Biomedical Engineering Reference
In-Depth Information
via oriented attachment to control the reactivity of nanophase
materials in nature [19, 496]. A model of “bricks and mortar” was
suggested to explain the biological aggregation of nano-sized apatite
[497]. In this model, ACP acts as “mortar” to cement the crystallized
“bricks” of nano-sized HA. Meanwhile, biological molecules control
the construction process. By using nanodimensional spheres of
HA as the building blocks, highly ordered enamel-like and bone-
like apatites were hierarchically constructed in the presence of
glycine and glutamate, respectively. It is interesting that, during
the evolution of biological apatite, the amorphous “mortar” can be
eventually turned into the “brick” by phase-to-phase transformation
to ensure the integrity of biominerals [497].
3.7
Biomedical Applications of the
Nanodimensional and Nanocrystalline
Calcium Orthophosphates
3.7.1
Bone Repair
Due to advances in surgical practice and a fast aging of the population,
there is a permanently increasing demand for bone grafts [498].
Modern grafts should not only replace the missing bones, but also
should be intrinsically osteoinductive by acting as scaffolds for guided
bone growth. Furthermore, an ability to form a biologically active
apatite layer to bond to living bone it is an essential requirement to
modern biomaterials [499]. In addition, a good graft should provide
a framework to support new blood vessels and soft tissues in forming
a bridge to existing bones [498].
Calcium orthophosphate bioceramics of micron dimensions have
been used in dentistry, orthopedics, and surgery for over 30 years
(Chapters 1, 4, 5, 6) because of their chemical similarity to calcified
tissues of mammals and, therefore, excellent biocompatibility [123,
174-176, 226, 227]. Due to a rapid development of nanotechnology,
the potential of nanodimensional and nanocrystalline forms of
calcium orthophosphates has received a considerable attention [18]
because they produce favorable results in repair of bone defects
[500]. For example, due to an improved sinterability, an enhanced
densification, and a better bioactivity than coarser crystals, they
might be chosen as the major components of self-setting bone
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