# Recent Progress and Challenges Regarding Magnetic-Based Nanoparticles for Targeted Drug Delivery
## 4 Multifunctional Magnetite-Based Nanomaterials
The in vitro MRI studies, similar to the previous examples, showed that the nanocarvier could be suitable as a negative contrast agent. The in vivo MRI studies showed differences in the images before and after injection of the contrast agent (the nanocarvier). The values of negative contrast enhancement (NCE) were different for different times after injection, and the highest NCE level was observed after 1 h. A more detailed in vivo MRI analysis was performed on the composite system containing Fe\({}_{3}\)O\({}_{4}\)/poly (\(\varepsilon\)-caprolactone) NPs functionalized with chitosan, (Fe\({}_{3}\)O\({}_{4}\)/PCL)/CS for gemc-itabine (GEM) delivery [113]. After the NP injection (Fe concentration of 5 mg/kg), rapid liver uptake occurred, manifested by a fast relative enhancement increase (40%) within 5 min. Lower uptake (about 20%) was observed for spleen and kidneys (Figure 8a-c). The analysis of T\({}_{2}\)-weighted images (Figure 8d-f) showed darker areas in the liver, kidneys, and spleen at 1 and 24 h post-injection. However, based on the quantitative analysis of the NPs biodistribution (T\({}_{2}\)-mapping), the liver and kidneys demonstrated a statistically significant increase in relaxivity R\({}_{2}\) (1/T\({}_{2}\)), and the values of \(\Delta\) R\({}_{2}\) were 3.9 and 8.0 s\({}^{-1}\) after 1 h, while being 8.9 and 15.7 s\({}^{-1}\) after 24 h, respectively (Figure 8g). Additionally, the changes observed in muscles were negligible. Finally, it is essential to highlight multifunctional systems that integrate potential applications in chemotherapy, enhanced by heat generation (MHT, PTT), and diagnosis (MRI). Magnetic nanorings--Fe\({}_{3}\)O\({}_{4}\)@polyvinylpyrrolidone (PVP)--loaded with doxorubicin were applied for synergetic magnetic hyperthermia and chemotherapy [114]. The investigation of MHT was additionally carried out using two types of magnetite nanoparticles--isotropic superparamagnetic (SNPs) and anisotropic ellipsoid ferrimagnetic (FNPs)--as reference samples. Under the same AMF, the temperature rises to 12.5, 27, and 33 \({}^{\circ}\)C for SNPs, FNPs, and the nanorings, respectively. The in vivo MHT studies were investigated after direct injection of the DOX-loaded nanocarvier. The local temperature was raised to 44 \({}^{\circ}\)C under AMF. On the other hand, the in vitro T\({}_{2}\) MR images tended to darken with increasing Fe concentrations; thus, the nanocarvier could expand the \({}^{1}\)H spin relaxation time (negative  
Figure 8: In vivo time courses of the (Fe\({}_{3}\)O\({}_{4}\)/PCL)/CS NPs: (**a**) liver; (**b**) spleen; and (**c**) kidney. T\({}_{2}\)-weighted MR images of the kidney, spleen, and liver after the NPs injection at: (**d**) 0, (**e**) 1, and (**f**) 24 h. (**g**) \(\Delta\)R\({}_{2}\) (s\({}^{-1}\)) as a function of time of muscle, liver, spleen, and kidney after NP injection. The statistical test was significant for data with \({}^{*}\) (\(p<\) 0.05). Reprinted from [113], Copyright (2023), with permission from Elsevier. contrast agent). The in vivo animal experiments proved the synergistic effect of heat therapy and DOX release in inhibiting tumor growth without side effects. Another approach was based on magnetite NPs stabilized by different plant extract concentrations (_Punica granatum_ fruit peel) [115]. The maximum temperature rise under AMF was observed for the lowest extract concentration, and it increased with increasing AMF strength (up to 54 \({}^{\circ}\)C). However, only the highest extract concentration (8%) guaranteed the secure hyperthermia range. According to the in vitro MRI studies, the relaxivity increased with increasing concentration, while the extract showed almost no value. Another interesting multifunctional nanoplatform, Au NPs loaded on mesoporous magnetite nanospheres, combined chemotherapeutic activity improved by NIR laser irradiation with MRI diagnostics [116]. A more advanced nanosystem for simultaneously therapeutic and diagnostic properties was designed for multimodality imaging and synergistic chemo-photothermal therapy [117].