Insights on thermoreversible properties of Pluronic® tri-block copolymers
This investigation presents a study on the effect of various polymers on gelling properties of tri-block (Pluronic®) copolymers and increasing the stability parameter of in situ gelling system by altering their composition. The tri-block copolymers finds their importance in fabrication of in situ gelling system for the delivery of various kinds of drugs, which can be administered by topical, ophthalmic or parenteral routes. Pluronic®, is a category of non-toxic, water soluble, biodegradable poly (ethylene oxide)/poly (propylene oxide)/poly ethylene oxide), tri-block copolymers which have application in formulation of various in situ gelling systems. This formulation undergo thermo-reversible gelation, where it exists as a free flowing liquid at low temperature and gels in the range of body temperature to form stable depot in aqueous environment. Gelling system was prepared according to the ‚Cold Method‘ using different concentration of polymers (15%–20% w/v) and subjected to the determination of gelation temperature (GT), viscosity study and effect of various polymers on the strength of gelation. Overall study on the gelation of system at particular temperature is the important parameter for formulation of in situ drug delivery system. It was established that addition of 0.5% w/v of HPMC K4M into gelling system make it stable for forming gel in the range of body temperature whereas methyl cellulose, carbopol 934P, and HPMC E-50 restrict the gel formation.
Gelation temperature of the gelling system plays important role in the formulation of thermoresponsive depot system. As these formulations have GT near to the body temperature it opens the door for forming depot after insertion into the body, either in muscle or beneath the skin. So, it is necessary to optimize the gelation temperature of gelling system to form a potential depot system. In this study it was revealed that GT1 and GT2 of Plutonic® F127 decrease with increase in polymer concentration. However, addition of 0.5% w/v of HPMC K4M into gelling system make it stable for forming gel in the range of body temperature whereas carpool 934P and methyl cellulose restrict the gel formation. Besides the effect of addition of copolymer on the gelation temperature of gelling system, the role of model drug on the GT of system is also one of the major aspects as far as depot formulation is concern. Regardless of the other concentrations of the drug and polymers, the addition of 0.2% w/v docetaxel trihydrate increases the GT of polymer solution by 2-3°C. On the other hand presence of 0.5% w/v of HPMC K4M drops down the GT unto ambient temperature, which is the decisive factor for formation of in situ gel or depot system. Hence the prepared gelling system and the results obtained during this study can be utilized for the formulation of a potential depot forming drug delivery system.
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