Biomedical Engineering Reference
In-Depth Information
3.6 Chemogradient Surfaces for Cell and Protein Interaction
The behavior of the adsorption and desorption of blood proteins or adhesion and proliferation of dif-
ferent types of mammalian cells on polymeric materials depends on the surface characteristics such as
wettability, hydrophilicity/hydrophobicity ratio, bulk chemistry, surface charge and charge distribu-
tion, surface roughness, and rigidity.
Many research groups have studied the effect of the surface wettability on the interactions of biologi-
cal species with polymeric materials. Some have studied the interactions of different types of cultured
cells or blood proteins with various polymers with different wettabilities to correlate the surface wet-
tability and blood or tissue compatibility (Baier et al., 1984). One problem encountered from the study
using different kinds of polymers is that the surfaces are heterogeneous, both chemically and physically
(different surface chemistry, roughness, rigidity, crystallinity, etc.), which caused widely varying results.
Some others have studied the interactions of different types of cells or proteins with a range of methac-
rylate copolymers with different wettabilities and have the same kind of chemistry but are still physi-
cally heterogeneous (van Wachem et al., 1985). Another methodological problem is that such studies are
often tedious, laborious, and time-consuming because a large number of samples must be prepared to
characterize the complete range of the desired surface properties.
Many studies have been focused on the preparation of surfaces whose properties are changed gradu-
ally along the material length. Such chemogradient surfaces are of particular interest in basic stud-
ies of the interactions between biological species and synthetic material surfaces since the effect of a
selected property can be examined in a single experiment on one surface preparation. A chemogradi-
ent of methyl groups was formed by diffusion of dimethyldichlorosilane through xylene on flat hydro-
philic silicon dioxide surfaces (Elwing et al., 1989). The wettability chemogradient surfaces were made
to investigate hydrophilicity-induced changes of adsorbed proteins.
Recently, a method for preparing wettability chemogradients on various polymer surfaces was devel-
oped (Lee et al., 1989, 1990a; Khang et al., 1997b). The wettability chemogradients were produced via
radio frequency and plasma discharge treatment by exposing the polymer sheets continuously to the
plasma (Lee et al., 1991). The polymer surfaces oxidized gradually along the sample length with increas-
ing plasma exposure time and thus the wettability chemogradient was created. Another method for
preparing a wettability chemogradient on polymer surfaces using corona discharge treatment has been
developed as shown in Figure 3.6 (Lee et al., 1992). The wettability chemogradient was produced by
treating the polymer sheets with corona from a knife-type electrode whose power was gradually changed
along the sample length. The polymer surface gradually oxidized with the increasing power and the
wettability chemogradient was created. Chemogradient surfaces with different functional groups such
Connected to RF generator
with continuously
increased power
Dry-air
outlet
Knife-type
electrode
Polymer
sample
Dry-air
inlet
Movable sample bed
FIGURE 3.6
Schematic diagram showing corona discharge apparatus for the preparation of wettability chemo-
gradient surfaces.
