Design Realization/Detailed Design - Medical Device Design: Innovation from Concept to Market - page 189

8.7.3 Design for Disassembly (DFDA)
This is a relatively new concept that has come into force since recycling of materials has
become an important feature of household items and cars. However the lessons are important
to medical device designers. You must remember that some of your devices will break and
they will need repairing; how easy is it to take them apart to do the repair?
Some of your devices will be repeatedly assembled and disassembled by the end-user.
We considered assembling them in the previous section; but after use how easy is it to
take them apart? Will the disassembly process damage the components - even if not
intentionally?
Where do the components go to when disassembled? Are they placed somewhere logical so
that when reassembly is required the components are easily found? Are they easily detectable
(e.g., different colors)?
Many designers forget this simple but logical part of the design's life.
8.7.4 Design for Sterilization (DFS)
This is a special part of DFX just for the medical devices industry. If your device needs to be
sterilized, which it most likely will be, how does the sterilization process affect your design?
First you need to consider which of the three common methods of sterilization will be used:
steam, gamma irradiation, or ethyl oxide. Clearly each method has its own deleterious effect
on specific components, but your design must withstand these.
Are you sure your device can be sterilized? If it is reusable does it actually it into a
standard sterilization system? There are trays of all sizes that can be made, but which do
your customers want? Do they have a preferred footprint? The tray will need marking
so that the theater staff can identify any missing components. You may wish to have a
purpose-built tray with supports so that your device does not rattle around in an empty box.
All the above needs considering beforehand. If your device is reusable it will, with most
probability, be repeatedly steam sterilized. How will repeated exposure to steam at 130°C
affect your materials or components? Will some components need to be replaced after each
sterilization?
One aspect of sterilization most people forget is cleaning. All devices are cleaned before
being sterilized. Can your device be cleaned? Blind holes are not recommended, nor are
very long, small bore holes (for obvious reasons). Anything trapped during the cleaning
process will be sterilized. It will be rubbish (called bio-burden ), albeit sterile rubbish;
or at least it should be - remember that if your bio-burden levels increase significantly
then the sterilization process is at risk of failure and this puts your patients at risk. The
last thing anyone wants to see is your device emitting “gunk” - sterile or not. This is not