Biomedical Engineering Reference
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synthesis. The structure of cytoskeleton is also visible. Cytoskeleton is typically
made up of three proteinaceous structures: actin fi lament, microtubule and inter-
mediate fi laments. Specifi c chatrcaterisitcs of cytoskeleton allows the constituent
proteins to rearrange or reorganize themselves when desired, e.g., in case of
change of cell shape in response to external stimulation.
It is critical that any implant material must, to a minimum extent, elicit a toxic
response, that kills cells in the surrounding tissues or releases chemicals that can
migrate within tissue fl uids and cause systemic damage to the patient. Therefore, it
is important, in the fi rst place, to understand biomaterial-cell interaction. A sche-
matic illustration of the fundamental mechanisms involved in biomaterial-cell in-
teraction is shown in Figure 1.3b. It can be recalled that once a material is implanted
in an animal, a large number of protein molecules are adsorbed on biomaterial sur-
face. This is because of the abundance of protein as an order of 10
9
number of pro-
tein molecules per eukaryotic cell is estimated in the human body. Also, a simple
calculation shows an order of 10
14
number of eukaryotic cells in a healthy human.
From the phenomenological point of view, protein adsorption on an implant
takes place fi rst because of faster adsorption kinetics, and this acts as precursor to
the cell-material interaction. A schematic of protein adsorption phenomenon as
well as experimental results to illustrate the protein adsorption isotherm have
been provided in Figure 1.4. Therefore, a material does not “see” a cell directly
(a)
Langmuir
500
400
300
200
100
0
0123
Protein concentratin (mg/ml)
45
(b)
View at plateau:
Substrate
Slide view
Top view
Adsorbed protein molecules
Figure 1.4.
Schematic illustration showing the anatomy of a eukaryotic animal cell (a) and
the fundamental mechanisms involved in biomaterial-cell interaction, established by the
adsorbed proteins (circles, boxes and triangles) with the integrin proteins of a biological cell
(b). [Reproduced from BD Ratner, AS Hoffman, FJ Schoen, JE Lemons, Biomaterials Science—
An Introduction to Materials in Medicine, 2
nd
edition, Academic Press, New York, 2004.]
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