Biomechanical analysis of human chorioamniotic membranes.

The biomechanical properties of human fetal membranes were analyzed by means of a materials testing machine. Special attention was paid to the biomechanical properties of the intact chorioamniotic membrane and the amniotic and chorionic components, separately, and thickness and storage of membrane samples. The load-strain and stress-strain relationships, and parameters calculated from the curves: extensibility, strength, elastic stiffness and failure energy, express the visco-elastic behavior of these membranes. The mechanical properties of the chorioamniotic membranes are determined by the interaction between the amniotic and chorionic components of the membrane. The strength of the intact chorioamniotic membrane, however, is primarily determined by the amniotic component, because the amniotic component is much less extensible. Thus, the chorionic component only contributes 10-15% of the strength when the amniotic component breaks. The chorionic component is twice as extensible as the amniotic component. Samples of fetal membranes can be stored at -70 degrees C, with no significant changes in the biomechanical properties. No significant differences were found between specimens, which were oriented in parallel with and at right angles to the placental edge. Small samples can be analysed and the localization of samples in relation to the placental edge and rupture site of the membranes can be standardized. The method is well suited for studies of premature rupture of fetal membranes.