Biomedical Engineering Reference
In-Depth Information
0.1 M HCl for 10 min, which led to the decomposition of DNA/Sp complex formed in aqueous solu-
tion at neutral pH [144]. As a result, low-molecular weight sperimidine was released and further
removed from the capsule interior. DNA may be released through high-salt solutions since DNA/Sp
pairs fall apart in such an environment due to high-ionic strength [144]. The estimated average
concentration of DNA encapsulated via DNA/Sp complex is 0.4 mg/mL. Shells were examined
under CLSM before and after dissolution of the inner DNA/Sp complex (Figure 10.6). Figure 10.6a
illustrates a typical fl uorescence image of (DNA/Sp)PA/PG capsules immediately after dissolution
of template, and the fl uorescence signal is caused by presence of Rhodamine-labeled DNA in the
capsule wall. In comparison, the capsule fi lled with freely fl oating DNA molecules had fl uorescence
signal from the whole capsule volume with even distribution (Figure 10.6b). The circular dichroism
(CD) spectrum also demonstrated successful loading of active DNA inside capsules. The CD spec-
trum of a double-stranded DNA has a strong signal in the 230-350 nm range [145]. After decom-
position of the DNA/Sp complex, the CD spectrum of DNA captured inside PA/PG microcapsules
reveals minor changes (
90% of the helicity preserved) compared with initial DNA. Shchukin et al.
suggested that sperimidine and polyarginine partially compensate in capsule volume and reduce the
negative effect of low-pH, forming pH gradient across the capsule shell.
∼
10.3.4 D
IRECT
C
OATING
ON
P
ROTEIN
A
GGREGATES
Protein crystal formulation is preferred in pharmaceutical industry for its advantages in handling,
stability, bioavailability, and controlled release [146]. Furthermore, protein crystals have shown
(a)
(b)
4
µ
m
4
m
µ
100
(a)
80
60
(b)
40
20
0
0
1
6
2
3
4
5
FIGURE 10.6
Fluorescence confocal microscopy images of the DNA-containing capsules composed of
four PA/PG bilayers just after decomposition of template core (a) and after dissolution of the inner DNA/Sp
complex (b). Areas under the curves are similar. The inset demonstrates the fl uorescence profi le for both
cases. (Reproduced from Shchukin, D.G., Patel, A.A., Sukhorukov, G.B., and Lvov, Y.,
J. Am. Chem. Soc
.,
126, 3374-3375, 2004. With permission.)
