Biomedical Engineering Reference
In-Depth Information
Fig. 5 Synthesis of g -PGA
hydrophobic derivatives
against many proteases because g -linked glutamic acids are not easily recognized
by common proteases [ 53 , 54 ]. Moreover, several studies have shown that g -PGA
by itself is a poor immunogen and does not induce booster responses, probably
because of its simple homopolymeric structure, similar to those of polysaccharides
[ 55 - 59 ]. Therefore, the potential applications of g -PGA and its derivatives have
been of interest in a broad range of fields, including medicine, food, cosmetics, and
water treatment [ 60 ].
Akashi et al. prepared nanoparticles composed of hydrophobically modified
g -PGA [ 38 , 61 , 62 ] (Fig. 5 ). g -PGA (400 kDa) as the hydrophilic backbone and
L -phenylalanine (Phe) as the hydrophobic segment were synthesized by grafting Phe
to g -PGA using water-soluble carbodiimide. The g -PGA- graft -Phe copolymers
( g -PGA-Phe) with more than 50% grafting degree formed monodispersed
nanoparticles in water due to their amphiphilic properties. To prepare nanoparticles,
g -PGA-Phe dissolved in dimethyl sulfoxide (DMSO) was added to various concen-
tration of NaCl solution, and then the resulting solutions were dialyzed and freeze-
dried. The g -PGA-Phe formed monodispersed nanoparticles, and the particle size of
the g -PGA-Phe nanoparticles could be easily controlled (30-200 nm) by changing
NaCl concentration [ 63 ]. Similarly, g -PGA conjugated with L -tryptophan ( g -PGA-
Trp) showed the same tendency (Fig. 6 ). The size of the nanoparticles increased with
increasing NaCl concentration during formation of particles. The addition of NaCl
leads to enhanced screening of the Coulomb interactions between the carboxyl
groups of g -PGA-Phe. Therefore, according to the increase in NaCl concentration,
a larger number of graft copolymers was involved in the formation nanoparticles.
The nanoparticles showed a highly negative zeta potential (
25 mV) due to the
ionization of the carboxyl groups of g -PGA located near the surfaces. The specific
self-assembly behavior of g -PGA-Phe in aqueous solution was due to multiple
stacking of phenyl groups. Beside the particle formation of g -PGA by using hydro-
phobic interaction, nanoparticles formed by complexation of g -PGA with a bivalent
metal ion complex [ 64 ] or by chemical crosslinking of carboxyl groups of g -PGA
[ 65 ] have been reported.
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