Biomedical Engineering Reference
In-Depth Information
unwashed surfaces and after washing this was reduced
to ~2.5 atom %.
Figure 10.4
shows the incorporation
of oxygen into C1s narrow scan spectra for 600 s-
treated PEEK and untreated PEEK compared to
freshly cleaved surface of PEEK.
The narrow scan C1s spectra show that the func-
tional groups present within the envelope could be
resolved into three or four peaks: the main C
e
C/
C
e
H hydrocarbon, C
e
O alcohols/ethers, C
]
O
carbonyl/diether groups, O
e
C
]
O carboxyl/ester
groups and finally the Pi
e
Pi
)
shake-up satellite. The
freshly cleaved surface is missing the carboxyl/ester
groups, O
e
C
]
O, exemplifying how reactive
surfaces are, as the untreated PEEK does contain
carboxyl/ester groups.
The concentrations of the functional groups
changed upon exposure to the oxygen plasma; the
greatest change for the PEEK surfaces was observed
in the carboxyl/ester (O
e
C
]
O) and carbonyl/
diether (C
]
O) groups. Carboxyl/ester groups
increased from ~8.7 to 12.0 atom % after 600 s
treatment and remained at this concentration even up
to 2400 s treatment. The concentration of carbonyl/
diether groups also increased, but more gradually
from ~7.7 to 11.4 atom % after 1800 s, but then
increased to ~14.4 atom % by 2400 s treatment. The
alcohol/ether groups stayed relatively constant
throughout, increasing slightly from ~17.4 to
18.0 atom % after 900 s of treatment, but then
decreased to ~16.6 atom % after 2400 s. Finally the
Pi
e
Pi
)
shake-up satellites did not change until after
900 s of treatment, and the reduction observed was
very small; however, after 1800 s, the decrease was
just under 1.0 atom %. This would indicate that
minimal ring opening occurred after 900 s of treat-
ment, but after 1800 s, plasma treatment ring opening
was more substantial, indicating that oxygen was
being incorporated into the backbone of the polymer.
Having confirmed that the surface chemistry of the
PEEK surfaces had been modified by the oxygen
plasma, the next stage was then to investigate the
stability of the surface. Plasma surface modification
has often been reported to age or be unstable, where
the newly modified surface is thermodynamically
driven to reorientate the polar functional groups
created into the surface
[32,83,98,105]
. One of the
major aspects of this study was therefore to identify
a means to stabilize the modified surface. By washing
the surface immediately after the plasma treatment,
the surface was found to be stabilized, which was
confirmed by both contact angle and XPS
[107]
.Over
Figure 10.4
Narrow scan spectra of the carbon 1s
peak envelope for
fresh exposed PEEK surface,
untreated PEEK
, and treated PEEK, which had been
exposed to oxygen plasma for 600 s, showing the
residual functional groups resolved after the surface
had been washed and sterilized.
