Biomedical Engineering Reference
In-Depth Information
Cu(I) cations towards cells. During this process, killing efficiency depends on the
amount of copper that has been released and accumulated by cells.
6.3.2.4 Osmotic Stress
Cells that are applied directly onto the surface without a buffer intermediate (dry
method) suffer osmotic stress. Upon exposure to dry surfaces (copper and
non-copper containing surfaces), survival decreases due to the additional stress of
adaptation to a new environment. Osmotic protectants, such as sucrose, are able to
ease the adaptation to the surfaces and increase the survival counts at the beginning
of exposure. Nevertheless, protection is not permanent; cells will eventually suc-
cumb to metallic copper toxicity (Fig. 6.8 ).
6.3.2.5 Reactive Oxygen Species
Upon exposure cells provoke surface oxidation with subsequent copper release by both
wet and dry methods, and this causes the production of ROS [ 27 , 72 , 86 ], as was
discussed in the previous section “Ionic copper toxicity”. ROS formed by surface
oxidation and copper release are very harmful to cells, therefore introducing ROS
quenchers in the experiment increases survival on metallic copper. Upon both wet and
dry exposure, simultaneous events, where catalase catalyzes the decomposition of
hydrogen peroxide (H 2 O 2 ); superoxide dismutase catalyzes superoxide (O 2 )
dismutation; and finally, mannitol acts as hydroxyl radical scavenger, are capable of
effectively protecting the cells and prolonging their survival (Fig. 6.8 )[ 27 , 72 , 86 ].
Ultimately, due to the surface oxidation, ROS are produced continuously, thus deplet-
ing the protective effect and eventually cells succumb to metallic copper toxicity.
6.3.2.6 Cellular Physiology
Intrinsic physiological characteristics and structures of cells are able to affect
survival on metallic copper surfaces. Here, we will focus only on the best
studied ones.
Cell Wall Structure
Prokaryotes can be divided into two groups based on their cell wall organization:
Gram-positive and Gram-negative bacteria. Gram-positive bacteria have a thicker
peptidoglycan layer and a cytoplasmic membrane. Instead, Gram-negative
bacteria have two membranes, the outer and the cytoplasmic membrane, and a
thinner peptidoglycan layer in between the membranes. In general, Gram-positive
bacteria are able to survive longer on metallic copper surfaces than
Gram-negative bacteria with both methods (wet and dry) [ 23 , 26 , 28 , 61 ,
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