Page 46 - Handbook of Adhesion Promoters

2.12 Microbiological and biological adhesion 39

78
and molecules with antimicrobial properties. The biofilm formation accounts for most
hospital-acquired infections and presents a significant risk to the world’s population. 78
Prior to adherence, bacteria must make physical contact with the surface, therefore, motil-
78
ity plays an essential role. Microorganisms can move around by Brownian motion, fla-
gellar motility (swimming, swarming, and tumbling), and non-flagellar motility
78
(twitching, gliding, or sliding motility). Bacteria utilize macromolecular complexes
known as pili that are anchored to the cell surface for adherence to host cells and abiotic
78
surfaces. Bacteria can also form capsules from polysaccharides which can adhere to the
78
surfaces. Once primary contact with a surface is made, the initial interaction can be tran-
sient and reversible either due to weak interactions of bacteria with the surface that result
from the hydrodynamics of the surrounding environment, the presence of a strong chemot-
actic signal away from the surface, or simply the lack of adhesive components that are
78
compatible with the surface. The biofilm is produced by secretion of extracellular matrix
78
which provides external protection to the microorganisms residing in the biofilm. As the
biofilm matures, bacteria from within the community can disperse from the biomass into
78
the surrounding environment and cause secondary infections.
Conventional physicochemical approaches based on Lifshitz-van der Waals, electro-
79
static, and acid–base interactions are important models of bacterial adhesion. At the
same time, they have a limited capacity to provide a complete understanding of the com-
79
plex adhesion process of real bacterial cells. The bacterial adhesion has been frequently
described by the DLVO theory originally developed for the interaction of colloidal parti-
79
cles (bacteria have the sizes similar to colloids − 0.5-2 μm). The interaction between a
surface and a particle is the summation of their van der Waals (major component) and
79
Coulomb interactions. This approach was frequently modified to include electric double
79
layer interaction, acid-base interaction, electrophoretic mobility, and zeta-potential.
Bacterial adhesion on dental implants may cause peri-implant (peri-implant mucosi-
82
tis and peri-implantitis). The peri-implantitis may cause the bone resorption and lead to
82
the loss of the implant. Many factors
82
affect potential bacterial adhesion. The
surface of implant plays an essential role,
causing vulnerability because of surface
roughness of implant, its surface free
energy (most microorganisms, such as
strains of Streptococcus mutans, S. sanguis
and S. salivarius have high surface free
energy − lower retention on hydrophobic
surface because of lower surface free
energy and excellent adhesion to hydro-
philic surfaces with high surface free
Figure 2.44. Biological reaction between the titanium energy), surface chemistry (titanium oxides
surface (negatively-charged), adsorbed protein on the surface of implant can hydrolyze
(positively-charged) and the cell (negatively-charged), and produce electrically charged groups
showing the linkages for cell interaction. [Adapted, by
permission, from Han, A; Tsoi, JKH; Rodrigues, FP; which can enhance biological activity and
Leprince, JG; Palin, WM; Int. J. Adh. Adh., 69, 58-71, attraction, see Figure 2.44), and titanium
2016.]