Microemulsions as transdermal drug delivery vehicles.

Gold nanoparticles (AuNP) were prepared by the homogeneous mixing of continuous flows of an aqueous tetrachloroauric acid solution and a sodium borohydride solution applying a microstructured static mixer. The online characterization and screening of this fast process (∼2 s) was enabled by coupling a micromixer operating in continuous-flow mode with a conventional in-house small angle X-ray scattering (SAXS) setup. This online characterization technique enables the time-resolved investigation of the growth process of the nanoparticles from an average radius of ca. 0.8 nm to about 2 nm. To the best of our knowledge, this is the first demonstration of a continuous-flow SAXS setup for time-resolved studies of nanoparticle formation mechanisms that does not require the use of synchrotron facilities. In combination with X-ray absorption near edge structure microscopy, scanning electron microscopy, and UV−vis spectroscopy the obtained data allow the deduction of a two-step mechanism of gold nanoparticle formati...

Nucleation and Growth of Gold Nanoparticles Studied via in situ Small Angle X-ray Scattering at Millisecond Time Resolution

Microemulsions are thermodynamically stable, transparent, low viscosity, and isotropic dispersions consisting of oil and water stabilized by an interfacial film of surfactant molecules, typically in conjunction with a cosurfactant. Microemulsions (so-called due to their small particle size; 5-100 nm) have found application in a wide variety of systems, such as pharmaceutical and oil recovery, but their application in food systems has been hindered by the types of surfactant permissible for use in food. The objective of this review is to provide an overview of the structures and phase behavior of microemulsions, methods of microemulsion formation, and techniques which may be used for characterization. A comprehensive review of previous work on both food-grade microemulsion systems, and non-food-grade systems of specific food interest is included. The application of microemulsions as reaction media, their ability to solubilize proteins and hence their use as a separation technique is also documented. In addition, attention is focused on the application of microemulsions as delivery systems for delivery of bioactive compounds, and the links between microemulsions and increased bioavailability. Future research, both applied and fundamental, should focus on surfactants which are not restricted for use in foods.

Microemulsions: A Potential Delivery System for Bioactives in Food

Beverage emulsions: Recent developments in formulation, production, and applications

Microemulsions are isotropic, thermodynamically stable transparent (or translucent) systems of oil, water and surfactant, frequently in combination with a cosurfactant with a droplet size usually in the range of 20-200 nm. They can be classified as oil-in-water (o/w), water-in-oil (w/o) or bicontinuous systems depending on their structure and are characterized by ultra low interfacial tension between oil and water phases. These versatile systems are currently of great technological and scientific interest to the researchers because of their potential to incorporate a wide range of drug molecules (hydrophilic and hydrophobic) due to the presence of both lipophilic and hydrophilic domains. These adaptable delivery systems provide protection against oxidation, enzymatic hydrolysis and improve the solubilization of lipophilic drugs and hence enhance their bioavailability. In addition to oral and intravenous delivery, they are amenable for sustained and targeted delivery through ophthalmic, dental, pulmonary, vaginal and topical routes. Microemulsions are experiencing a very active development as reflected by the numerous publications and patents being granted on these systems. They have been used to improve the oral bioavailability of various poorly soluble drugs including cyclosporine and paclitaxel as professed by Hauer et al., US patent 7235248, and Gao et al., US patent 7115565, respectively. Furthermore, they can be employed for challenging tasks such as carrying chemotherapeutic agents to neoplastic cells and oral delivery of insulin as diligently described by Maranhao, US patent 5578583 and Burnside et al., US patent 5824638 respectively. The recent commercial success of Sandimmune Neoral (Cyclosporine A), Fortovase (Saquinavir), Norvir (Ritonavir), etc. also reflects the tremendous potential of these newer drug therapeutic systems. A critical evaluation of recent patents claiming different approaches to improve the drug delivery is the focus of the current review.

Microemulsions: a novel approach to enhanced drug delivery.

http://www.scientificspectator.com/documents/suggested%20reading/Sucrose%20Ester%20Article.pdf

Sugar-Ester Nonionic Microemulsion: Structural Characterization.

Laboratory X-ray sources emit a highly divergent beam The Kratky compact camera is constructed to maximize the intensity in the sample using a slit collimation system The performance of this camera can be further increased if the primary beam is collimated from a divergent into a parallel beam A recently developed device for this purpose is the so-called `Gobel mirror' This mirror is made of parabolically bent multilayers, designed to collimate divergent X-rays from laboratory X-ray sources into a parallel and monochromatic beam of high brilliance Modification of the block collimation system in combination with a Gobel mirror leads to a different beam geometry, resulting in an intensity increase by a factor of about 10 The gain in intensity implicates the use of imaging-plate detectors, which have a wide linear range in intensity and allow the full use of the increased intensity Hence the quality of the SAXS data is improved by the higher intensity primary beam, the much lower background due to the exclusive use of Cu Kα radiation, and a detection unit which is linear in the measured intensity regime All these advantages, such as intensity gain, lower background, better quality of the data, are demonstrated with some selected experimental results

Improvement of SAXS measurements on Kratky slit systems by Göbel mirrors and imaging‐plate detectors

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.

Günther Scherf

Papers

Sugar-Ester Nonionic Microemulsion: Structural Characterization.

Improvement of SAXS measurements on Kratky slit systems by Göbel mirrors and imaging‐plate detectors

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

Light-sensitive lamellar phases.