Biomedical Engineering Reference
In-Depth Information
Biomedical interpretability requires that the
data gathered by the surface analytical method
comes in a form that can be interpreted in terms
of the biological response to material surfaces. It
is not immediately evident that chemical composi-
tion detected by spectroscopies, or morphological
evidence obtained by microscopy, or the surface
energetics detected by tensiometry are immedi-
ately applicable to understanding the biological
response. After all, knowing chemical composi-
tion, even in exquisite detail, does not provide the
mechanistic information captured in
Figure 8.4
that permits formulation of structure-property
relationships
[77]
. The same is true for surface
energetic and morphological lines of evidence.
Perhaps the most stringent attribute of the
three ideal analytical criteria stated in Section
8.4.2
is that of biomedical relevance, as can be
appreciated by considering
Figure 8.4
in this
regard. Biomedical relevant characterization
obtains analytical results from hydrated sur-
faces, is sensitive to the energetics that drive
adsorption and adhesion to hydrated surfaces,
and is applicable to a chemically undefined
milieu. That is to say, it would be beneficial to
somehow characterize the hydrated biomaterial
surface in contact with the biological milieu
rather than in the vacuum of an electron micro-
scope or spectrometer
[77]
.
FIGURE 8.6
Venn diagram expressing the overlap of
surface analytical techniques simultaneously offering sur-
face sensitivity, biomedical relevance, and interpretability of
the analytical information in the context of biomedical appli-
cations. The overlap is small, perhaps vanishingly small,
creating considerable analytical difficulties in biomaterials
surface science.
analytical techniques where these ideal char-
acteristics converge is very small, perhaps
vanishingly small. This is to say, that there are
numerous methods that, on an individual basis,
may offer any one, or possibly two, of these ideal
attributes, but there are few that offer all three.
A restatement of the old project-management
adage “quick, cheap, good…choose any two”
relevant to biomaterials surface characterization
would be “sensitive, interpretable, relevant…
choose any two (or maybe one).”
Surface-sensitivity requirements are at the
upper nanometer or so of the surface, where the
terminal functional groups reside that influence
the biological response to materials, as discussed
in Sections
8.2 and 8.3.2.1
. Surface sensitivity at
this level is all but limited to high-vacuum
spectroscopies
[129, 130]
and a few relatively
new and sophisticated optical spectroscopies,
such as secondary harmonic generation (SHG)
and sum frequency generation (SFG) techniques
[131-134]
.
8.4.3 A Quantitative Measure of the
Biological Response
Biomedical devices are used in specialized bio-
technical applications or come into contact with
specific physiological compartments. For exam-
ple, sterile disposables used in the culture of ani-
mal cells in the laboratory come into contact with
cells and protein-containing media, ophthalmic
materials contact the ocular environment, and
blood contacts vascular grafts and artificial
heart valves. From this end-use environment,
meaningful measures of the biological response,
hopefully predictive of biocompatibility in use,
