Biomedical Engineering Reference
In-Depth Information
ceramics were introduced in the following years, including hydroxyapatite
(HAp) and TZP (tetragonal zirconia polycrystals) in the 1970s.
Over the past 50 years, therefore, there has been a significant move
forward in the use of bioceramics for biomedical applications. The
development of bioceramics can be classified into three generations
(Vallet-Regi, 2010). The first generation would correspond to bioinert
bioceramics, such as alumina and zirconia, which are mostly used for inert
orthopaedic and dental implants. The second generation comprises
bioactive and bioabsorbable ceramics, such as calcium phosphates or
bioglasses. Finally, scaffolds for tissue engineering are the third generation;
these aim to drive the regeneration of living tissues. In the meantime, many
studies have demonstrated that better and unusual material properties can
be achieved by manipulating ceramic length scales in the nano range. For
that reason, during the last two decades, nanostructured materials have been
widely studied and significant steps forward have been made in their
understanding in recent years.
Nanostructured materials are defined as solid materials with at least one
characteristic structural length in the order of a few nanometres
(1 nm=10
9
m) (Gleiter, 1995). Although some authors (e.g. Meyers
et al., 2006) define an upper limit of 250 nm for considering a material as
nanometric, in general the nanometric grain size is meant to be below
100 nm (Nazarov and Mulyukov, 2002; Narayan et al., 2004; Tjong and
Chen, 2004; Liu and Webster, 2007; Kim and Estrin, 2008). Over this limit,
the terms ultrafine grained materials or submicrometric materials (100-
300 nm) are used.
This chapter discusses the advantages of using ceramic nanocomposites
for biomedical applications. A material is defined as nanocomposite when at
least one of the solid phases is in the nanometric range. First, the
improvements achieved using nanocomposites are described. The next
section focuses on inert ceramic nanocomposites for orthopaedic and dental
implants. The applications of bioactive ceramics, such as calcium
phosphates, in bone tissue engineering are then reviewed and future trends
are presented.
16.2 Why ceramic nanocomposites are used in
biomedical applications
Ceramics are broadly used in a large variety of technological applications
requiring both structural and functional properties. They have received
significant attention as candidate materials for use as structural materials
under conditions of high loading rates, high temperature, wear and chemical
etching too severe for metals. In this sense, bone-related biomedical
