Carrier preparation
1 The exact manufacturing process depends on the type of patch being constructed. In general, patch membranes are made by one of several techniques, all of which are designed to create a series of uniform diffusion pores. For example, in the polymer precipitation method, a polymer film is cast on a steel belt containing a solvent-water mixture. As the polymer film hardens, the solvent evaporates and creates a multitude of tiny holes. Porous membranes can also be created by stretching a thin melted film of polymer. As the film is uniformly stretched, small pores are formed. This method is typically used for Nicotine Patch polypropylene films. Polycarbonate films can be perforated by exposure to certain forms of nuclear particles. Regardless of the process, the goal is to create a thin plastic membrane with a multitude of microscopic channels through which the drug can diffuse. These membranes can be attached to the plastic housing containing the drug in subsequent operations.
2 In systems where the drug is intermingled with the patch material, like the matrix type and the mixed adhesive type, the process is somewhat different. The mixture is prepared in a special type of mixer known as a Hockenmeyer mixer. The adhesive is added first and premixed at high speeds for a predetermined period of time. Next, other additives such as viscosity control agents may be added, and further mixing occurs. Then the drug component is slowly added and the mixing speed is increased. Final adjustments in pH or viscosity may be made at this point.