The failure of synthetic polymeric medical devices - Durability and Reliability of Medical Polymers - page 181

grade developed for a particular product, with traces of metal catalysts (or
any other remnants of polymerization which might be harmful) removed
because they pose a potential leaching risk. The moulding conditions must
be chosen so as not to expose the hot melt to excessive temperatures when
degradation starts to occur. Such traces might be difficult if not impossible
to see by eye alone, remaining hidden unless special checks are made of
product quality.
Most regulatory bodies, such as the Federal Drugs Administration (FDA)
in the UsA and the Medicines and Healthcare Products Regulatory Agency
(MHRA) in the UK, insist on a programme of tests to ensure that a new
product or device does not prove damaging to patients. The testing usually
includes toxicity tests, integrity tests (such as for mechanical strength under
expected loading conditions in the body) and in vivo tests as a final check
on compatibility with the body. This might include tests using animals,
the first balloon catheters being tested in this way, for example. Testing
must be rigorous and demanding so as to assure the integrity of the final
product. in reality, this is not always the case, as some of the following
examples show very clearly. There is always the chance of unexpected
damage, not caught by the rigorous quality testing demanded of medical
products.

9.2 Forensic methods
investigation should normally follow any serious failure of a medical product,
starting with the remains of the product but also including a record of the
circumstances of the failure. The way in which it failed often provides
clues as to why the product broke, or otherwise did not fulfill its intended
function. Comparison with intact or new products of identical design is a
vital part of the process of assessing the failure modes concerned. when a
product breaks into two or more parts, examination of the fracture can show
how the cracks grew at the critical time, and here the fracture surface is an
important piece of evidence.
every product failure demands individual treatment, which usually starts
with simple visual examination, careful measurement of its dimensions and
determination of its condition compared with an equivalent intact component.
Comparison is a simple way of checking if the parts really are identical and,
if not, the reason for divergence. Many products are now identifiable from
logos, date stamps and manufacturing codes either printed or embossed
on the product outer surface. if the material is unknown, or degradation is
suspected, it must be analyzed for the constituent parts: the matrix polymer,
filler and any minor additives (such as UV absorbent). The analysis should
aim to be non-destructive, but, if necessary, sampling needs to be away from
critical features such as fracture surfaces. Although direct comparison with

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