Bacterial Interactions with Polyaryletheretherketone - PEEK Biomaterials - page 92

This chapter aims to provide a brief overview of
the mechanisms behind bacterial adhesion and the
properties of biomaterials that influence this process.
Particular focus is on the state of the art in the
understanding of bacterial adhesion to standard
PEEK implant materials, both machined and injec-
tion molded. In addition, we describe the effect
of oxygen plasma treatment on bacterial adhesion.
Oxygen plasma treatment is known to increase
surface energy and alter topography, greatly
impacting upon osteoblast adhesion and behavior
[23] . This is expected to improve tissue integration to
PEEK implants in the body. However, it is important
to understand what, if any, effect this modification
has on bacterial adhesion. Finally, we also describe
the incorporation of antimicrobial agents into PEEK,
specifically silver, illustrating the versatility in
strategies available to impact bacterial adhesion and
impart

normally cause any harm [24,25] . These bacteria
come in many different shapes and sizes: bacilli
(rods), cocci (spheres), and spirals, typically between
0.5 and 5

m [26] .
In the context of biomaterial-associated infections,
the causative agents are often opportunistic patho-
gens that can be found associated with host without
causing disease. Typical biomaterial infecting
organisms include Staphylococcus aureus, Staphy-
lococcus epidermidis, Pseudomonas aeruginosa, and
Escherichia coli ( Fig. 8.2 ) [12,27,28] . These organ-
isms can be found on the skin, in the nasal cavity, or
in the gut of healthy humans. However, when the
immune system is compromised by the presence of
a traumatic injury and/or implanted biomaterial,
these once harmless organisms may cause infection,
leading to significant patient morbidity and possibly
mortality.
At the most fundamental level, bacteria can
generally be divided into two broad categories by cell
wall structure: Gram positive and Gram negative.
Gram-positive bacteria have a thick peptidoglycan
layer coating the cell membrane and include clini-
cally important organisms such as S. aureus,
S. epidermidis, and Streptococcus mutans [29] .
Gram-negative bacteria have an outer layer of lipo-
polysaccharide and a thin layer of peptidoglycan
encapsulating the cellular membrane. Important
Gram-negative bacteria include E. coli, P. aerugi-
nosa, and Salmonella [29] . Because the cell wall
interfaces the bacterium with the environment, cell
wall structure is an important distinction, both for
bacterial adhesion and infection remediation. For
example, some common antibiotics are Gram
specific and target the cell wall; therefore, the Gram
character of the infecting agent is generally deter-
mined before a specific treatment is applied.

m

antimicrobial properties onto a single

biomaterial.

8.2 Bacterial Adhesion to
Biomaterials

8.2.1 Bacteria: The Agents of
Infection
To understand bacterial interactions with PEEK, it
is important to understand the substrate (PEEK), the
host (the patient), and the bacteria involved. As
a brief introduction for nonbiologists, bacteria are
ubiquitous, prokaryotic, unicellular microorganisms
generally lacking membrane-bound organelles.
Bacteria demonstrate a broad diversity both between
and within species. The human body alone is host to
more than 10 14 bacteria at any one time, which do not

Figure 8.2 Some commonly isolated bacteria from biomaterial-associated infections. (1A) staphylococcus aureus ,
(1B) staphylococcus epidermidis , and (1C) pseudomonas , aeruginosa .