Aqueous gels are much more studied than non aqueous gels because hydrophilic gelling agents are readily available. However water poses a risk of hydrolytic reactions and the alternative formulations of hydro alcoholic compounds (e.g. ethanol) can neither eliminate the possibility of drag hydrolysis nor prevent undesirable variation in formulation owing to high evaporative potential. A non-aqueous gel system consisting of ethyl cellulose and propylene glycol dicaprylate was reported to be a good delivery system for water-sensitive drugs showing good rheological and mechanical properties for different formulations and different storage time. Among the many variants of cellulose, ethyl cellulose (EC) has garnered considerable attention since it can be used as a binder, dispersing agent, stabilizer, water conserving agent, and a slow releasing agent in many kinds of medicinal applications. The EC repeat group can form inter- and intra molecular hydrogen bonds, which restricts the motion of the polymer backbone resulting in a material that is highly crystalline and oriented. EC does not dissolve in water but does dissolve in organic solvents. This makes it an ideal polymer for use in a non aqueous drug delivery system. Although EC is a popular polymer in film forming applications, its use in the formulation of non aqueous gels remains largely unexplored. Non-aqueous solvents are of increasing interest since they can be used as vehicles of topical drug delivery. A topical dosage form that ensures clinical efficacy and patient acceptability must satisfy certain physicochemical and aesthetic criteria, but fundamental understanding of EC properties in non-aqueous systems is scarce in the literature. Formation of clear and thermoreversible gels has been reported upon cooling of EC/diester phthalate solutions. Thixotropic gels with an extended linear viscoelastic region that exhibit desirable wetting behaviour in their function as a moisture barrier were produced with 11 to 16% EC in the formulation at various particle grades.Blends of ethyl cellulose with polypropylene carbonate) exhibited a range of viscoelastic consistencies from predominantly amorphous regions to cholesteric liquid crystalline structures in the rich EC composition range. We felt that a study on the molecular characteristics of the polymer in a non-aqueous solvent will go a long way to fill in gaps associated with the functionality of these systems in industrial applications relevant to topical drug delivery.
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