Fig. 5 Number of adherent bacteria about roughness[52]
(1) Nano-roughness
When the roughness is minor (Ra:0.23-6.13 nm), smooth surfaces under
static conditions are more conducive to bacterial adhesion; as the
surface roughness decreases, the more bacteria adhere to the surface[53-56]. This phenomenon is associated with
cellular metabolic activity, such as an increase in bacterial size and
an increase in EPS production on smooth surfaces[54-55]. For example, the adhesion ofStaphylococcus aureus decreases with increasing nanostructure
size. This is because the macromolecules on the bacterial cell wall can
only bind the top region of the material surface, and the top part
decreases with increasing nanostructure size [57],
as shown in Figure 6(a).
When the roughness is relatively large (Ra:6-30 nm), the rough surface
is more conducive to bacterial adhesion. The number of bacteria adhering
to the surface increases as the surface roughness increases[58-60]. For example, oral restorative materials
with greater roughness and surface energy can increase the adhesion of
S. aureus [61]. A saliva coating alters this
causal relation, and the layer may change the surface roughness[12].
(2) Submicron and micron roughness
Many researchers have reported that bacterial adhesion positively
correlates with the submicron or micron-scale roughness[62-67]. The adhesion force between bacteria and
surfaces with submicron scale roughness was enhanced as the roughness
increased until the necessary roughness was reached[68-70]. Bacteria attached to rougher surfaces
have more obvious deformation. More considerable deformation of bacteria
could increase the contact area and the adhesion force. If the roughness
of the character is so high, the bacteria on the bacterial probe could
only touch the protruding parts of the surface [63,
70], as shown in Figure 6 (b). Higher roughness didn’t further
promote the initial adhesion in static culture conditions. At the same
time, the deep valleys on the rough surface could trap bacteria and
protect them from the sheer force of the washing procedure, as shown in
Figures 6 (b) and 6 (d).
Compared with Ra, peak density (Spd) also has a
significant effect on bacterial adhesion, especially at lower roughness[73]. Siegismund et al. combined the XDLVO theory
with the surface element integration method to compare the impact of Ra
and S PD on bacterial adhesion on rough titanium surfaces[70], as shown in Figure 6. The calculation result
revealed that when the average roughness was low (Ra < 70 nm),
the interaction energy had a negative correlation with the peak density;
when the average roughness was higher (Ra > 150 nm), the
interaction energy only depended on Ra.