Biomedical Engineering Reference
In-Depth Information
metals chemistry, and powder metallurgy process for the fabrication
of titanium (Ni-free stainless steel)-ceramic nanocomposites with
a unique microstructure were developed. Those processes permit
the control of microstructural properties such as the size of pore
openings, surfaces properties, and the nature of the base metal/
alloy. A new type of bulk three-dimensional porous Ti (Ni-free
stainless steel)-based nanocomposite biomaterials with desired
size of porous and three-dimensional capillary-porous coatings on
these nanobiocomposites was developed. Materials with nanoscale
grains would offer new structural and functional properties for
innovative products in medical/dental applications.
Various methodologies are being used in an effort to improve
the interfacial properties between the biological tissues and the
existing implants, e.g., Ti and Ti-based alloy. The electrochemical
technique, a simpler and faster method, can be used as a potential
alternative for producing porous Ti-based metals for medical
implants. Good corrosion resistance of the titanium is provided by
the passive titanium oxide ilm on the surface. This layer is important
for the good biocompatibility. The native oxide has thickness of a
few nanometers. In the case of anodic oxidation, the oxide thickness
can be multiplied up to the micrometer range. The structure
and thickness of the grown oxide depend on the electrochemical
etching conditions, for example: current density, voltage, electrolyte
composition. In the electrochemical etching of titanium, electrolytes
containing H
3
PO
4
, CH
3
COOH, and H
2
SO
4
are used. In Ti anodization,
the dissolution is enhanced by HF- or NH
4
F-containing electrolytes,
which results in pore or nanotube formation. The current density
in this case is much higher than in the electrolyte without HF or
NH
4
F [22]. Fluoride ions form soluble [TiF
6
]
2-
complexes resulting
in the dissolution of the titanium oxides. In this way, the dissolution
process limits the thickness of the porous layer.
Porous implants layer has lower density than respective bulk,
and good mechanical strength is provided by bulk substrate. Hence,
the latter is attractive with respect to bulk titanium alloys. The
porous layer on the Ti substrate is necessary for osseointegration
with bones, which is not normally provided by the native oxide.
On the other hand, Ti and its alloys possess favorable properties,
such as relatively low modulus, low density, and high strength.
Apart from that, these alloys are generally regarded to have good
biocompatibility and high corrosion resistance but cannot directly
