## 3 Results and Discussion
Figure 2: The morphology and mesostructure of nanoparticles: (**A**) SEM image of MSNs and (**B**) SEM image of PDEAEMA–MSNs. The pH-responsive behavior of MSNs-PDEAEMA, MSNs-PDEAEMA-SH, and MSNs-PDEAEMA-POEGMEA were also explored at 25 \({}^{\circ}\)C. As illustrated in Figure 5A, the size distribution of MSNs-PDEAEMA and the average hydrodynamic diameter (D\({}_{\text{h}}\)) were determined at different pH using dynamic light scattering (DLS). At pH \(<\) 7, the D\({}_{\text{h}}\) of the sample was ca. 300-1000 nm. The hydration layer had a larger particle diameter distribution due to the repulsion force between the polymer chains. When the brushes became hydrophobic in basic media, the hydrodynamic diameter of sample was found to be between 200 and 400 nm. When MSNs-PDEAEMA, MSNs-PDEAEMA-SH, and MSNs-PDEAEMA-POEGMEA became fully protonated in acidic media, the zeta potential was positively charged, whereas the zeta potential became close to zero when the brushes were deprotonated, as shown in Figure 5B. However, the zeta potential of MSNs-PDEAEMA-POEGMEA exhibited a lower value in acidic media with ca. 30 mV, compared to 42 mV for MSNs-PDEAEMA and MSNs-PDEAEMA-SH. At pH 9, the zeta potential of all examined nanosystems was ca. 8 mV, due to the deprotonation process of tertiary amines present in the polymer chains. The RhB dye-loading capacity in the synthesized nanomaterials (MSNs-PDEAEMA, MSNs-PDEAEMA-SH, and MSNs-PDEAEMA-POEGMEA) was determined using Equation (1). Figure 4: X-ray photoelectron (XPS) high-resolution C1s spectra of (**A**) MSNs-PDEAEMA, (**B**) MSNs-PDEAEMA-SH, and (**C**) MSNs-PDEAEMA-POEGMEA. Figure 5: (**A**) Size distribution at different pH values of MSNs-PDEAEMA. (**B**) Zeta potential values at different pH and 25 \({}^{\circ}\)C for MSNs-PDEAEMA, MSNs-PDEAEMA-SH, and MSNs-PDEAEMA-POEGMEA. The loading capacity was found to be similar, ca. 74%, for all selected samples. FTIR technique was used to confirm the successful RhB dye-loaded into the system. Two peaks were observed at -1400 and -1570 cm\({}^{-1}\), pointed to C-C stretches of the aromatic ring in the dye's molecule (data not shown). The released amount of the RhB dye was examined from the selected samples in buffer solutions at different pH values (5, 6.5, 7.4, and 8). For CTAB free MSNs, the dye release was noticed to be the same at different pH values. The dye release behavior was found to be similar for the three-polymer shell coated MSNs, in both basic and acidic media, as shown in Figure 6. The cumulative dye released from all examined samples reached 60% after ca. 8 h, when the nanosystems were exposed to a solution of pH 5 and 6.5. Such fast dye release could be referred to the protonation process of the tertiary amine presented in PDEAEMA segments. However, in basic media, almost 22% of the loaded dye was released within ca. 12 h from both MSNs-PDEAEMA and MSNs-PDEAEMA-SH, as presented in Figure 6A,B. A notable difference was observed in the release profile of the dye loaded in MSNs-PDEAEMA-POEGMEA in basic media. The dye was released from MSNs-PDEAEMA-POEGMEA with an accelerated drug release of ca. 15% after 15 h (Figure 6C). These results indicated that POEGMEA molecules capped with MSNs-PDEAEMA could hinder the dye release. Cytotoxicity assay showed that all three fabricated nanoparticles (MSNs-PDEAEMA, MSNs-PDEAEMA-SH, and MSNs-PDEAEMA-POEGMEA) were non-toxic to the hMSCs, as shown in Figure 7. The cytotoxicity assay of MSNs-PDEAEMA at all three concentrations were statistically the same, even after 48 h of incubation; however, there is some slight increase in cell proliferation, but it is statistically insignificant. MSNs-PDEAEMA-SH was not toxic to cells, although there was some statistically significant increase in cell proliferation for the 50 \(\upmu\)g/mL after 24 h of incubation. After 48 h, both 50 and 100 \(\upmu\)g/mL showed a substantial increase in cell proliferation but with no toxicity. MSNs-PDEAEMA-POEGMEA was non-toxic at all three concentrations after both 24 and 48 h of incubation.