The Research And Application On Rheology Of Cataplasm Bases

Cataplasm originates from Japan and it has been introduced in the field of traditional Chinese medicine (TCM) in China to transform traditional dosage forms such as plaster etc. Cataplasm has many advantages over other topical dosage forms: large drug loading, low irritation to the skin and convenient for use. Especially, it contains high moisture content helps to keep the skin moisturized and comfortable. Cataplasm consists of adhesive polymers, i.e., hydrogel layer containing drug, non-woven cloth as backing material and release liner. The bases of cataplasm compose of polymer matrix material, crosslinking agents, crosslinking regulators, fillers, adhesion promoters, transdermal enhancers, moisturizers, water and so on. The hydrogel layer plays an important part in determining its adhesion, release and transdermal characteristics of the cataplasm. In the past, hydrogel layer mainly consisted of non-crosslinking hydrophilic polymers. Recently, cross-linked base has been wide application in cataplasm for its simpler formulation and easy preparation.Viscoelasticity is one of the fundamental properties for cross-linked hydrogels. Viscoelasticity affects manufacturing processes such as mixing, stirring, coating and in vitro drug release. Especially, concerning the adhesion and duration to the skin surface, viscoelastic measurements could provide some important information. Generally, the index of apparent adhesiveness and hardness were used to characterize the performance of cataplasm. To date, there have been few studies on rheological properties of cataplasm.Rheological properties can be reflected through a variety of rheological parameters such as complex modulus G*, elastic modulus G’, viscous modulus G" and phase angle δ. The elastic modulus G’ describes the "solid-like" character. It enables the base have greater cohesion so that the cataplasm can be peeled off without leaving any residue avoiding contaminating clothing. It also can avoid the phenomenon of "cold flow". The viscous modulus G" describes the "liquid-like" character. It is associated with tack of cataplasm and enables the base flow sufficiently to promote close contact between itself and the skin. The complex modulus G*and phase angle δ is also used to determine the extent of elasticity of a hydrogel.In the first part, using the rotational rheometer to determine rheological properties of cataplasm bases, the overall aim of the study was to investigate the effects that the basic formulation parameters have on the rheological characteristics of cataplasm bases, including those of the different grades and concentrations of Viscomate as well as the different concentrations of dihydroxyaluminum aminoacetate. For illustrative purposes, we also considered the hardness, which is a commonly used parameter for testing gel strength. Different basic formulation parameters were found to be important in determining the properties of the base of cataplasm. The results also proved that the bases of cataplasm mainly showed characteristics of elastomers.In the second part, the results showed that the fillers took part in forming elastomers of cataplasm to some extent, which contributed more significantly to bases elastomer, while less to apparent adherence and viscidity. The tackifiers significantly increased cataplasm bases viscous modulus G", and the tack and peel force increased accordingly. A high G" value would enable the base to flow to a sufficient degree to promote close contact between itself and the skin. It showed that the tackifiers had good basic rheological mechanisms. The tackifiers also significantly increased the elastic modulus G’and complex modulus G*, indicating that the tackifiers could replace the fillers to enhance the cataplasm bases force and rigidity in the prescription of cataplasm, avoiding the phenomenon of "cold flow", which often occurs during the storage of cataplasms. PVPK-90at the concentration of2%was usually chosen as one of the basic formulas of cataplasm because of its better rheological performance.In the third part, the preparation of indomethacin cataplasm base on the optimum of the formula of cataplasm bases, we compared it with indomethacin cataplasm produced in Japan in transdermal properties. The results showed that indomethacin cataplasm produced by ourselves had a good transdermal absorption property.