polymerization of acrylic acid (AAC) in the presence of chitosan [176]. The AAC
molecules are bound electrostatically to chitosan to form the shell of the micelles.
Upon polymerization, PAAC interacts with chitosan at the interface of the micelles.
The shrinkage of spheres brought about by electrostatic attraction between chitosan
and PAAC, as well as the expansion of the spheres due to electrostatic repulsion
among the chitosan molecules, causes phase separation between the polymer and
the solvent resulting in the formation of HPNSPs.
The template method is also frequently used for the fabrication of hollow spheres.
The appropriate selection of template materials plays a crucial role in controlling the
core size of the hollow spheres. Further, hollow structures can be easily obtained
after removing the template by dissolution, evaporation, or thermolysis. This method
requires large amount of surfactants, which can modify the surface of the template to
make the template active to interact with shell substance. Wang et al. [177] reported
the production of chitosan hollow nanospheres (HNPs) by employing uniform poly
(D,L-lactide)–poly(ethylene glycol) (PELA) nanoparticles as templates. Chitosan
was adsorbed onto the surface of PELA nanoparticle templates through the electrostatic interaction between the sulfuric acid groups from SDS on the templates
and the amino groups of the chitosan. Subsequently, the core-coated structure of
chitosan–PELA nanospheres was obtained, with the adsorbed chitosan layer being
further crosslinked with glutaraldehyde. After the removal of the PELA cores with
acetone, chitosan HNPs were achieved. The mean size of initial PELA nanospheres
was 180 Æ 2 nm whereas that of chitosan–PELA nanospheres was 280 Æ 12 nm
and the zeta potential changed from À31.5 to 41.3 mV. The change in zeta potential
and size were noteworthy, which indicated that chitosan was absorbed on the surface
of PELA nanospheres. Thus, it is possible to form hollow chitosan nanospheres by
removing the PELA core.
In order to avoid the post-treatment processes, including organic solvent dissolution or calcination at elevated temperature, for the production of hollow spheres,
Deng et al. [178] reported a simple method for fabrication of monodispersed silica
hollow nanospheres in a one-step, one-medium process. The nanospheres were then
decorated with chitosan using a crosslinking reaction with (3-glycidyloxypropyl)
trimethoxysilane (GTPMS) to produce pH-sensitive chitosan–silica hollow
nanospheres (CS–SiO 2 HNPs). GPTMS was first used to modify the SiO 2 HNPs in
an acidic ethanol medium in which GPMTS reacts with the silanol groups on the
SiO 2 surface via the formation of Si–O–Si bonds. The chitosan solution was then
added to accomplish crosslinking on the surface of the SiO 2 HNPs [179, 180]. The
hydrodynamic diameters (D h ) of SiO 2 and CS–SiO 2 HNPs determined from
the dynamic light scattering measurement were 242.8 and 263.7 nm respectively.
The zeta potential measurement showed that the SiO 2 HNPs had a negative potential
of about À35 mV, whereas the zeta potential of the CS–SiO 2 HNPs increased to
+24.7 mV due to the cationic polysaccharide-chitosan decoration. These results
demonstrate that chitosan had been successfully introduced to the SiO 2 HNPs.
Engineering of Polysaccharides via Nanotechnology
115
molecules are bound electrostatically to chitosan to form the shell of the micelles.
Upon polymerization, PAAC interacts with chitosan at the interface of the micelles.
The shrinkage of spheres brought about by electrostatic attraction between chitosan
and PAAC, as well as the expansion of the spheres due to electrostatic repulsion
among the chitosan molecules, causes phase separation between the polymer and
the solvent resulting in the formation of HPNSPs.
The template method is also frequently used for the fabrication of hollow spheres.
The appropriate selection of template materials plays a crucial role in controlling the
core size of the hollow spheres. Further, hollow structures can be easily obtained
after removing the template by dissolution, evaporation, or thermolysis. This method
requires large amount of surfactants, which can modify the surface of the template to
make the template active to interact with shell substance. Wang et al. [177] reported
the production of chitosan hollow nanospheres (HNPs) by employing uniform poly
(D,L-lactide)–poly(ethylene glycol) (PELA) nanoparticles as templates. Chitosan
was adsorbed onto the surface of PELA nanoparticle templates through the electrostatic interaction between the sulfuric acid groups from SDS on the templates
and the amino groups of the chitosan. Subsequently, the core-coated structure of
chitosan–PELA nanospheres was obtained, with the adsorbed chitosan layer being
further crosslinked with glutaraldehyde. After the removal of the PELA cores with
acetone, chitosan HNPs were achieved. The mean size of initial PELA nanospheres
was 180 Æ 2 nm whereas that of chitosan–PELA nanospheres was 280 Æ 12 nm
and the zeta potential changed from À31.5 to 41.3 mV. The change in zeta potential
and size were noteworthy, which indicated that chitosan was absorbed on the surface
of PELA nanospheres. Thus, it is possible to form hollow chitosan nanospheres by
removing the PELA core.
In order to avoid the post-treatment processes, including organic solvent dissolution or calcination at elevated temperature, for the production of hollow spheres,
Deng et al. [178] reported a simple method for fabrication of monodispersed silica
hollow nanospheres in a one-step, one-medium process. The nanospheres were then
decorated with chitosan using a crosslinking reaction with (3-glycidyloxypropyl)
trimethoxysilane (GTPMS) to produce pH-sensitive chitosan–silica hollow
nanospheres (CS–SiO 2 HNPs). GPTMS was first used to modify the SiO 2 HNPs in
an acidic ethanol medium in which GPMTS reacts with the silanol groups on the
SiO 2 surface via the formation of Si–O–Si bonds. The chitosan solution was then
added to accomplish crosslinking on the surface of the SiO 2 HNPs [179, 180]. The
hydrodynamic diameters (D h ) of SiO 2 and CS–SiO 2 HNPs determined from
the dynamic light scattering measurement were 242.8 and 263.7 nm respectively.
The zeta potential measurement showed that the SiO 2 HNPs had a negative potential
of about À35 mV, whereas the zeta potential of the CS–SiO 2 HNPs increased to
+24.7 mV due to the cationic polysaccharide-chitosan decoration. These results
demonstrate that chitosan had been successfully introduced to the SiO 2 HNPs.
Engineering of Polysaccharides via Nanotechnology
115