An organogel, a viscoelastic system, can be regarded as a semi-solid preparation which has an immobilized external apolar phase. The apolar phase is immobilized within spaces of the three-dimensional network structure formed due to the physical interactions amongst the self-assembling structures of compounds regarded as gelators. In general, organogels are thermodynamically stable in nature and have been explored as matrices for the delivery of bioactive agents. In the current paper, attempts have been made to understand the properties of organogels, various types of organogelators and some applications of the organogels in controlled delivery.

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The current study explores the properties of starch and non‐starch polysaccharides based bigels containing sunflower oil and their application in controlled delivery of metronidazole and probiotics. The bigels were prepared by mixing span‐40 and sunflower oil organogels with the aqueous polysaccharide sol. The microstructure of the bigels was characterized by fluorescent microscope. The bigels were then characterized for their mechanical properties using texture analysis. The flow behavior of the gels was studied using rheometer. The micrographs suggested uniform distribution of the organogels in the continuous aqueous phase. The bigels were viscoelastic in nature with a shear thinning behavior. The release of metronidazole from the bigels was diffusion mediated. These bigels showed good antimicrobial efficacy. The probiotics encapsulated within the bigels were tolerant to gastric and intestinal environment compared to the free cells. The preliminary studies suggest that the developed bigels can be used effectively for the delivery of poorly soluble drugs and probiotics.

Modulation of crystallization of stearic acid and its derivatives is important for tuning the properties of stearate oleogels. The present study delineates the crystallization of stearic acid in stearate oleogels in the presence of Span 60. Microarchitecture analysis revealed that stearic acid crystals in the oleogels changed its shape from plate-like structure to a branched architecture in the presence of Span 60. Consequently, a significant variation in the mobility of the solute molecules inside the oleogel (Fluorescence recovery after photobleaching studies, FRAP analysis) was observed. Thermal analysis (gelation kinetics and DSC) revealed shortening of nucleation induction time and secondary crystallization with an increase in the Span 60 concentration. Furthermore, isosolid diagram suggested better physical stability of the formulations at higher proportions of Span 60. XRD analysis indicated that there was a decrease in the crystal size and the crystallinity of the stearic acid crystals with an increase in Span 60 concentration in the Span 60 containing oleogels. However, crystal growth orientation was unidirectional and found unaltered with Span 60 concentration (Avarmi analysis using DSC data). The mechanical study indicated a composition-dependent variation in the viscoelastic properties (instantaneous [τ 1 ], intermediate [τ 2 ], and delayed [τ 3 ] relaxation times) of the formulations. In conclusion, Span 60 can be used to alter the kinetics of the crystallization, crystal habit and crystal structure of stearic acid. This study provides a number of clues that could be used further for developing oleogel based formulation.Practical Application: Stearic acid can be used for the solidification of vegetable oils. This will allow easy handling, storage and transportation of the oils. The physical and the thermal properties of the oleogels can be altered by tailoring the microstructure of the oleogels using Span 60 (nonionic surfactant). The oleogels can be used for the controlled delivery of nutraceuticals and drugs.

The present work deals with preparation of the olive oil (OO) based organogels using sorbitan monostearate (SMS) and sorbitan monopalmitate (SMP) as organogelators for controlled drug delivery applications. Metronidazole (MZ) was used as the model drug. Gels were prepared by solubilizing the organogelators in OO at 60°C under stirring. As the solution was cooled down, the gelator molecules precipitate as an isotropic phase having networked structures, which immobilized OO. Formation of 3D networked structure was confirmed by light, phase contrast, and scanning electron microscopy. Accelerated thermal stability studies demonstrated the thermal stability and thermoreversibility of the organogels. DSC and gel disintegration studies suggested that the SMS based organogels were having higher thermal and physical strength as compared to the SMP based organogels. Viscometric analysis suggested the pseudoplastic flow behavior of the gels. The SMS organogels were more amorphous as compared to the SMP organogels of same composition. Drug release from the organogels followed Fickian diffusion kinetics. The drug loaded gels have shown good antimicrobial property against Escherichia coli and Bacillus subtilis and were found to be highly hemocompatible in nature. On the basis of the preliminary results, the developed organogels can be used as matrices for the topical drug delivery. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

The current study describes the in-depth characterization of agar-gelatin based co-hydrogels, emulgels and bigels to have an insight about the differences in the properties of the formulations. Hydrogels have been extensively studied as vehicle for controlled drug release, whereas, the concept of emulgels and bigels is relatively new. The formulations were characterized by scanning electron microscopy, FTIR spectroscopy, XRD and mechanical properties. The biocompatibility and the ability of the formulations to be used as drug delivery vehicle were also studied. The scanning electron micrographs suggested the presence of internal phases within the agar-gelatin composite matrices of co-hydrogel, emulgel and bigel. FTIR and XRD studies suggested higher crystallinity of emulgels and bigels. Electrical impedance and mechanical stability of the emulgel and the bigel was higher than the hydrogel. The prepared formulations were found to be biocompatible and suitable for drug delivery applications.