Biomedical Engineering Reference
In-Depth Information
be solved by the fabrication of HA-Ti composites. Recently the studies
on the fabrication and characterization of HA-based composites
reinforced with Ti particles have been reported [22, 23, 98]. The
signiicant toughening effect by energy-absorbing mechanism due to
the plastic deformation of ductile Ti particles at the tips of cracks was
found in both HA-20 vol%Ti composite and HA-40 vol%Ti composite
[22]. Ti-20 vol% HA composite with a relative density of 97.86% was
fabricated by a hot pressing technique. The phase constitution of
Ti-20 vol% HA composite is similar to that of HA-based composite
with Ti and HA as the predominant phases. TEM observation
shows the bonding state of Ti/HA interface is good, however, there
exists an interfacial transition zone between Ti and HA. Elastic
modulus and Vicker's hardness of Ti-20 vol% HA composite are
102.6 and 3.41 GPa respectively. In comparison with pure Ti
metal fabricated under the same conditions, the composite has a
much lower bending strength (170.1 MPa) and fracture toughness
(3.57 MPa · m
1
/
2
), which are only about 17.5 and 12% of those of pure
Ti metal, nevertheless it can meet the basic strength and toughness
demands of replacing hard tissue in heavy load-bearing applications.
Both Ti matrix in the composite and pure Ti metal fabricated by hot-
pressing process present quasi-cleavage fracture. The
in vivo
studies
indicate that Ti-20 vol% HA composite has good biocompatibility
and can integrate with bone. The osteointegration ability of the
composite is better than that of pure titanium, especially in the early
stage after the implantation, which may be due to the presence of HA
ceramic in the Ti-matrix composite.
Bioactivity of the Ti-HA composite in a simulated body luid
(SBF) was investigated [23, 98]. Main crystal phases of the as-
fabricated composite are found to be Ti
2
O, CaTiO
3
, CaO,
α
-Ti, and a
TiP-like phase. When the composite is immersed in the simulated
body luid for a certain time, a poor-crystallized, calcium-deicient,
carbonate-containing apatite ilm will form on the surface of the
composite. It can be concluded that the biocomposite, fabricated
from HA and Ti powders by powder metallurgy technique, has the
ability to induce apatite nucleation and growth on its surface from
the SBF. Among all the crystal phases in the as-fabricated composite,
Ti
2
O has the ability to induce apatite formation. Furthermore, the
dissolve of CaO phase also provides favorable conditions for the
apatite nucleation and growth.
