The ability to control the growth and orientation of neurites over long distances has significant implications for regenerative therapies and the development of realistic brain tissue models. In this study, the forces generated on magnetic nanoparticles internalised within intracellular endosomes are used to direct the orientation of neuronal outgrowth in vitro. Results indicate that following differentiation, neurite orientation is observed after 3 days application of magnetic forces to human neuroblastoma (SH-SY5Y) cells, and after 4 days application to rat cortical primary neurons. The direction of neurite outgrowth is quantified using a 2D Fourier transform analysis, showing excellent agreement with the derived magnetic force vectors. Orientation control is found to be effective over areas >1cm2 using modest forces of ~10 fN per endosome, apparently limited only by the local confluence of the cells. However, in regions where the force vectors converge, large (~100 µm) nanoparticle loaded SH-SY5Y neurospheres are found, connected by unusually thick linear neurite fibres. This could suggest a magnetically driven enhancement of neurosphere growth, with the neurospheres themselves contributing to the local forces that direct outgrowth. Such structures, which have not been previously observed, could provide new insights into the development and possible enhancement of neural circuitry.
