Biomedical subjects

Otto Glatter

Publications and source records attributed to Otto Glatter.

17 recordsLinked to original sources

PubMed2006

Control of the internal structure of MLO-based isasomes by the addition of diglycerol monooleate and soybean phosphatidylcholine.

This work describes the effect of two different surfactants on the internal nanostructure of the kinetically stabilized isasomes (internally self-assembled particles or "somes"), which are a new family of colloidal particles (cubosomes, hexosomes, micellar cubosomes, and emulsified microemulsions, EME). The stabilization of these systems is performed by using the polymeric stabilizer F127. We demonstrate that the internal structure of these oil-free and oil-loaded dispersed particles can be modulated by varying the lipid composition. To achieve this goal, we replaced part of our primary lipid monolinolein (MLO) with diglycerol monooleate (DGMO) or soybean phosphatidylcholine (PC). We found that DGMO has a counter effect to that of tetradecane (TC) and allows us to tune back the self-assembled nanostructure in the TC-loaded dispersions from H2 (hexosomes) to Im3m (cubosomes). Although TC has a higher impact on confined structures than does DGMO, we demonstrate that the addition of DGMO significantly affects the internal structure of the TC-solubilized dispersions and favors the formation of large water channels. PC can also be used to modify the internal structure for MLO-based systems. It is somehow different from DGMO due to the fact that the fully hydrated Pn3m cubic structure in the presence of PC for the TC-free dispersion is preserved after dispersing. The results also indicate that PC is less effective than DGMO for tuning back the TC-loaded internal structure from H2 to cubic phase, in which it makes the confined structure less ordered. In addition, we found that DGMO has a significant effect on the internal structure of isasomes. It increases the water solubilization capacity for dispersed and nondispersed bulk phases. In contrast to the MLO-based dispersions, the present results indicate that F127 plays an important role in the internal structure of these dispersions due to its penetration into the oil-free cubic phase changing the symmetry from Pn3m to Im3m.

Chemistry↗

PubMed2006

Portable dynamic light scattering instrument and method for the measurement of blood platelet suspensions.

No routine test exists to determine the quality of blood platelet transfusions although every year millions of patients require platelet transfusions to survive cancer chemotherapy, surgery or trauma. A new, portable dynamic light scattering instrument is described that is suitable for the measurement of turbid solutions of large particles under temperature-controlled conditions. The challenges of small sample size, short light path through the sample and accurate temperature control have been solved with a specially designed temperature-controlled sample holder for small diameter, disposable capillaries. Efficient heating and cooling is achieved with Peltier elements in direct contact with the sample capillary. Focusing optical fibres are used for light delivery and collection of scattered light. The practical use of this new technique was shown by the reproducible measurement of latex microspheres and the temperature-induced morphological changes of human blood platelets. The measured parameters for platelet transfusions are platelet size, number of platelet-derived microparticles and the response of platelets to temperature changes. This three-dimensional analysis provides a high degree of confidence for the determination of platelet quality. The experimental data are compared to a matrix and facilitate automated, unbiased quality testing.

Blood Platelets↗

PubMed2006

Oil-loaded monolinolein-based particles with confined inverse discontinuous cubic structure (Fd3m).

In our recent work, we reported on the effect of varying temperature and solubilizing tetradecane (TC) on the structural transitions observed in dispersed particles based on the monolinolein (MLO)-water-TC system. At a given temperature, the addition of TC induces a transition of the internal structure from the bicontinuous cubic phase, Pn3m, to the reversed hexagonal, H2, and to the isotropic liquid phase (water-in-oil (W/O) microemulsions). Our present study focuses on the discovery of a Fd3m phase (reversed discontinuous micellar cubic), which is formed in the MLO-water-TC system at a specific TC/MLO weight ratio. It is situated between the H2 and the isotropic liquid phase (W/O microemulsion). Remarkably, it is not found in the absence of TC by increasing the temperature. The Fd3m structure was investigated in detail by means of small-angle X-ray scattering (SAXS), and cryogenic transmission electron microscopy (cryo-TEM). The present work proves that the structural transformation in the dispersed particles from H2 (hexosomes) to the W/O microemulsion system (emulsified microemulsion (EME)) is indirect and it occurs gradually via an emulsified intermediate phase. Specifically, in addition to the nanostructured aqueous dispersions described above, we present new TC-loaded aqueous dispersions with a confined intermediate phase, which is a discontinuous micellar cubic phase of the symmetry Fd3m. We denoted this type of emulsified particles as "micellar cubosomes".

Journal Article↗

PubMed2005

Formation of internally nanostructured triblock copolymer particles.

Particles with an internal structure have been found in dilute water solutions of a triblock copolymer of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), which has short hydrophilic PEO endblocks compared to the central hydrophobic PPO block (EO5PO68EO5, L121). The properties of the block copolymer particles (i.e., their structure, size, and time stability) have been investigated using cryogenic transmission electron microscopy (cryo-TEM) in combination with dynamic light scattering (DLS) and turbidity measurements. The particles were formed in dilute solutions by quenching the temperature to temperatures where the reversed hexagonal phase is in equilibrium with a solution of unaggregated L121 copolymers (L1). From the DLS measurements, a mean hydrodynamic radius of 158 nm was extracted. The time-scan turbidity measurements were found to be unchanged for about 46 h. At higher copolymer concentrations, a reversed hexagonal phase (H2) exists in the L121/water system. SAXS was used to investigate the internal structure of the dispersed L121-based particles containing 15 wt % L121. It was found that the internal structure transforms from H2 to an inverse micellar system (L2) as the temperature increases from 37 to 70 degrees C.

Journal Article↗

PubMed2005

Viscoelastic wormlike micellar solutions made from nonionic surfactants: structural investigations by SANS and DLS.

A highly viscoelastic micellar solution of nonionic surfactants in a dilute region was recently reported. A transient network of wormlike micelles formed with the addition of short-EO-chain poly(oxyethylene) dodecyl ether surfactants (C12EO(j), j = 1-4) to poly(oxyethylene) cholesteryl ethers (ChEO(m), m = 10 and 15). A gradual increase in micellar length with an increasing C12EO(j) concentration was assumed from the results of model calculations and rheological measurements. We report in this study the results of structural investigations with small-angle neutron scattering (SANS) to confirm this assumption. Tuning from spherical to wormlike and to locally flat structures can be achieved by way of three methods. One can either increase the C12EO(j) concentration or decrease j (smaller headgroup size) at a fixed concentration of C12EO(j). The third possibility is to increase the temperature at a fixed composition. All three methods result in the same structural transition. The formation of a transient network of wormlike micelles analogous to polymer solutions can be observed with dynamic light scattering (DLS). A stretched exponential approach was applied to fit the correlation functions.

Journal Article↗

PubMed2005

Ternary systems of nonionic surfactant Brij 35, water and various simple alcohols: Structural investigations by small-angle X-ray scattering and dynamic light scattering.

Structural properties of ternary systems composed of nonionic surfactant dodecyl-poly(ethylene oxide-23) ether (C12E23, commercial name: Brij 35), water and various alcohols from ethanol to 1-decanol have been investigated using small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS) techniques. All measurements were performed at the temperature 25 degrees C. SAXS experimental data were put on absolute scale using water as a secondary standard. The data of water-rich mixtures at low to moderate surfactant concentrations were evaluated using the generalized indirect Fourier transformation method (GIFT), which is based on the simultaneous determination of the intra- and inter-particle scattering contributions. In this way, the size and the shape of interacting scattering particles in real space could be deduced. The systems with a relatively low surfactant concentration (5 mass%) were studied most extensively. In these cases, the water-rich regions of the phase diagrams could be investigated into more detail, since in the alcohol-rich regions problems with the GIFT evaluation of the SAXS data were encountered. The presented results demonstrate the level of structural details that can be obtained on the basis of scattering methods and point out the specific stages of data evaluation and interpretation where one must be extremely precautious. As such they reveal the inner structuration of the complex ternary systems of our present interest. In parallel, they also indicate that the longer chain alcohols actually behave as real oil phases in the studied systems, as one might expect, and also confirm the well-known properties of different short to medium chain alcohols that act as co-solvents and/or co-surfactants in microemulsion systems depending on their chain length.

Journal Article↗

PubMed2005

Coil-globule transition of DNA molecules induced by cationic surfactants: a dynamic light scattering study.

The compaction and aggregation of DNA induced by cationic surfactants was studied by dynamic light scattering (DLS). Furthermore, the effect on surfactant-compacted DNA of the addition of nonionic amphiphiles and salt was studied. When using sufficiently low amounts of DNA and cetyltrimethylammonium bromide (CTAB), compacted DNA molecules could be monitored by the appearance of a band characterized by lower hydrodynamic radius and by the decrease in the intensity of the peak corresponding to extended DNA molecules. Notably, we observed a region where compacted molecules coexist with extended ones; these two populations were found to be stable with time. For higher concentrations of CTAB, only compacted molecules were observed and the size of the particles increased with time indicating aggregation. The number of globules present in the coexistence region increased linearly with the surfactant concentrations, as given by the area of the band corresponding to this population, which indicates a double-cooperativity of the binding. The DLS experiments were in good agreement with previous fluorescence microscopy studies, with certain advantages over this technique since there is no need to add fluorescence dyes and antioxidants. Furthermore, it allows the study of molecules which are too small to be visualized by fluorescence microscopy.

Cations↗

PubMed2005

Small-angle X-ray scattering, light scattering, and NMR study of PEO-PPO-PEO triblock copolymer/cationic surfactant complexes in aqueous solution.

The formation of triblock copolymer/surfactant complexes upon mixing a nonionic Pluronic polymer (PEO-PPO-PEO) with a cationic surfactant, hexadecyltrimethylammonium chloride (CTAC), has been studied in dilute aqueous solutions using small-angle X-ray scattering, static and dynamic light scattering, and self-diffusion NMR. The studied copolymer (denoted P123, EO(20)PO(68)EO(20)) forms micelles with a radius of 10 nm and a molecular weight of 7.5 x 10(5), composed of a hydrophobic PPO-rich core of radius 4 nm and a water swollen PEO corona. The P123/CTAC system has been investigated between 1 and 5 wt % P123 and with varying surfactant concentration up to approximately 170 mM CTAC (or a molar ratio n(CTAC)/n(P123) = 19.3). When CTAC is mixed with micellar P123 solutions, two different types of complexes are observed at various CTAC concentrations. At low molar ratios (>/=0.5) a "P123 micelle-CTAC" complex is obtained as the CTAC monomers associate noncooperatively with the P123 micelle, forming a spherical complex. Here, an increased interaction between the complexes with increasing CTAC concentration is observed. The interaction has been investigated by determining the structure factor obtained by using the generalized indirect Fourier transformation (GIFT) method. The interaction between the P123 micelle-CTAC complexes was modeled using the Percus-Yevick closure. For the low molar ratios a small decrease in the apparent molecular weight of the complex was obtained, whereas the major effect was the increase in electrostatic repulsion between the complexes. Between molar ratios 1.9 and 9 two coexisting complexes were found, one P123 micelle-CTAC complex and one "CTAC-P123" complex. The latter one consists of one or a few P123 unimers and a few CTAC monomers. As the CTAC concentration increases above a molar ratio of 9, the P123 micelles are broken up and only the CTAC-P123 complex that is slightly smaller than a CTAC micelle exists. The interaction between the P123/CTAC complexes was modeled with the hypernetted-chain closure using a Yukawa type potential in the GIFT analysis, due to the stronger electrostatic repulsion.

Journal Article↗

PubMed2005

Emulsified microemulsions and oil-containing liquid crystalline phases.

Self-assembled nanostructures, such as inverted type mesophases of the cubic or hexagonal geometry or reverse microemulsion phases, can be dispersed using a polymeric stabilizer, such as the PEO-PPO-PEO triblock copolymer Pluronic F127. The particles, which are described in the present study, are based on monolinolein (MLO)-water mixtures. When adding tetradecane (TC) to the MLO-water-F127 system at constant temperature, the internal nanostructure of the kinetically stabilized particles transforms from a Pn3m (cubosomes) to a H2 (hexosomes) and to a water-in-oil (W/O, L2) microemulsion phase (emulsified microemulsion (EME)). To our knowledge, this is the first time that the formation of stable emulsified microemulsion (EME) systems has been described and proven to exist even at room temperature. The same structural transitions can also be induced by increasing temperature at constant tetradecane content. The internal nanostructure of the emulsified particles is probed using small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM). At each investigated composition and temperature, the internal structure of the dispersions is observed to be identical to the corresponding structure of the nondispersed, fully hydrated bulk phase. This is clear evidence for the fact that the self-assembled inner particle nanostructure is preserved during the dispersion procedure. In addition, the internal structure of the particles is in thermodynamic equilibrium with the surrounding water phase. The internal structure of the dispersed, kinetically stabilized particles is a "real" and stable self-assembled nanostructure. To emphasize this fact, we denoted this new family of colloidal particles (cubosomes, hexosomes, and EMEs) as "ISASOMES" (internally self-assembled particles or "somes").

Journal Article↗

PubMed2004

Endothelial lipase-modified high-density lipoprotein exhibits diminished ability to mediate SR-BI (scavenger receptor B type I)-dependent free-cholesterol efflux.

Endothelial lipase (EL) is a phospholipase with little triacylglycerol lipase activity. To assess structural and functional properties of EL-HDL (EL-modified high-density lipoprotein), HDL was incubated with conditioned medium from Cos-7 cells infected with adenovirus encoding human EL. After re-isolation of HDL by ultracentrifugation, TLC and HPLC analyses revealed that EL-HDL was markedly depleted in phosphatidylcholine and enriched in lyso-phosphatidylcholine compared with LacZ-HDL (control HDL) incubated with conditioned medium from Cos-7 cells infected with adenovirus encoding beta-galactosidase. The EL-HDL was enriched in non-esterified fatty acids and, as revealed by lipid electrophoresis, was more negatively charged than control HDL. The HDL particle size as well as the total cholesterol, free cholesterol and triacylglycerol content of HDL were not significantly altered after EL modification. The ability of EL-HDL to mediate 3H-cholesterol efflux from SR-BI (scavenger receptor B type I) overexpressing Chinese-hamster ovary cells was impaired and markedly lower compared with LacZ-HDL at HDL concentrations of 100 microg/ml and above. Studies with 125I-labelled HDL showed almost unaltered binding affinity (K(m) values) and a slightly but significantly decreased binding capacity (B(max) values) of EL-HDL to SR-BI, compared with LacZ-HDL. The ATP-binding-cassette transporter A1-dependent cholesterol and phospholipid effluxes were not affected by EL modification. From these results, we concluded that EL modification alters chemical composition and physical properties of HDL, resulting in its decreased binding capacity to SR-BI and a diminished ability to mediate SR-BI-dependent cholesterol efflux.

ATP-Binding Cassette Transporters↗

PubMed2004

Dependence of lipoprotein-lipase-catalyzed triacylglycerol hydrolysis on droplet size of synthetic monodisperse emulsions measured with static light scattering.

Well-defined triolein emulsions of low polydispersity were prepared by shearing a crude emulsion in a modified Couette cell, resulting in radii in the range of 300 to 900 nm. These emulsions were used as synthetic substrates for lipoprotein lipase, a key enzyme for the hydrolysis of serum triacylglycerols. The change in radius with time was studied with on-line static light scattering at 37 degrees C. An optimum radius of about 750 nm was found for this reaction.

Journal Article↗

PubMed2004

Reversible phase transitions in emulsified nanostructured lipid systems.

Aqueous submicron-sized dispersions of the binary monolinolein/water system, which are stabilized by means of a polymer, internally possess a distinct nanostructure. Taking this as our starting point, we were able to demonstrate for the first time that the internal structure of the dispersed particles can be tuned by temperature in a reversible way. Upon increasing the temperature, the internal structure undergoes a transition from cubic via hexagonal to fluid isotropic, the so-called L2 phase, and vice versa. Intriguingly, in addition to the structural changes in topology, the particles expel (take up) water to (from) the aqueous continuous phase when increasing (decreasing) the temperature in a reversible way. At each temperature, the internal structure of the dispersed particles corresponds very well to the structure observed in nondispersed binary monolinolein with excess water. This agreement is independent of any thermal history (including phase transitions), which proves that the structures in the dispersed particles actually are in thermodynamic equilibrium with the surrounding water phase.

Cryoelectron Microscopy↗

PubMed2004

Five-component food-grade microemulsions: structural characterization by SANS.

In this paper we present the structural characterization of a five-component food-grade microemulsion containing Tween 80, R(+)-limonene, ethanol, glycerol, and water. Our main approach to investigating the microstructure of dense microemulsions, and how it can be influenced by the various components, was to employ small-angle neutron scattering and the new evaluation technique for dense, interacting systems, the Generalized Indirect Fourier Transformation. We started our investigation with the impact of glycerol and ethanol on Tween 80 micelles in water. We found that glycerol increases the aggregation number and withdraws the hydrating agents from the headgroup region of the surfactant, resulting in a higher packing density of molecules in a micelle at slightly increasing size. The same trend holds when the micelles are oil swollen and/or ethanol is present. Ethanol, on the other hand, redistributes mainly between water and the interface-headgroup region of the surfactant. Part of it replaces surfactant molecules in the micelles, which increases the available interface and results in a higher number of micelles with shrinking size. The same trend holds when the micelles are oil swollen and/or glycerol is present in the aqueous phase. We also investigated samples along the dilution of a mixture of surfactant and oil phase (R(+)-limonene and ethanol), which can be diluted with aqueous phase (mixture of water and glycerol) without the occurrence of phase separation. In some samples of this dilution most probably bicontinuous structures are present. To elucidate this point, we also employed dynamic light scattering, viscosity, and conductivity measurements.

Journal Article↗

PubMed2004

Small-angle static light scattering of concentrated silica suspensions during in situ destabilization.

The aggregation of concentrated aqueous silica suspensions is characterized by means of static light scattering. We use an in situ destabilization mechanism based on the enzyme-catalyzed hydrolysis of urea. This method enables us to continuously and homogeneously change the interparticle potential from repulsive to attractive without disturbing the aggregation process. Moreover, our electrostatically stabilized suspensions can be destabilized by two different methods. In the first method, the pH is shifted toward the isoelectric point of the particles ( Delta pH method), thereby leading to a decrease of their surface charge. In the second method, the ionic strength is continuously increased at constant pH ( Delta I method), leading to a compression of the electrical double layer around the charged particles. A laboratory-built flat-cell light-scattering instrument is used, which allows fast data acquisition and an adjustment of the sample cell thickness. To circumvent multiple scattering effects, we use a very small sample thickness ( approximately 13 microm). In addition, the refractive index difference between the aqueous phase and the particles is reduced by adding sucrose to the liquid phase of our suspensions. We are able to characterize the structural changes at the very early stages of the destabilization process, where no significant effects are yet detected in macroscopic rheological measurements. While during the Delta pH destabilization, the scattering curve shows significant changes only after some characteristic delay time, it changes continuously during the Delta I destabilization. The latter is attributed to the formation of a weak pre-gel structure in the suspensions, as a shallow secondary minimum appears in the interparticle potential. Data are evaluated by using a HMSA square-well structure factor model. Results are in good agreement with those predicted from DLVO theory.

Journal Article↗

PubMed2003

Dynamic and static properties of the concentrated micellar solution and gel phase of a triblock copolymer in water.

The dynamic and static behavior of the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer "P94" is studied in aqueous solution. This polymer forms transparent micellar phase structures through the whole phase diagram. The characteristics of these structures can be tuned by variation of temperature and concentration. The transparent gel at high concentrations and at ambient temperatures is the main interest in this study. The transition from the ergodic solution to this nonergodic gel or glass state can be reached in two ways: at constant temperature with an increase of concentration or at constant concentration with increasing temperature. We characterize the system in both ways with dynamic and static light scattering and with small-angle x-ray scattering experiments. At 40 degrees C, no concentration dependent change in the micellar structure of the system can be detected from the small-angle x-ray scattering results. Even in the gel we find globular particles. This is important for the evaluation and interpretation of the dynamic light scattering measurements. In the ergodic phase region at constant temperature, we find that a ratio of 2.17 gives a perfect fit to the experimental data when we allow the effective volume fraction to be proportional to the mass fraction. In the gel region we find two diffusional decays in the intensity correlation functions and an arrested part. The diffusion coefficients from the faster decay stay constant inside the gel and the nonergodicity parameter increases linearly with concentration. Both, the fast and slow diffusional modes show no angular dependence of their scattering intensities, indicating their origin from small objects, while the arrested mode comes, as expected, from structures larger than the resolution of the experiments.

Journal Article↗

PubMed2001

Sugar-Ester Nonionic Microemulsion: Structural Characterization.

Surfactants containing sugar components and fatty acids satisfy the quality standards for food application. The food grade sugar ester in this study is a commercial sucrose monoester of stearic acid (abbreviated SES), the oil phase consists of a 1:1 mixture of n-tetradecane and l-butanol. The originally planned food grade oil, a medium chain triglyceride, is substituted by tetradecane because tetradecane is available as a fully deuterated product, which is necessary for some structural investigations. The investigated system is solid at room temperature, but liquefies and structures into a homogeneous microemulsion when heated to above 37 degrees C. The structural characterization of such microemulsions is the aim of this work. The established methods for this purpose are scattering methods, such as small-angle scattering of X-rays and neutrons and dynamic light scattering. These scattering techniques can be used to obtain valuable information on the size, shape, and internal structure of colloids and complex fluids. We started our investigation with the pseudobinary system SES, tetradecane and l-butanol, varying the SES content. The scattering results show that the sugar ester form inverse globular micelles in the oil phase. The size of these micelles is about 6 nm. While the size is nearly constant in a wide SES concentration regime (5 up to 40% surfactant), the volume or aggregation number increases significantly with SES. This is explained by an increasing replacement of l-butanol molecules by sugar-ester molecules in the micelles formed. Moreover, it can be shown that these micelles strongly overlap. Their center-to-center distance is about 3.8 nm at 40% SES at a micellar diameter of 6 nm. The micellar overlap leads to a highly reduced diffusion of the micelles as was found with dynamic light scattering. When incorporating water in the micellar core, the micelles swell up to about 10 nm and the shape of the aggregates becomes more and more elongated with higher water content. Copyright 2001 Academic Press.

Journal Article↗

PubMed2001

Osmotic Pressure, Small-Angle X-Ray, and Dynamic Light Scattering Studies of Human Serum Albumin in Aqueous Solutions.

Osmotic pressure measurements of human serum albumin (HSA) dissolved in water and in 0.01, 0.1, and 1.0 M phosphate buffer are reported as a function of the protein concentration. Two different forms of the protein were studied: defatted HSA (HSA1) and HSA with fatty acids (HSA2). The measured values of the osmotic coefficient were well below 1, indicating large deviations from ideality even for dilute protein solutions. The measured values increased with increasing HSA concentration and the increase was a function of pH. For higher concentrations of added phosphate buffer, the pH of solution had less influence on the measured osmotic pressure. The osmotic pressure of HSA1 in water was found to be considerably lower than that of the HSA2 modification. This effect was ascribed to formation of dimers in the HSA1 solution. The osmotic measurements were complemented by the small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS) studies of dilute HSA solutions in water. The SAXS and DLS data confirmed the dimerization of HSA1 molecules under these conditions. Detailed analysis of the SAXS data suggested a parallel orientation of two protein molecules in a dimer. Copyright 2001 Academic Press.

Journal Article↗