Biomedical Engineering Reference
In-Depth Information
3.3.2
Polyethyleneimine
Numerous publications have demonstrated the antimicrobial utility of cationic polymers with quater-
nary ammonium groups, as discussed above. In particular, it was reported that quaternary ammonium
PEI (QPEI) possesses high antibacterial activities
[39,40]
. PEI is a branched water-soluble polyamine
in which the ratio of primary, secondary, and tertiary amine groups is equal to approximately 1:2:1
(
Figure 3.1
).
The effectual antibacterial activity of QPEI is attributed to the greater density of quaternary
ammonium groups along its backbone. Compared to small molecular weight quaternary ammonium
salts, QPEI has a stronger antibacterial effectiveness because of the macromolecular effect of concen-
trating antibacterial groups.
The mechanism of action of antibacterial quaternary ammonium compounds is believed to be a
sequence of events beginning with cationic binding and electrostatic interaction between the QPEI to
the microorganism cell wall components, causing a strong adsorption which later disrupts the mem-
brane function, resulting in leakage of constituents such as K
ions, DNA, and RNA, and subsequently
causing cell death
[41,42]
. Accordingly, quaternary ammonium causes lysis of bacterial cells and
shows strong bactericidal effect. Thus, the antibacterial mechanism of QPEI is a sterilization process.
QPEI was reported to have a 100% antibacterial ratio against
Escherichia coli
cells following con-
tact time of 4 min
[40]
. Lin et al. determined that
N
-alkylated poly(ethyleneimine) may be effective
against a variety of Gram-positive and Gram-negative bacteria. Its antibacterial activity was found to
be dependent on molecular weight of the conjugate. The results showed for example that
N
-alkylated
PEI of 2 and 0.8 kDa had a weak bactericidal activity. Furthermore, a structure-activity relationship
analysis has revealed that in order to create antibacterial surfaces, immobilized long polymeric chains
have to be positively charged and moderately hydrophobic
[39,43]
. This design strategy has been val-
idated not only with macroscopic surfaces but also with nanoparticles
[40]
.
H
H
2
N
N
N
NH
N
N
N
H
2
N
NH
z
N
N
N
N
H
FIGURE 3.1
Chemical structure of PEI.
