Biomedical Engineering Reference
In-Depth Information
modifi cation agents [64, 65]. In consideration of the microspheres as bio-
medical materials, it is not favorable to use surface modifi cation agents
such as silane coupling agents or long-chain alcohols. Instead, we used a
biodegradable polymer, which eventually serves as the base material of
the microspheres, as the surface modifi er. Hydrophobic HAp nanopar-
ticles were prepared by mixing PLLA and HAp nanoparticles and heat-
ing at 200
C, which is higher than the melting point of PLLA. By heating
above the melting point, the mobility of polymer increases and the poly-
mer can adhere to the HAp surface. The PLLA-modifi ed HAp nanopar-
ticles have high hydrophobicity and can stabilize a W/O emulsion. The
W/O emulsion was subsequently emulsifi ed into an aqueous dispersion
of hydrophilic HAp nanoparticles, which have no surface modifi cation,
allowing a formation of W/O/W multiphase emulsion (Figure 9.9a). By
evaporation of CH 2 Cl 2 from the multiple Pickering emulsion, multihol-
low microspheres carrying inner water domains were fabricated. From the
TEM observation of an ultra-thin crosssection of the dried microspheres, it
was confi rmed that HAp nanoparticles was adsorbed on the inner domain
and on the microsphere surfaces (Figs. 9.9b and c). Multihollow HAp
nanoparticle-coated PLLA microspheres fabricated from Pickering-type
multiple emulsions are expected to be utilized in medical fi elds, because
°
( a )
( c )
( e )
E
(g)
(f)
H
10 μm
5 μm
50 μm
5 μm
( f )
E
( b )
( d )
R
S
S
100 nm
10 μm
( g )
H
R
R
50 μm
500 nm
100 nm
Figure 9.9 (a,b) Optical micrographs of the W/O/W emulsion stabilized with
spherical HAp (SHAp) and PLLA-rod-shaped HAp (RHAp) treated at 200˚C (a)
before and (b) after evaporation of CH 2 Cl 2 . The insets in the micrographs (a,b)
show magnifi ed images. (c,d) SEM images of the multihollow microspheres. The
image (d) is a magnifi ed image. (e-g) TEM images of ultra-thin cross sections of
the microspheres. The images (f,g) show magnifi ed images of the area shown in
the image (e). The symbols E, H, S, and R indicate the exterior of the microsphere
(epoxy resin), hollow inside the microsphere, SHAp, and RHAp, respectively.
Reprinted with permission from [55]. Copyright © 2010 American Chemical Society.
 
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