Nanostructured Selenium – A Novel Biologically-Inspired Material for Antibacterial Medical Device Applications - Biomimetics: Advancing Nanobiomaterials and Tissue Engineering - page 204

feature of nanomaterials or nanoparticles is the vastly increased ratio of
surface area to volume, which allows for potentially increased interactions
between nanomaterials and biological targets, such as mammalian cells
and bacteria [28]. As a result, nanomaterials will likely exert a stronger
interaction with bacterial cells which may affect their growth and propa-
gation. Thus, various nanomaterials were developed and studied for their
potential antibacterial applications.
One of the most widely investigated antibacterial materials are silver
nanoparticles and silver-based materials [29]. Silver nanoparticles interact
with and kill bacteria through two possible mechanisms [30]. As shown in
Figure 8.3, one mechanism is that silver nanoparticles bind to the bacterial
cell wall and cell membrane and interact with thiol group compounds found
in the respiratory enzymes of bacterial cells, thus inhibiting the respiration
process [31]. Silver forms stable S-Ag bonds with thiol group compounds
or participate in catalytic oxidation reactions resulting in the formation of
disulfi de bonds (R-S-S-R). In the other mechanism, the silver nanoparticles
penetrate inside the bacterial cell and interact with DNA molecules because
of releasing reactive oxygen species (ROS) and silver ions. DNA molecules
turn into a condensed form (only when DNA molecules are in a relaxed
state, do they replicate effectively) and lose their replication ability leading
to cell death [33]. Besides silver nanoparticles, copper containing materials
[34, 35], ZnO nanoparticles [36], polymer fi lms [37] and so on have also
been studied for antibacterial purposes. But how these materials interact

H +
H + H +

H +

H +

ROS

-3

PO 4

ROS

Nano-scaled silver
Silver iron

Membrane protein

Figure 8.3 Diagram summarizing nanoscaled silver interactions with bacteria [32].
Nanoscaled silver may (1) release silver ions and generate reactive oxygen species
(ROS); (2) interact with membrane proteins affecting their correct function;
(3) accumulate in the cell membrane affecting membrane permeability; and
(4) enter into the cell where it can generate ROS, release silver ions, and affect DNA.