Biomedical Engineering Reference
In-Depth Information
very high surface-to-volume ratio of nanodimensional materials
provides a tremendous driving force for diffusion, especially at
elevated temperatures, as well as causes a self-aggregation into
larger particles. Besides, solubility of many substances increases
with particle size decreasing [111, 112]. What's more, nanophase
materials could have surface features (e.g
a higher amount of
nano-scale pores) to influence the type and amount of adsorption
of selective proteins that could enhance specific osteoblast adhesion
[113]. Finally and yet importantly, the nanodimensional and
nanocrystalline materials have different mechanical, electrical,
magnetic, and optical properties if compared to the larger grained
materials of the same chemical composition [114-117].
The nanostructured materials can take the form of powders,
dispersions, coatings or bulk materials. In general, nanostructured
materials contain a large volume fraction (greater than 50%) of defects
such as grain boundaries, interphase boundaries, and dislocations,
which strongly influence their chemical and physical properties.
The great advantages of nanostructuring were first understood
in electronic industry with the advent of thin film deposition
processes. Other application areas have followed. For example,
nanostructured bioceramics was found to improve friction and wear
problems associated with joint replacement components because it
was tougher and stronger than coarser-grained bioceramics [118].
Furthermore, nanostructuring has allowed chemical homogeneity
and structural uniformity to an extent, which was once thought to
impossible to achieve [92]. In calcium orthophosphate bioceramics,
the major target of nanostructuring is to mimic the architecture of
bones and teeth [119, 120].
.
,
3.3
Micron- and Submicron-Sized
Calcium Orthophosphates Versus the
Nanodimensional Ones
The micron-sized calcium orthophosphate-based bioceramic
powders suffer from poor sinterability, mainly due to a low
surface area (typically 2-5 m
2
/g), while the specific surface area
of nanodimensional calcium orthophosphates exceeds 100 m
2
/g
[121]. In addition, the resorption process of synthetic micron-sized
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