5.1. Metal and metal oxides
Among the numerous nanoparticles used for functionalizing
polymeric materials, silver nanoparticles have been
one of the most widely used for the development of innovative
packaging materials. This is mainly due to their unique
properties such as electric, optical, catalytic, thermal stability,
and particularly antimicrobial properties [119,120].
In particular, the benefits of silver materials have been recognized
in the many applications including packaging due
to the strong antimicrobial activity of silver against a broad
spectrum of bacteria, viruses, and fungi [121].
The antimicrobial function of silver is mainly attributed
to the action of silver ions and metallic silver nanoparticles.
It has been proposed that silver ions interact with negatively
charged biomacromolecular components (disulfide
or sulfhydryl groups of enzymes) and nucleic acids, causing
structural changes and deformation in bacterial cell walls
and membranes that lead to disruption of metabolic processes
followed by cell death [122,123]. The antimicrobial
action of silver nanoparticles is due to the increase surface
area and associated increased potential for the release
of Ag+. The antimicrobial mechanism of silver nanoparticles
has also been suggested to be related to membrane
damage due to free radicals derived from the surface of the
nanoparticles [124]. Silver nanoparticles may accumulate
in the bacterial cytoplasmic membrane, causing a significant
increase in permeability and cell death