Fig. 2.

Assembling strategies for microgel assembly: (a) chemical reaction, including enzymatic catalysis (scale bar: N/A) [19], photo-induced radical polymerization (scale bar: 1 mm) [31], click chemistry (scale bar: 10 mm) [39] and non-enzymatic amidation reaction (scale bar: 1 mm) [43]; (b) physical reaction, including host-guest interaction (scale bar: N/A) [48], electrostatic interaction (scale bar: 500 μm) [50], hydrogen bonding (scale bar: 250 μm) [55] and biotin-streptavidin conjugation (scale bar: 20 μm) [40]; (c) cell-cell interaction (scale bar: 1 mm) [60]; and (d) external driving force, including fluidic force (scale bar: 150 μm) [63], surface tension (scale bar: 200 μm) [67], magnetic and acoustic force (scale bar: 1 mm) [70]). All the cited literatures are discussed in section 2 where readers can find more details. N/A: not available. Reprinted with the permission from Springer Nature, John Wiley and Sons, American Chemical Society, Elsevier, IOP Publishing, The Royal Society of Chemistry, National Academy of Sciences.