Peter Holmqvist

Thermosetting microemulsions and mixed micellar solutions as drug delivery systems for periodontal anesthesia

In the present study, thermosetting microemulsions and mixed micellar solutions were investigated as drug delivery systems for anesthetizing the periodontal pocket. The structure of the systems, consisting of the active ingredients lidocaine and prilocaine, as well as two block copolymers (Lutrol F127 and Lutrol F68), was investigated by NMR spectroscopy and photon correlation spectroscopy (PCS). The results obtained for dilute (1-3% w/w) solutions show discrete micelles with a diameter of 20-30 nm and a critical micellization temperature of 25-35 degrees C. Gel permeation chromatography (GPC) was used to study the distribution of the active ingredients, and indicates a preferential solubilization of the active components in micelles over unimers. Analogous to the Lutrol F127 single component system these formulations display an abrupt gelation on increasing temperature. The gelation temperature was found to depend on both the drug ionization and concentration. These systems have several advantages over emulsion-based formulations including good stability, ease of preparation, increased drug release rate, and improved handling due to the transparency of the formulations.

Pair structure of the hard-sphere Yukawa fluid: An improved analytic method versus simulations, Rogers-Young scheme, and experiment

We present a comprehensive study of the equilibrium pair structure in fluids of nonoverlapping spheres interacting by a repulsive Yukawa-like pair potential, with special focus on suspensions of charged colloidal particles. The accuracy of several integral equation schemes for the static structure factor, S(q), and radial distribution function, g(r), is investigated in comparison to computer simulation results and static light scattering data on charge-stabilized silica spheres. In particular, we show that an improved version of the so-called penetrating-background corrected rescaled mean spherical approximation (PB-RMSA) by Snook and Hayter [Langmuir 8, 2880 (1992)], referred to as the modified PB-RMSA (MPB-RMSA), gives pair structure functions which are in general in very good agreement with Monte Carlo simulations and results from the accurate but nonanalytical and therefore computationally more expensive Rogers-Young integral equation scheme. The MPB-RMSA preserves the analytic simplicity of the standard rescaled mean spherical (RMSA) solution. The combination of high accuracy and fast evaluation makes the MPB-RMSA ideally suited for extensive parameter scans and experimental data evaluation, and for providing the static input to dynamic theories. We discuss the results of extensive parameter scans probing the concentration scaling of the pair structure of strongly correlated Yukawa particles, and we determine the liquid-solid coexistence line using the Hansen-Verlet freezing rule.

Colloidal dynamics near a wall studied by evanescent wave light scattering: Experimental and theoretical improvements and methodological limitations

The dynamics of colloidal spheres near to a wall is studied with an evanescent wave scattering setup that allows for an independent variation of the components of the scattering wave vector normal and parallel to the wall. The correlation functions obtained with this novel instrumentation are interpreted on the basis of an expression for their short time behavior that includes hydrodynamic interactions between the colloidal spheres and the wall. The combination of the evanescent wave scattering setup and the exact expression for the short time behavior of correlation functions allows for an unambiguous measurement of the particle mobility parallel and normal to the wall by means of light scattering. It is possible to measure the viscous wall drag effect on the dynamics of particles with radii as small as 27 nm, where, however, the method reaches its limits due to the low scattering intensities of such small particles.

Structure and short-time dynamics in suspensions of charged silica spheres in the entire fluid regime.

We present an experimental study of short-time diffusion properties in fluidlike suspensions of monodisperse charge-stabilized silica spheres suspended in dimethylformamide. The static structure factor S(q), the short-time diffusion function D(q), and the hydrodynamic function H(q) have been probed by combining x-ray photon correlation spectroscopy experiments with static small-angle x-ray scattering. Our experiments cover the full liquid-state part of the phase diagram, including de-ionized systems right at the liquid-solid phase boundary. We show that the dynamic data can be consistently described by the renormalized density fluctuation expansion theory of Beenakker and Mazur over a wide range of concentrations and ionic strengths. In accordance with this theory and Stokesian dynamics computer simulations, the measured short-time properties cross over monotonically, with increasing salt content, from the bounding values of salt-free suspensions to those of neutral hard spheres. Moreover, we discuss an upper bound for the hydrodynamic function peak height of fluid systems based on the Hansen-Verlet freezing criterion.

Lyotropic Smectic B Phase Formed in Suspensions of Charged Colloidal Platelets

Here, we present the first observation of a smectic B (Sm(B)) phase in a system of charged colloidal gibbsite platelets suspended in dimethyl sulfoxide (DMSO). The use of DMSO, a polar aprotic solvent, leads to a long range of the electrostatic Coulomb repulsion between platelets. We believe this to be responsible for the formation of the layered liquid crystalline phase consisting of hexagonally ordered particles, that is, the Sm(B) phase. We support our finding by high-resolution X-ray scattering experiments, which additionally indicate a high degree of ordering in the Sm(B) phase.

Structures and Phase Behavior in Mixtures of Charged Colloidal Spheres and Platelets

The experimental phase diagram for aqueous mixtures of charged gibbsite platelets and silica spheres is presented. The platelets are 95 nm in diameter, and the diameter ratio between the spheres and the platelets is 0.18. Here the spheres are acting as depletants in the mixtures perturbing the phase behavior of the pure platelet suspensions. An important finding is that a large isotropic/columnar coexistence region has been identified in the phase diagram, which appeared already at low concentrations of the platelets. Microradian X-ray diffraction measurements revealed the structure of the liquid crystalline phases and the orientational order of platelets. An interesting observation is that in the columnar phase the silica spheres are located between the columnar stacks. All samples were in equilibrium because sedimentation did not affect the system because of the relatively small size of the colloidal particles and the charges present at their surfaces.

Poly(ethylene oxide)-containing amphiphilic block copolymers in ternary mixtures with water and organic solvent : effect of copolymer and solvent type on phase behavior and structure

The phase behavior and microstructure in ternary systems composed of an amphiphilic copolymer, an aqueous solvent (‘water’) and an organic solvent (‘oil’) are the subjects of an ongoing investigation by our research group. Results (at 25°C) for a number of different block copolymers, consisting of poly(ethylene oxide) (E) as the hydrophilic block and poly(propylene oxide) (P), poly(1,2-butylene oxide) (B), poly(n-butylene oxide)  poly(tetrahydrofurane) (T) or poly(styrene) (S) as hydrophobic blocks, and for the p-xylene, n-butyl acetate and butan-1-ol organic solvents are reviewed here. The effects on self-assembly of the copolymer and ‘oil’ type are thus revealed. Oil-in-water (‘normal’) micellar solutions (denoted L1) and lyotropic liquid crystalline regions of normal micellar cubic (I1), normal hexagonal (H1) and lamellar (Lα) structure can be formed with an increase of the copolymer concentration along the oil-lean side of the ternary phase diagrams (water being a selective solvent for the E blocks). When ‘oil’ is the selective solvent for the hydrophobic blocks, micellar solutions (L2) and lyotropic liquid crystalline regions of micellar cubic (I2), hexagonal (H2) and bicontinuous cubic (V2) structure, all of the water-in-oil (‘reverse’) morphology can be formed in the water-lean part of the phase diagram with increasing copolymer concentration, provided that some water is present. Such a notable structural polymorphism (which cannot be attained by low molecular-weight surfactants) is attributed to the macromolecular nature of the amphiphilic block copolymers, which allows fine-tuning of the interfacial curvature by varying the degree of swelling of the hydrophilic and hydrophobic blocks. The location of the different phases in the ternary phase diagram depends primarily on the relative amount of hydrophobic-hydrophilic material. When the ‘oil’ is not a selective solvent for the hydrophobic blocks, the liquid crystalline structure at water-lean compositions is lost. Crystalline/glassy precipitates are formed when the oil is a ‘bad’ solvent for the hydrophobic blocks, and isotropic solutions can be obtained when the oil is a ‘good’ solvent. In the case of a σgood’ solvent, the liquid crystalline phases formed at oil-lean compositions swell with ‘oil’.

Thermal diffusion of a stiff rod-like mutant Y21M fd-virus.

We investigated the thermal diffusion phenomena of a rodlike mutant filamentous fd-Y21M virus in the isotropic phase by means of an improved infrared thermal-diffusion-forced Rayleigh scattering (IR-TDFRS) setup optimized for measurements of slowly diffusing systems. Because this is the first thermal diffusion study of a stiff anisotropic solute, we investigate the influence of the shape anisotropy on the thermal diffusion behavior. The influence of temperature, fd-Y21M concentration, and ionic strength in relation with the thermodiffusion properties is discussed. We characterize and eliminate the effect of these parameters on the absolute diffusion of the rods and show that diffusion determines the behavior of the Soret coefficient because the thermal diffusion coefficient is constant in the investigated regime. Our results indicate that for the thermal diffusion behavior structural changes of the surrounding water are more important than structural changes between the charged macroions. In the investigated temperature and concentration range, the fd-Y21M virus is thermophobic for the low salt content, whereas the solutions with the high salt content change from thermophobic to thermophilic behavior with decreasing temperature. A comparison with recent measurements of other charged soft and biological matter systems shows that the shape anisotropy of the fd-virus becomes not visible in the results.

Collective diffusion in charge-stabilized suspensions: Concentration and salt effects

The authors present a joint experimental-theoretical study of collective diffusion properties in aqueous suspensions of charge-stabilized fluorinated latex spheres. Small-angle x-ray scattering and x-ray photon correlation spectroscopy have been used to explore the concentration and ionic-strength dependence of the static and short-time dynamic properties including the hydrodynamic function H(q), the wave-number-dependent collective diffusion coefficient D(q), and the intermediate scattering function over the entire accessible range. They show that all experimental data can be quantitatively described and explained by means of a recently developed accelerated Stokesian dynamics simulation method, in combination with a modified hydrodynamic many-body theory. In particular, the behavior of H(q) for de-ionized and dense suspensions can be attributed to the influence of many-body hydrodynamics, without any need for postulating hydrodynamic screening to be present, as it was done in earlier work. Upper and lower boundaries are provided for the peak height of the hydrodynamic function and for the short-time self-diffusion coefficient over the entire range of added salt concentrations.

Laparoscopic aided cholecystostomy as a treatment of inspissated bile syndrome.

We report a case of a newborn girl with inspissated bile syndrome (IBS) that did not respond to treatment with oral ursodeoxycholic acid (Ursofalk). A solution was found using laparoscopic aided cholecystostomy with an indwelling catheter for local Ursofalk flushing in the gallbladder and the choledochus. This is the first report of a laparoscopic aided management of IBS without cholecystectomy or exploration of the bile ducts. This minimal invasive approach showed a clear advantage for the patient. There were no complications. The method is recommended in the treatment of IBS.