Biomedical Engineering Reference
In-Depth Information
(a)
(b)
500
nm
250
nm
Figure 7.11.
Scanning electron microscopy images of the short-nanotube layer formed by
anodization of titanium in 1 M H
2
SO
4
+ 0.15 wt % HF at 20 V. (a) Top-view and (b) cross-section.
Adapted from [122].
well - established surface nano - modifi cation technique for metals like titanium to
produce protective layers that possibly enhance bone growth [122].
Essentially, electrochemical approaches have been reported to form highly-
defi ned porous TiO
2
layers. Under specifi c electrochemical conditions, self-organized
TiO
2
nanotube layers can be grown on Ti simply by the anodization of Ti in dilute HF
electrolytes. With this approach, TiO
2
layers could be grown consisting of tubes with
a diameter of
500 nm. This oxide layer that forms on titani-
um implants can be manipulated chemically and there has been speculation about
whether the biological properties of the oxide surface may then be changed, and even
improved, as a result. The signifi cance of surface chemistry can be illustrated by the
varied cellular responses reported on different titanium alloys, different grades of c.p.
titanium, and different bulk metals. Chemical modifi cation of titanium surfaces by
their treatment in simulated body fl uid, covalent attachment of biological molecules,
changes in the surface ion content, and alkali treatment have all been reported to
affect cellular responses to the implant [123-125]. It is noteworthy that this approach
is successful not only for Ti, but also for other metals and for the formation of nano-
tube layers on biomedical Ti alloys such as Ti - 6Al - 4V and Ti - 6Al - 7Nb [126] . In this
light, it is important to note that to date many studies highlighting the ability of nano-
materials to increase tissue growth have been performed on nano, compared to
conventional materials of the same chemistry.
Another emerging area, still at the experimental stage, is the use of photoli-
thography to produce micro and nano-fabricated surfaces [127]. Such surfaces,
made of silicon and titanium, incorporate intentional surface chemical and topo-
graphical features in the nano- and micrometer scales and provide greater op-
portunities to control cell behavior.
The biological performance of biomedical implants strongly depends on the
fi rst interaction occurring when implant surfaces come into contact with a bio-
logical environment. Extra-cellular matrix proteins that contain the cell-binding
domain RGD have a critical role in mediating cell behavior because they regulate
gene expression by signal transduction set in motion by cell adhesion to proteins
∼
100 nm and a length of
∼
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