# Application in Nanomedicine of Manganese-Zinc Ferrite Nanoparticles
## 4 In Vivo Applications of Mn-Zn Ferrites  
In this section, the studies that exploited manganese-zinc ferrites nanoparticles into in vivo experiments will be analyzed. For the medical validation of this quite novel nanomaterial, the administration in a living system is very important, because many results concerning magnetic nanoparticles, fully demonstrated in solution or by in vitro experiments, were not reproduced in vivo. As in the previous section, the analysis is focused on those papers that provided real advancement in the medical usage of Mn-Zn ferrite nanoparticles. It should be noted that all these studies have been published in the last six years, reflecting the very recent development of the medical application of these ferrites. In 2015, [PERSON] et al. reported the preparation of hydrophobic spherical Mn\({}_{0.6}\)Zn\({}_{0.4}\)Fe\({}_{2}\)O\({}_{4}\) nanocrystals, with an average diameter of 8 nm, and a star-shaped copolymer 4 sPCL-\(b\)-P(MEO\({}_{2}\)MA-\(co\)-OEGMA), starting from the in vitro study reported in [41], described in Section 3. The magnetic nanoparticles, obtained by a standard thermal decomposition method, were then resuspended in THF with the polymer and quite small nanoclusterswere obtained, with an average size of 122 nm. These composites showed low toxicity, by in vitro assay, and a relevant \(r_{2}\) of 138 mM\({}^{-1}\) s\({}^{-1}\) at 3.0 T. For assessing the MRI potential of the system, the magnetic micelles were intravenously injected in mice that were bearing a xenograft tumor at a low dose of 0.007 mmol Fe/kg. By MRI, a significant darkening of the tumor region was observed after 1 h in T\({}_{2}\)-weighted spin-echo analyses, with a maximum signal recorded at 4 h. At 8h after injection, the signal in the tumor region recovered the contrast level of pre-injection imaging [41; 44]. [PERSON] et al. presented the synthesis of superparamagnetic silica-coated small nanoclusters of Mn-Zn ferrite nanoparticles. In this structure, few nanoparticles represent the magnetic core (about 30 nm) entrapped in silica beads with an overall size of 80-100 nm. Interestingly, the \(r_{2}\) relaxivity reached 295 mM\({}^{-1}\) s\({}^{-1}\) at 0.5 T, which is approximately two times higher than commercial analogs of Resovist. Within this framework, some bioluminescent cells from the adipose tissue were labeled with the silica-coated nanoparticles and were grafted into rat muscle, in order to monitor the signal in a long-term experiment. The bioluminescent signal was revealed after one day, but after a week the luminescence decreased at 10%. On the opposite, the MRI signal recorded by T\({}_{2}\)/T\({}_{2}\)* images was detected from day 1 to day 28 without visible change [45]. Another assembly of hydrophobic Mn\({}_{0.63}\)Zn\({}_{0.37}\)Fe\({}_{2}\)O\({}_{4}\) nanoparticles in dense spherical clusters or in small chains of few crystals, namely worm-like clusters, was reported by [PERSON] et al. The three different configurations offered quite different MRI profiles at 1.5 T, with \(r_{2}\) values ranging from 237 mM\({}^{-1}\) s\({}^{-1}\) for single nanoparticles, to 318 mM\({}^{-1}\) s\({}^{-1}\) for spherical clusters and 474 mM\({}^{-1}\) s\({}^{-1}\) for the worm-like chains. The trend was also observed for the magnetization values of the three nanosystems, with the worm-like cluster showing the higher saturation, slightly higher even than the hydrophobic Mn-Zn ferrite nanoparticles. Moreover, the nanosystems were transferred in water by means of a modified polymer, in which an arginylglyaspartic acid moiety (RGD) was included to target the integrin \(\alpha\)v\(\beta\)3 that is overexpressed in HUVEC endothelial cells. No relevant differences were observed by in vitro test, but the MRI analysis after intravenous administration revealed that the worm-like structure induced a higher penetration in the tumor region.