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AMPHIPHILIC LIQUID CRYSTALS: AN EMERGING DRUG DELIVERY SYSTEM

INTRODUCTION

The whole scenario of drug delivery technologies is changing nowadays. Patient looks for an inexpensive and more effective treatment having minimum adverse effects. Stressful conditions of pharmaceutical industries are becoming worse to cover the expectations of society in this post-TRIPS era. So, they are looking for newer drug delivery technologies having more benefits over the previous one’s in aspects of cost and effectiveness. Along with these benefits, industries can easily get patent over these technologies as more of blockbuster drug’s patents are expiring. By the end of last decade, 39% of pharmaceutical products are based on novel drug delivery technologies. This clearly shows their popularity [1].

Progressive research on advance delivery technology has direct to the development of newer techniques of controlled release (CR) formulations for the effective release of therapeutic molecule to the desired site of action. In particular, the use of newer types of polymers and amphiphiles provide novel approaches in the development of CR formulations, with a focus to achieve desired therapeutic outcomes, as well as optimize the CR of drug to obtain the maximum dose regimen with minimum adverse effects [2]. Depending on the drug delivery technologies, the release of drug may be from a few hours to a month to several years. A variety of synthetic/natural polymers and amphiphiles have been studied as drug carriers, and drug delivery systems (DDSs) [3]. Even there can be limitless combinations of polymers/amphiphiles to explore, researchers are restricted by material biocompatibility, toxic byproducts, surgical removal of DDSs, and manufacturing cost. One of the amphiphilic based drug delivery system is lipid based liquid crystals (LLC) systems that consist of amphiphilic lipid molecules and solvents. Luzzati et al described that lipids can self-assemble into different nonlamellar superstructures e.g. sponge (L3), reversed bicontinuous cubic (Q2), reversed hexagonal (H2), and reversed micellar cubic (I3) phases etc [4]. From last few years, researchers are getting more focused on LLC systems because of their excellent applicability as drug carrier system. Among these systems, reversed cubic (Q2) and hexagonal mesophases (H2) have been widely studied for their ability to sustain the release of a broad range of therapeutic molecules from low molecular weight drugs to proteins, peptides and nucleic acids [5]. The amphiphilic lipids, when mixed with small amount of solvent form gel-like phases with unique superstructures, into which therapeutic moiety can be easily incorporated. Moreover, non-toxic, biodegradable and biocompatible properties of amphiphilic lipids also contribute to their applications for drug delivery. Reversed cubic and hexagonal mesophases form colloidal dispersions having superior thermodynamic stability when dispersed with aqueous phase because of their infinite swelling capacity [6]. The goal of stable and reproducible formulation can be achieved with the combinations of various available amphiphilic lipids [7]. Various types of amphiphiles are used for the development of self assembled lipid based superstructures e.g. ethylene oxide, monoacylglycerol, glycolipid, phosphatidylethanolamine, and urea-based amphiphiles [8].

REFERENCES

[1]	Hoffman, J. M., Shah, N. D., Vermeulen, L. C., Hunkler, R. J., Hontz, K. M., Projecting Future Drug Expenditures--2004. Am J Health Syst Pharm. (2004) 61, 145-148.

[2]	Garcia, M.O., Blanco, D., Martin, J.A., Teijon, J. M., 5-Fluorouracil trapping in poly(2-hydroxyethyl methacrylate) hydrogels: in       vitro drug delivery studies. Eur. Polymer J. (2000) 36, 111–122.

[3]	Hoffman, A.S., Hydrogels for biomedical applications, Adv. Drug Deliv. Rev. (2002) 54, 3–12.

[4]	Luzzati, V., Husson, F., The structure of the liquid-crystalline phases of lipid-water systems. J. Cell Biol. (1962) 12, 207-219.

[5]	Clogston, J., Caffrey, M., Controlling release from the lipidic cubic phase. Amino acids, peptides, proteins and nucleic acids. J.       Control. Release. (2005) 107, 97–111.

[6]	Spicer, P.T., Progress in liquid crystalline dispersions: cubosomes. Curr. Opin. Colloid Interface Sci. (2005) 10, 274–279.

[7]	Barauskas, J., Johnsson, M., Tiberg, F., Self-Assembled Lipid Superstructures: Beyond Vesicles and Liposomes. Nano Letters. (2005) 5:8, 1615-1619.

[8]	Kaasgaard, T., Drummond, C. J., Ordered 2-D and 3-D nanostructured amphiphile self-assembly materials stable in excess solvent. Phys. Chem. Chem. Phys. (2006) 8, 4957-4975.