ABSTRACT
Gels have been dened as the semisolid formulations. Gels usually exhibit viscoelastic properties. Structurally, gels contain two components: one being the solid component and the other being the liquid component.1 The solid component is regarded as gelator. The gelator undergo self-assembly to subsequently form a three-dimensional (3D) network.2 The liquid component is accommodated within this 3D brous network. The associative forces and the surface active forces (surface tension) amongst the liquid component and the gelator do not allow the leakage of the liquid component.3 Depending on the polarity of the liquid component, the gels may be broadly classied into two groups, namely, hydrogels and organogels. Hydrogels contain polar liquid whereas organogels contain apolar liquid.4 Organogels have often been sub-classied as oleogels and amphiphilogels. Oleogels are the formulations that contain vegetable oil (e.g., corn oil, mustard oil, olive oil, sesame oil, and castor oil) or mineral oil (e.g., liquid parafn) as the liquid component.5 Both the solid (e.g., span 40 and span 60) and the liquid (e.g., Tween 80 and Tween 20) components in amphiphilogels
46.1 Introduction ........................................................................................................................ 1035 46.2Mechanisms of Organogellation ......................................................................................... 1036
46.2.1Solid Fiber Mechanism ........................................................................................... 1036 46.2.2Fluid Filled Structure Mechanism .......................................................................... 1038 46.2.3Polymeric Matrix Mechanism ................................................................................ 1039 46.2.4 Microemulsion-Based Mechanism ......................................................................... 1040
46.3Characterization Techniques.............................................................................................. 1040 46.3.1Accelerated Stability Study .................................................................................... 1040 46.3.2Microscopic Studies ................................................................................................ 1041 46.3.3Molecular Properties .............................................................................................. 1046 46.3.4 Mechanical Properties ............................................................................................ 1047 46.3.5Thermal Properties ................................................................................................. 1053 46.3.6Impedance Spectroscopy ........................................................................................ 1054 46.3.7Biocompatibility Studies........................................................................................ 1055
46.4Applications of Organogels ................................................................................................ 1056 46.4.1 Topical Delivery...................................................................................................... 1056 46.4.2Dermal and Transdermal ........................................................................................ 1059 46.4.3Parenteral Delivery ................................................................................................. 1059 46.4.4Nasal Delivery ........................................................................................................ 1059 46.4.5Oral Delivery .......................................................................................................... 1060
46.5 Conclusion .......................................................................................................................... 1060 Acknowledgment ......................................................................................................................... 1060 References .................................................................................................................................... 1060
are surfactant molecules. In the recent past, there has been an exponential increase in the use of organogels as matrices for controlled drug delivery.2 This may be attributed to the advantages of the organogels over the conventional delivery vehicles. The main advantages of the gels include easy preparation methodology, conversion of the liquid formulations into semisolid formulations, and its ability to accommodate both hydrophilic and hydrophobic drugs.6 It is also possible to modulate the release behavior of the drugs, incorporated within the gels, by altering the chemical and physical properties of the gels.7 Since the external phase of the organogels is apolar in nature, the chances of microbial contamination are reduced many folds.8 Even the biphasic organogels has apolar solvents as the external phase, that is, the aqueous phase is totally protected from the external environment with the apolar phase.9
