3796 wileyonlinelibrary.com nanorods as the fi llers are believed to be the best candidates for materials working in extreme environment and hence they are on demand in aerospace and space exploration applications. [39][40][41][42][43] In composite fi lms needed for inductor and antennae applications, the alignment of magnetic particles is required to increase the high frequency permeability and to lower the hysteresis losses. [44][45][46][47] In applications to manufacturing of high density recording fi lms and discs, spin alignment is required to carry the recorded information when spins in magnetic nanorods are prone to align parallel to the nanorod axis. [ 37,[48][49][50] In optical applications, magnetic liquid crystals are attractive candidates for making reconfi gurable magnetooptical devices with the fast time response measured in milliseconds. [11][12][13][14][15][16][17][18][51][52][53] In all these applications, one needs to control the alignment of magnetic nanorods in liquid medium. Therefore, this problem is actively discussed in the literature; however, the general strategy for making macroscopic samples with ordered nanorods has not been developed yet and it remains the main challenge of materials engineering [32][33][34][35][39][40][41][42]54 ] Processing of multifunctional coatings and thin fi lms require many steps and hence one needs to control the fi lm properties at each step.Rheological properties of the fi lms at each stage of their processing play the most important role in nanorod ordering and keeping nanorods in place. Characterization of thin coating fi lms during composite manufacturing remains challenging. Different experimental methods have been proposed and developed for in situ characterization of rheological properties of thin fi lms and coatings. [ 20,[25][26][27][55][56][57][58][59][60] It appears that unique features of rotation of ferromagnetic nanorods can be used for characterization of very thin fi lms when other methods fall short. Recently introduced magnetic rotational spectroscopy (MRS) with nanoparticles and nanorods allows one to probe fl uid rheology in very thin fi lms and nanoliter droplets. [ 12,20,22,25,60,61 ] MRS takes advantage of a distinguishable behavior of rotating magnetic tracers as the frequency of applied rotating fi eld changes. Unlike many methods based on the analysis of small oscillations, which are diffi cult to interpret when the fi lm is very thin, MRS with magnetic nanorods enjoys analysis of full revolutions of magnetic tracers. [ 20,22,24,25,60,62,63 ] Understanding of the characteristic features of rotation of a single nanorod in complex fl uids and alignment of an assembly

Magnetic nanoparticles (MNPs), primarily iron oxide nanoparticles, have been incorporated into cellular spheroids to allow for magnetic manipulation into desired shapes, patterns and 3-D tissue constructs using magnetic forces. However, the direct and long-term interaction of iron oxide nanoparticles with cells and biological systems can induce adverse effects on cell viability, phenotype and function, and remain a critical concern. Here we report the preparation of biological magnetic cellular spheroids containing magnetoferritin, a biological MNP, capable of serving as a biological alternative to iron oxide magnetic cellular spheroids as tissue engineered building blocks. Magnetoferritin NPs were incorporated into 3-D cellular spheroids with no adverse effects on cell viability up to 1 week. Additionally, cellular spheroids containing magnetoferritin NPs were magnetically patterned and fused into a tissue ring to demonstrate its potential for tissue engineering applications. These results present a biological approach that can serve as an alternative to the commonly used iron oxide magnetic cellular spheroids, which often require complex surface modifications of iron oxide NPs to reduce the adverse effects on cells.

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