Biomedical Engineering Reference
In-Depth Information
which are released to the medium in a controlled way. in this way, they are
beginning to be used in applications related to tissue engineering.
12
On the other hand, bioceramics must be biocompatible and functional
for the required implantation time. in addition, they must not be toxic,
carcinogenic, allergic or inflammatory. In general, because of their ionic bonds
and chemical stability, ceramic materials are generally biocompatible.
In this chapter, bioceramics will be studied, divided into first, second and
third generations. The study of first generation bioceramics started in the
1960s, when the goal was to have as low a reactivity as possible. the more
representative examples of this kind of bioceramics are alumina, al
2
O
3
, and
zirconia, ZrO
2
. they are widely used as biomaterials because of their high
strength, excellent corrosion and wear resistance, stability, non-toxicity and
in vivo
biocompatibility. around the 1980s the objective changed to obtaining
favourable interactions with the living body, namely a bioactive response
or degradation. Specific compositions of calcium phosphates or sulphates,
bioactive glasses and glass-ceramics are examples of second generation
bioceramics used for bone tissue augmentation, as bone cements or for metallic
implants coating. in the last decade, bioceramics with more demanding
properties were required. the studies of third generation bioceramics are
more based in biology and follow the purpose of substituting 'replace' tissues
by 'regenerate' tissues. this category includes bioceramics based on porous
second generation bioceramics, loaded with biologically active substances,
and new advanced bioceramics like silica mesoporous materials, mesoporous
ordered glasses or organic-inorganic hybrids. table 7.1 shows important
first, second and third generation bioceramics that will be presented in this
chapter.
7.1.1 Biological ceramics: biominerals
if we look at how nature solves the task of fabricating hard tissue, we will
find first that biomineralization processes mainly use calcium and silicon
combined with carbonates, phosphates and oxides. Figure 7.4 depicts the
four most abundant inorganic phases present in different living species.
13
thus, bone is formed by biomineralization processes, natural sequences of
physical-chemical reactions that form hard tissues in vertebrates or protective
tissues in invertebrates and inferior zoological species. as a result, natural
composites are formed. in this way, materials with exceptional mechanical
properties that are impossible to obtain with pure materials are reached.
in this section, we will focus on materials that induce bone formation.
However, before dealing with the production of some ceramics in the
laboratory, we should recall that the inorganic phase of our bones is an
apatite-like phase. its structure has the special ability to accommodate several
different ions in its three sublattices. Bone apatites can be considered to be
