Biomedical Engineering Reference
In-Depth Information
implantation process (Cu/N
2
PIII) can better regulate the copper release rate and improve the
long-term antibacterial properties of the PE samples. This process thus creates a buried (stored)
layer of the antimicrobial reagent with the ability to control the release of Cu by means of N
2
PIII.
The antibacterial properties of the treated PE can thus be signifi cantly enhanced particularly with
respect to the long-term effects.
Medical-grade PE was inserted into the plasma immersion ion implanter equipped with a Cu
cathodic arc plasma source. The arc was ignited using pulse duration of 300 μs, repetition rate of
30 Hz, and arc current of 1 A. The copper plasma was guided into the vacuum chamber by an elec-
tromagnetic fi eld. The Cu PIII process was conducted by applying an in-phase bias voltage of
5 kV
with a repetition rate of 30 Hz and a pulse width of 300 μs to the PE samples [36,63,197]. Another
PE sample underwent N
2
plasma implantation at the same time. The nitrogen gas
was bled into the
vicinity of the copper arc discharge plume at a fl ow rate of 10 sccm (standard cubic centimeter) with
the other processing conditions being similar to those of Cu PIII [200].
The working pressure in the
vacuum chamber was 1
-
10
-
4
Torr and the implantation time was 10 min.
Figure 19.51a shows that the implanted copper is located in the near-surface region as a result of
the low implantation energy. The amount of implanted copper is about 11% at the peak (by compar-
ing the ratio of copper to carbon), and the surface Cu concentration is about 3%, which stems from
some surface deposition during PIII. Such surface Cu concentration offers immediate and direct
killing of bacteria or inhibition of cells that are in contact with the materials surface [188,203].
Based on the metal ion antimicrobial mechanism [186,191],
Cu ions are consumed during the anti-
bacterial reactions, and so the effects of surface Cu can be short-lived. Furthermore, if the surface
Cu concentration is too high, there are side effects on cells directly in contact with the material
surface. Therefore, the sample, which has a relatively small amount of surface Cu and larger amount
of embedded Cu, has many advantages. Most importantly, the buried Cu serves as a continuous
supply of the antibacterial reagent to the surface to produce longer lasting antimicrobial effects. As
shown in the result acquired from the Cu/N
2
PIII PE sample (Figure 19.51b), the in-depth copper
profi le is not affected signifi cantly by N
2
plasma coimplantation. The nitrogen distribution is also
similar to that of copper and so both chemical and physical interactions between the implanted N
and Cu or polymer matrix in the implanted region can occur (to be discussed later in this chapter).
The cross-sectional TEM image (Figure 19.52) of the Cu PIII PE sample reveals that the implanted
Cu is segregated in the polymer matrix. In addition, no diffraction patterns can be obtained from the
-
2
×
100
100
95
95
(a)
(b )
90
90
85
85
80
80
75
Cu2p
C1s
N1s
20
15
Cu2p
C1s
15
10
10
5
5
0
0
0
4
6
8
2
0
2
4
6
8
Sputtering time (min)
Sputtering time (min)
FIGURE 19.51
Elemental depth profi les acquired by XPS from (a) Cu PIII PE and (b) Cu/N
2
PIII PE. The
argon ion-sputtering rate of 1 nm/min is approximated using that of silicon oxide under similar conditions.
(From Zhang, W., Zhang, Y.H., Ji, J.H., Yan, Q., Huang, A.P., and Chu, P.K.,
J. Biomed. Mater. Res.: Part
A
,
in press DOI.10.1002. With permission.)
