Biomedical Engineering Reference
In-Depth Information
Ti implant for clinical applications, by surface modiications
(electrochemical etching, or plasma treatment).
The above-mentioned basic assumptions are relatively easy
and simple to achieve and the following section is concentrated
on electrochemical ways of the Ti-based surface modiications
necessary for improving implant mechanical properties, corrosion
resistance, biocompatibility, osseointegration, and other related
surface properties. Increase of surface roughness of the hard tissue
implant promotes the implant-tissue integration.
9.2
Electrochemical Anodic Oxidation
9.2.1
Electrochemically Grown Porous TiO
2
Anodic oxidation (anodization) is an electrochemical treatment
made at potentials positive from the open-circuit-potential (ocp).
In the anodic conditions, the metallic implant is the working
electrode immersed in the special type of electrolyte. The
current low results in surface oxidation and formation of titania.
Depending on the electrochemical conditions, the oxide thickness,
its structure (anatase, rutile or amorphous), and adhesion can
vary as well as in the surface of formed pores with diameter from
nano- to micrometer range.
In the electrochemical etching of titanium, used electrolytes
often containing H
3
PO
4
, CH
3
COOH, and H
2
SO
4
[50, 59]. In the
Ti anodization, the dissolution is enhanced mostly by HF- or
NH
4
F-containing electrolytes [88]. The current density for these
electrolytes is much higher than in electrolyte without HF or NH
4
F
[88]. Unfortunately, luoride ions form soluble [TiF
6
]
2−
complexes,
results in dissolution of the titanium oxides. In this way the
dissolution process limits the thickness of the porous layer [5].
Application of electrolyte containing phosphorus (like H
3
PO
4
),
makes a possible incorporation of phosphorus into the oxide
layer. As we know, phosphorus is a basic component of the human
bone, so the increase of P-content in the surface layer can improve
the osseointegration. The growing anodic oxide layer is mostly
porous, which makes it easy to grow a tissue into the implants. For
this process, the surface should have suficient pores diameter and
