Biomedical Engineering Reference
In-Depth Information
after 24 weeks incubation period. No/little change in weight of the HAp
nanocrystal-coated PLCL microspheres and molecular weight of PLCL and
surface morphology was observed after 1 week in PBS at 37
°
C.
9.7 Conclusions
HAp exhibits excellent biocompatibility with various kinds of cells and
tissues, making it an ideal candidate for tissue engineering, orthopedic
and dental applications. However, low mechanical strength and low
solubility of traditional HAp sintered ceramics generally restricts its use.
Therefore the interest is directed to hybridization of HAp with other
compounds such as biodegradable polymers. HAp-based nanocompos-
ite microspheres have received much attention as carriers of drugs, pro-
teins and cells because there is a wide ranging choice of polymers, which
show different degradation properties. HAp-based nanocomposite micro-
spheres are generally prepared from emulsion droplets (oil-in-water type
emulsions for hydrophobic polymers such as biodegradable polyesters,
or water-in-oil type ones for water-soluble polymers such as collagen) in
which both HAp nanoparticles and polymer are dispersed and dissolved.
We described the fi rst use of HAp particles as Pickering-type emulsifi ers to
fabricate the HAp-polymer nanocomposite microspheres. Neither molec-
ular-level surfactant, polymeric stabilizer nor animal-originated materials
such as collagen was used in this method. The surface of the microspheres
was covered with HAp particulate emulsifi ers, which are expected to have
a pristine HAp surface exposed to the continuous aqueous phase, because
the particulate emulsifi er was used without any surface-active modifi ca-
tion and no surface-active molecules were added. Thus, this method is
appealing in fi elds of application where severe restrictions are set for the
use of molecular-level surfactants.
From the standpoint of the progress of Pickering emulsions, we have
clearly demonstrated that the interactions between polymers dissolved
in an oil (dispersed) phase and nanoparticles in an aqueous (continu-
ous) phase at the oil-water interface play important roles in stabilizing
Pickering-type emulsions and in controlling the morphology of nanocom-
posite microspheres. Although this chapter focused on HAp particles as
the particulate emulsifi er and biodegradable polymers, these novel fi nd-
ings can be extended to other combinations of nanoparticles and polymers.
Acknowledgments
We would like to thank Professor Yoshinobu Nakamura at Osaka Institute
of Technology (Department of Applied Chemistry, Faculty of Engineering),
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