Role of liquid crystal in the emulsification of a gel emulsion with high internal phase fraction

Lipid-liquid crystals for 2 months controlled risperidone release: In-vitro evaluation and pharmacokinetics in rabbits

In this study, a drug delivery system based on lipid liquid crystal (LLC) was developed for the long-term delivery of risperidone to improve psychological treatment. Optimal LLC formulation was achieved based on maximum release after 60 days with different ratios of phosphatidylcholine (PC) to sorbitol monooleate (PC: SMO), tween grade 80 (w/w %), and tocopherol acetate (TA) (w/w %) using the Box-Behnken method. In vitro and ex vivo studies, pharmacokinetics, and histopathological examination in rabbits were conducted to compare the optimal LLC with Risperdal CONSTA®. The optimum formulation containing the PC to SMO ratio of 58.6%, tween 0.82% w/w, and TA 3.6% w/w was selected because it had the highest drug release percentage (100%) during about two months. Polarized optical microscopy (POM) revealed H_II mesophase with a 2-dimensional structure. Cell culture also revealed moderate cytotoxicity for LLC-risperidone. Pharmacokinetic data displayed that the optimal LLC created a more consistent drug serum level within 60 days, and histopathology results demonstrated slight to moderate damage in rabbits' organs. Furthermore, the accelerated stability test confirmed optimum stability for LLC and risperidone. This study confirmed the better pharmacokinetic potentials of SMO-based LLC systems compared with Risperdal CONSTA®, which would promote patient compliance and obviate the difficulties of additional oral therapy.

Oral and transdermal drug delivery systems: role of lipid-based lyotropic liquid crystals

Liquid crystal (LC) dosage forms, particularly those using lipid-based lyotropic LCs (LLCs), have generated considerable interest as potential drug delivery systems. LCs have the physical properties of liquids but retain some of the structural characteristics of crystalline solids. They are compatible with hydrophobic and hydrophilic compounds of many different classes and can protect even biologicals and nucleic acids from degradation. This review, focused on research conducted over the past 5 years, discusses the structural evaluation of LCs and their effects in drug formulations. The structural classification of LLCs into lamellar, hexagonal and micellar cubic phases is described. The structures of these phases are influenced by the addition of surfactants, which include a variety of nontoxic, biodegradable lipids; these also enhance drug solubility. LLC structure influences drug localization, particle size and viscosity, which, in turn, determine drug delivery properties. Through several specific examples, we describe the applications of LLCs in oral and topical drug formulations, the latter including transdermal and ocular delivery. In oral LLC formulations, micelle compositions and the resulting LLC structures can determine drug solubilization and stability as well as intestinal transport and absorption. Similarly, in topical LLC formulations, composition can influence whether the drug is retained in the skin or delivered transdermally. Owing to their enhancement of drug stability and promotion of controlled drug delivery, LLCs are becoming increasingly popular in pharmaceutical formulations.

Phase inversion emulsification: Current understanding and applications

This review is addressed to the phase inversion process, which is not only a common, low-energy route to make stable emulsions for a variety of industrial products spanning from food to pharmaceuticals, but can also be an undesired effect in some applications, such as crude oil transportation in pipelines. Two main ways to induce phase inversion are described in the literature, i.e., phase inversion composition (PIC or catastrophic) and phase inversion temperature (PIT or transitional). In the former, starting from one phase (oil or water) with surfactants, the other phase is more or less gradually added until it reverts to the continuous phase. In PIT, phase inversion is driven by a temperature change without varying system composition. Given its industrial relevance and scientific challenge, phase inversion has been the subject of a number of papers in the literature, including extensive reviews. Due to the variety of applications and the complexity of the problem, most of the publications have been focused either on the phase behavior or the interfacial properties or the mixing process of the two phases. Although all these aspects are quite important in studying phase inversion and much progress has been done on this topic, a comprehensive picture is still lacking. In particular, the general mechanisms governing the inversion phenomenon have not been completely elucidated and quantitative predictions of the phase inversion point are limited to specific systems and experimental conditions. Here, we review the different approaches on phase inversion and highlight some related applications, including future and emerging perspectives.

One-step inversion process to a Janus emulsion with two mutually insoluble oils

High internal phase ratio (HIPR) aqueous Janus emulsions of two immiscible oils, silicone oil (SO) and a vegetable oil (VO), were prepared using a vibration mixer. The simple HIPR Janus emulsions, (VO + SO)/W, were found at weight fractions of the aqueous phase in excess of 0.3, while at a corresponding fraction of 0.1, a triple emulsion was obtained with the Janus emulsion forming a drop inside the vegetable oil to give a double Janus emulsion, (VO + SO)/W/VO, which in turn formed drops in the silicone oil resulting in a triple Janus emulsion (VO + SO)/W/VO/SO. Increasing the aqueous-phase fraction from 0.1 to 0.3 consequently meant an inversion, of which one intermediate stage was observed: a more complex configuration, e.g., one in which large SO drops with highly distorted VO drops attached were dispersed in a regular aqueous emulsion with spherical Janus (VO + SO) drops. A preliminary investigation was made into the destabilization process of the triple emulsions.

Perspectives of phase changes and reversibility on a case of emulsion inversion

The conventional treatment of catastrophic inversion is based on a two-phase model of oil-in-water (O/W) or water-in-oil (W/O). The present investigation takes a closer look at the process of inversion with focus on its relation to the detailed phase changes in the system. It is found that phase behavior inserts a decisive call for when the inversion starts and completes, even for an inversion seemingly brought by a simple change of water-to-oil ratio. The phases involved also play a critical role in the fine details of the emulsion structure, during both emulsification and evaporation. The presence of liquid crystal is instrumental in the inversion process as substantiated by the observation that its presence coincides with the presence of the intermediate multiple emulsions during emulsification. Multiple emulsions also appear during evaporation, though the mechanism of their formation is different from that during emulsification. The temporary stability of the multiple emulsions during both emulsification and evaporation is affected by the presence of the liquid crystal. It had been well established that the phase behavior plays a decisive role in transitional inversions and that the transformation to the inverse state is a gradual one. This is apparently also the case with the catastrophic inversion investigated here.