Biomedical Engineering Reference
In-Depth Information
Biological effects of surface
microtexture
The role of standardized surface texture in inducing
a specific cellular response is a field of active research. For
example, various reports have suggested that a regular
surface microtexture can benefit the clinical success of
skin penetrating devices by preventing epithelial down-
growth (
Brunette
et al.
, 1983; Chehroudi
et al.
, 1988
)
and reduce the inflammatory response (Campbell
et al.
,
1989) and fibrous encapsulation (
Chehroudi
et al.
, 1991
)
of subcutaneous implants. Closely related to these
studies, certain porosities have led to an increase of the
vascularity of the healing response and a reduction
of collagenous capsule density (
Brauker
et al.
, 1995;
Sharkawy
et al.
, 1998
). The literature on the effect of
surface texture on the healing of silicone breast implants
is extensive (for example, see
Pollock, 1992
). Therefore,
much current research has been focused on the effect of
standardized surface roughness on the soft tissue re-
action. Excellent reviews on the effect of surface
microtexturing on cellular growth, migration, and at-
tachment have been written by
Singhvi
et al.
(1994)
, von
Recum and van Kooten (1995),
Brunette (1996), Curtis
and Wilkinson (1997)
, and
Folch and Toner (2000)
.
Fig. 3.2.15-2 Results of a confocal laser scanning microscope
(CLSM) surface analysis of a microgrooved substratum. CLSM
has to be considered as a noncontact technique. A three- and
two-dimensional surface representation is obtained, composed
from 256 optical Z sections. To the right of the 3D surface profile,
the size of the scanned area (30 mm
2
) and the difference in X
versus Z enlargement can be found (Scale 1:1.64).
system. AFM is frequently used as a contact method.
However, noncontact and transient contact modes of
analysis are also available. The advantage of AFM above
other contact techniques is that AFM is generally not as
destructive. Considering resolution, a limiting factor in
AFM is again the size of the used tip (
Fig. 3.2.15-3
). Still,
a significantly smaller tip diameter is used compared with
conventional contact methods such as profilometry.
Hypotheses on contact guidance
Contact guidance is the phenomenon that cells adapt
and orient to the substrate surface microtopography
(
Harrison, 1912
). Early studies on contact guidance de-
scribe the alignment of cells and focal adhesions to mi-
crogrooves with dimensions 1.65-8.96
m
m in width and
0.69
m
m in depth. This cellular behavior was suggested to
be due to the mechanical properties of the cytoskeleton
(
Dunn, 1982; Dunn and Brown, 1986
). The relative in-
flexibility of cytoskeletal components was considered to
prevent bending of cell protrusions over surface config-
urations with too large an angle.
Later studies and hypotheses focused on the re-
lationships among cell contact site, deposited ECM,
surface microtexture, and cell response. For example,
a microtextured surface was supposed to possess local
differences in surface free energy resulting in a specific
deposition pattern of the substratum bound attachment
proteins (
Brunette, 1996; Maroudas, 1972
; von Recum
and van Kooten, 1995). The spatial arrangement of the
adsorbed proteins and their conformational state were
hypothesized to be affected. In addition to wettability
properties, the specific geometric dimensions of the cell
adhesion sites were suggested to induce a cell orienta-
tional effect (
Dunn, 1982; Dunn and Brown, 1986
; Ohara
and Buck, 1979). A recent hypothesis suggests that con-
tact guidance on microtextured surfaces is a part of the
Fig. 3.2.15-3 Three-dimensional representation of an AFM
measurement of a silicon wafer provided with 10-mm-wide and
0.5-mm-deep microgrooves. The raised wall of the edge shows
a small inclination. This is a distortion due to the size and
movement of the tip over the silicon surface.
