3D magnetic assembly of cellular structures with "printing" manipulation by microrobot-controlled microfluidic system

Microfluidic technology provides a mild way to fabricate cell-laden hydrogel three-dimensional (3D) modules. However, the poor controllability of hydrogels and unstable microfluidic fabrication process are still problems during the assembly process. In this paper, a novel "bottom-up" method is used to assemble the complex shapes with magnetic alginate microflbers (MAMs) under an optimized magnetic field and a robotic assembly system. MAMs encapsulating Fe₃O₄ magnetic nanoparticles (MNs) and fibroblasts (NIH/3T3) are spun and automatically assembled under the magnetic field produced by a ring magnet. Experimental results show that the MAMs can respond quickly to the magnetic field, which enhances the controllability of hydrogels. The spinning process can be more stable with immersing the spinning orifice of microfluidic device into deionized water and using the "pinch-off" scheme to wash the blockage off. Moreover, an optimization of magnetic assembly area of ring magnet is completed. Because of magnetic field, the complex assembly can be completed just by controlling robot arm which fixes the microfluidic device to move in XY plane. The secondary cross-linking method is employed to shape the structure on the support model. Finally, from the LIVE/DEAD assay, cells can survive well during the magnetic assembly process.