Biomedical Engineering Reference
In-Depth Information
bacteria were more sensitive to QPEI compared with the Gram-negative strains. This can be ascribed
to the substantial dissimilarity in the cell wall structure. In the Gram-negative bacteria such as
P. aeruginosa
and
E. coli
, the presumed antimicrobial mechanism involves displacement of the diva-
lent cations that hold together the negatively charged surface of the lipopolysaccharide network,
resulting in outer membrane disruption
[50]
. Furthermore, damage to the outer membrane perme-
ability barrier may cause further penetration of the cationic groups into the inner membrane, caus-
ing leakage. Alternatively, Gram-positive bacteria such as
S. aureus
,
E. faecalis
, and
S. epidermidis
have a less complicated cell wall structure consisting only of a rigid peptidoglycan layer. This layer,
although thick, has numerous pores, which allow different molecules to readily penetrate the cell wall
and access the cytoplasmic membrane. Although it is not known how the initial damage to the outer
and/or cytoplasmic membrane ultimately kills the bacteria, these nanoparticles presumably actively
participate by inducing autolysis.
However, biocompatibility of the nanoparticles should also be considered. Incorporation of the
QPEI nanoparticles at various concentrations showed no change in cell viability or of specific altera-
tions in cell activity when compared to the base restorative composite materials, thus indicating simi-
lar
in vitro
biocompatibility properties
[48]
. Moreover,
in vivo
toxicity tests assessed on Wistar rats by
the implantation of modified composite specimens revealed no inflammatory response after 1 week
of the implantation of restorative composite resin that was embedded with up to 2% w/w QPEI
[47]
.
Furthermore, the release of QPEI from the restorative composites was also studied using various bio-
logical and chemical methods. In these tests, no residual particles or polymers were detected in the
eluted supernatants; bacterial growth was similar to the growth that was obtained from the eluted
supernatants of the base restorative composites. Consequently, it may be deduced that the bioactivity
of restorative composites incorporating QPEI nanoparticles is not through the release of compounds
to the medium and that the activity is associated with surface contact.
3.5
CONCLUSIONS
Incorporation of QPEI nanoparticles in a resin composite has a long-lasing antimicrobial effect
against a wide range of bacteria with no apparent negative effect on biocompatibility.
QPEI nanoparticles were found to have a strong bactericidal activity against
S. mutans
and a
wide variety of microorganisms rapidly killing bacterial cells when incorporated at small concentra-
tions into restorative composites. QPEI nanoparticles have a potential to be incorporated into den-
tal resin-based restorative materials to provide bactericidal activity without causing adverse effect on
physiologic properties or on biocompatibility. Further
in vivo
tests are needed to clarify the clinical
significance of the addition of QPEI nanoparticles into restorative composites.
In conclusion, QPEI nanoparticles are suitable candidates as additives for the restorative compos-
ite materials possessing antibacterial activity.
References
[1] K.K. Skjorland, Plaque accumulation on different dental filling materials, Scand. J. Dent. Res. 81 (7) (1973) 538.
[2] R.T. Weitman, W.B. Eames, Plaque accumulation on composite surfaces after various finishing procedures,
J. Am. Dent. Assoc. 91 (1) (1975) 101.
