The failure of synthetic polymeric medical devices - Durability and Reliability of Medical Polymers - page 213

in addition, the broken halves did not match up, indicating that the bleed
hole had been lost in a separate fragment which had fallen away, and been
lost entirely. That the fractures had been initiated at the bleed hole seemed
to be confirmed when another intact catheter was inspected. It showed that
fragments had been lost from the sides of the hole, leaving a rough and jagged
appearance (Fig. 9.37). This was confirmed when a new catheter obtained
independently was examined: it had a round and smooth bleed hole (Fig.
9.38).
The defective catheters had been poorly manufactured, and the data supplied
by the manufacturers (based in the Far east) proved to be of no assistance in
tracing the origin of the faulty batch of devices. There are several dangers
during manufacture, including overcure, when too high a density of crosslinks
are present. Other parts may be undercured and the purity of the raw material
must also be carefully controlled to prevent inclusions. if the distribution of
crosslinks varies across the walls of the device then asymmetric stresses are
set up when loaded, and these encourage crack growth. it is likely that the
main tube was extruded (given that it is of constant section), and that the
other parts were either hot moulded onto the tube or attached by silicone
adhesives. A selection of finished devices are normally selected for detailed
inspection and testing, but for several defective catheters to penetrate the
security is unusual, and indicative of a serious lapse in quality control.
500 µm
￿ ￿ ￿ ￿ ￿ ￿
9.37 Irregular bleed hole in new intact catheter.