Manufacturing defects in polymeric medical devices - Durability and Reliability of Medical Polymers - page 221

10
Manufacturing defects in polymeric
medical devices

P. R. Lewis, The Open University, UK

Abstract: injection moulding, extrusion and other processes for
manufacturing polymer components are discussed. several case studies are
presented where manufacture of polymer components is crucial to product
performance, such as injection-moulded polycarbonate connectors in a
catheter, cylinder guard fractures, sight tubes, a crutch failure, and ozone
cracking of tubing and a condom.

Key words: medical devices, implants, manufacturing defects, anaesthetics,
sight tube, condom, crutch.

Note: This chapter is a revised and updated version of Chapters 2
'examination and analysis of failed components', 3 'Polymer medical
devices' and 8 'Tools and ladders' by P. R. Lewis, originally published in
Forensic polymer engineering: why polymer products fail in service ,
P. R. Lewis and C. Gagg, woodhead Publishing Limited, 2010,
isBN: 978-1-84569-185-1.

10.1 Introduction
Medical equipment, such as the implants and other devices discussed in the
previous chapter, has developed rapidly as medical treatment has advanced,
and polymeric materials have played a large part in the progress in providing
effective relief for patients suffering from all manner of illnesses. Their low
densities make them ideal for prostheses for example, and the high strength
of composite materials has led to many innovative designs in artificial
limbs. such materials can exploit the extraordinary properties of carbon
fibre, which when combined with a strong matrix such as epoxy resin, gives
products which resist fatigue or repeated loading to a much greater extent
than conventional materials. However, their high cost both as raw materials
and manufacturing prohibits their use in common medical equipment, where
mass manufacture demands low unit costs. Thermoplastic polymers have
been widely adopted for many different parts of medical equipment, but their
design and manufacture demands very high quality constraints, an objective
not always met in practice, as described in some of the cases discussed in
this chapter.

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The way products are made is important for the features that can arise from

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