Biomedical Engineering Reference
In-Depth Information
there is no learning that teaches how to make
that miracle happen again in another applica-
tion. Conversely, and much more frequently, a
particular material is found not be biocompati-
ble, and even failure does not teach how or why.
A second problem with purely design-
directed and trial-and-error approaches to engi-
neered biocompatibility is that invention alone
does not readily allow prediction of liability in
end use. This is extremely important to medical-
device manufacturers who need good estimates
of service lifetimes and the ability to predict
modes of failure. A case in point is the extensive
litigation associated with silicone breast implants
[31-33]
. Patients claimed that connective-tissue
disease, autoimmune responses, and pain were
among many other health issues associated with
silicone breast implants. A lengthy litigation
took place involving a number of companies.
Among the many serious outcomes of this litiga-
tion, Dow Corning was forced into bankruptcy,
negatively affecting the many stakeholders in
this company. Finally, after nearly a decade of
legal and scientific wrangling, the Institute of
Medicine of the National Academy of Science
concluded that there was no direct relationship
between silicone implants and major diseases
[34]
. Although there are many facets to this long
and complex story, the need to define and meas-
ure liability clearly stands out.
A third reason why prospective engineering
is much needed is that it seems that most of the
low-hanging fruit has been picked. Most of the
materials used in medical devices, especially the
sterile disposable devices, have been in exist-
ence for about 50 years
[35]
. Few new materials
are on the horizon. Methods of tissue engineer-
ing promise a new approach to implanted medi-
cal devices, but it seems unlikely that tissue
engineering can be used to make medical devices
in high volume, such as the temporary implants
or sterile disposables of
Figure 8.1
. And even so,
tissue engineering relies on materials as scaf-
folds and rigid supports. Development of mate-
rials at the nanoscopic level is a very active area
of research at this writing, and many promising
pathways toward engineered biocompatibility
have been uncovered. But especially with these
new material forms, liability in use is important
to thoroughly understand.
Finally on this topic, it is to be admitted that
full reliance on trial-and-error development of
biomaterials bankrupts the future of biomateri-
als because, in the words of David Williams, “ it
is difficult to optimize biomaterial characteris-
tics through purely physiology-based assay
techniques because all that can be observed are
macroscopic medical outcomes—not molecular
interactions with biomaterials that lead to these
outcomes”
[30]
. Without understanding core
mechanisms of biocompatibility, biomaterials
development is condemned to an uncertain
future controlled by serendipity.
8.2.5.1 Medical Mediocrity
Yet another downside to purely discovery-based
materials development is that there is little eco-
nomic motivation to improve on what happens
to work or to find out why the material works
well in the first place. As a consequence, bioma-
terials comprising commodity medical devices
generally meet minimal medical requirements,
and that is all. Healthcare works around the
remaining biocompatibility issues that cause
mediocre medical-device performance.
A primary reason why few new biomaterials
enter the medical field is that it is difficult to
economically justify continuous improvement
in medical-device performance unless these
improvements substantially reduce time and
expense of medical care. Patients and medical
doctors might want continuous medical-device
improvement, but the fact of the matter is that
patients and doctors are seldom the customer
who can demand such improvements. Much
more frequently, the choices of medical devices
are made by hospital purchasing departments
or insurance companies that focus on medical
costs and return on investment. Introduction of
new biomaterials into healthcare most usually
