Biomedical Engineering Reference
In-Depth Information
electron correlation effects, and spin dynamics
[61,62]
. Copper oxide is relatively cheap, easily
mixed with polarized liquids (i.e., water) and polymers, and relatively stable in terms of both chem-
ical and physical properties. Highly ionic nanoparticulate metal oxides, such as CuO, may be par-
ticularly valuable antimicrobial agents as they can be prepared with extremely high surface areas
and unusual crystal morphologies
[59]
.
Copper oxide (CuO) nanoparticles have been characterized, both physically and chemically,
and investigated with respect to potential antimicrobial applications
[40]
. It was found that
nanoscaled CuO, as generated by thermal plasma technology, demonstrated particle sizes in the
range 20
95 nm with a mean surface area of 15.7 m
2
/g (
Figure 10.1D
). CuO nanoparticles in
suspension showed activity against a range of bacterial pathogens, including MRSA and E. coli,
with MBCs ranging from 0.1 to 5.0 mg/mL. As with silver, studies of CuO nanoparticles incor-
porated into polymers suggest that the release of ions may be required for optimum killing
[40]
.
Incorporation of nano-CuO into porous elastomeric polyurethane films has demonstrated poten-
tial for a number of applications. Studies have shown this approach to be effective against
MRSA within 4 h of contact
[63]
.
Cu
2
O (copper (I) oxide; cuprous oxide) is a red powder and can also be produced as nanoparticles.
Similar activity to CuO (copper(II) oxide; cupric oxide) has been shown against a range of species and
strains
[40]
.
10.3.2.2
Zinc oxide (ZnO)
As in the case of other nanoparticulate metals and metal oxides, the antimicrobial mechanisms of
zinc are not completely understood. Nano-zinc oxide has received increasing attention, not only
because it is stable under harsh processing conditions but also because it is generally regarded as
safe and biocompatible
[59]
. Studies have shown that some nanoparticulate metal oxides, such as
ZnO, have a degree of selective toxicity to bacteria with a minimal effect on human cells
[64,65,66]
. The proposed mechanisms of antibacterial activity include induction of ROS
[67,68]
and damage to the cell membrane with subsequent interaction of the nanoparticle with the intracel-
lular contents
[64]
.
Liu et al.
[69]
investigated the antimicrobial properties of ZnO nanoparticles against E. coli
strain O157:H7 (verocytotoxin-producing). This strain was significantly inhibited as shown using
scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses to
assess the morphological changes of bacterial cells. Leakage of intracellular contents and a
degree of membrane disorganization were observed. Using Raman spectroscopy, the intensities
of lipid and protein bands were shown to increase after exposure to ZnO nanoparticles, whereas
no significant change to nucleic acid was indicated. In comparison to silver nanoparticles
(0.1 mg/mL), a higher concentration of zinc oxide (particle size: approximately 15
20 nm; sur-
face area: 47 m
2
/g) is required to have growth inhibitory (0.5
2.5 mg/mL) and killing effects
(
2.5 mg/mL) against a range of pathogens including E. coli and MRSA (K. Memarzadeh and
R.P. Allaker, unpublished observations). While with those organisms implicated in oral infec-
tions, including A. actinomycetemcomitans, P. gingivalis, Prev. intermedia and F. nucleatum,
greater sensitivity was demonstrated under anaerobic conditions, with growth inhibitory and kill-
ing concentrations of 0.25
2.5 and 0.25
2.5 mg/mL, respectively
[41]
.
.
