

Epitaxial growth and photochemical annealing of graded CdS/ZnS shells on colloidal CdSe nanorods.

We report the preparation and structural characterization of core/shell CdSe/CdS/ZnS nanorods. A graded shell of larger band gap is grown around CdSe rods using trioctylphosphine oxide as a surfactant. Interfacial segregation is used to preferentially deposit CdS near the core, providing relaxation of the strain at the core/shell interface. The reported synthesis allows for variation of the shell thickness between one and six monolayers, on core nanorods ranging from aspect ratios of 2:1 to 10:1. After an irreversible photochemical annealing process, the core/shell nanorods have increased quantum efficiencies and are stable in air under visible or UV excitation. In addition to their robust optical properties, these samples provide an opportunity for the study of the evolution of epitaxial strain as the shape of the core varies from nearly spherical to nearly cylindrical.

Journal Article↗
PubMed2004

Cooperative binding of monodisperse anionic amphiphiles to the i-face: phospholipase A2-paradigm for interfacial binding.

Equilibrium parameters for the binding of monodisperse alkyl sulfate along the i-face (the interface binding surface) of pig pancreatic IB phospholipase A(2) (PLA2) to form the premicellar complexes (E(i)(#)) are characterized to discern the short-range specific interactions. Typically, E(i)(#) complexes are reversible on dilution. The triphasic binding isotherm, monitored as the fluorescence emission from the single tryptophan of PLA2, is interpreted as a cooperative equilibrium for the sequential formation of three premicellar complexes (E(i)(#), i = 1, 2, 3). In the presence of calcium, the dissociation constant K(1) for the E(1)(#) complex of PLA2 with decyl sulfate (CMC = 4500 microM) is 70 microM with a Hill coefficient n(1) = 2.1 +/- 0.2; K(2) for E(2)(#) is 750 microM with n(2) = 8 +/- 1, and K(3) for E(3)(#) is 4000 microM with an n(3) value of about 12. Controls show that (a) self-aggregation of decyl sulfate alone is not significant below the CMC; (b) occupancy of the active site is not necessary for the formation of E(i)(#); (c) K(i) and n(i) do not change significantly due to the absence of calcium, possibly because alkyl sulfate does not bind to the active site of PLA2; (d) the E(i)(#) complexes show a significant propensity for aggregation; and (e) PLA2 is not denatured in E(i)(#). The results are interpreted to elaborate the model for atomic level interactions along the i-face: The chain length dependence of the fit parameters suggests that short-range specific anion binding of the headgroup is accompanied by desolvation of the i-face of E(i)(#). We suggest that allosteric activation of PLA2 results from such specific interactions of the amphiplies and the desolvation of the i-face. The significance of these primary interfacial binding events and the coexistence of the E and E(i)(#) aggregates is discussed.

Animals↗
PubMed2005

Synthesis and phase characterization of a double-tailed pyrrole-containing surfactant: a novel tecton for the production of functional nanostructured materials.

A double-tailed polymerizable (pyrrolylalkyl) ammonium amphiphile has been synthesized, and its interfacial properties and aqueous phase behavior have been studied by polarized optical microscopy and X-ray diffraction. The Krafft temperature is about 27 degrees C, and the critical micelle concentration at 40 degrees C is about 1 mM, as obtained from surface tension measurements, potentiometry, and isothermal titration calorimetry. The lyotropic behavior of the surfactant is found to be of a complex nature. At concentrations higher than the micellar (L1) region, two mesophases have been identified: a second isotropic (L2) phase, which is probably micellar but not fully miscible with water, and a lamellar (L(alpha)) phase, showing interesting alignment properties. Small-angle X-ray scattering analysis of the mesophases has been evaluated in terms of a model of spherical micelles, which describes a mutual arrangement by a structure factor derived from a hard-sphere potential (Percus-Yevick, "PY", approach). Interest in the comprehensive phase behavior of the polymerizable surfactant is based on the desire to integrate the system into a composite material to obtain potentially conducting self-assembled hybrid mesostructures.

Journal Article↗
PubMed2006

Effects of organic ligands, electrostatic and magnetic interactions in formation of colloidal and interfacial inorganic nanostructures.

This paper discusses effects of organic ligands, electrostatic and magnetic interactions involved in morphological control of chemically synthesized inorganic nanostructures including colloid and planar systems. The special attention was concentrated on noble metal (gold and palladium) nanoparticles and nanostructures formed at the gas-liquid interface. The analysis of experimental data showed that electrostatic and ligand-related interactions influence very strongly on the metal nanostructure morphology. The hydrophobicity of ligand, charge and binding affinity to inorganic phase are important factors influencing the morphology of inorganic nanostructures formed in a layer at the gas/liquid interface by the interfacial synthesis method. The important point of this method is the quasi two-dimensional character of reaction area and possibilities to realize ultimately thin and anisotropic dynamic monomolecular reaction system with two-dimensional diffusion and interactions of precursors, intermediates and ligands resulting in planar growth and organization of inorganic nanoparticles and nanostructures in the plain of Langmuir monolayer. The morphology of resulting inorganic nanostructures can be controlled efficiently by variations of growth conditions via changes in state and composition of interfacial planar reaction media with the same precursor, and by variations of composition of adjacent bulk phases. The extreme anisotropy and heterogeneity of two-dimensional interfacial reaction system allows creating conditions when growing inorganic particles floating on the aqueous phase surface interact selectively with hydrophobic water-insoluble ligands in interfacial monolayer or with hydrophilic bulk-phase ligands, or at the same time with ligands of different nature present in monolayer and in aqueous phase. The spatial anisotropy of interfacial reaction system and non-homogeneity of ligand binding to inorganic phase gives possibilities for growth of integrated anisotropic nanostructures with unique morphologies, in particularly those characterized by very high surface/volume ratio, high effective perimeter, and labyrinth-like structure. In a case of magnetic nanoparticles dispersed in colloids specific magnetic dipolar interactions can result in formation of chains, rings and more complex nanoparticulate structures or separated highly anisotropic nanoparticles. Theoretical considerations indicate to the importance of system dimensionality in relation to the energy balance which determines specific features of structure organization in planar charged metallic and magnetic nanostructures. For example, a requirement of Coulomb energy minimum, the possibility of free electron redistribution and strengthened attractive interactions between particles in metallic nanostructures can explain formation of very branchy systems with extremely high "effective perimeter". The obtained experimental and literature data show that system dimensionality, organic ligand nature along with electrostatic and magnetic interactions are most important factors of morphological control of chemically synthesized inorganic nanomaterials. The understanding and appropriate exploitation of these factors can be useful for further developments of efficient nanofabrication techniques based on colloidal and interfacial synthetic methods.

Journal Article↗
PubMedDate not supplied

Preparation and characterization of microencapsulated gelospheres for controlled oral theophylline delivery.

Microencapsulated gelospheres were prepared using the water swellable polymers, poly(vinyl alcohol) and polyacrylamide in which the drug was embedded. Polymeric coating was formed by interfacial polymerization using 1,6 hexamine and sebacoyl chloride. The size, shape, in vitro release, kinetics and in vivo efficiency of the formulation were determined. The shape was found to be spherical with a size range below 100 microm. The per cent drug loaded was found to be higher in the case of gelospheres prepared with polyacrylamide than those prepared with poly(vinyl alcohol). The release rate was found to be near zero order. The AUC was found to be higher in the case of polyacrylamide and polyvinyl alcohol gelospheres as compared to plain drug solution.

Acrylic Resins↗
PubMed2001

Characterization of compression-molded UHMWPE, PMMA and PMMA/MMA treated UHMWPE: density measurement, FTIR-ATR, and DSC.

Considered one of the weak links in the total hip replacement (THR), efforts to enhance the interfacial strength between bone cement and ultra-high molecular weight polyethylene (UHMWPE) acetabular cup had been conducted in this laboratory. Following the successful demonstration of high interfacial strengths for our new acetabular component design, the nature of physical, chemical, and thermal property of the compression-molded specimens, including UHMWPE, PMMA/MMA treated UHMWPE, and PMMA has been investigated in this study. Density results from a density gradient column showed that the molding processes and conditions were adequate for complete sintering of UHMWPE and PMMA powders. FTIR-ATR results gave a direct evidence that PMMA did exist in the PMMA/MMA treated UHMWPE matrix. It also revealed a clear diffusion-related behavior across the interface. Under the high temperature and pressure, the UHMWPE powders undergo drastic changes of their morphology and crystalline structures. These changes were examined by differential scanning calorimeter (DSC) which showed a large difference in terms of % crystallinity. The percent of PMMA deposited in the treated UHMWPE was 17.8%, 18.8%, and 24.3% from the analyses of density, FTIR-ATR, and DSC, respectively. Finally, an evidence of diffusive behavior at the interface exhibited diffusion of PMMA occurring across the interfaces between the treated UHMWPE and UHMWPE or PMMA.

Bone Cements↗
PubMed2006

Structural changes in poly(ethyleneimine) modified microemulsion.

The influence of branched poly(ethyleneimine) on the phase behavior of the system sodium dodecylsulfate/toluene-pentanol (1:1)/water has been studied. The isotropic microemulsions still exist when water is replaced with aqueous solutions of PEI (up to 30% in weight), but their stability is significantly influenced. From a polymer concentration of 20 wt%, the polymer enhances the solubilization of water in oil, changes the sign of the spontaneous curvature of the surfactant film, and induces an inversion of the microemulsion type from water-in-oil (L(2)) to oil-in-water (L(1)), by the formation of a bicontinuous channel. Further investigations show that the addition of polymer in the L(2) phase changes the droplet-droplet interactions as the conductivity drops and the percolation disappears. In the bicontinuous channel, higher viscosities can be detected, as well as a weak percolation followed by a steep increase of the conductivity, which can be related to evident structural changes in the system. DSC measurements allow then to follow the changes of the water properties in the system, from interfacial-water in the L(2) phase to free-water in the sponge-like phase. Finally, all the measurements performed permit to characterize the structural transitions in the system and to understand the role of the added polymer.

Calorimetry, Differential Scanning↗
PubMed2005

Identification and characterization of the putative fusion peptide of the severe acute respiratory syndrome-associated coronavirus spike protein.

Severe acute respiratory syndrome-associated coronavirus (SARS-CoV) is a newly identified member of the family Coronaviridae and poses a serious public health threat. Recent studies indicated that the SARS-CoV viral spike glycoprotein is a class I viral fusion protein. A fusion peptide present at the N-terminal region of class I viral fusion proteins is believed to initiate viral and cell membrane interactions and subsequent fusion. Although the SARS-CoV fusion protein heptad repeats have been well characterized, the fusion peptide has yet to be identified. Based on the conserved features of known viral fusion peptides and using Wimley and White interfacial hydrophobicity plots, we have identified two putative fusion peptides (SARS(WW-I) and SARS(WW-II)) at the N terminus of the SARS-CoV S2 subunit. Both peptides are hydrophobic and rich in alanine, glycine, and/or phenylalanine residues and contain a canonical fusion tripeptide along with a central proline residue. Only the SARS(WW-I) peptide strongly partitioned into the membranes of large unilamellar vesicles (LUV), adopting a beta-sheet structure. Likewise, only SARS(WW-I) induced the fusion of LUV and caused membrane leakage of vesicle contents at peptide/lipid ratios of 1:50 and 1:100, respectively. The activity of this synthetic peptide appeared to be dependent on its amino acid (aa) sequence, as scrambling the peptide rendered it unable to partition into LUV, assume a defined secondary structure, or induce both fusion and leakage of LUV. Based on the activity of SARS(WW-I), we propose that the hydrophobic stretch of 19 aa corresponding to residues 770 to 788 is a fusion peptide of the SARS-CoV S2 subunit.

Amino Acid Sequence↗
PubMed2005

Development of a fluid functionalized lipidic matrix applied to direct in situ polynucleotide detection.

This work presents a new approach for direct detection of polyelectrolytes at the air-water interface, based on the investigation of the interfacial properties of an active lipidic matrix especially designed for polynucleotide immobilization. A synthetic lipid with a cationic spermine headgroup, DiOctadecylamidoGlycylSpermine (DOGS), was spread at the interface to form a distortable film able to capture polynucleotides. The control of the organization state of this functionalized monolayer upon compression was achieved by recording surface pressure-area (pi-A) isotherm diagrams, presenting a specific shape with a typical liquid expanded-liquid condensed phase transition on a pure water subphase. In the presence of various dsDNA concentrations in the subphase, the isotherms were markedly modified in a time and concentration-dependent manner. The main modifications, corresponding to a large shift towards higher molecular areas and a clear fading of the phase transition, were corroborated by the fine analysis of the monolayer compressibility profile, thus suggesting a characteristic change in the monolayer fluidity as a function of both time and DNA concentration. Moreover, an ATR-Fourier transform infrared (ATR-FTIR) characterization showed evidences for the adsorption of DNA strands onto the lipidic matrix. The direct observation of the mixed monolayer morphology by Brewster angle microscopy (BAM) strongly suggests that DNA adsorption induces a reorganization of lipids at the interface, as evidenced by the change in the condensed lipidic domains morphology in the presence of DNA in the subphase. The immobilization of various polynucleotidic probes of 4000, 400 and 22 base length, confirmed by fluorescence microscopy, had similar effects on DOGS interfacial properties. Preliminary studies are finally presented to explore the possibility of using this system for the study of hybridization between complementary strands. Hence, this study demonstrates this functionalized matrix behaves as a fluid support where polynucleotide immobilization induces interfacial properties modifications, which could be further exploited through the experimental characterization of Faraday instabilities sensitive to visco-elasticity variations.

Adsorption↗
PubMed1977

Effects of polymer surface molecular structure and force-field characteristics on blood interfacial phenomena.

To quantify the effects of major surface structural factors influencing interfacial reactions induced by polymers in native blood, model surfaces of solvent-cast films of two analogous poly(ether urethanes) and three homologous polyamides (nylon 4, 6/6, and 12) were exposed ex vivo to canine blood under the well-defined hemodynamic conditions of the Stagnation Point Flow Experiment. The selected surfaces allow for incremental changes in properties and were characterized by their "Composite Surface Free ENergy Function," gamma'S, which describes the surface force field as the sum of the mean dispersion (gammaSd) and polar (gammaSp) contributions and is computed from wettability spectra obtained with ultrapure diagnostic liquids. Blood interfacial effects were measured by the shear-limited diameter of the white cell circle formed around the stagnation point, the flow parameter at which symmetric aggregation occurred, and the surface-number density of platelets, [P s], remaining adherent under fixed conditions. At identical flows, within each group of polymers, both the WBC-circle diameter and [P s] scale with gamma Sp/gamma'S, implying that 1) only the magnitude but not the interaction mechanism varies as a function of incremental structural and surface changes, 2) the primary determinant of surface-induced effects is the polar force contribution, and 3) the magnitude of gamma'S is secondary if gammaSd/gamma'S is sufficiently great.

Adsorption↗
PubMed2003

Preparation and characterization of ibuprofen-cetyl alcohol beads by melt solidification technique: effect of variables.

Ibuprofen (IBU) exhibits short half-life, poor compressibility, flowability and caking tendency. IBU melt has sufficiently low viscosity and exhibits interfacial tension sufficient to form droplet even at low temperature. A single step novel melt solidification technique (MST) was developed to produce IBU beads with lower amounts of excipient. Effect of variables was studied using a 3(2) factorial approach with speed of agitation and amount of cetyl alcohol (CA) as variables. The beads were evaluated using DSC, FT-IR and scanning electron microscope (SEM). Yield, micromeritic properties, crushing strength and release kinetics were also studied. Spherical beads with a method yield of above 90% were obtained. The data was analyzed by response surface methodology. The variables showed curvilinear relationship with yield in desired particle size range, crushing strength and, bulk and tap density. The drug release followed non-Fickian case II transport and the release rate decreased linearly with respect to amount of CA in the initial stages followed by curvilinearity at later stages of elution. The effect of changing porosity and tortuosity was well correlated.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1994

Use of a compact sandwich specimen to evaluate fracture toughness and interfacial bonding of bone.

The objective of the present study was to develop a reliable and statistically valid test to measure the fracture toughness of small specimens of bone, and by extension, prosthetic materials, using a compact sandwich specimen. Samples of bone were sandwiched between holders of a different material and using this specimen configuration a new technique was developed to test the fracture toughness of the bone interlayer. The effects of different specimens sizes and holder materials were investigated empirically. Using finite element analysis a correction factor was determined to account for the finite thickness of the interlayer and the analytical solutions governing the test specimen were accordingly modified. Bulk compact tension specimens of bone were tested for comparison. Both wet and dry bone were evaluated and the fracture surface morphology characterized using scanning electron microscopy. The results indicate no statistically significant differences between the fracture toughness values obtained from the compact tension and sandwich specimens. The application of this technique to the testing of interfacial bonding between bone and biomaterials is discussed.

Aluminum↗
PubMed2006

A less irritant norcantharidin lipid microspheres: formulation and drug distribution.

Lipid microspheres (LM) have recently been used as intravenous (i.v.) carriers for drugs, which are sufficiently soluble in oil. However, in the case of norcantharidin (NCTD), which is poorly soluble in both the water and oil phases, this approach is not feasible. In this study, NCTD-loaded LM was prepared by transferring the drug to the interfacial surface of the oil and aqueous phases to produce a less irritating i.v. formulation of NCTD. A probe type sonicator was used to disperse NCTD into the oil phase together with lecithin and Tween 80. A high-pressure homogenization process was used to prepare the lipid microspheres and localize the drug at the surfactant layer. The LM loaded with NCTD consisted of 0.02% drug. Characterization of LMs and short-term stability was performed by photon correlation spectroscopy (PCS) and a centrifugation test was also carried out. The results showed that NCTD-loaded LM (2 mg/ml) with over 80% NCTD loaded in the interfacial surface were stable for a period of 2 months, and were suitable for i.v. injection in terms of size and stability, whether be diluted or not. Such formulations produced less pain and irritation in animal studies.

Animals↗
PubMed1999

A novel approach to AFM characterization of adhesive tooth-biomaterial interfaces.

A novel approach is proposed for studying tooth-biomaterial interactions with high resolution. Thus far, polished interfaces examined by AFM have not disclosed much detail, mainly due to the destruction of soft surface texture and the smearing of polishing debris across the interface that obscures the actual ultra-structure. Therefore the practical utility of diamond-knife microtomy as a sample preparation technique for imaging tooth-biomaterial interfaces by AFM with high resolution was tested in this study and compared to that of ultra-fine mechanical polishing techniques. The AFM images clearly demonstrated the enhanced potential of diamond-knife microtomy for nondestructively producing clean cross-sections through interfaces that allow the interfacial ultra-structure to be imaged by AFM with a resolution equaling that of TEM. This novel approach opens the field to the full range of scanning probe microscopy, including physical and chemical surface characterization of interfaces with a mix of soft and hard substrates.

Dental Cements↗