Polymeric Biomaterials - Biomaterials - page 73

as -COOH, -CH 2 OH, -CONH 2 , and -CH 2 NH 2 were produced on PE surfaces by the above corona
treatment followed by vinyl monomer grafting and substitution reactions (Kim et al., 1993; Lee et al.,
1994a,b). We have also prepared chargeable functional groups (Lee et al., 1997c,d, 1998), comb-like
polyethyleneoxide (PEO) (Jeong et al., 1996; Lee et al., 1997a), and phospholipid polymer chemogradi-
ent surfaces (Iwasaki et al., 1997) by the corona discharge treatment, followed by graft copolymerization
with subsequent substitution reaction of functional vinyl monomers such as acrylic acid, sodium p -sul-
fonic styrene, and N,N -dimethyl aminopropyl acrylamide, poly(ethyleneglycol) mono-methacrylate,
and ω-methacryloyloxyalkyl phosphorylcholine, respectively.
The water contact angles of the corona-treated PE surfaces gradually decrease along the sample length
with increasing corona power (from about 95° to about 45°) as shown in Figure 3.7. The decrease in
contact angles, that is, the increase in wettability along the sample length was due to the oxygen-based
polar functionalities incorporated on the surface by the corona treatment. It was also confirmed by
Fourier transform infrared spectroscopy in the attenuated total reflectance mode and electron spectros-
copy for chemical analysis (ESCA).
In order to investigate the interaction of different types of cells in terms of the surface hydrophilicity/
hydrophobicity of polymeric materials, Chinese hamster ovaries (CHO), fibroblasts, and bovine aortic
EC were cultured for 1 and 2 days on the PE wettability chemogradient surfaces. The maximum adhe-
sion and growth of the cells appeared around a water contact angle of 50-55° as shown in Figure 3.8.
The observation of scanning electron microscopy (SEM) also verified that the cells are more adhered,
spread, and grown onto the sections with moderate hydrophilicity as shown in Figure 3.9.
To determine the cell proliferation rates, the migration of fibroblasts on PE wettability chemogradient
surfaces was observed (Khang et al., 1999b). After the change of culture media at 24 h, cell growth mor-
phology was recorded for 1 or 2 h intervals at the position of 0.5, 1.5, 2.5, and 4.5 cm for the counting of
grown cells and the observation of cell morphology with a video tape recorder. The proliferation rates of
fibroblast cells were calculated from the slopes of Figure 3.10 as given in Table 3.8. The proliferation rates
on the PE surfaces with wettability chemogradient showed that as the surface wettability increased, it
increased and then decreased. The maximum proliferation rate of the cells as 1111 cells/h cm 2 appeared
at around the position 2.5 cm.

100

80

60

40

0 1 2 3 4 5

Distance from untreated end (cm)

FIGURE 3.7 Changes in water contact angle of corona-treated PE surface along the sample length. Sample

numbers, n = 3.