Biomedical Engineering Reference
In-Depth Information
especially the fracture toughness of some silicate bioceramic bulks, is obvi-
ously higher than that of conventional HAp ceramics, as shown in TableĀ 2.2.
Most silicate ceramic bulks possess a comparable bending strength and
elastic modulus with human cortical bone (50-150 MPa) (Hench 1991). SPS-
sintered silicate bioceramics, such as wollastonite and dicalcium silicate,
have significantly improved mechanical strength compared to conventional
pressureless sintered silicate ceramics (Long et al. 2006; Zhong et al. 2011).
The bending strength of SPS-sintered silicate ceramics is higher than that of
human cortical bone. The fracture toughness of SPS-sintered silicate ceramics
is comparable to that of human cortical bone (Wu and Chang, forthcoming).
It is observed that CaSiO 3 scaffolds prepared by porogen methods have
high compressive strength due to their low porosity and interconnectivity.
The compressive strength of silicate ceramic scaffolds prepared by the poly-
urethane foam templating method is mainly in the range of 0.2 to 1.4 MPa, a
relatively low mechanical strength. The compressive strength of 3D-plotted
CaSiO 3 scaffolds is 3.6 MPa. The compressive strength of 3D-printed CaSiO 3
scaffolds is around 10 times that of polyurethane-templated CaSiO 3 scaffolds
(TableĀ  2.2). It was found that the mechanical profile of 3D-printed CaSiO 3
scaffolds increased almost linearly with the deformation of materials.
Interestingly, after compressive testing, 3D-printed CaSiO 3 scaffolds partly
maintain a scaffold configuration in the center position and only the border
area collapses (Wu et al. 2012; Wu and Chang, forthcoming).
2.3 Physicochemical and Self-Setting
Properties of Silicate Ceramics
After implantation of bioactive ceramics in the human body, a series of bio-
chemical reactions occurred at the interface of the materials and host bone
whereby a layer of bonelike apatite was formed on this interface, stimulat-
ing bone regeneration (Hench 1991). A first step in this process involved the
release of Na + /C a 2+ ions from bioactive ceramics and formation of Si-OH
groups at the surface of materials. This was followed by Ca 2+ and PO 4 3- ions
being absorbed from body fluids forming an amorphous Ca-P deposition on
the surface of ceramics. With the increase of implantation time, crystallized
Ca-P (apatite) phase was formed. Finally, a matrix was produced stimulating
the formation of new bone tissue. One possible way of investigating the in
vitro bioactivity of bioceramics is by determining their ability to form an apa-
tite layer in SBF. In this section, we introduce the interface chemistry reac-
tion of ceramics with SBF solution and the apatite-formation mechanism on
silicate ceramics in SBF. It is interesting to find that some silicate bioceramics
possess distinct apatite-mineralization ability. Their apatite-mineralization
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