Biomedical Engineering Reference
In-Depth Information
Chapter 10
Surface Modification Techniques
of Polyetheretherketone, Including
Plasma Surface Treatment
Alexandra H.C. Poulsson and R. Geoff Richards
10.1 PEEKeTissue Interactions
possible interactions with cells and the environment
[12] . Fibronectin is one of the influential proteins for
cell adhesion and has been shown to strongly adsorb
to hydrophobic surfaces. However, owing to the
conformation caused by this adsorption, fibronectin
is unable to reorientate to aid cell adhesion on such
highly hydrophobic surfaces. When adsorbed onto
less hydrophobic surfaces, however, fibronectin can
orientate to aid cell adhesion [12,13] .
The interactions between proteins and biomaterials
are therefore determined by the surface properties and
can govern whether an implant will succeed or fail in
a given application. Many polymers, including
PEEK, have bulk properties such as radiolucency,
high strength, and good wear resistance, as described
throughout this topic, which are advantageous for
orthopedic biomaterials. PEEK is currently used in
medical device applications such as spine cages (to
fuse vertebrae where intervertebral disc degeneration
has occurred), patient-specific craniomaxillofacial
implants (such as skull plates where PEEK can be
formed to perfectly match the defect area), and suture
anchors (for applications such as anterior cruciate
ligament repair). Over the past 11 years, PEEK has
come into the spotlight as a replacement for metals in
medical devices due to the aforementioned bulk
mechanical properties [14 e 21] . However, an intrinsic
problem for many polymers, including PEEK, is low
surface energy. This low surface energy, as a result of
a relatively hydrophobic surface, can limit cellular
adhesion due to the orientation of cell adhesion
proteins such as fibronectin and vitronectin, as
described earlier.
In biomedical applications, the success of any
implant material is to a great extent governed by the
bulk properties of the implant material. However,
upon implantation, it is the surface structure and
surface chemistry that determine the biological
response. When a biomaterial, such as poly-
etheretherketone (PEEK), is placed in a biological
environment, among the first molecules to reach the
surface is water, which is adsorbed to the surface
within nanoseconds. The orientation of the polar
water molecules on the surface is influenced by the
surface properties of the polymer. The subsequent
protein interactions are consequently influenced by
the orientation of these initially adsorbed water
molecules [1,2] . The implant will quickly come in
contact with blood plasma, which has an array of
more than 200 proteins. These proteins can interact
with the polymer surface and these interactions are
influenced by surface chemistry, surface charge, and
surface structure, all of which also affect the surface
wettability. In turn, this adsorbed protein layer
influences cellular interactions. The surface of
a material is therefore integral in controlling the
cell e surface interactions [3 e 5] . Although protein
adsorption is not yet fully understood, it is well
established that proteins are strongly affected by
interactions with solid materials [1,6 e 11] . Surfaces
that are neither extremely hydrophobic nor hydro-
philic are thought to bind protein moderately,
allowing reorientation of the protein depending on
surrounding biological molecules,
thus increasing
In addition, proteins
such as
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