Biomedical Engineering Reference
In-Depth Information
direct contact, and in some cases (i.e., hydroxyapatite)
can also play an active role in converting early formed
fibrotic tissue to bone
[11]
.
With the aim of accelerating and maximizing
direct osteointegration for PEEK medical devices,
many researchers and designers have proposed PEEK
surface functionalization. One potentially successful
strategy for reaching this target is changing the
chemical
e
physical nature of the surface by apposi-
tion of rough titanium or hydroxyapatite layers,
which are well known for their osteoconductive
properties. This chapter describes PEEK surface
osteoconductive functionalization by application of
coatings using plasma spray technology.
techniques significantly reduced the fatigue proper-
ties of the implant material
[15]
and result in clinical
problems related to implant instability
[16,17]
.
Thermal spray coatings, having many different
levels of roughness or porosity, have been found to be
much more reliable than the previous surface treat-
ments as far as fatigue strength
[15,18]
and osteoin-
tegration capability of the surface are concerned
[19,20]
. Generally speaking, thermal spray technolo-
gies
[21
e
25]
can be classified according to the type of
their main energy sources (
Fig. 9.1
); among them,
plasma spraying is the most widely used technology
for surfacing implants with highly osteointegrating
coatings. A plasma spray device consists of a power
supply, a control unit for the regulation of gas, cooling
water, a powder supply system, and a plasma-gener-
ating gun, as well as other auxiliary equipment. The
key of the system is the plasma gun, or torch, shown
schematically in
Fig. 9.2
. The plasma is created by
striking a DC discharge between a tungsten cathode
and a nozzle made of copper, which acts as anode
inside the plasma gun. The electrical arc is stabilized
into the nozzle by a gas, such as argon, helium,
nitrogen, or hydrogen, or a gas mixture. The gas
stream is heated, accelerated, and partially ionized by
the arc, thus forming a plasma jet. The term “plasma”
9.2 Coating Technology
In the past, a variety of surface modifications have
been tested to obtain three-dimensional structured
surfaces. These sponge-like structures can be
produced by bonding metal beads or grains to the
bulk material through sintering processes, by
attaching metal fibers through diffusion welding, and
by replicating a polymeric sponge with metals and
then
brazing
[12
e
14]
. Unfortunately,
these
Figure 9.1
Classification of thermal spray technologies according to energy sources, and subclassification of plasma
spraying techniques. Modified from Refs
[21,23]
.
