Biomedical Engineering Reference
In-Depth Information
involves use of high pressures to compress powder particles together into
simple shapes in a closed mould. it is used for ultra-high molecular weight
polyethylene (UHMwPe) used in hip joint sockets for example. shaping by
machining can then be used, although costs are high because each product
must be shaped individually. UHMwPe has the advantage of a very high
strength needed to resist hip loads owing to its high molecular weight of
several millions.
10.2.4 Other manufacturing routes
welding is an important secondary process used to bond components
together to make a composite product. Thermal or fusion welding presents
the problem of temperature control. Because high temperatures are needed,
the problem of oxidation is ever present, and good control of the process is
needed to achieve a reliable bond. Ultrasonic or radio frequency vibrations
can also be used to weld two plastic surfaces in contact by means of the heat
generated at the interface. However, care is needed to ensure that the two
surfaces are always in direct contact so as to achieve a good bond and, as it
is almost impossible for a weld to match the strength of the bulk polymer,
welds are a key zone where failure can occur. Adhesives are also widely
used to join separate parts. The manufacturing method, always an important
part of product design, is of particular importance for medical products
that have to resist a very wide range of stresses, abuse, and environments.
In determining root cause of specific incidents, the manufacturing process
must be considered alongside the physical design of the device as well as
the documentary and witness evidence.
10.3 Catheter systems
Intravenous (IV) catheter lines find extensive use in intensive care and for
drip feeds to many other groups of patients (the elderly, chronically sick and
premature babies, for example). it is natural, therefore, that systems have
been developed for allowing different drugs to be fed through the same tube,
for other fluids to be supplied, such as serum and total parental nutrition
(TPN), which is a synthetic equivalent of milk. Multiple supply implies use
of junctions (Y-junctions for example), connections and ways of supplying
drugs via hypodermic needles to prevent any possibility of contamination
within the lines. There are many such medical plumbing systems available
to medical staff in hospitals, and indeed for self-medication to chronically
ill, but stable patients, who have been transferred home. Many systems
were developed in the 1980s and 1990s, and they are still being actively
developed further. Various materials have been used for the catheters of such
systems, including crosslinked silicone rubber, for example, which is a very
Search WWH ::
Custom Search