Biomedical Engineering Reference
In-Depth Information
Ag
nanoprisms
100 nm
Ag
spheres
100 nm
Ag
spheres
50 nm
Ag
spheres
100 nm
Ag
spheres
80 nm
Ag
spheres
40 nm
−
200 nm (the same for all the images)
FIGURE 9.2
Influence of size on the light scattering of silver nanoparticles
[5]
.
9.2
Nanoparticles X “BUGS”
9.2.1
Microbial biofilms and tolerance
Microbial biofilms are communities of microorganisms attached to a living or inert surface in an
aqueous environment and surrounded in a matrix of extracellular polymeric substances (EPS)
[7]
.
The EPS synthesized by microbial cells consist of polysaccharides, proteins, glycoproteins, glyco-
lipids and, in some cases, extracellular DNA. These substances form a network that influence the
porosity, density, water content, charge, sorption, hydrophobicity, and mechanical stability of bio-
films. In addition, the extracellular matrix provides nutrients for biofilm cells through interaction
with the environment
[8]
.
Oral biofilms (
Figure 9.3
) are polymicrobial and formed by more than 700 different species of
microorganisms, and their composition may vary according to different substrates (soft shedding
tissues and hard nonshedding surfaces) within the oral cavity
[7,9]
. In healthy oral environment,
there is a balance between the biofilm cells and human host
[9]
; however, the accumulation of oral
bacteria and yeast biofilms can lead to the development of diseases such as caries, periodontitis,
candidiasis (e.g., denture stomatitis), peri-implantitis, and endodontic infections
[10]
. Biofilm cells
are different from their planktonic counterparts, given that biofilms exhibit increased tolerance/
resistance to antimicrobial agents and to the host immune response. Thus, the control of oral bio-
films is crucial to prevent disease and preserve the homeostasis in the oral cavity.
However, biofilms are known to be more tolerant to antimicrobials than planktonic cells.
Although over the years the traditional minimal inhibitory concentration (MIC) and minimal bacte-
ricidal concentration (MBC) have been used to determine antimicrobial doses in vitro, they cannot
be used to correctly predict the doses of antimicrobials needed to control biofilm infections
[11]
.
