A new obstetrical polyurethane versus stainless steel forceps: a comparison of forces generated to the base of the fetal skull during simulated deliveries.

BACKGROUND: Decreasing the maximum force applied during traction to the base of the fetal skull using a less rigid polyurethane forceps is the basis of this study. Our hypothesis was that less force would be generated with polyurethane forceps than with steel forceps. OBJECTIVE: To test a new soft polyurethane obstetrical forceps for maximal force generated to the base of the skull during simulated occiput anterior deliveries and to compare this to a similar shaped steel forceps. METHODS: After designing a prototype polyurethane forceps, we used a pelvic manikin model and a fetal manikin model. Force and load sensors were attached at the inner tips of the distal forceps blade. A Tekscan 201 (accurate for measuring 0-25 pounds of force) 0.0008 inches flexible printed circuit was used that measured contact forces. Forceps with an attached calibrated sensor were applied to the fetal head while inside the pelvic model. RESULTS: The median maximum traction force at the base of the fetal skull was 4.60 pounds (range 4.3-4.62) for polyurethane forceps vs. 9.52 pounds (range 9.22-9.52) for steel forceps (P=0.027). CONCLUSION: The polyurethane forceps applied 50% less overall mechanical force than the steel forceps at the tip of the forceps and base of the skull during simulated occiput anterior outlet deliveries.

Apolipophorin III: lipopolysaccharide binding requires helix bundle opening.

Apolipophorin III (apoLp-III) is a prototypical apolipoprotein used for structure-function studies. Besides its crucial role in lipid transport, apoLp-III is able to associate with fungal and bacterial membranes and stimulate cellular immune responses. We recently demonstrated binding interaction of apoLp-III of the greater wax moth, Galleria mellonella, with lipopolysaccharides (LPS). In the present study, the requirement of helix bundle opening for LPS binding interaction was investigated. Using site-directed mutagenesis, two cysteine residues were introduced in close spatial proximity (P5C/A135C). When the helix bundle was locked by disulfide bond formation, the tethered helix bundle failed to associate with LPS. In contrast, the mutant protein regained its ability to bind upon reduction with dithiothreitol. Thus, helix bundle opening is a critical event in apoLp-III binding interaction with LPS. This mechanism implies that the hydrophobic interior of the protein interacts directly with LPS, analogous to that observed for lipid interaction.