Liquid Crystal Systems in Drug Delivery

Introduction

Liquid Crystals (LCs) are determined as one of the most important state of matter subsisting amongst the crystalline solid and the liquid, qualified by the fond or consummate loss of perspective order in crystalline solids, although holding the orientational order of the constituent molecules. This orientational order can remain in the solid state and therefore LCs might demonstrate mechanical stableness like solids as well as flow like liquids. LCs demonstrates universal attributes like double refraction, reaction to magnetized and electrical areas, optical activity in twisted nematic phases and sensitiveness to temperature leading in color changes. Molecular orientation in LCs is the origin of the double refraction that is not exhibit in the glassy state, as it does not have the molecular orientational order. All LCs are condensed state of matter organized by anisotropic organic molecules but all the anisotropic molecules cannot form LCs. These molecules are named mesogens and are either of rod shape or less normally disc shape. Summary of several classes of drugs examined for liquid crystals as drug delivery system given in Table 1. Crystalline solids are characterized by long-range positional and orientational order in three dimensions. Whereas amorphous liquids lack long-range order in any dimensions. LCs (mesophases) depict structural, mechanical and optical attributes intermediate to those of crystalline solids, amorphous and liquid state of matter as shown in Figure 1. LCs, nevertheless, are not a mixture of solids and liquids, but surely a separate state of matter (Lara, 2005). Liquid crystalline systems (mesophases) have been looked into as modern formulations by many authors (Lasson, 2009; Libster, 2007; Liu & Guo, 2007; Bunjes & Rades, 2005; Cervin et al., 2009).