Biomedical Engineering Reference
In-Depth Information
Table 8.4
Descriptions of the Antimicrobial Silver Particulates that Inhibited Growth of S. aureus and E. coli
Surface
Area (m
2
/g)
Density (g/cm
3
)
Material
Type of Additive
Particle Size
Sigma Nano-Ag
Pure Ag
100 nm
10.49
5
<
BioGate HyMedic
4000
Porous Ag
7.5
m
(3.5e18
m
10.49
3e5.0
m
m)
Milliken Zr2k
10% w/w Ag loaded
1.3
m
m
0.30
7.69 (calculated)
up to 48 h. Both injection-molded and machined
surfaces were also monitored for any effect that could
potentially be caused by lower surface deposition
of silver during the injection-molding process.
However, incorporation of up to 5% w/w of bacteri-
cidal silver agents in the PEEK matrix caused no
significant reduction in adherent bacteria with both
injection-molded and machined surfaces (
Fig. 8.11
).
To ensure that the inactivity of the silver was not due
to media, the trial was repeated using brain heart
infusion (BHI) media with NaCl content increased to
1%. This sodium content was double the original
content and was based on the recommendation of the
manufacturer of the silver ceramic particles (Milli-
ken & Company, USA), that 1% NaCl can be used to
increase Ag
รพ
elution from the silver ceramic parti-
cles. After 24-h bacterial incubation trials, no
significant differences could be observed between
Ag-composites and unfilled controls. As a further
investigation, the NaCl concentration was increased
further to induce greater silver ion release from
the ceramic. Despite the potential increase in biofilm
formation previously observed to be induced by
increased NaCl concentration
[183
e
185]
, the
number of adherent bacteria was detected at
approximately the same levels independent of
different media additives. In particular, nanosilver
was hypothesized to be more effective as an antimi-
crobial than its larger particle counterparts because of
its higher surface area. In our studies, its inclusion in
the PEEKmatrix did not alter the ability of the matrix
to resist bacterial colonization. Therefore, our
conclusion was that the silver agents were no longer
effective due to the method by which the silver was
incorporated. MicroCT analysis revealed some large
aggregations of silver particles throughout both the
nanoparticle and microparticle containing PEEK, and
to a lesser extent in the silver ceramic (
Fig. 8.12
).
Therefore, it is possible that the loss of antimicrobial
activity for the silver additives may have been
linked to agglomeration of the material in the matrix.
However, it should be noted that the silver ceramic
particles were only 10% silver w/w while the other
additives were pure silver. This may reduce the
potential of observing large metallic deposits. Using
backscatter imaging on SEM to highlight elemental
differences, large silver deposits could be observed
throughout the cross-section for the nano- and porous
silver particulate-PEEK composites.
The addition of silver to a PEEK matrix is not
a simple process; however, techniques are currently
being developed to reduce particle agglomeration
and increase composite concentrations of silver
particulates at the surface to impart antimicrobial
properties to PEEK. Because of the manufacturing
conditions required, including the high temperature,
silver remains a good candidate as a PEEK-associated
Figure 8.11
Comparison of bacterial adherence on
silver composite PEEK with injection-molded surfaces.
The gray area describes the mean and standard devia-
tion of the unfilled PEEK control.
