Performance of the polypropylene fiber tailstring on the Copper 7 intrauterine device

Surface roughness enhances upward migration of bacteria on polymer fibers above liquid cultures

Monofilament polypropylene (PP) fibers, very similar to fibers that have been used as monofilament tailstrings of interuterine contraceptive devices, were suspended vertically in bacterial liquid monocultures so that a portion of a fiber extended above the liquid surface. In some cases these highly oriented, cold drawn fibers were abraded prior to insertion in the cultures in order to produce surface roughness characterized by axial channels and protruding microfibrils that partially peeled from the fiber surface thereby forming the channels. Extent of migration on a fiber was assessed by aseptically cutting it into small segments, followed by culturing each segment on agar containing growth medium. Such assessment of the PP fibers after 48 h of incubation in the cultures revealed upward migration of Eschericia coli, Pseudomonas aeruginosa, and Staphylococcus aureus over significantly longer distances on the pre-roughened fibers than on those not so pre-treated. Mean measured distances of migration during 48 h were: for E. coli 2.7+/-0.6 mm on roughened fibers (n = 16) and 0.4+/-0.7 mm on fibers not roughened (n = 17); for S. aureus 9.0+/-4.3 mm on roughened fibers (n = 13) and 0.2+/-0.3 mm on fibers not roughened (n = 14); for P. aeruginosa 8.5+/-3.7 mm on roughened fibers (n = 26) and 0.2+/-0.5 mm on fibers not roughened (n = 5). Although no statistically significant (95% confidence level) difference could be discerned between the migration distances of S. aureus and P. aeruginosa, each of these species migrated a greater distance on the PP than did E. coli. The migrations observed are attributed predominantly to wicking of the liquid cultures upward in the axial grooves developed on the surface of the PP by the eruption and peeling of microfibrils from the surface. Surface tension of the growth medium was significantly lower than that of water and its contact angle on PP was less than 90 deg, thereby indicating a tendency to wet the PP. Bacterial growth in the medium further reduced its contact angle on PP, thereby indicating an even greater tendency to wet PP after such growth.

Assessment of olefin-based IUD tail strings

The "tail string" that extends from a contraceptive intrauterine device (IUD) into the vagina is an illustrative case in materials engineering design. The strings must satisfy certain criteria for strength and other properties in order to fulfill the function of providing a means of insuring that the IUD has not been ejected, and eventually of helping remove the IUD. This must be done without contributing to an additional risk of unwanted medical side effects beyond those that may be inherent in any such device. Oriented monofilament olefins appear to satisfy these criteria, and have been used successfully in several IUD designs. This article describes a study of two such monofilaments taken from new IUDs, showing how the material's processing, structure, and properties lead to effective performance as tail strings. Several types of used IUDs were also studied, to insure that nothing occurred during use that would alter the conclusions drawn from the study of new strings.

Polypropylene IUCD retrieval fibers: surface morphology, material properties, microbial attachment, and migration

Highly drawn and oriented polypropylene fibers used for the retrieval thread of the Cu-7 intrauterine contraceptive device (IUCD) are compared as to surface morphology and crystallinity with polypropylene fibers prepared under different conditions. A series of experiments also demonstrates the colonization of the surface of polyolefin fibers by pathogenic bacteria that are often found in the human vagina. Moreover, it is demonstrated that the retrieval threads appear to encourage pathogenic bacteria to migrate across the surface of agar. The results also indicate that control of drawing and annealing can avoid the surface fibrillation and tendency to fail by separation into a bundle of multifilaments that are observed with the IUCD retrieval threads.

Evidence against tailstrings increasing the rate of pelvic inflammatory disease among IUD users

A meta-analysis was conducted to determine whether the presence of an IUD tailstring is associated with increased rates of pelvic inflammatory disease among IUD users. Included were seven clinical studies that compared the same IUD with and without a tail, and fifteen clinical studies that compared two similar copper IUDs that differed in the polymer used for the tailstring (polypropylene versus polyethylene). No increase in PID rates was found among users of IUDs with versus without a tail (RR = 1.2, 95% confidence interval 0.6-1.7), or among users of copper IUDs with different tailstring materials (polypropylene vs. polyethylene, RR = 0.9, 95% confidence interval 0.4-1.5). These findings support the hypothesis that the presence of a tailstring does not increase the rate of PID among users of IUDs.