Magnetic property determination
Saturation magnetization of nanoparticles ranged from 70.6 to 165.2
emu/g. The FeCo nanoparticles showed high saturation magnetization
(165.2 emu/g), however these quantities decreased after coating the FeCo
with PEI. The values for saturation magnetization of FeCo and FeCo-PEI
were determined as 165.2 and 131.4 emu/g respectively (Figure 6 A).
The saturation magnetization values for NPsA, NPsB, and NPsAB were lower
than the FeCo and FeCo-PEI nanoparticles (99.41, 107.84 and 94.8 emu/g
for NPsA, NPsB, and NPsAB nanoparticles respectively) (Fig. 6 A). Such
attenuation pattern of saturation magnetization is often seen in
nanoparticles after coating the nanoparticles with non-magnetic
compounds.(Pouponneau, Leroux, & Martel, 2009). In general, the
saturation magnetization of nanoparticles was reduced with encapsulation
of siRNA and PTX into NPsA, NPsB and NPsAB nanoparticles (Fig. 6 A).
However, there was no significant difference between the magnetic
properties of the nanoparticles after PTX and siRNA encapsulation.
Magnetite properties of nanoparticles is an important factor in imaging
and targeting using magnetic nanoparticles. Previous studies showed that
nanoparticles with magnetite properties up to 9 emu/g are suitable for
use in imaging and targeting nanoparticles (Chorny et al., 2010; Yan,
Li, Li, Zhu, Shen, Yi, Wu, Yeung, Xu, Xu, & others, 2014). Therefore,
it seems that the nanoparticles synthesized in this experiment appear to
be suitable for such purposes.
The results of siRNA-FAM and PTX encapsulation efficiency in NPsA, NPsB
and NPsAB are shown in Fig. 7. Generally, the encapsulation efficiency
of siRNA-FAM was significantly higher than that of PTX. The
encapsulation efficiency of siRNA-FAM in various nanoparticles was in
the range of 78 to 85% while, in the case of PTX, it was in the range
of 38 to 42%. There is no significant difference between encapsulation
efficiency of the nanoparticles in each group (Fig. 7). The maximum
difference between the high and low encapsulation efficiency values of
siRNA-FAM and PTX loaded samples
was 7 and 4% respectively (Fig. 6 B). It seems that electrostatic
interactions between the negative charge of siRNA-FAM molecules and the
positive charge of polyethyleneimine in the nanoparticles is responsible
for the increased values of siRNA-FAM encapsulation efficiency compared
to PTX.
There was no significant difference between release behavior of PTX and
also siRNA from NPsA/siRNA/PTX, NPsB/siRNA/PTX and NPsAB/siRNA/PTX
nanoparticles. However, the cumulative release percentage of siRNA from
nanoparticles were significantly lower than PTX after 30 days. The
cumulative release percentage of siRNA was found to be significantly
lower than that of PTX after 30 days incubation at 37 °C in PBS buffer
(Fig. 7). It seems that the electrostatic interaction between siRNA and
PEI of the nanoparticles may be responsible to this phenomenon.
Therefore, it is plausible that electrostatic interactions between the
phosphate groups of siRNA and the NH2 groups of the
nanoparticles resulted in a reduction in the release rate of siRNA from
the nanoparticles.
The PTX and siRNA release from the nanoparticles was observed in two
different stages. In the first stage, more than 50% of the PTX-loaded
into the nanoparticles was released in the first three days. It was
found that the rate of PTX release decreased significantly with
increasing the incubation time more than three days. A similar release
pattern was observed for siRNA. These results are in agreement with
previous studies (Abebe et al., 2015b; Perez et al., 2001b). Those
reports have attributed the sustained release property of the
nanoparticles to the PLA segment in the structure of the nanoparticles.
This property of nanoparticles can be used for intracellular controlled
drug release in tumor cells.