Biomedical Engineering Reference
In-Depth Information
b
H
2
N
NH
a
z
H
N
H
2
N
N
H
2
N
NH
2
n
H
NH
2
x
y
Fig. 1
Linear (
a
) and branched (
b
) polyethylenimine (PEI)
3.2
Polyethylenimine (PEI) and Its Modifications
3.2.1
PEI
PEI is a synthetic polymer that has been widely used in processes such as water
purification, paper production, and shampoo manufacturing. Two main forms of
this polymer are commercially available, i.e. linear and branched, and both of them
can be conveniently synthesized by the polymerization of aziridine monomers
(Fig.
1
) (Godbey et al.
1999
). There are PEIs of various molecular weights, from
<1,000 Da to 1,600 kDa, provided by various manufacturers. Since the pioneer
work by Behr and coworkers (Boussif et al.
1995
), there have be increasing inter-
ests to develop non-viral vectors based on PEI and its derivatives (Godbey et al.
1999
; Kircheis et al.
2001b
; Neu et al.
2005
; Demeneix and Behr
2005
). Among
the various synthetic vectors, PEIs have shown particularly promising efficacy in
transfections in both
in vitro
and
in vivo
experiments. Broadly available studies
have substantiated that the branched PEIs (bPEIs) possess significantly higher
transfection efficiency for variety of cell lines. As a consequence, they have fre-
quently served as the gold standard to measure the efficacy of newly developed
synthetic vectors in a variety of studies. For example, bPEI of 25 kDa (PEI25) is
the most frequently utilized positive control for gene transfection experiments of
synthetic materials. The high cationic charge density is the most prominent feature
of bPEI. There is one nitrogen atom in every three atoms of bPEI, and the amine
groups covers the primary, secondary, and tertiary ones, each with the potential to
be protonated. These structural characters make bPEI effective for buffering over a
very wide pH range(Boussif et al.
1995
).
The structure of PEI dominates the physicochemical and biological properties of
the polyplexes with DNA or RNA to a large extent, and therefore it is closely related
to the efficiency for gene transfection. Studies by Kissel' group have revealed that
higher branched PEIs exhibited a stronger condensation capacity for DNA, formed
smaller polyplexes, and induced the expression of pDNAs to a higher extent than
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