Hydroxyapatite-Biodegradable Polymer Nanocomposite Microspheres Toward Injectable Cell Scaffold - Biomimetics: Advancing Nanobiomaterials and Tissue Engineering - page 223

of the Pickering-type emulsion. The results shown above indicate that the
wettability of the particles to the oil phase is an important factor for the
formation of a stable emulsion. In addition, it has been clarifi ed that the
stabilization of emulsions is possible even using an oil such as CH 2 Cl 2 ,
which has no ester groups, by introduction of ester groups into the oil
phase by dissolving polymers such as poly(ethylene terephthalate) and
poly(methyl methacrylate), which have ester groups on the main/side
chain. In this case, the ester groups on polymer chain interact with HAp
at the oil/water interface and function as an adsorption promoter (wet-
tability modifi er) for nanosized HAp particles to be adsorbed to the oil/
water interface.

9.3 Fabrication of HAp-Polymer Nanocomposite

Microspheres by Pickering Emulsion Method

As described in Section 9.2.2 above, the HAp nanoparticles (or nanocrystals)
cannot effectively function alone as an emulsifi er for oils such as CH 2 Cl 2 ,
which has no ester groups. However, when a hydrophobic polymer hav-
ing ester groups is dissolved into the oil phase as an adsorption promoter
(wettability modifi er), HAp particles can be adsorbed to the oil/water
interface and function as an effective particulate emulsifi er. Furthermore,
evaporation of the organic solvent from the HAp-stabilized polymer solu-
tion-in-water emulsion droplets through the aqueous medium can lead
to fabrication of HAp-polymer nanocomposite microspheres (Figure 9.3).
The nanocomposite microsphere fabrication method has been called the
“Pickering emulsion method.” The merits of this method are as follows:
(1) no molecular-level emulsifi er is used; (2) industrial-scale synthesis is
possible due to the simple procedure and easy up-scaling; (3) a wide range
of polymers can be utilized; and (4) functional materials such as drugs and
fl uorescent chemicals can be easily introduced into the microspheres.

Water

HAp nanoparticle HAp nanoparticle

Evaporation
of oil

CH 2 Cl 2 solution of polymer
(Oil phase)

Polymer

HAp nanoparticle stabilized
emulsion
(Pickering emulsion)

HAp nanoparticle-coated
polymer microsphere

Figure 9.3 Fabrication of nanocomposite microspheres with polymer core-HAp
nanoparticle shell morphology by Pickering emulsion method.