Biomedical Engineering Reference
In-Depth Information
Fig. 5
TEM images of acid-soluble collagen fibrils formed
a
in the absence and
b
in
the presence of DNA.
c
Schematic model of collagen-DNA complex formed in aqueous
solution
interact with the charges in collagen and play key roles in the collagen fib-
ril forming process. It has also been reported that some materials containing
phosphate groups, such as phosphoproteins, promote collagen fibril forming
process [19]. Recently, Mrevlishvili's group proposed a model of the com-
plex of DNA and collagen [20, 21]. Their model proposes that the DNA helical
structure becomes more rigid when the rigid rod-like structures of triple he-
lix collagen (300 nm) overlap and envelop the backbone of DNA (Fig. 5c).
Although only a few reports on the collagen-DNA complex have been pub-
lished, these initial approaches are encouraging, as collagen-DNA complexes
will open up future opportunities for the construction of nanoscale ordered
materials.
2.3
DNA and Cationic Lipids
Cationic lipid or surfactant binding to DNA molecules can lead to compact,
ordered complexes. In a series of works [22-27], Okahata et al. described
the preparation and characterizations of the DNA-cationic lipid complexes
(Fig. 6a). Generally, the DNA-lipid complex can be readily prepared by mix-
ing aqueous solutions of anionic DNA and cationic lipid, which forms a water-
insoluble precipitate. These complexes are often soluble in common organic
solvents, and can be cast to form thin films. The results from the investigation
of CD spectra of DNA strands showed that the self-assembly of DNA and the
cationic lipids form a double-helical structure similar to B-DNA. The results
from the polarized absorption spectra of intercalated dye molecules indicated
that the DNA-lipid complexes exhibit intercalation behavior in chloroform
solution. Interestingly, when the DNA-lipid cast film was stretched to three
times in length, DNA strands could be aligned in the stretching direction [24].
X-ray diffraction of the cast film confirmed the ordered structure. In add-
ition, as shown in Fig. 7, electric conductivity in the aligned DNA cast film
was demonstrated [28, 29]. Kawabe [30-32] and coworkers found that some
dye molecules intercalated in DNA-lipid complex films can lead to amplified
spontaneous emission during nanosecond optical pumping. The durability
