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.