Biomedical Engineering Reference
In-Depth Information
(a)
(b)
1 µm
1 µm
FIGURE 5.4
SEM images of SBF-soaked (a) β-TCP and (b) HA.
5.3.3 Biomineralization of Phosphate-Based Bioceramics
Phosphate-based bioceramics, such as the calcium phosphate family, are one
of the famous materials in biomedical application. Typically, calcium and
phosphate ions are always involved in a bone mineralization. Supersaturated
calcium and phosphate ions are induced by collagen to form from ACP to OCP
to CDHA. The calcium phosphate family itself is biomineral. Furthermore,
they can still induce apatite precipitated on their surfaces. Compared to the
silicate-based bioceramics, the precipitation rate is slow. It is a dissolution
and reprecipitation process. The release of calcium and phosphate ions from
the surfaces will determine the mineralization rate. That means not only
the phase composition but also surface area and preparation methods will
influence the deposition. The final deposition is not the original phase, but
a bonelike apatite that is calcium deficient, multi-ion substituted, and nano-
sized (see Figure 5.4). Therefore, a completely crystalized and stoichiometric
hydroxyapatite is not a good material that can induce new mineral deposit-
ing on its surface if there is not any surface functionalization. A-W glass-
ceramic is a biphase ceramic containing apatite and calcium silicate. The
mechanism of apatite deposition on A-W surface is similar to that on bioac-
tive glasses (Kokubo et al. 1992). However, the silica gel layer has not been
observed on its surface after apatite forms because there is not a continuous
calcium silicate phase along the surface (Ohtsuki et al. 1995).
5.4 In Vitro and In Vivo Reaction of Biomimetic
and Biomineralized Bioceramics
5.4.1 Clinical Background
For many years, the clinical application of bioceramics in medicine and den-
tistry has been largely limited to nonload bearing parts of the skeleton due to
 
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