Robotics-based micro-reeling of magnetic microfibers to fabricate helical structure for smooth muscle cells culture

Helical structure assembled by hydrogel microfibers is significant for culture of smooth muscle cells. However, the helical structure is only fabricated at the macroscale, while the fabrication of helical microstructure is still a challenge due to the lack of assembly method. In this paper, we propose a robotics-based assembly method to handle such challenge. An electromagnetic needle (EMN) is employed as end-effector to magnetically reel the microfiber encapsulating magnetic nanoparticles around a micropillar, and a dual-ring structure is designed to keep the microfiber being attracted at the EMN tip. For enhancing the stability of tip attraction, the manipulation mode of anticlockwise pushing microfiber is established. Moreover, the interaction mechanism between EMN tip and microfiber is analyzed by developing a static force model, and then the key condition of stably reeling microfiber is concluded. Furthermore, a robotics-based motion trajectory of EMN tip is planned to achieve a smooth reeling process. Based on such planning, the size of dual-ring structure is further optimized to improve the success rate of reeling. Finally, the helical microstructure with there-turn coils is successfully fabricated.