Molding of biomedical segmented polyurethane delamination events and stretching behavior

Segmented polyurethane devices for medical applications are generally processed by the solution-casting technique. The processing parameters in the molding and demolding stages strongly affect the physicochemical properties of the finished articles. Thus, the solution concentration, immersion cycle and drying temperature, type of mold (material and geometry), additives, and the drying time between the casting of successive layers define the surface and bulk properties of the manufactured articles. In this work, new commercially available medical-grade segmented polyurethanes were processed by two techniques to obtain multilayer films. Processing parameters were chosen to ensure the generation of a coating with the desired structural and surface characteristics. In the solution-casting technique, multiple dipping of the preshaped former into the polymer solution were used to obtain proper film thickness. Thin and uniform plaques were produced by the spin-casting technique. The two materials selected have different chemical compositions: one is an aromatic poly(ether urethane urea) (Biospan^TM) and the other an aromatic ether-free polyurethane (Chronoflex^TM). An analysis of the possibility of delamination events, considering the influence of surface-modifying additives and drying times, is presented. The freeze–fracture surface appearance is qualitatively described by SEM. In addition, tensile properties are determined and their influence on demolding and assembling procedures are also discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2159–2167, 1998