Liquid crystalline phases drug delivery systems

Engstrdm S, Larsson K, Lindman B (1988) In Liquid crystalline phases as delivery systems for drugs. I. Basic principles (Proc Int Symp Control Rel Bioactive Mater). Controlled Release Society, Lincolnshire, IL, 15 105... 

A liquid crystal is a general term used to describe a variety of anisotropic structures formed by amphiphilic molecules, typically but not exclusively at high concentrations. Hexagonal, lamellar, and cubic phases are all examples of liquid crystalline phases. These phases have been examined as drug delivery systems because of their stability, broad solubilization potential, ability to delay the release of encapsulated drug, and, in the case of lamellar phases, their ability to form closed, spherical bilayer structures known as vesicles, which can entrap both hydrophobic and hydrophilic drug. This section will review SANS studies performed on all liquid crystalline phases, except vesicles, which will be considered separately. Vesicles will be considered separately because, with a few exceptions, generally mixed systems, vesicles (unlike the other liquid crystalline phases mentioned) do not form spontaneously upon dispersal of the surfactant in water and because there have been many more SANS studies performed on these systems. 

Thermotropic liquid crystals and also lyotropic liquid crystals generate functional molecular assemblies. lyotropic liquid crystalline phases are exhibited by amphiphilic molecules in appropriate solvents. They form nano-segregated structures because the molecular structures consist of hydrophilic and hydrophobic components. In Chapter 6, Gin and co-workers describe how lyotropic liquid crystals may be used to form functional materials. Lyotropic liquid crystals can act as templates for inorganic materials, ion conductors, catalysts, drug delivery systems, and nanofilters. 

Liquid crystals are intermediate states of matter or mesophases, halfway between an isotropic liquid and a solid crystal. In nature, some substances, or even mixtures of substances, present these mesomorphic states. These liquid crystalline phases exhibit a local disorder ( liquid-like behavior) and are dynamic at a molecular level, but a long-range order exists, which endows it with unique rheological, mass transport, and optical properties. Liquid crystals offer a number of useful properties for the drug delivery. Solubilization of drug in the liquid crystalline is similar to the solubilization of drug in micelles. Simultaneously, increase in viscosity of the system helps to provide more... 

Boyd BJ, Whittaker DV, Khoo S-M, Davey G. Lyotropic liquid crystalline phases formed from glycer-ate surfactants as sustained release drug delivery systems. International Journal of Pharmaceutics. 2006 309(l-2) 218-226. 

Yaghmur, A., Rappolt, M. Larsen, S. W. (2013). In situ forming drug delivery systems based on lyotropic liquid crystalline phases Structural characterization and release properties. Journal of Drug Delivery Science and Technology. 23(4), 325-32. 

Apart from micelles, surfactants, block copolymers and polar lipids self-assemble to a wide range of liquid crystalline phases and microemulsions [Ij. These systems offer opportunities for increased solubilization of hydrophobic drugs. Similarly, due to their water compartments, some liquid crystalline phases (e.g. cubic) are also interesting delivery systems for proteins, peptides and other biomolecular drugs. Depending on its physicochemical properties, a drug incorporated in such self-assembly systems may localize preferentially in the oil or water compartment(s), or at the interface between these, thereby affecting the structure and stability of the self-assembled system. 

The phase behavior of mixtures of polyoxyethylene phytosterol surfactants and paraiSn as well as ternary mixtures of the surfactants, water, and paraiSn has also been studied [18]. The objective of this work was to find creamy mixtures to be used in topical preparations. Uchegbu et al. investigated the phase behavior of cholesterol with 24 oxyethylene units with free cholesterol and hexadecyldiglycerol in order to find phases that can be used as drug delivery systems [25]. No liquid crystalline phases were found. 

Interfaces play a central role in electrochemistry, biophysics, drug delivery, and surfactant science. The study of interfacial phenomena at the molecular or atomic level is an active field with significant contributions from both experiment [1,2] and theory [3]. In this article, we will present some initial results concerning the structure and electrostatics of the surfactant-water interface. In particular, we will focus on the sodium oc-tanoate-water system in the lyotropic liquid crystalline mesophase (E). In this phase the surfactant forms very long micelles which pack in a hexagonal pattern. This is a good... 

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