Applications of magnetic nanostructures to cell patterning and heterotypic cell-cell interactions

Magnetic nanowires were employed to apply forces to cells, and were used to assemble cells into ordered structures. Ferromagnetic nickel nanowires were fabricated by electrodeposition and attached to biological cells. The high remanent magnetization of these nanowires allowed for effective manipulation of cells in suspension. Arrays of elliptically shaped micromagnets were patterned on substrates, and the magnetic fields from these microstructures guided cells with attached nanowires into positions determined by the ellipses. Varying the spacing of the ellipses allowed the formation of different patterns on the substrate. The addition of a magnetic field perpendicular to the substrate created arrays of vertical cell chains anchored to one end of the micromagnets.;Magnetic forces were also used to form arrays of heterotypic cell pairs. For these experiments, arrays of elliptically shaped holes were etched into ferromagnetic thin films. After magnetization, the ends of the holes served as magnetic poles. An applied field perpendicular to the substrate resulted in selective cell trapping of one cell type to an end of the ellipses, and reversing this field trapped the second cell type to the opposite end. The arrays were chemically functionalized to confine the cell pairs in the traps. This technique created heterotypic pair yields of up to 17%.;Additional experiments made heterotypic pairs using a random seeding process. Mixtures of bovine pulmonary artery endothelial and smooth muscle cells were sedimented onto nonmagnetic arrays of holes that were functionalized to promote cell adhesion in the holes and prevent it elsewhere. The pair yield with this process approached 10%, but the use of custom software provided the ability to analyze thousands of array sites, and resulted in large numbers of heterotypic pairs. These heterotypic arrays were used to perform cell proliferation studies of the endothelial and smooth muscle cell pairs. An increase in proliferation rates was measured for smooth muscle cells in the heterotypic configuration.