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 physicochemic al properties of the finished articles. Thus, the solution concentrati on, immersion cycle and drying temperature, type of mold (material and geometry), additives, and the drying time between the casting of succ essive layers define the surface and bulk properties of the manufactur ed articles. In this work, new commercially available medical-grade se gmented polyurethanes were processed by two techniques to obtain multi layer films. Processing parameters were chosen to ensure the generatio n 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 thic kness. Thin and uniform plaques were produced by the spin-casting tech nique. The two materials selected have different chemical compositions : one is an aromatic poly(ether urethane urea) (Biospan(TM)) and the o ther 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 fre eze-fracture surface appearance is qualitatively described by SEM. In addition, tensile properties are determined and their influence on dem olding and assembling procedures are also discussed. (C) 1998 John Wil ey & Sons, Inc.