Effect of nonionic surfactant on transport of model drugs in emulsions

In Vitro Dissolution Testing Strategies for Nanoparticulate Drug Delivery Systems: Recent Developments and Challenges

Nanoparticulate systems have emerged as prevalent drug delivery systems over the past few decades. These delivery systems (such as liposomes, emulsions, nanocrystals, and polymeric nanocarriers) have been extensively used to improve bioavailability, prolong pharmacological effects, achieve targeted drug delivery, as well as reduce side effects. Considering that any unanticipated change in product performance of such systems may result in toxicity and/or change in vivo efficacy, it is essential to develop suitable in vitro dissolution/release testing methods to ensure product quality and performance, and to assist in product development. The present review provides an overview of the current in vitro dissolution/release testing methods such as dialysis, sample and separate, as well as continuous flow methods. Challenges and future directions in the development of standardized and biorelevant in vitro dissolution/release testing methods for novel nanoparticulate systems are discussed.

Surfactants in droplet-based microfluidics

Surfactants are an essential part of the droplet-based microfluidic technology. They are involved in the stabilization of droplet interfaces, in the biocompatibility of the system and in the process of molecular exchange between droplets. The recent progress in the applications of droplet-based microfluidics has been made possible by the development of new molecules and their characterizations. In this review, the role of the surfactant in droplet-based microfluidics is discussed with an emphasis on the new molecules developed specifically to overcome the limitations of 'standard' surfactants. Emulsion properties and interfacial rheology of surfactant-laden layers strongly determine the overall capabilities of the technology. Dynamic properties of droplets, interfaces and emulsions are therefore very important to be characterized, understood and controlled. In this respect, microfluidic systems themselves appear to be very powerful tools for the study of surfactant dynamics at the time- and length-scale relevant to the corresponding microfluidic applications. More generally, microfluidic systems are becoming a new type of experimental platform for the study of the dynamics of interfaces in complex systems.

Emulsifiers' composition modulates venous irritation of the nanoemulsions as a lipophilic and venous irritant drug delivery system

In this study, a nanoemulsion (NE) system was investigated for intravenous delivery of lipophilic and venous irritant drugs. NEs were prepared to deliver diallyl trisulfide (DT) for systemic therapy of bacterial and fungal infection, egg phospholipid was chosen as the main emulsifier, and two co-emulsifiers were also incorporated, including Poloxamer 188 (P188) and Solutol HS 15 (S15). Soybean oil was used as the dispersed phases, forming stable DT NEs with small particle sizes. The venous irritation of DT NEs was evaluated by in vitro human umbilical cord endothelial cells (CRL 1730) compatibility model with the intracellular adenosine triphosphate (ATP) and guanosine triphosphate (GTP) concentrations as the indices. The intracellular ATP and GTP reduction changed with the incorporation of a variety of co-emulsifiers, which varied in a free DT concentration-dependent manner. It was deduced that the free DT concentrations of NEs containing co-emulsifiers were determined by the partition coefficient of DT between oil and surfactant buffer solution. In conclusion, NE was an appropriate delivery system for lipophilic and venous irritant drug, and optimization of the composition of emulsifiers was an effective method to alleviate the venous irritation of DT NEs.

The Behavior of Sorbitan Surfactants at the Water-Oil Interface: Straight-Chained Hydrocarbons from Pentane to Dodecane as an Oil Phase

The interfacial tension of four sorbitan surfactants (Span 20, sorbitan monolaurate; Span 40, sorbitan monopalmitate; Span 60, sorbitan monostearate; and Span 80, sorbitan monooleate) was determined at the water-oil interface. Seven straight-chained hydrocarbons from pentane to dodecane were used as an oil phase. From the interfacial tension measurements the following values were calculated: critical micelle concentration (cmc), the interfacial tension at the cmc (gamma(cmc)), surface pressure at the cmc (pi(cmc)), area per molecule at the cmc (A(cmc)), standard free energy of micellization (DeltaG degrees (mic)), and standard free energy of adsorption (DeltaG degrees (ad)). The shorter chained Span 20 and unsaturated Span 80 had higher cmc values and Span 80 had a larger molecular area than the other surfactants. With the same oil phase, differences between pi(cmc) values of the four sorbitan monoesters were small, but the gamma(cmc) was slightly lowered as the hydrophobicity of the surfactant was increased. DeltaG degrees (mic) was less negative for Span 20 and the DeltaG degrees (ad) value was slightly more negative for Span 80. The effect of the oil phase was obvious. Increasing the hydrocarbon chain length of the oil phase increased gamma(cmc) and cmc values while pi(cmc) and A(cmc) were decreased. As the length of the hydrocarbon chain of the oil phase was increased, DeltaG degrees (mic) and DeltaG degrees (ad) became less negative, which means a less spontaneous reaction. Copyright 2001 Academic Press.

Surface Pressure, Hysteresis, Interfacial Tension, and CMC of Four Sorbitan Monoesters at Water-Air, Water-Hexane, and Hexane-Air Interfaces

The purpose of this study was to investigate the interfacial properties of sorbitan monoesters (Span 20, 40, 60, and 80). The surface pressure was investigated at the water-air interface using a Langmuir-Blodgett apparatus. Interfacial tensions at n-hexane-air and water-n-hexane interfaces were measured by a du Nouy tensiometer. The effects of different surface-active agents and their concentrations on the interfacial properties of surfactant films were determined. With saturated sorbitan monoesters the lengthening of the hydrocarbon chain increases the collapse pressure and molecular area at the water-air interface. Unsaturated Span 80 had a lower collapse pressure and a larger molecular area than its saturated counterpart Span 60. Under compression-expansion cycles, all sorbitan monoesters showed hysteresis effects. At the n-hexane-air interface there were no differences in the interfacial tension between different sorbitan monoesters. At the water-n-hexane interface, differences in CMCs were small, but the surface excess of Span 80 was markedly smaller and the molecular area larger than the corresponding values of other sorbitan monoesters. Copyright 2000 Academic Press.

Release of a model molecule from highly concentrated fluorinated reverse emulsions. Influence of composition variables and temperature

Highly concentrated reverse emulsions have been used to study the diffusion of a model molecule entrapped in these gel-emulsions. The influence of several parameters on the release of coumarin from fluorinated gel-emulsions has been investigated, and a computational method has been elaborated to determine the numerical value of the diffusion coefficients. The amount of probe molecule released depends on the initial loading amount, whereas the diffusion coefficient is not influenced by the initial concentration or by the amount of surfactant in the emulsions (in the range of the oil-to-surfactant ratios studied). The predominant factor seems to be the amount of water permitting the increase of the inter-phase area. Moreover, we have shown that the release of coumarin from gel-emulsions is in accord with the 'Arrhenius' law and the 'activation energy' deduced can be due to a barrier counteracting the diffusion.

Mathematical modelling of drug transport in emulsion systems

Two mathematical models for the prediction of drug transport in triphasic (oil, water and micellar) emulsion systems as a function of micellar concentration have been developed and these models were evaluated by comparing experimental and simulated data. Fick's first law was used to derive a transport model for hydrophilic drugs, assuming that the oil/water (o/w) partitioning process was fast compared with membrane transport and therefore drug transport was limited by the membrane. Consecutive rate equations were used to model transport of hydrophobic drugs in emulsion systems assuming that the o/w interface acts as a barrier to drug transport. Benzoic acid and phenol were selected as hydrophilic model drugs. Phenylazoaniline and benzocaine were selected as hydrophobic model drugs. Transport studies at pH 3.0 and 7.0 were conducted using side-by-side diffusion cells. According to the hydrophilic model, an increase in micellar concentration is expected to decrease drug transport rates. The effective permeability coefficients (Peff) of drugs were calculated using an equation relating Peff and the total apparent volume of drug distribution (determined experimentally using drug/membrane permeability and partition coefficient values). The hydrophobic model was fitted to the experimental data for the cumulative amount of model drug in the receiver cells using a weighted least-squares estimation program (PCNONLIN). The oil/continuous phase partitioning rates (k1) and the membrane transport rates (k2) were estimated. The goodness of fit was assessed from the correlation coefficients of plots of predicted versus experimental data. The predicted data were consistent with the experimental data for both the hydrophilic and hydrophobic models.

Effect of cationic surfactant on transport of model drugs in emulsion systems

Excess surfactant present in emulsions can influence the rates of transport of incorporated drugs by micellar solubilization, alteration of the partitioning process and by drug-surfactant complexation. Cetyltrimethylammonium bromide (CTAB), a cationic surfactant was selected to investigate these phenomena as it forms relatively stable mineral oil-water (O-W) emulsions and has the potential for ionic interaction. Phenylazoaniline, benzocaine, benzoic acid and phenol were chosen as model drugs for this study. The emulsion critical micelle concentration (CMC) for CTAB determined using a combination of a membrane equilibrium technique and surface-tension measurement was 1.0% w/v in 10% v/v% O-W emulsion systems. Ionic interaction between model drugs and surfactants and drug hydrophobicity affected their transport rates in the emulsion systems. The transport rates of the lipophilic drugs (benzocaine and phenylazoaniline) and the ionized hydrophillic drug (benzoic acid, pH 7.0) in the emulsion systems increased with increasing CTAB concentration up to 0.5% w/v micellar concentration and then decreased at higher concentrations. The rate of transport of phenol was not affected by the presence of micellar phase. Ionic interaction between surfactant and model drugs affected transport rates of model drugs in emulsion systems. The micellar phase was considered to affect the overall transport rates of model drugs.

Interfacial properties as stability predictors of lecithin-stabilized perfluorocarbon emulsions

The purpose of this study was to determine whether the addition of small quantities of minor lecithin components (phosphatidylinositol, phosphatidic acid, lysophosphatidylethanolamine, and cholesterol) and Pluronic F68 to lecithin could improve the stability of lecithin-stabilized perfluorocarbon emulsions. Attempts were made to correlate emulsion stability with interfacial properties (tension and charge). Dynamic interfacial tension was determined using a Teflon Wilhelmy plate method [reported previously (1)]. Emulsions were prepared by microfluidization. Microelectrophoresis was used to measure emulsion droplet charge, and photon correlation spectroscopy and Coulter analysis were used to determine emulsion stability as a function of droplet size. Thermal kinetic accelerated stability testing was conducted. Various droplet size parameters were used to compare emulsion stabilities, and an overall stability ranking, based on these parameters, was obtained for each emulsion. Small quantities of additives altered emulsion stability and these data were correlated with interfacial properties and initial droplet diameters. The addition of cholesterol to lecithin resulted in the most stable perfluorocarbon emulsion.