Biomedical Engineering Reference
In-Depth Information
as alpha-melanocyte-stimulating hormone (
α
-MSH), with anti-inflammatory properties,
have also successfully been integrated into multilayer films. Initially coupled with PLL,
α
-MSH was effective toward melanoma cells that were induced to produce melanocortin
(Chluba et al. 2001.) Then, coupled with PGA and introduced into PLL/PGA films, it was
efficient in annihilating the effect of a bacterial endotoxin that stimulated an inflammatory
response in human monocytic cells (Jessel et al. 2004). The morphology of the monocytes
was also affected by
α
-MSH as the cells formed many “fiber like” protrusions not visible
on standard PLL/PGA films.
Importantly, however, the question has been raised as to whether these chemical modi-
fications in the polyelectrolytes alter other physical chemical properties such as protein
adsorption or mechanical properties, in turn influencing cell adhesion and prolifera-
tion. This is supported by recent findings by Thompson et al. (2006) and Schneider et al.
(2006b), who measured the mechanical properties of the films with or without modified
polyelectrolytes.
Antibacterial Coatings
The use of CHI in antibacterial dressings has received considerable attention in the past
decade (Kumar 2000). The exact antibacterial mechanism of CHI is still unknown. One
mechanism proposed is based on the interaction between positively charged chitosan
molecules and negatively charged microbial membranes causing leakage of intracellular
constituents.
Bacterial adhesion (
Escherichia coli
Gram-negative strain) was investigated on cer-
tain types of natural based multilayer films containing CHI and/or HEP. (CHI/HA)
10
films (built in 0.15 M NaCl) are highly resistant to bacterial adhesion and lead to a ≈80%
decrease in bacterial adhesion as compared to bare glass (Richert et al. 2004c). On the
other hand, (CHI/HA)
20
films built in 10
−2
M NaCl were less resistant to bacterial adhesion
(40% less than control on the CHI ending films and 20% less on the HA-ending films).
The differences observed were explained by the lower thickness of the (CHI/HA) films
built in 10
−2
M NaCl (120 nm as compared to 300 nm for those built in 0.15 M NaCl).
CHI/κ-carrageenan films were found to have a greater effect in decreasing initial bacterial
adhesion than a thinner CHI coating, which was explained by the greater hydration of the
multilayer films (Bratskaya et al. 2007). Adhesion of negatively charged enterococci was
slightly enhanced on CHI-terminated multilayers, but the antibacterial effect was absent
on κ-carregan-terminated multilayers.
Heparin, with its antithrombogenicity and strong hydrophilicity, also prevented adhe-
sion of bacteria. The antibacterial properties of films containing both polysaccharides have
thus been explored. CHI/HEP multilayer films were found to kill the bacteria that had
adhered to the surface. Initial
E. coli
adhesion was also greatly decreased on the multilayer
films (Fu et al. 2005). The assembly pH was found to be an important parameter in the
design of efficient antiadhesive and antibacterial films.
To enhance the antibacterial effect of multilayer films, the same authors prepared films
containing silver nanoparticles and coated a polyethylene terephthalate graft with alter-
nating layers of CHI/HEP, chitosan being complexed with silver nanoparticles of 10-40 nm
in size (Fu et al. 2006). The multilayer films containing nanosilver not only had effective
antibacterial properties but also anticoagulant properties, while remaining nontoxic for
the cells. Other types of film, such as PGA/lysozyme, were also found to inhibit bacterial
adhesion (Rudra et al. 2006).
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