Biomedical Engineering Reference
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Fig. 6 Size changes of (a) g -PGA-Phe and (c) g -PGA-Trp nanoparticles prepared at various NaCl
concentrations. The size of nanoparticles was measured by DLS. (b) Photographs of g -PGA-Phe
nanoparticles (2.5 mg/mL) dispersed in water. (d) Scanning electron microscope (SEM) images of
g -PGA-Trp nanoparticles prepared at various NaCl concentrations
Poly( e -lysine) ( e -PL) is produced by a Streptomyces albulus strain, and has
been used as a food additive due to its antimicrobial activities [ 66 , 67 ]. e -PL is
water soluble and biodegradable and has a molecular weight of approximately
5,000. e -PL is an L -lysine homopolymer (25-30 residues) with a linkage between
the carboxyl group and the e -amino group (Fig. 4 ). Matsusaki et al. reported the
nanoparticle formation of amphiphilic e -PL- graft -cholesterol hydrogen succinate
( e -PL-CHS) in water. e -PL was hydrophobically modified by CHS in the presence
of N,N -dicyclohexyl carbodiimide (DCC) and 1-hydroxybenzotriazole (HOBt) in
N,N -dimethylformamide (DMF) (Fig. 7 )[ 39 ]. e -PL-CHS nanoparticles were
prepared by the solvent (tetrahydrofuran) exchange method. e -PL-CHS could
form stable nanoparticles in water following the hydrophobic interactions of its
CHS groups. The size of the e -PL-CHS nanoparticles was approximately
150-200 nm. For the purposes of nonviral gene delivery, cationic polymers
such as poly( L -lysine) and polyethylenimine (PEI) have been used as carriers
for complexing gene vectors into polyplexes [ 68 - 70 ]. A polyplex can be easily
formed when the oppositely charged DNA and polycation are mixed in aqueous
solution and interact via electrostatic interactions. These polyplexes result in an
increased net positive charge of the complexes, and promote cellular uptake and
transfection efficiency. However, the in vivo applications of polyplexes are limited
by low gene expression and toxicity due to their cationic nature [ 71 - 73 ]. e -PL is
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