Biomedical Engineering Reference
In-Depth Information
Fig. 6.4 Copper release
from metallic copper
surfaces. The
red line
represents copper release in
a droplet which contains
buffer and
E. coli
cells; the
blue line
corresponds to
copper release in buffer
alone (Esp´rito Santo and
Grass, unpublished results)
6.3.1.1 Copper Surface Oxidation and Cell Accumulation
Both under wet and dry exposure to metallic copper surfaces, microbes, when in
contact with the surface, enhance the release (or “solubilization”) of copper ions
from the surface [
23
,
27
,
61
].
Copper Release and Accumulation Under Wet Conditions
When a droplet gets in contact to a copper surface, oxidation of the metal surface
occurs which leads to increase concentrations of dissolved copper. Moreover, when
the droplet contains bacterial cells copper concentration increases significantly over
time compared with a buffer-only-containing droplet (Fig.
6.4
). Cell inactivation
occurs due to the increase of copper ion concentrations within the droplet [
23
,
27
,
61
], and after hours of exposure, when copper concentration reaches a critical level,
cells are unable to sustain survival accumulating toxic amount of copper.
Combined data for copper accumulation and killing kinetics have clearly dem-
onstrated direct correlation between release of copper from the coupon surface and
its accumulation by the cells, with lethal consequences (Fig.
6.5
). Therefore, cells
are killed by result of deadly concentrations of copper ions and copper-induced
stress (Fig.
6.5
)[
27
,
61
].
Copper Release and Accumulation Under Dry Conditions
Under dry exposure, cells are exposed with the smallest amount of buffer possible,
which dries very quickly. Cells are exposed directly to the surface, which undergoes
oxidation and cells accumulate copper almost instantaneously and are killed within
minutes of exposure (Fig.
6.5
). At the shortest time (few seconds) of exposure,
cells accumulate large amounts of copper ions (10
9
atoms/cell) from dry metallic
copper surfaces (Fig.
6.5
)[
27
,
28
,
72
]. As a result, cells are unable to keep
up copper homeostasis and struggle to survive such high copper concentrations.
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