Biomedical Engineering Reference
In-Depth Information
an interior surface that exactly matches a par-
ticular protein used to create the nanocavity.
These
template chemistry
techniques offer a num-
ber of advantages over biomolecule immobiliza-
tion including preparation of a dry surface that
does not require the special storage or handling
that may be required for immobilized biological
molecules.
integrins, and selectins)
[99, 121, 122]
suggests
that immobilized biological molecules are
indeed active in this regard. Another example
is that immobilized heparin can control blood
coagulation
[123]
.
The interaction of template surfaces with the
biological milieu is more like considerations
already outlined in Sections
8.3.2 and 8.3.3
. The
dry template undergoes the instantaneous
hydration reactions that establish a vicinal-
water layer that interacts with the proteins of the
biological milieu. In this case, however, the
nanocavity created by templating can recognize
target proteins through shape selectivity and
hydrogen-bonding reactions through a
recogni-
tion-of-the-fittest
effect
[117]
that leads to adsorp-
tion selectivity of the target protein(s) that may
subsequently direct a desirable biological
response through “control of interactions with
components of living systems.”
The full power of the biomimetic surfaces
will be unleashed if and when the sequence of
steps of the biological response labeled
amenable
to comprehension
in
Figure 8.4
can be understood
in a way that identifies the biological molecules
most important in obtaining a desired biological
response. After all, one cannot mimic what one
cannot observe. Template chemistry has particu-
lar potential in rational design of biomaterials
because it promises to deliver biological selec-
tivity without the technical difficulties imposed
by fragile biological molecules, attributes that
greatly facilitate manufacturing and distribution
of medical devices lying low in the healthcare
pyramid of
Figure 8.1
.
8.3.4.2 The Biological Response to
Biomimetic Surfaces
Biomimetic surfaces do not subvert the sequence
of steps outlined in
Figure 8.4
, but these surfaces
can amplify or initiate biological responses
that might not occur to ordinary materials.
If the biomimetic surface bears immobilized
biomolecules, it most likely is already hydrated
because desiccation can cause loss in bioactivity.
In this case, the initial hydration reactions
have already occurred before the biomimetic
surface is immersed in the biological milieu.
Nevertheless, it can be expected that there
will be an exchange of ions between the
water of hydration and the biological milieu,
leading to vicinal-water region that is different
than the water of hydration. Thereafter, the
biomimetic surface will be subject to the same
physicochemical rules that control adsorption
of proteins as apply to any other surface.
The dynamic interphase, which includes
immobilized biological molecules, interacts
with the biological milieu through adsorbed
protein if protein adsorbs to these surfaces.
And, in a manner paralleling the discussion
of water interaction with a surface functional
group on a SAM surface in Section
8.3.3.1
, the
immobilized biological molecule must shine
through water and adsorbed protein to interact
with constituents of the biological milieu. The
fact that biological cells can specifically interact
with surfaces bearing immobilized RGD amino
acid sequences (arginine-glycine-aspartic
acid or similar) or bind to various so-called
adhesion molecules
(proteins such as cadherins,
neural cell adhesion molecules or N-CAMs,
8.4 A BIOMATERIALS SURFACE
SC
IENCE LAB OF YOUR OW
N
It seems appropriate to close this chapter with
a brief discussion of the tools required to suc-
cessfully engineer surfaces or to modify surfaces
of existing materials for improved biocompat-
ibility. The intent of doing so is not to create a
