Figure 11.

Schematic diagram of assembly guided by magnetic field. (A) The hydrogel units are fabricated using optical graphics with patterned masks. The hydrogel prepolymer solution is moved onto a slide and then exposed to ultraviolet light (a). In a magnetic device consisting of two opposite magnets with the same magnetic pole, the suspended cells are guided by magnetic forces to assemble into structural blocks (b). If the magnetic susceptibility of the object is lower than that of the suspended medium, the object moves from a higher magnetic field intensity to a lower magnetic field intensity at the center line between the two magnets. The forces acting on the suspended object at equilibrium height include magnetic force (Fm) and modified gravity (Fg), which is the difference value between gravity and buoyancy. (Reproduced with permission from the Reference [70].) (B) The cells labeled with magnetic nanoparticles are wrapped in microgel, and the microgels are assembled under the action of magnetic field, and then the macro-scale engineered tissue can be formed. (Reproduced with permission from the Reference [68]). (C) Magnetic levitation three-dimensional cell culture. The upper row is the schematic diagram of cell suspension, and the lower row is the corresponding optical micrograph of neural stem cells at each stage. The dark spots are remnants of hydrogel fragments. Wash to remove excess hydrogel fragments. After placing a magnet above the liquid level of a petri dish, cell-encased microgels are found to accumulate beneath the surface of the liquid. After suspension for 12 h, characteristic multicellular structures (single structure in the schematic diagram) are formed. (Reproduced with permission from the Reference [67]). (D) A biocompatible magnetic levitation assembly system. (a) This system consists of two magnets with a glass microcapillary between them and a mirror added on the side for imaging and real-time monitoring. (b) Aggregation of cells in a microcapillary under magnetic force. (c) Fuse single cells and spheres of different or similar sizes under magnetic guidance to obtain cellular structures with heterogeneous compositions.