Classes of materials used in medicine - Biomedical Engineering Desk Reference - page 311

Thousands of atoms
may move

Sputtered
atoms
from
substrate

Ti +
50 KeV

Vacancies
created

Reflected
primary ions

Heating in
surface region

Ti
distribution
with depth

Fig. 3.2.14-5 Some considerations for the ion implantation process.

properties (Picraux and Pope, 1984; Colligon, 1986;
Sioshansi, 1987; Nastasi etal., 1996).
Specific examples of biomaterials that have been
surface altered by ion implantation processes are plenti-
ful. Iridium was ion implanted in a Ti-6Al-4V alloy to
improve corrosion resistance (Buchanan et al., 1990).
Nitrogen implanted into titanium greatly reduces wear
(Sioshansi, 1987). The ion implantation of boron and
carbon into type 316L stainless steel improves the high
cycle fatigue life of these alloys (Sioshansi, 1987). Silver
ions implanted into polystyrene permit cell attachment
(Tsuji et al. , 1998).

multilayer structures can be created. Some compounds
that form organized LB layers are shown in Fig. 3.2.14-7 .
The advantages of films deposited on surfaces by this
method are their high degree of order and uniformity.
Also, since a wide range of chemical structures can form
LB films, there are many options for incorporating new
chemistries at surfaces. The stability of LB films can be
improved by cross-linking or internally polymerizing the
molecules after film formation, often through double
bonds in the alkyl portion of the chains (Meller et al.,
1989). A number of research groups have investigated LB
films for biomedical applications (Hayward and Chap-
man, 1984; Bird et al. , 1989; Cho et al. , 1990; Heens
et al. , 1991). A unique cross between silane thin films and
LB layers has been developed for biomedical surface
modification (Takahara et al. , 2000). Many general re-
views on these surface structures are available (Knobler,
1990; Ulman, 1991).

LB deposition

The (LB) deposition method overcoats a surface with
one or more highly ordered layers of surfactant mole-
cules. Each of the molecules that assemble into this layer
contains a polar ''head'' group and a nonpolar ''tail'' group.
The deposition of an LB film using an LB trough is il-
lustrated schematically in Fig. 3.2.14-6 . By withdrawing
the vertical plate through the air-water interface, and
then pushing the plate down through the interface,
keeping the surface film at the air-water interface com-
pressed at all times (as illustrated in Fig. 3.2.14-6 ),

SAMs

SAMs are surface films that spontaneously form as
highly ordered structures (two-dimensional crystals) on
specific substrates (Maoz et al. , 1988; Ulman, 1990,
1991; Whitesides et al. , 1991; Knoll, 1996). In some