Resistance of fetal membranes to concentrated force applications and reconciliation of puncture and burst testing.

To further the characterization of the chorioamniotic membrane's physical properties, we assessed its ability to withstand a concentrated force. Probes of various diameters were used to puncture 275 specimens from 11 membranes. Values for "strength"/thickness, "stiffness"/thickness, and "toughness"/thickness all showed positive linear correlations (p < 0.001) with the increase of d/D, the ratio of probe diameter to specimen diameter. "Ductility" was independent of diameter, though a logarithmic regression did fit the data marginally (p < 0.05). The separate fracture of the amnion and chorion, which is reflected in ductility measurements, results in an increase in the distance the membrane can be deflected in vitro. In vivo, this behavior would translate to a reduction of pressure exerted on the remaining membrane, while the integrity of the protective sac is maintained. The data pool of mechanical characteristics was enlarged by reconciling data that were gathered by either of two testing methods: puncturing or bursting; the latter method involves the application of force over the entire surface of the test specimen.