Testing and introduction of new materials - Orthopaedic Biomaterials in Research and Practice - page 376

two types of margin: narrow for features critical to safety and efficacy
and wider for those that are not.
Setting specifications produces the first significant constraint to the
design process and thus the completion of step 3 is a good place for a
formal review of the progress to date. This may be held with the “cus-
tomers”; in this case, the device design team, the engineering manager,
and the sales manager. In any case, the acts of reviewing and presenting
the process and its results at this point are important to the material's
designer and may produce new insights and revisions of previous ideas.
Early feedback from a multidisciplinary team in reviewing the specifica-
tions can help avoid delays down the road. If specifications are set by the
engineering team, but say without input from the sales team who may
have on-the-ground feedback from the users, a device may be developed
that does not meet the users' needs.
Step 4: Develop concepts Development of design concepts is the heart
of the design process and the point at which most fatal mistakes are made.
It requires, again, a suspension of self-criticism and a source of external
stimulation. For most people, design concepts evolve more readily in
a group situation in which one person's ideas trigger another person's
imagination. Nevertheless, the goal is the same as that in the first substep
of step 2: developing as many essentially independent approaches to the
problem at hand as is possible.
As an introduction to this step, the material's designer begins to
gather supporting information on past and present materials used for
THR prosthesis components as well as current progress in materials'
design, and processing is started. Information acquired at this time
serves the subconscious as a source of ideas. In addition, such informa-
tion is needed for the next steps of the design process.
Table 15.2 presents a list of ideas that might arise from such a step 4
exercise. The initial list was developed in two creative sessions; the final
list was developed some days later after review of the initial list.
In this hypothetical case, the “blue sky” idea sessions produced an
initial list of 18 concepts (left-hand column), which could be grouped,
with some ideas eliminated, into four concepts (right-hand column).
Three focus on fabrication processes and might require full design
cycles themselves, whereas the fourth, a new titanium-base alloy, is
more restrictive and could be addressed by simple continuation of this
cycle.
Step 5: Select approach At this point, a very limited design develop-
ment of as many final concepts as possible (all if time and resources
allow) is performed to begin step 5. The goal is to provide just enough
information to allow an estimate to be made of which one or two
approaches seem best able to meet the ranked goals developed in step 2.
It is also possible at this point to combine approaches that have aspects in
common. This preliminary evaluation may result in the conclusion that a
particular approach is unworkable or unable to meet a high priority (H)
goal, and it may be abandoned. It is the general experience that one or at