Testing and introduction of new materials - Orthopaedic Biomaterials in Research and Practice - page 374

Table 15.1 hypothetical design goals: new thr material

Initial
Specific
Modulus <0.5 times Ti6AI4V
Strength as high as possible
Endurance limit as high as possible
Corrosion/release rate “low”
No wear against ultrahigh-molecular-weight polyethylene (UHMWPE)
Color: yellow
General
Minimum cost
No limit on source of supply
Simplicity in fabrication

Reined a
Specific
Modulus <0.5 times Ti6AI4V (H)
Strength as high as possible (M)
Endurance limit as high as possible (H)
Corrosion/release rate as low as possible (H)
Wear rate (against UHMWPE) lower than current rates (M)
Color: yellow (L)
General
Minimum cost per kilogram (L)
No limit on source of supply (M)
Simplicity in fabrication (M)

a

Priorities: H, high; M, medium; L, low.

of what is wanted as an end product of the design process. The mate-
rial's design team must now put its talents to work to understand these
desires and to satisfy them. Some of these initial objectives may come
from other sources: the engineering manager is always worried about
the manufacturing costs of the designs that the group produces; the color
was suggested by the sales manager since yellow is widely used in the
company's packaging and has come to be identified with it.
The material's design team must go through two substeps to produce
the refined set of goals, also shown in Table 15.1. The first is the initial
creative act in the design cycle. The question is posed: “What should an
improved material for a THR prosthesis look like?”
Creation of ideas is not an easy process for engineers. There is a
tendency to “freeze,” to be unable to produce ideas, or to have an ini-
tial thought and then to proceed to develop it. The general solution for
the individual designer is to produce a situation that is both stimula-
tory and non-self-critical. (Because of the need for continuing review
and creative stimulation, design is generally best played as a team sport.
However, from here on, they will be referred to as a single individual
for simplicity's sake. All of the comments here apply equally to design