How to achieve high encapsulation efficiencies for macromolecular and sensitive apis in liposomes

This research highlights the capacity of a newly introduced centrifugation process to form liposomes from water-in-fluorocarbon nano-emulsions stabilized with phospholipids to incorporate macromolecular and sensitive active pharmaceutical ingredients (API). The encapsulation efficiency of the produced liposomes, incorporating fluorescein-sodium, bovine serum albumin and fluorecein isothiocyanate dextran as model APIs, is determined by applying Vivaspin® centrifugation filtration and quantified by UV-Vis spectroscopy. It was found that higher densities of the fluorocarbons used as the hydrophobic phase enable a higher encapsulation efficiency and that an efficiency of up to 98% is possible depending on the used phospholipid. Among the engineering aspects of the process, a comparison between different membrane substances was performed. Efficiency increases with a higher phospholipid concentration but decreases with the addition of cholesterol. Due to the higher bending modulus, liposome formation is slowed down by cholesterol during liposome closure leading to a greater leakage of the model API. The encapsulation of bovine serum albumin and dextran, both investigated under different osmotic conditions, shows that an efflux negatively affects the encapsulation efficiency while an influx increases the stability. Overall, the process shows the potential for a very high encapsulation efficiency for macromolecules and future pharmaceutical applications

Water-in-Fluorocarbon Nanoemulsions Stabilized by Phospholipids and Characterized for Pharmaceutical Applications

Fluorocarbons are one of the most promising hydrophobic phases for future pharmaceutical production processes and various biomedical applications. Yet, because of their specific characteristics such as high density and refractive index similar to water, analysis of water‐in‐fluorocarbon (w/fc) nanoemulsions remains a challenge. The present work examines w/fc nanoemulsions stabilized with phospholipids as natural emulsifiers and tackles the measuring problems of photon correlation spectroscopy (PCS) when used for investigation of fluorocarbon nanoemulsions. These emulsions are suitable to form liposomes via centrifugation and thus, are required to meet certain criteria such as stability and size. The results imply a stability of up to 4 weeks with an average size of 180 nm. The intensity mean diameter gained from PCS measurements shows large scattering directly after sonication which is due to gas bubbles from sonication. The number mean is not influenced by gas bubbles and gives a more accurate depiction of the produced nanoemulsions. These findings are supported by small‐angle X‐ray scattering data, which are additionally applied for liposome analysis measuring a size of approximately 60 nm

Phospholipids as emulsifiers für micro/nano droplets suitable for biotechnological systems integration

We studied the emulsifying properties of palmitoyl oleoyl phosphatidylcholine (POPC) using the biocompatible compounds water and squalene as immiscible fluid phases. We tested the solubility limit of POPC in squalene and its equilibrium distribution between bulk phases. POPC is dissolvable in squalene up to 0.3% (w/v) with an ultrasonication procedure. Above this limit, aggregates of >1 μm are formed which are resistant to prolonged ultrasonication in size and quantity. Emulsifying properties of POPC were elaborated by measuring the droplet size ranges of emulsions. Nanofluidics was studied by pressure driven transport of nanometer sized emulsion droplets through defined nanochannels whereby droplet sizes 500 nm can be produced. The mechanical properties of the emulsifying phospholipid monolayer at the water/squalene interface were studied by profile analysis tensiometry (PAT). The dynamic interfacial tension was measured and the adsorption isotherms were established from long-time approximations of the diffusion-controlled adsorption. With PAT a critical aggregation concentration was determined in the same range as the solubility limit, which was measured by dynamic light scattering. The minimum interfacial tension for POPC as emulsifier was found to be below 1 mN/m. Thus, it can be concluded that phospholipids are suitable emulsifiers for microfluidics and produce adsorbed layers of remarkably small interfacial tension

Compressible air flow through a collapsing liquid cavity

We present a multiscale approach to simulate the impact of a solid object on a liquid surface: upon impact a thin liquid sheet is thrown upwards all around the rim of the impactor while in its wake a large surface cavity forms. Under the influence of hydrostatic pressure the cavity immediately starts to collapse and eventually closes in a single point from which a thin, needle-like jet is ejected. Existing numerical treatments of liquid impact either consider the surrounding air as an incompressible fluid or neglect air effects altogether. In contrast, our approach couples a boundary-integral method for the liquid with a Roe scheme for the gas domain and is thus able to handle the fully \emph{compressible} gas stream that is pushed out of the collapsing impact cavity. Taking into account air compressibility is crucial, since, as we show in this work, the impact crater collapses so violently that the air flow through the cavity neck attains supersonic velocities already at cavity diameters larger than 1 mm. Our computational results are validated through corresponding experimental data.Comment: Submitted to Comput Mec

Heat Transport through Rough Channels

We investigate the two-dimensional transport of heat through viscous flow between two parallel rough interfaces with a given fractal geometry. The flow and heat transport equations are solved through direct numerical simulations, and for different conduction-convection conditions. Compared with the behavior of a channel with smooth interfaces, the results for the rough channel at low and moderate values of the Peclet number indicate that the effect of roughness is almost negligible on the efficiency of the heat transport system. This is explained here in terms of the Makarov's theorem, using the notion of active zone in Laplacian transport. At sufficiently high Peclet numbers, where convection becomes the dominant mechanism of heat transport, the role of the interface roughness is to generally increase both the heat flux across the wall as well as the active length of heat exchange, when compared with the smooth channel. Finally, we show that this last behavior is closely related with the presence of recirculation zones in the reentrant regions of the fractal geometry.Comment: 12 pages, 8 figure

Liposomal formulations of mistletoe produced by centrifugal technologies and cell proliferation analysis of both mistletoe extracts and isolated mistletoe lectin I = Liposomale Formulierung von Mistelextrakten durch Zentrifugationsverfahren und Analyse der Zellproliferation von Gesamtextrakten und isoliertem Mistellektin I

Um Liposomen aus Nanoemulsionen herzustellen, wird ein Zentrifugationsverfahren entwickelt, das eine hohe Einkapselungseffizienz und asymmetrische Membranen ermöglicht. Heparin-Komplexe werden für die Bildung einer stabilen Schutzschicht verwendet. Um die Erprobung der liposomalen Formulierungen in vitro und in vivo zu ermöglichen, wurden Mistelpräparate mit unterschiedlicher Viscotoxin-(VT) und Mistellektin-(ML) Zusammensetzung sowie isoliertes ML°I an Maus-Zelllinien erprobt. Ein Proliferationstest wurde durchgeführt, um die inhibierenden Konzentrationen (IC50) zu ermitteln und sensitive Zelllinien für in vivo Experimente auszuwählen. abnobaVISCUM (AV) Pini Präparate, die den geringsten Gesamtgehalt an ML und eine Dominanz von ML III aufweisen, zeigten bei B16-F10 Melanomzellen eine stärkere Inhibierung der Proliferation im Vergleich zu den ML I reichen Präparaten AV Fraxini und Quercus. Für AV Fraxnini und AV Quercus wurde gezeigt, dass die Zytotoxizität überwiegend auf ML I zurückzuführen ist und ML I daher als potentieller Wirkstoff zur Verkapselung in Liposomen geeignet ist. Auf isoliertes ML I reagiert die getestete Kolonkarzinomzelllinie C26 deutlich empfindlicher als die aggressive B16-F10 Melanomzelllinie. Diese Ergebnisse erlauben den Vergleich eines sensitiven mit einem aggressiven Tumormodell in vivo. Im Vergleich zu C26 ist die Makrophagenzelllinie RAW264.7 relativ unempfindlich gegenüber isoliertem ML I. Die Ergebnisse deuten auf die Möglichkeit einer gezielten Therapie von z.B. Kolontumoren hin, bei der die Immunfunktionen intakt bleiben