Biomedical Engineering Reference
In-Depth Information
cements. These biocomposites were implanted into cranial defects
of rats and a content of ~30 wt.% of the microparticles was found to
give the best results [567], while the addition of a growth factor to the
biocomposites significantly increased bone contact at 2 weeks and
enhanced new bone formation at 8 weeks [573]. The
rabbit
femur implant tests showed that PLGA/calcium orthophosphate
cement formulations exhibited outstanding biocompatibility and
bioactivity, as well as a better osteoconduction and degradability
than pure calcium orthophosphate cements [568]. Further details
on this subject are available in section
in vivo
5.7
.
6.4.3
Biocomposites Based on Nanodimensional
Calcium Orthophosphates and Nanodimensional
Biocomposites
Nanodimensional and nanophasic materials are the materials
that have particles or grain sizes under ~100 nm, respectively
(see section
for details). Thus, one should clearly differentiate
between nanodimensional composites and composites based on
nanodimensional compounds. The former might be any type of
composites but disintegrated to particles with dimensions < 100 nm,
while the latter consist of two or more materials, in which at least
one of the materials is of a nanometer-scale.
Nanodimensional and nanophasic materials have different
mechanical and optical properties if compared to the large grained
materials of the same chemical composition. Namely, they possess
the unique surface properties, such as an increased number of
atoms, grain boundaries and defects at the surface, huge surface area
and altered electronic structure, if compared to the conventional
micron-sized materials. For example, nanodimensional HA (size
~ 67 nm) has a higher surface roughness of 17 nm if compared to
10 nm for the conventional submicron size HA (~ 180 nm), while
the contact angles (a quantitative measure of the wetting of a solid
by a liquid) are significantly lower for nanodimensional HA (6.1) if
compared to the conventional HA (11.51). Additionally, the diameter
of individual pores in nanodimensional HA compacts is five times
smaller (pore diameter ~ 6.6 Å) than that in the conventional
grain-sized HA compacts (pore diameter within 19.8-31.0 Å)
[574-576]. Besides, nanodimensional HA promotes osteoblast cells
3.2
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