Evaluation of adhesive properties of patches based on acrylic matrices

Adhesion is an essential property of the dermal and transdermal therapeutic systems (TS). It is influenced by the composition and the thickness of the matrix and also by the characteristics of the backing layer. Our aim was to evaluate the usefulness of the 'thumb tack test,' the 'tack rolling ball test,' and the 'peel adhesion 180°test' in the development studies and quality control of TS. These tests were performed on two series of placebo patches in which the backing layer was made of artificial silk (series 1) and polyurethane film (series 2). The patches of both series were prepared using five different mixtures of a hydrophilic adhesive copolymer and a hydrophobic nonadhesive copolymer as matrices. Plastoid® E 35 L, a copolymer of dimethylaminoethyl methacrylate and neutral methacrylic esters, was used as the adhesive polymer. Eudragit® NE 40 D, a copolymer of ethylacrylate and methylmethacrylate, was used as the nonadhesive copolymer. In the standard procedure for the peel adhesion 180°test, used in the tape industries, the adherent is made of stainless steel. Because the latter has a high surface energy, it was not suitable for the analysis of the patches with a polyurethane backing layer. Therefore, the critical surface tension of five alternative materials (rubber, polysiloxane, polyethylene, nylon, polyvinyl chloride) was evaluated. Polyethylene was selected for the modified peel adhesion 180°test, and better results were obtained in terms of feasibility of the test and ability to discriminate between the different patches prepared.