Bacterial Interactions with Polyaryletheretherketone - PEEK Biomaterials - page 95

asurface(R a ) simply describes themean height profile;
this does not take into account whether that profile is
a single large or many small surface features. Because
bacterial adhesion is affected by a critical range of
topographical features, it is therefore important to
consider an array of roughness descriptors and confirm
with another method such as scanning electron
microscopy (SEM). Tabl e 8 .3 summarizes some of the
roughness parameters available for assessing

biomaterials.
Topography is an important factor in bacterial
adhesion, for example the interaction of bacteria with
two surfaces of identical chemistry, but differing
topography can result in significantly different
densities of adherent bacteria in vitro [61] .Rough-
ening a surface both increases the available surface
area for colonization and generates turbulent fluid
flow. Therefore, increasing topography can lead to

Figure 8.4 Specific adhesion between a bacterium and
biomaterial surface proceeds via adhesins interacting
with target functionalities of a eukaryotic conditioning
film.

molecules associated with the cell wall. These adhe-
sins permit adhesion to a broad range of common
eukaryotic molecules, such as fibrinogen, fibronectin,
elastin, collagen, and von Willebrand factor [59] . The
same proteins are often associated in vivo with the
adhesion of eukaryotic cells, and it is no coincidence
that bacterial adhesins have evolved to target these
proteins commonly found in the body due to the long
evolutionary history of human pathogens.

Table 8.3 Some of the Roughness Parameters
Available for Characterizing a Surface [60]

Roughness
Parameter Abbreviation Description

Roughness
average

R a Measures the

average height
of the surface

8.3 The Role of Surface
Topography and Chemistry in
Bacterial Adhesion

Root mean
squared
roughness

R q /RMS Measures the

average
deviation of
the surface
from the mean
height

8.3.1 The Influence of Topography
on Bacterial Adhesion
To successfully characterize the topography of
a material, it is important to consider a number of
parameters. In the field of biomaterial research, pro-
filometry or atomic force microscopy (AFM) are
regularly employed to measure surface roughness.
Typically, an AFM is used to measure average surface
roughness (R a ) and generate three-dimensional repre-
sentative images of the surface of a biomaterial.
Although this method is widely used, interpretation or
prediction of bacterial adhesion from the data gener-
ated is generally difficult. The first limitation of AFM
is that the results gained are the summation of two-
dimensional scans and therefore undercuts or arches in
topography, important for bacterial adhesion, may not
be detected. Additionally, the calculation of multiple
roughness parameters is required to fully characterize
a surface. For example, the average roughness of

Skew R sq A measure of

whether the
surface is
primarily
composed of
valleys or
peaks

Kurtosis R k Describes

whether the
surface is
spiky (R k > 3),

bumpy
(R k < 3), or

random
(R k ¼ 3)