Biomedical Engineering Reference
In-Depth Information
dental applications. Consequently, ATZ and ZTA nanocomposites appear
to be adequate materials for use in the fabrication of implants and
abutments instead of the pure oxides currently in use. Moreover, the
relatively lower hardness in some of these composites (compared with
alumina) is said to be an advantage, since the final form of the implant can
be easily processed by machining. Equally, a composite with high hardness
would have a disadvantage due to the prolonged milling times needed and
high wear rates of the diamond milling CAM machines. Therefore, it is
established that ATZ and ZTA composites present an intermediate hardness
and higher fracture toughness, which is the ideal combination of mechanical
properties for specific dental applications. The use of alumina whisker
reinforced alumina-zirconia nanocomposites in dental applications has also
been investigated (Nevarez-Rascon et al., 2010). The reported hardness and
fracture values of these nanocomposites can compete with commercially
available materials for different dental applications.
In summary, while the mechanical properties of zirconia-alumina
nanocomposites are very interesting for dental implants, both oxides are
bioinert. However, with the addition of bioactive calcium phosphates such
as HAp and TCP, the biocompatibility of zirconia-alumina nanocomposites
in load-bearing applications is significantly enhanced and osseointegration
and bone regeneration are improved. Kong et al. (2005) focused their study
on a zirconia-alumina matrix composed of nanocomposite powder. HAp
was added to the nanocomposite powder and the potential of these
nanocomposites for use in load-bearing applications was verified.
Yousefpour et al. (2011) also developed hydroxyapatite-zirconia-alumina
bionanocomposites by the mechanical blending of separately synthesized
nano-scaled powders. They state that 10Ce-TZP/Al
2
O
3
/HA nanocompo-
sites with 30 vol% of HAp show the optimal composition for biological
applications.
16.4 Tissue engineering
Tissue engineering has shown tremendous promise in creating biological
alternatives for tissue repair and regeneration (Mooney and Mikos, 1999).
In a general approach, a porous scaffold serves as a temporary template for
cells seeding in vitro and for the consequent formation of new tissue (Hua
et al., 2002). The ideal scaffold should be a three-dimensional biocompatible
highly porous network (Karageorgiou and Kaplan, 2005; Rezwana et al.,
2006), with an appropriate surface for cell adhesion, proliferation and
differentiation (Cima et al., 1991). It should also allow easy invasion of
blood vessels in order to supply nutrients to the cells (Mikos et al., 1993).
They also ought to provide the necessary mechanical strength or, in other
words, to maintain proper mechanical properties until the new tissue grows
