Classes of materials used in medicine - Biomedical Engineering Desk Reference - page 306

Zone 1 Zone 2 Zone 3

Samples
to be
coated

Reactor
geometry

Capacitor plate Capacitor plate

Flow rate

Pressure

Energy density

Gas
Outlet

Gas
inlet

Temperature

Pressure
regulation
valve

Matching
network

Contamination and
backstreaming
trap

Gas
mixing
and flow
control

Gas
1

Gas
2

Gas
3

Pressure
gauge

RF generator

Vacuum
pump

Power
continuous or pulsed

Fig. 3.2.14-2 A diagram of a capacitively coupled RF plasma reactor. Important experimental variables are indicated in bold typeface.
Zone 1 shows gas storage and mixing. Zone 2 shows components that power the reactor. Zone 3 highlights components of the vacuum
system.

a hydrophobic monomer in the grafting mixture (Ratner
and Hoffman, 1980; Ratner et al., 1979).
Photoinitiated grafting (usually with visible or UV
light) represents a unique subcategory of surface modi-
fications in which there is growing interest. There are
many approaches to effect this photoinitiated covalent
coupling. For example, a phenyl azide group can be
converted to a highly reactive nitrene upon UV exposure.
This nitrene will quickly react with many organic groups.
If a synthetic polymer is prepared with phenyl azide side
groups and this polymer is exposed simultaneously to UV
light and a substrate polymer or polymeric medical
device, the polymer containing the phenyl azide side
groups will be immobilized to the substrate (Matsuda
and Inoue, 1990). Another method involves the coupling
of a benzophenone molecule to a hydrophilic polymer
(Dunkirk et al. , 1991). In the presence of UV irradiation,
the benzophenone is excited to a reactive triplet state
that can abstract a hydrogen leading to radical cross-
linking.
Radiation, electron beam, and photografting have
frequently been used to bond hydrogels to the surfaces of
hydrophobic polymers (Matsuda and Inoue, 1990;
Dunkirk et al. , 1991). Electron beam grafting of
N -isopropyl acrylamide to polystyrene has been used to

create a new class of temperature-dependent surfaces for
cell growth (Kwon et al. , 2000) (also see Section 3.2.6).
The protein interactions (Horbett and Hoffman, 1975),
cell interactions (Ratner et al. , 1975; Matsuda and Inoue,
1990), blood compatibility (Chapiro, 1983; Hoffman
et al. , 1983), and tissue reactions (Greer et al. , 1979) of
hydrogel graft surfaces have been investigated.

RFGD plasma deposition and other
plasma gas processes

RFGD plasmas, as used for surface modification, are low-
pressure ionized gas environments typically at ambient
(or slightly above ambient) temperature. They are also
referred to as glow discharge or gas discharge depositions
or treatments. Plasmas can be used to modify existing
surfaces by ablation or etching reactions or, in a de-
position mode, to overcoat surfaces ( Fig. 3.2.14-1 ).
Good review articles on plasma deposition and its ap-
plication to biomaterials are available (Yasuda and
Gazicki, 1982; Hoffman, 1988; Ratner et al. , 1990; Chu
et al., 2002; Kitching et al. , 2003). Some biomedical
applications of plasma-modified biomaterials are listed in
Table 3.2.14-3 .