Transdermal drug delivery is the administration of therapeutic agents through intact skin for systemic effect. Polymers are the backbone of the matrix-type transdermal patches. Based on the nature of origin, these polymers can be Natural, Semi-synthetic, and Synthetic polymers. Several experimental results have revealed the fact that in the case of the fabrication of matrix-type patches, the use of a polymeric blend becomes more effective than the use of a single polymer to control the rate of drug release from the patch. In this context, the selection of an appropriate combination of polymers becomes very crucial to modulate the rate and extent of release of drugs from matrix-type patches. It is essential to have sound knowledge of the inherent properties of different polymers for the selection of an appropriate combination of polymers to achieve the controlled drug release from the matrix-type patches. This article assembles comprehensive up-to-date information on various categories of polymers and polymer blends being used for the development of matrix type patches, the inherent characteristics of these different categories of polymers, and their impact on physio-mechanical properties as well as the rate of drug release from drug-loaded patches.

Among the various strategies employed to enhance solubility, dissolution and bioavailability of poorly soluble drugs in vivo, formulation of solid dispersion using hydrophilic and/or water-soluble carriers with varying physicochemical characteristics seems to be a developable, economically viable and easy option. The present study is aimed to use skimmed milk(SKM)-urea(U) as a novel binary mixture of classical carrier-hydrotrope in solid dispersion of poorly water-soluble aceclofenac (ACF). Compatibility of ACF and binary mixture of SKM-U was confirmed by FTIR spectroscopic analysis. Solid dispersions of ACF-SKM and ACF-SKM-U were prepared in varying ratios of 1:1 to 1: 5 for ACF-SKM and 1:4.5:0.5, 1:4.25:0.75 and 1:4:1 for ACF-SKM-U by solvent evaporation technique using ethanol(95%) as the common solvent and were characterised by their physical appearance, solubility enhancement (compared to pure drug) in double distilled water and phosphate buffer (pH 6.8) at 25 ⁰C and drug dissolution profiles in the above mentioned media. Based on solubility enhancement data(71.53%  and 31.03%) and maximum cumulative percentage release data (82.37% in 9 mins and 68.03% in 90 secs ) in double distilled water and phosphate buffer respectively, ACF-SKM (1:5) was found to the best which was used for studying the effect of addition of urea as hydrotrope. ACF: SKM: U (1 : 4.5 : 0.75) exhibited maximum solubility enhancement of 75% .and 36.51% and cumulative percentage release of 83.83 % in 9 mins and 69.24% in 90 secs in double distilled water and  buffer respectively. Therefore, the binary mixture of skimmed milk-urea has been proved to be marginally superior over skimmed milk in terms of solubility enhancement and drug release profile of aceclofenac.