Biomedical Engineering Reference
In-Depth Information
that describes the properties you want, then those materials lying on, or near, this line are the
ones that suit your specification.
The lines illustrated are various ratios of E/r: as the ratio increases, stiffness compared with
density increases. Thus those lying above a line are stiff and light, and those below are flexible
and heavy. For example, if your PDS stated that the ratio of stiffness to weight should be between
1 and 10 then only PEEK, from the materials shown in
Figure 8.8
, falls into this category.
You should refer to
Ashby (2004)
for more details of this selection methodology. If you use
materials data sources correctly (such as MatWeb) you can build graphs of this nature for
yourself using actual material data, rather than general data.
8.5.8 Advisory Bodies
Virtually every material has an advisory body of some form or other. These bodies are, almost
always, not-for-profit organizations and are there to encourage industry to make use of their
materials. Therefore if you have an idea that you want to use a ceramic, then hunt down your
ceramics advisory body and simply ask. Remember, good designers are not afraid to ask!
8.5.9 Consultancies
If you feel you are out of your depth, then the advisory bodies mentioned previously will have
lists of consultants they are able to recommend. Of course, you will have to pay, but on the
other hand if the material selection is wrong it is their fault and the burden of blame shifts to
them.
8.5.10 Animal Products
We cannot escape this. All regulatory bodies now ask if your device has any animal products
(includes human and nonhuman sources) associated with it. This used to be confined to those
that had some derivative tissue, or an agent that had been developed from an animal source.
However the fear of prions and their resistance to normal sterilization methods means that
all animal derivatives come into play. Unfortunately, animal products are used heavily in
manufacturing, especially the manufacturing of plastic products.
If you are going to make your life easy then avoid animal-based products; this means you
must provide assurance that your whole manufacturing chain also avoids the use of animal
products. You must ask the question, “Do you use animal-based products, such as lubricants,
in your manufacturing process?” You must get the answer “No,” or you have lots of work to
do to prove its safety.
If, however, you
must
use an animal-based product then you should follow the relevant
guidelines laid down by the FDA and MDD. For example, an FDA guideline can be found at
Search WWH ::
Custom Search