Biomedical Engineering Reference
In-Depth Information
treatment, the release of Cu to the surface can be regulated. Consequently, the antimicrobial ability of
the treated polymer can be prolonged signifi cantly to increase its usefulness in medicine.
19.6.2 G
RAFTING
OF
A
NTIMICROBIAL
R
EAGENTS
ON
P
OLYMERS
To obtain anti-infective properties, medical polymers are usually impregnated or compounded with
some antibacterial or antimicrobial reagents [209,210]. These technologies require large quantities
of the antimicrobial reagents, typically on the order of a few grams per square meter and the rea-
gents are not immobilized on the surface. As a result, they are gradually released when these anti-
infective polymers are embedded inside humans. They, therefore, pose great health hazards and it is
necessary to develop alternative medical polymers or antibacterial surface treatments.
One of the ways to tackle this problem is to control the physicochemical interactions between the
bacteria and medical polymer surface [211]. Surface modifi cation of medical polymers or devices is
a relatively simple and effective strategy to create a desirable surface and a number of surface modi-
fi cation techniques have been proposed to produce devices with antibacterial surfaces. Silver coat-
ings, surface-immobilized PE oxide, surface thiocyanation, and surface modifi cation by various
gas plasmas (such as oxygen and argon) have been suggested [212-217]. PIII can be used to conduct
surface modifi cation for yielding superior surface with antibacterial properties. Polyvinyl chloride
(PVC) is one of the common medical polymers [218-220]. Triclosan (2,4,4P-trichloro-2P-hydroxy-
diphenylether) and bronopol (2-bromo-2-nitropropane-1,3-diol) are two types of compounds that
exhibit immediate, persistent, broad-spectrum antimicrobial effectiveness as well as little toxicity
in clinical use. They also deliver excellent biochemical and physical performances after plasma sur-
face modifi cation [221-223]. It is very signifi cant and feasible to improve its antibacterial properties
and decrease the degree of bacteria adhesion on medical-grade PVC using PIII technology.
The PVC was inserted into the plasma immersion ion implanter [36,63]. The O
2
plasma treatment
was performed at the optimal conditions based on many trial experiments: Bias voltage
12 kV, volt-
age pulse width 20 µs, pulsing frequency 30 Hz, gas fl ow 35 sccm, RF power 1000 W, and treatment
time 30 min. Under these conditions, sample charging was not serious and no arcing was observed
during the experiments. After the initial plasma treatment, the samples were uniformly coated with
the antibacterial reagent triclosan or bronopol in 20% alcohol. After the alcohol had volatilized, the
samples were reloaded into the implanter and then underwent argon plasma ion bombardment to
ensure that antibacterial reagent combined well with the PVC surface. The processing parameters
were bias voltage
-
4 kV, RF power 1000 W, treatment time 30 min, and gas fl ow 35 sccm [224].
Again, these treatment conditions were based on trial experiments. Finally, the samples were washed
three times using 70% ethanol to scour off loose triclosan or bronopol on the surface.
The surface of most medical-grade PVC is hydrophobic. On the other hand, triclosan and bro-
nopol are hydrophilic and easily crystallized. In order to coat the PVC samples with these two
antibacterial materials, the PVC surface must be modifi ed. The PVC surface was fi rstly treated
using oxygen plasma. The contact angles of distilled water in contact with the PVC surface before
and after oxygen plasma modifi cation were about 96° and 20°, respectively. This indicates that the
O
2
PIII PVC surfaces are quite hydrophilic and the modifi ed PVC can be coated effectively with the
antibacterial reagents. The change in the surface hydrophilicity is because the C
-
-
C or C
-
H group
227].
The antibacterial properties of samples treated with an oxygen plasma, coated with triclosan or bro-
nopol, and then treated with an argon plasma are evaluated by plate-counting of
Staphylococcus
aureus
and
E. coli
, which are the most representative bacteria, and the results are shown in Table 19.9. The
antibacterial effects of the samples coated with triclosan against
S. aureus
and
E. coli
are 82.2% and
79.5%, respectively. This illustrates that after combining with the PVC surface, triclosan still possesses
antibacterial properties. This phenomenon should be interpreted from the antibacterial mechanism of
triclosan. Based on the results reported recently [221-223], triclosan acts as a nonspecifi c biocide by
affecting the membrane structure and function of the bacteria. When it reacts with bacteria, triclosan
on the surface of PVC is changed to C
-
O or C
=
O group by the oxygen plasma [36,63,225
-
