Biomedical Engineering Reference
In-Depth Information
CHaPTer FIFTeeN
Testing and introduction
of new materials
The selection of materials for incorporation into medical and surgical
devices and implants is not an arbitrary process. The role of the proper-
ties of materials in dictating which designs will work and which will fail
is critical. How did the materials in use today come to be?
As a general rule, they represent the survivors of a trial-and-error
process of the application of existing materials in engineering use to
the solution of medical problems. The most common engineering fields
have been aviation and marine engineering, since the high demands of
these applications have led to the production of strong, highly corrosion-
resistant materials. In some cases, specific materials have been selected
for particular properties, as in the initial, unsuccessful use of “slippery”
polytetrafluoroethylene as an acetabular cup material in Charnley's low-
friction arthroplasty.
The vast majority of materials in use in orthopaedic devices now
have clinical histories exceeding 10 and, in some cases, 35-50 years,
in at least one application. They have proven satisfactory in many appli-
cations, but new concerns and design concepts are acting to call forth
new materials. However, there are few “candidate” materials remaining
for adaptation; thus, these new materials must be designed rather than
converted to new uses. Furthermore, the medical-legal environment
has changed radically from that present in the 1960s when orthopaedic
implantology began to stride forward.
Therefore, this chapter will review the design process, as it applies
to prosthetic materials, and lay out the course that a new material must
take from concept to routine clinical use. It may be expected that the
full process will require up to a decade, particularly for novel materials.
This seems like a long period but, depending on the material, may be too
short to answer some concerns raised by new materials.
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