ratio of 2:1 gave the smaller nanoparticle sizes (177 Æ 7 nm) whereas CS-g-PEG:
PGA at 2:1 gave the bigger nanoparticle sizes (456 Æ 8 nm). Therefore, the production of nanoparticles with lower particle sizes is attributed to the high reactivity of
TPP compared to PGA.
In another study, Yao et al. [153] reported a mild method for the preparation of
PEGylated carboxymethylchitosan (CMCTS) nanoparticles via amino groups
grafted or crosslinked with mPEG-aldehyde or PEG-bisaldehyde in aqueous
media. Synthesis schemes for mPEG-g-CMCTS and PEG-CMTCS are depicted
in Fig. 9. In brief, mPEG-g-CMCTS (Fig. 9a) was synthesized by alkylation of
CMCTS followed by Schiff base formation. CMCTS was dissolved in 100 mL
water and mPEG-aldehyde added to the solution. The solution was then adjusted to
pH 7 with saturated sodium carbonate. The reaction mixture was stirred at about
5
C for 24 h. The solution containing CMCTS nanoparticles was purified by
dialysis for 3 days against distilled water and then freeze-dried. PEG-CMCTS
was prepared by a similar method to mPEG-g-CMCTS, as shown in Fig. 9b. The
differences were that PEG was used instead of mPEG and it was crosslinked with
CMCTS. The particle size of mPEG-g-CMCTC measured by transmission electron
microscopy (TEM) varied in the range of 300 nm to 1.1 μm, depending on the graft
volume of mPEG 2000. The average size of PEG-CMCTS nanoparticles measured
by DLS was 122–500 nm, depending on the molecular weight of PEG. Schiff bases
contain a chemical bond that is acid-sensitive at pH 5.4, which is consistent with the
pH of tumor tissue. These nanoparticles might give the antitumor drug passive
targeting after combining. Therefore, they have great potential as antitumor drug
carriers, especially for drug delivery and release.
It is known that exposure of chitosan to γ-irradiation reduces the molecular
weight of chitosan, but there has been no report about nanoscale chitosan products
being created by γ-irradiation. Pang et al. [154] reported the preparation of
deoxycholate-chitosan with the size of 200–600 nm and showed that it had the
ability to encapsulate tocopherol acetate and steric methyl ester. As nanoscale
material is defined as being smaller than 100 nm, a systematic protocol to reduce
and control the particle size of chitosan still requires further studies to achieve not
only a simple and effective preparation protocol but also a superior potential
product. Pasanphan et al. [155] investigated the systematic preparation of chitosan
nanoparticles in the potential range 1–100 nm using γ-irradiation. They showed the
effect of irradiation conditions in terms of the physical form of chitosan (i.e., flake,
colloidal, and acidic solution) and γ-ray dose. Interestingly, heterogeneous chemical
conjugation of deoxycholic acid onto 10 kGy-irradiated colloidal chitosan resulted in
particle sizes as small as 50 nm.
Ultrasonication is a common tool for the preparation and processing of polymer
nanoparticles. It is particularly effective in breaking up aggregates and in reducing
the size and polydispersity of nanoparticles. The physical stability and in vivo
distribution of nanoparticles are affected by their mean size, polydispersity, and
surface charge density. Despite the widespread applications of ultrasonication
in nanotechnology, its effects on chitosan nanoparticles are not well understood.
Engineering of Polysaccharides via Nanotechnology
109
PGA at 2:1 gave the bigger nanoparticle sizes (456 Æ 8 nm). Therefore, the production of nanoparticles with lower particle sizes is attributed to the high reactivity of
TPP compared to PGA.
In another study, Yao et al. [153] reported a mild method for the preparation of
PEGylated carboxymethylchitosan (CMCTS) nanoparticles via amino groups
grafted or crosslinked with mPEG-aldehyde or PEG-bisaldehyde in aqueous
media. Synthesis schemes for mPEG-g-CMCTS and PEG-CMTCS are depicted
in Fig. 9. In brief, mPEG-g-CMCTS (Fig. 9a) was synthesized by alkylation of
CMCTS followed by Schiff base formation. CMCTS was dissolved in 100 mL
water and mPEG-aldehyde added to the solution. The solution was then adjusted to
pH 7 with saturated sodium carbonate. The reaction mixture was stirred at about
5
C for 24 h. The solution containing CMCTS nanoparticles was purified by
dialysis for 3 days against distilled water and then freeze-dried. PEG-CMCTS
was prepared by a similar method to mPEG-g-CMCTS, as shown in Fig. 9b. The
differences were that PEG was used instead of mPEG and it was crosslinked with
CMCTS. The particle size of mPEG-g-CMCTC measured by transmission electron
microscopy (TEM) varied in the range of 300 nm to 1.1 μm, depending on the graft
volume of mPEG 2000. The average size of PEG-CMCTS nanoparticles measured
by DLS was 122–500 nm, depending on the molecular weight of PEG. Schiff bases
contain a chemical bond that is acid-sensitive at pH 5.4, which is consistent with the
pH of tumor tissue. These nanoparticles might give the antitumor drug passive
targeting after combining. Therefore, they have great potential as antitumor drug
carriers, especially for drug delivery and release.
It is known that exposure of chitosan to γ-irradiation reduces the molecular
weight of chitosan, but there has been no report about nanoscale chitosan products
being created by γ-irradiation. Pang et al. [154] reported the preparation of
deoxycholate-chitosan with the size of 200–600 nm and showed that it had the
ability to encapsulate tocopherol acetate and steric methyl ester. As nanoscale
material is defined as being smaller than 100 nm, a systematic protocol to reduce
and control the particle size of chitosan still requires further studies to achieve not
only a simple and effective preparation protocol but also a superior potential
product. Pasanphan et al. [155] investigated the systematic preparation of chitosan
nanoparticles in the potential range 1–100 nm using γ-irradiation. They showed the
effect of irradiation conditions in terms of the physical form of chitosan (i.e., flake,
colloidal, and acidic solution) and γ-ray dose. Interestingly, heterogeneous chemical
conjugation of deoxycholic acid onto 10 kGy-irradiated colloidal chitosan resulted in
particle sizes as small as 50 nm.
Ultrasonication is a common tool for the preparation and processing of polymer
nanoparticles. It is particularly effective in breaking up aggregates and in reducing
the size and polydispersity of nanoparticles. The physical stability and in vivo
distribution of nanoparticles are affected by their mean size, polydispersity, and
surface charge density. Despite the widespread applications of ultrasonication
in nanotechnology, its effects on chitosan nanoparticles are not well understood.
Engineering of Polysaccharides via Nanotechnology
109