The failure of synthetic polymeric medical devices - Durability and Reliability of Medical Polymers - page 199

9.17 Expanded stent in artery acting to widen the channel.
needed to fish the broken parts from the artery. Use of balloon catheters
and stents has been extended to the many other passages within the body,
following the widespread development of endoscopy to explore the body.
For example, special stents are available for supporting the lower aorta
where aneurysm can develop with weak artery walls. An alert warning was
issued by the MHRA in 2009 for one design of abdominal aortic aneurysm
(AAA) endovascular graft, owing to problems with the trigger wire used
to deploy the stent. 10 it seems clear that such operations will become more
common as the technology develops, reducing the need for major invasive
surgery.
￿ ￿ ￿ ￿ ￿ ￿
9.5 Breast implants
There is a large range of implants available to surgeons for replacing diseased
tissue which needs to be removed. Many employ silicone polymer for its
inertness in the body and low modulus compatible with those of body tissues.
One such device is the breast tissue expander. The balloon device is designed
to be implanted after mastectomy under the chest muscles, and gradually
filled with saline solution via a bulb connected to the balloon. When the
process is complete, the device is removed and replaced with a permanent
breast implant. silicone elastomer is reinforced by PeT (at the rear of the
balloon), with a silicone catheter connecting the balloon to the bulb implanted
just under the skin above. The major problem with silicone rubber, however,
is its very poor mechanical properties, especially in fatigue.