c.)        CHEMICAL MEANS:                                                 

Carbopol polymers are polymers of acrylic acid cross-linked with polyalkenyl ethers or divinyl glycol. They are produced from primary polymer particles of about 0.2 to 6.0 micron average diameter. The flocculated agglomerates cannot be broken into the ultimate particles when produced. Each particle can be viewed as a network structure of polymer chains interconnected via cross-linking.  Carbomers were first prepared and patented in 1957. Since then, a number of extended release tablet formulations, which involve carbomer matrices, have been patented. Carbomers readily absorb water, get hydrated and swell. In addition to its hydrophilic nature, its cross-linked structure and its essentially insolubility in water makes Carbopol a potential candidate for use in controlled release drug delivery system. Carbopol polymers are manufactured by cross-linking process. Depending upon the degree of cross-linking and manufacturing conditions, various grades of Carbopol are available. Each grade is having its significance for its usefulness in pharmaceutical dosage forms Polymers produced in co solvent (a cyclohexane / ethyl acetate mixture) have a bulk density of 176 kg/m³ (11 lbs/ft³). Polymers produced in ethyl acetate have an ash content (as potassium sulfate) of 1-3% on average.  

Conclusion: Semisolids constitute a significant proportion of pharmaceutical dosage forms. It has their peculiar theological behavior; semisolids can adhere to the application surface for sufficiently long periods before they are washed off. The novel approaches discussed were applicable for transdermal delivery of pharmaceuticals.

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