Biomedical Engineering Reference
In-Depth Information
9.2.3 Ti-Based Nanocomposites
Ti-ceramic nanocomposites are a new class of biomaterials
with interesting properties for future medical applications [38, 61].
The bionanocomposites are based on Ti-ceramic phase mixture with
ultra ine grains. The nanograins essentially improve mechanical
properties, whereas the ceramic phase (hydroxyapatite or
bioglass, for example) improves osseointegration. For that reason,
the bionanocomposites are promising in implant applications.
The nanocomposites can be electrochemically etched, like
conventional micro-Ti-based biomaterials. During the surface
modiication by the electrochemical etching, a large volume of
the grain boundaries improve penetration of the nanograins by
the electrolyte, and consequently enhances the pores formation.
Jakubowicz
et al
. applied the electrochemical anodic oxidation
process for the surface modiication of the mechanically alloyed
bionanocomposites [31].
Ti-hydroxyapatite (HA) and Ti-glass (45S5 Bioglass) bio-
nanocomposites were prepared using mechanical alloying
(MA) [31]. After milling the nanocomposite, powder mixture
was uniaxially pressed at pressure of 500 MPa and sintered
at 1150°C for 2 h. After the process, the grain size reaches a value
of about 20-40 nm. The prepared Ti-HA and Ti-glass nanocom-
posites were electrochemically etched at 10 V vs. ocp in 1M H
3
PO
4
+ 2-10% HF electrolyte [31]. Preparation of Ti-HA and Ti-glass
nanocomposites by MA + powder metallurgical process, results
in porous compacts (Fig. 9.59a) with density of about 90% of the
theoretical value. For the implant application it is a very attrac-
tive property, but not suficient for the surface tissue bonding. On
the other hand, the mechanical strength is probably deteriorated
by relatively poor density. To improve the surface porosity neces-
sary for the human tissue growth and strong ixation, the compacts
were electrochemically etched in 1M H
3
PO
4
+ 2% HF electrolyte at
10 V vs. ocp for 15, 30, and 60 min [31]. The etching of Ti-HA for
15 min results in fast Ti atoms removal (Fig. 9.59b). In the nano-
composites, the large surface of the grain boundaries facilitates
the atoms removal and hence the HF concentration can be lower
for etching nanocomposites, than bulk microcrystalline Ti [28].
The surface after etching is rough with sponge pores with diameter
of 1-6 μm and signiicant depth, and deeper than in the case of pure
