Biomedical subjects

Tommy Nylander

Publications and source records attributed to Tommy Nylander.

At least 19 recordsLinked to original sources

PubMed2007

Liquid crystalline phases and their dispersions in aqueous mixtures of glycerol monooleate and glyceryl monooleyl ether.

The aqueous phase behavior of mixtures of 1-glycerol monooleate (GMO) and its ether analogue, 1-glyceryl monooleyl ether (GME) has been investigated by a combination of polarized microscopy, X-ray diffraction, and NMR techniques. Three phase diagrams of the ternary GMO/GME/water system have been constructed at 25, 40, and 55 degrees C. The results demonstrate that the increasing amount of GME favors the formation of the reversed phases, evidenced by the transformation of the lamellar and bicontinuous cubic liquid crystalline phases of the binary GMO/water system into reversed micellar or reversed hexagonal phases. For a particular liquid crystalline phase, increasing the GME content has no effect on the structural characteristics and hydration properties, thus suggesting ideal mixing with GMO. Investigations of dispersed nanoparticle samples using shear and a polymeric stabilizer, Pluronic F127, show the possibility of forming two different kinds of bicontinuous cubic phase nanoparticles by simply changing the GMO/GME ratio. Also NMR self-diffusion measurements confirm that the block copolymer, Pluronic F127, used to facilitate dispersion formation, is associated with nanoparticles and provides steric stabilization.

Chemistry, Physical↗

PubMed2006

Interfacial behavior of cubic liquid crystalline nanoparticles at hydrophilic and hydrophobic surfaces.

The adsorption behavior of self-assembled lipid liquid crystalline nanoparticles at different model surfaces was investigated in situ by use of ellipsometry. The technique allows time-resolved monitoring of the adsorbed amount and layer thickness under transient and steady-state conditions. The system under study was cubic-phase nanoparticle (CPNP) dispersions of glycerol monooleate stabilized by a nonionic block copolymer, Pluronic F-127. Depending on the surface properties and presence of electrolytes, different adsorption scenarios were discerned: At hydrophilic silica thick surface layers of CPNPs are generated by particle adsorption from dispersions containing added electrolyte, but no adsorption is observed in pure water. Adsorption at the hydrophobic surface involves extensive structural relaxation and formation, which is not electrolyte sensitive, of a classic monolayer structure. The different observations are rationalized in terms of differences in interactions among the CPNP aggregates, their unimer constituents, and the surface and show a strong influence of interfacial interactions on structure formation. Surface self-assembly structures with properties similar to those of the corresponding bulk aggregates appear exclusively in the weak interaction limit. This observation is in agreement with observations for surfactant self-assembly systems, and our findings indicate that this behavior is applicable also to complex self-assembly structures such as the CPNP structures discussed herein.

Adsorption↗

PubMed2006

Formation of polyelectrolyte-surfactant complexes on surfaces.

The interfacial behavior of polyelectrolytes, mainly cationic with varying content of amphiphilic groups, and their complexes with oppositely charged surfactant are discussed. Both the kinetics and the reversibility aspect of the adsorption are considered. The structure of adsorbed layer formed was found to be dependent not only on the bulk solution phase behavior, but also on the pre-applied conditions, i.e., the path used to obtain a particular solution condition (e.g., by changing pH and concentration of salt, surfactant or polymer). Polyelectrolyte adsorption appears only partly reversible, due to its high affinity to the surface, which slows down the adsorption process. In general, relaxation occurs more easily if the direction of the process is from low to high surface coverage. Association of the surfactant with the polymer, which depends on the surfactant concentration, can completely alter the interfacial behavior. Maximum adsorption occurs generally at a surfactant concentration just before the expected phase separation region, while the complex in some cases could desorb from the surface at high enough surfactant concentration (above the cmc). Different results were obtained for coadsorption of amphiphilic polyelectrolytes when surfactant was added to the preadsorbed polymer layers and when complexes were pre-formed in the solution prior to exposing the surface to the polymer-surfactant solution.

Adsorption↗

PubMed2006

An X-ray diffraction study of alterations in bovine lung surfactant bilayer structures induced by albumin.

Lung surfactant (LS) is an extra-cellular lipid-protein system responsible for maintaining low surface tension in the lung and alveolar stability. Serum proteins cause dysfunction of this material, e.g. in adult respiratory distress syndrome (ARDS). BLES is a clinically used LS consisting of most of the lipids and associated proteins from bovine lung lavage. Aqueous phases of BLES at 30% and 70% hydration, with and without 5% by weight of bovine serum albumin (BSA), calculated on the amount of lipids, were studied using X-ray diffraction during cooling from 42 to 5 degrees C. The diffraction curves are consistent with a transition from a lamellar liquid crystalline phase to a gel phase transition at cooling in the interval 30-20 degrees C. The long-spacings correspond to a reduction of the bilayer thickness during this transition. The wide-angle region shows a peak at 4.1 A below 25 degrees C, which is characteristic of the hexagonal chain packing of the gel phase. The perturbation of the bilayers by the presence of BSA seems to induce a significant decrease of the bilayer thickness. Calculations on the observed limits of swelling (taking place in the range 50-60%) indicate that BSA is closely associated with the BLES bilayers, probably due to electrostatic interaction with the cationic surfactant proteins SP-B and SP-C. This study show that the LS lipid structural organizations are extremely susceptible to small amounts of serum albumin, which may have implications in surfactant related lung disease and clinical applications of surfactant therapy.

Animals↗

PubMed2006

Thiol-specific and nonspecific interactions between DNA and gold nanoparticles.

The contribution of nonspecific interactions to the overall interactions of thiol-ssDNA and dsDNA macromolecules with gold nanoparticles was investigated. A systematic investigation utilizing dynamic light scattering and cryogenic transmission electron microscopy has been performed to directly measure and visualize the changes in particle size and appearance during functionalization of gold nanoparticles with thiol-ssDNA and nonthiolated dsDNA. The results show that both thiol-ssDNA and dsDNA do stabilize gold nanoparticle dispersions, but possible nonspecific interactions between the hydrophobic DNA bases and the gold surface promote interparticle interactions and cause aggregation within rather a short period of time. We also discuss the adsorption mechanisms of dsDNA and thiol-ssDNA to gold particles.

Adsorption↗

PubMed2005

DNA compaction onto hydrophobic surfaces by different cationic surfactants.

DNA compaction by alkyltrimethylammonium surfactants at hydrophobized silica surfaces and the effect of the counterion, as well as the hydrocarbon chain length, was investigated by in situ null-ellipsometry. In addition, DNA compaction in the presence of a gemini surfactant, hexyl-alpha,omega-bis(dodecyldimethylammonium bromide), was studied. The type of cationic amphiphile used was found not to have a pronounced effect on the mixed DNA-cationic surfactant adsorbed layer thickness, although the surface concentration excess for the mixed layers seemed to follow the same trend as that for DNA-free surfactant layers. Interestingly, it was also found that the stability of the mixed adsorbed layer largely depends on the cationic surfactant used.

Animals↗

PubMed2005

Equilibrium aspects of polycation adsorption on silica surface: how the adsorbed layer responds to changes in bulk solution.

Adsorption of cationic high molecular weight polyacrylamides (CPAM) (M(w) is about 800 kDa) with different fractions of cationic units tau = 0.09 and tau = 0.018 onto silica surface was studied over a wide range of pH (4-9) and KCl concentration (c(s) = 10(-3)-10(-1) M) by in-situ null ellipsometry. We discuss how the adsorbed layer depends on the bulk conditions as well as kinetically responds to changes in solution conditions. The adsorbed amount Gamma of CPAM increases with pH for all studied electrolyte concentrations until a plateau Gamma is reached at pH > 6. At low pH we observed an increase in adsorbed amount with electrolyte concentration. At high pH there is no remarkable influence of added salt on the values of the adsorbed amount. The thickness of adsorbed polymer layers, obtained by ellipsometry, increases with electrolyte concentration and decreases with pH. At low c(s) and high pH the polyelectrolyte adsorbs in a flat conformation. An overcompensation of the surface charge (charge reversal) by the adsorbed polyelectrolyte is observed at high c(s) and low pH. To reveal the reversibility of the polyelectrolyte adsorption with respect to the adsorbed amount and layer thickness, parameters such as polyelectrolyte concentration (c(p)), c(s), and pH were changed during the experiment. Generally, similar adsorbed layer properties were obtained independent of whether adsorption was obtained directly to initially bare surface or by changing pH, c(s), or the concentration of polyelectrolyte solution in the presence of a preadsorbed layer, provided that the coverage of the preadsorbed layer was low. Once a steady state of the measured parameters (Gamma, d) was reached, experimental conditions were restored to the original values and corresponding changes in Gamma and adsorbed layer thickness were recorded. For initially low surface coverage it was impossible to restore the layer properties, and in this case we always ended up with higher coverage than the initial values. For initial high surface coverage it was usually possible to restore the initial layer properties. Thus, we concluded that polyelectrolyte appears only partially reversible to changes in the solution conditions due the slow rearrangement process within the adsorbed layer.

Journal Article↗

PubMed2005

The interaction between DNA and cationic lipid films at the air-water interface.

The interaction between DNA and positively charged dioctadecyldimethylammonium bromide (DODAB) and DODAB/disteroylphosphatidylcholine (DSPC) monolayers at the air-aqueous interface was studied by a combination of the surface film balance and Brewster angle microscopy. In presence of DNA, the Pi-A isotherm of the cationic monolayer shifts to larger mean molecular areas due to the electrostatic interaction with DNA while the typical liquid expanded-liquid condensed phase transition for DODAB monolayers disappear and the monolayer remains to be in the liquid expanded phase. Furthermore, the morphology of the film dramatically changes, where the large dendritic-like condensed aggregates observed for DODAB monolayers vanish. The charge density of the monolayer was varied by using mixed monolayers with the zwitterionic DSPC and no large effect was observed on the interaction with DNA. By modeling the electrostatic interactions with the linearized Poisson-Boltzmann equation using the finite-element method and taking into account the assumption in the dielectric constants of the system, it was possible to corroborate the expansion of the cationic monolayer upon interaction with DNA as well as the fact that DNA does not seem to penetrate into the monolayer.

Air↗

PubMed2005

Cationic amphiphilic polyelectrolytes and oppositely charged surfactants at the silica-aqueous interface.

The influence of sodium dodecyl sulfate (SDS) on the interfacial behavior of two amphiphilic polyelectrolytes, which are copolymers of the cationic monomers triethyl(vinylbenzyl)ammonium chloride and dimethyldodecyl(vinylbenzyl)ammonium chloride, at the silica-aqueous interface was studied. The fraction of amphiphilic monomers was varied, where 0DT, 40DT, and 80DT contained 0, 40, and 80 mol % monomers with dodecyl side chains, respectively. We used in situ ellipsometry to follow the kinetics of adsorption, in terms of adsorbed amount and adsorbed layer thickness, as well as the response of the adsorbed layers to changes in ionic strength and surfactant concentration. Different results were obtained when surfactant was added to the preadsorbed layers compared to the cases when complexes were preformed in the solution prior to the adsorption. In the whole range of concentrations studied, SDS interacts with 40DT and 80DT noncooperatively, whereas for 0DT cooperativity of binding is observed. The amount adsorbed increased significantly as the SDS concentration was close to the cmc. At high SDS concentrations, a lowering of the layer density was observed. For the amphiphilic polyelectrolytes, 40 DT and 80DT, no desorption from the interface was detected for the range of SDS concentrations studied, while 0DT features a maximum in adsorbed amount at concentrations close to the cmc of SDS. Adsorption of 40DT and 80DT from their mixtures with SDS is found to be path dependent with respect to the variation in SDS concentration, where the reversibility decreases with increasing SDS concentration above the expected charge neutralization point. The coadsorption of 80DT and SDS is highly irreversible with respect to changes in the ionic strength within the time scale of the experiment. In this study, we attempt to illustrate both general mechanisms and specific effects. With regard to the general behavior, it is important to note the charge regulation of both the silica surfaces and the polyion/surfactant complexes; an interplay between the two charge-regulating effects is the key to understanding our observations.

Journal Article↗

PubMed2005

SANS study of the interactions among DNA, a cationic surfactant, and polystyrene latex particles.

The compaction of DNA by a cationic surfactant both in the bulk and adsorbed on the surface of latex particles was followed for the first time by SANS. In the bulk, a decrease in the overall size of the DNA coil in the presence of the cationic surfactant was observed at a negative-to-positive charge ratio far below the phase separation region, at a negative-to-positive charge ratio of 18. Additionally, large surfactant aggregates seem to form within the DNA-surfactant complex. On the other hand, DNA adsorbs onto the surface of latex particles, forming a thick layer, as evidenced by the fitting of the SANS data to a core-shell form factor. Addition of a cationic surfactant to the DNA-coated latex particles at a negative-to-positive charge ratio of 38 induces a slight decrease in the size of the particle layer, where the cationic surfactant is evenly distributed within the adsorbed layer. A further decrease of the negative-to-positive charge ratio to 18 induces a dramatic change in the SANS data that suggests significant compaction of the adsorbed layer and the formation of large surfactant aggregates, similar to those detected in the bulk.

Adsorption↗

PubMed2005

Adsorption and aggregation of cationic amphiphilic polyelectrolytes on silica.

The adsorption of two cationic amphiphilic polyelectrolytes, which are copolymers of two charged monomers, triethyl(vinylbenzyl)ammonium chloride and dimethyldodecyl(vinylbenzyl)ammonium chloride (which is the amphiphilic one) with different contents of amphiphilic groups (40% (40DT) and 80% (80DT)), onto the hydrophilic silica-aqueous solution interface has been studied by in situ null ellipsometry and tapping mode atomic force microscopy (AFM). Adsorption isotherms for both polyelectrolytes were obtained at 25 degrees C and at different ionic strengths, and the adsorption kinetics was also investigated. At low ionic strength, thin adsorbed layers were observed for both polyelectrolytes. The adsorption increases with polymer concentration and reaches, in most cases, a plateau at a concentration below 50 ppm. For the 80DT polymer, at higher ionic strength, an association into aggregates occurs at concentrations at and above 50 ppm. The aggregates were observed directly by AFM at the surface, and by dynamic light scattering in the solution. The adsorption data for this case demonstrated multilayer formation, which correlates well with the increase in viscosity with the ionic strength observed for 80DT.

Journal Article↗

PubMed2005

Formation of a liquid crystalline phase from phosphatidylcholine at the oil-aqueous interface.

Adsorption of phospholipid (1,2-dioleoyl-sn-glycero-3-phosphatidylcholine) and formation of a surface phase at the oil-water interface has been followed by using ellipsometry. The properties of the interfacial phase were found to depend strongly on whether phospholipid was added to the oil phase or to the aqueous phase as liposomal structures. In the latter case a monolayer formed, while if the phospholipid was supplied from the oil phase a lamellar phase appeared at the interface. The effect on the stabilizing surface phase of a surface-active protein (beta-lactoglobulin) was also investigated. The observations are important for understanding stabilizing properties of surface-active compounds commonly used to stabilize emulsions. In addition it has been demonstrated that ellipsometry can be used to study the initial process when a two-phase system consisting of a water and an oil phase is transformed into a three phase system or eventually to a one-phase system.

Crystallization↗

PubMed2005

Fengycin interaction with lipid monolayers at the air-aqueous interface-implications for the effect of fengycin on biological membranes.

In this study, we investigated the interaction of fengycin, a lipopeptide produced by Bacillus subtilis, with lipid monolayers using the Langmuir trough technique in combination with Brewster angle microscopy. Thermodynamic analyses were performed to get further information about the mixing behavior and the molecular interactions between the two components. The effect of fengycin on the structural and morphological characteristics of DPPC monolayers, as a simple model of biological membranes, depends on the fengycin molar ratio. With a small proportion of fengycin (X(f)0.1), the compressibility of the monolayer is modified but the morphological characteristics of the DPPC are not significantly affected. At an intermediate molar ratio (0.1<X(f)0.5), fengycin has a fluidizing effect on the DPPC monolayer by interacting partially with DPPC molecules. At higher molar ratio (X(f)=0.66), fengycin totally dissolves the ordered phase of the lipid. These results highlight the capacity of fengycin to perturb the DPPC organization and are discussed in relation to fengycin capacity to affect biological membranes.

Air↗

PubMed2005

Competitive adsorption between beta-casein or beta-lactoglobulin and model milk membrane lipids at oil-water interfaces.

This study investigated the competitive adsorption between milk proteins and model milk membrane lipids at the oil-water interface and its dependence on the state of the lipid dispersion and the formation of emulsions. Both protein and membrane lipid surface load were determined using a serum depletion technique. The membrane lipid mixture used was a model milk membrane lipid system, containing dioleoylphosphatidylcholine, dioleoylphosphatidylethanolamine, milk sphingomyelin, dioleoylphosphatidylserine, and soybean phosphatidylinositol. The model composition mimics the lipid composition of natural milk fat globule membranes. The interactions were studied for two proteins, beta-lactoglobulin and beta-casein. The mixing order was varied to allow for differentiation between equilibrium structures and nonequilibrium structures. The results showed more than monolayer adsorption for most combinations. Proteins dominated at the oil-water interface in the protein-emulsified emulsion even after 48 h of exposure to a vesicular dispersion of membrane lipids. The membrane lipids dominated the oil-water interface in the case of the membrane lipid emulsified emulsion even after equilibration with a protein solution. Protein displacement with time was observed only for emulsions in which both membrane lipids and beta-casein were included during the emulsification. This study shows that kinetics controls the structures rather than the thermodynamic equilibrium, possibly resulting in structures more complex than an adsorbed monolayer. Thus, it can be expected that procedures such as the mixing order during emulsion preparation are of crucial importance to the emulsification performance.

Adsorption↗

PubMed2005

Ellipsometry studies of nonionic surfactant adsorption at the oil--water interface.

In the presented study we have developed and implemented a methodology for ellipsometry measurements at liquid interfaces that makes it possible to determine the amount adsorbed without assumptions of refractive index or thickness of the adsorbed layer. It was demonstrated that this is possible by combined measurements from different aqueous phases, H(2)O and D(2)O, which were shown to have sufficiently different refractive indices. The methodology was tested by studying adsorption of two types of nonionic poly(ethylene glycol) alkyl ether surfactants, C(n)H(2)(n)(+1)(OC(2)H(4))(m)OH or C(n)E(m) at the decane--aqueous interface, where C(12)E(5) was adsorbed from the oil phase and C(18)E(50) from the aqueous phase. The observed plateau values of the adsorbed amounts were 1.38 and 0.93 mg/m(2) for C(12)E(5) and C(18)E(50), respectively, which is in agreement with the corresponding values of 1.49 and 1.15 mg/m(2) obtained from applying the Gibbs equation to interfacial tension data for the same systems. We will briefly discuss the adsorption behavior in relation to the molecular structure of the surfactant and the phase behavior of the oil--surfactant--aqueous systems in relation to our experimental results.

Journal Article↗

PubMed2004

DNA and cationic surfactant complexes at hydrophilic surfaces. An ellipsometry and surface force study.

The adsorption and formation of DNA and cationic surfactant complexes at the silica-aqueous interface have been studied by ellipsometry. The interaction between the DNA-surfactant complexes at the mica-aqueous interface has been determined by the interferometric surface force apparatus. Adsorption was as expected not observed on negatively charged hydrophilic surfaces for DNA and when DNA-cationic surfactant complexes were negatively charged. However, adsorption was observed when there is an excess of cationic surfactant, just below the point of phase separation. The adsorption process requires hours to reach steady state. The adsorbed layer thickness is large at low surface coverage but becomes more compact and thinner at high coverage. A long-range repulsive force was observed between adsorbed layers of DNA-cationic surfactant complexes, which was suggested to be of both electrostatic and steric origin. The forces were found to be dependent on the equilibration time and the experimental pathway.

Adsorption↗

PubMed2004

Adsorption of cationic cellulose derivative/anionic surfactant complexes onto solid surfaces. II. Hydrophobized silica surfaces.

The effect of the anionic surfactant SDS (sodium dodecyl sulfate) on the adsorption behavior of cationic hydroxyethyl cellulose (Polymer JR-400) and hydrophobically modified cationic cellulose (Quatrisoft LM-200) at hydrophobized silica has been investigated by null ellipsometry and compared with the previous data for adsorption onto hydrophilic silica surfaces. The adsorbed amount of LM-200 is found to be considerably larger than the adsorbed amount of JR-400 at both surfaces. Both polymers had higher affinity toward hydrophobized silica than to silica. The effect of SDS on polymer adsorption was studied under two different conditions: adsorption of polymer/SDS complexes from premixed solutions and addition of SDS to preadsorbed polymer layers. Association of the surfactant to the polymer seems to control the interfacial behavior, which depends on the surfactant concentration. For the JR-400/SDS complex, the adsorbed amount on hydrophobized silica started to increase progressively from much lower SDS concentrations, while the adsorbed amount on silica increased sharply only slightly below the phase separation region. For the LM-200/SDS complex, the adsorbed amounts increased progressively from very low SDS concentrations at both surfaces, and no large difference in the adsorption behavior was observed between two surfaces below the phase separation region. The complex desorbed from the surface at high SDS concentrations above the critical micelle concentration. The reversibility of the adsorption of polymer/SDS complexes upon rinsing was also investigated. When the premixed polymer/SDS solutions at high SDS concentrations (>5 mM) were diluted by adding water, the adsorbed amount increased due to the precipitation of the complex. The effect of the rinsing process on the adsorbed layer was determined by the hydrophobicity of the polymer and the surface.

Adsorption↗

PubMed2003

Vesicle formation and other structures in aqueous dispersions of monoolein and sodium oleate.

The macroscopic appearance and microstructure in the dilute corner of the ternary monoolein (MO)-sodium oleate (NaO)-water (2H2O) system have been investigated by visual inspection and by using direct structural imaging with light microscopy and cryogenic transmission electron microscopy. The microstructural transformations that take place between the micellar phase (binary NaO2H2O axis) and the dispersed cubic phase (binary MO2H2O axis) upon increasing the ratio of MO to NaO are micelles, ruptured multilamellar vesicles together with flexible threads, various vesicle structures, vesicles in equilibrium with densely packed layers that either represent bilayers or domains of H(II) tubes visible from the side, and finally a pattern that may be either a cubic phase or domains of H(II) tubes visible in a cross section. Spontaneously formed uni- and multilamellar vesicles that show long-term stability are found to be the dominant structure for mixed dispersions over almost the entire concentration range. The addition of NaOH to the non-bilayer-forming system, the ternary MOOA (oleic acid)-2H2O system, leads to the formation of vesicles. Vesicles were also observed in other ternary MO-aqueous-based systems with potassium oleate, cetyltrimethylammonium bromide, sodium taurodeoxycholate, or dipalmitoylphosphatidylcholine instead of NaO.

Cetrimonium↗