Biomedical Engineering Reference
In-Depth Information
it was decided to focus on the iodide form QA-PEI due to simplicity of the synthesis and further
study physical, chemical, and biological properties of the restorative composite resins incorporating
QPEI particles.
Surface chemical analysis of the restorative composites containing QPEI depicted surface modifi-
cation of higher hydrophobicity and presence of quaternary amino groups on the surface of the mod-
ified restorative composites compared to the corresponding commercial material although only one
percentage of the particles was added. In particular, the water contact angles were increased following
the addition of the QPEI nanoparticles, indicating an increase in the hydrophobicity of the material
surface
[47]
. The presence of active antibacterial components on the surface of the restorative com-
posite materials may also offer an additional explanation for the long-lasting antibacterial properties of
the materials following incorporation of QPEI. These findings add another aspect to the belief that the
effective antibacterial outcome of these components is through lethal direct contact with the bacteria.
3.4.1.3 Incorporation of PEI Nanoparticles
The combination of high antimicrobial potency of QPEI polycations together with the advantages of
nanoparticles may be used to produce improved restorative composite properties.
The polymeric particles may be physically entrapped within the matrix, chemically bound thereto,
or both. In case the particles are to be chemically bound to the polymeric host, they should have func-
tional groups that are capable of reacting with the host polymer, or with monomers thereof.
The antibacterial effect of incorporated QPEI nanoparticles in restorative composites was investi-
gated in detail by many
in vitro
tests
[45,47-49]
.
Various QPEI nanoparticles were tested for antibacterial effect in long-term studies.
N
-alkylation
was performed with a long-alkyl chain followed by
N
-methylation. Although some of the tested
nanoparticles were found to be effective in inhibition of bacterial growth, the octyl-alkylated QPEI
nanoparticles showed the most potent antibacterial properties when incorporated in a restorative com-
posite
[45]
.
The antibacterial activity of octyl-alkylated QPEI nanoparticles incorporated at 1% w/w in var-
ious restorative composite systems was further investigated. Bonding, flowable, and hybrid restor-
ative composites incorporating the nanoparticles were tested after being cured by light initiation.
Interestingly, although the nanoparticles were incorporated at a low concentration, a strong antibacte-
rial activity was evident upon contact with bacteria without leach-out of the nanoparticles or compro-
mising the mechanical properties of the restorative composites
[49]
. Furthermore, scanning electron
microscopy (SEM) of
S. mutans
revealed the presence of bacterial debris and no streptococcal chains
within 24 h of bacterial contact. Although the detailed mechanism of the antibacterial effect of these
materials has not been fully determined, it was suggested that quaternary ammonium compounds
cause lysis of the bacterial cells as was seen by the SEM.
The antibacterial spectrum was further assayed on
Staphylococcus aureus
,
Staphylococcus epi-
dermidis
,
Enterococcus faecalis
,
Pseudomonas aeruginosa
, and
E. coli
[48]
. Interestingly, 2% w/w
of the incorporated nanoparticles was sufficient to inhibit the growth of all bacterial strains tested.
Reducing the amount of the nanoparticles to 1% w/w resulted in complete inhibition of
S. aureus
and
E. faecalis
, and decreased the growth of
S. epidermidis
,
P. aeruginosa
, and
E. coli
. The bacterial sen-
sitivity in this study to the added QPEI nanoparticles was dependent on the stain of microorganism.
In some strains, low concentrations of nanoparticles resulted in complete inhibition, whereas in oth-
ers complete inhibition was obtained only at higher concentrations. It appears that the Gram-positive
