Figure 5.

(a) localized flow-blocking by UV induced gelation of alginate; upper panel: the fluid flows freely through all three channels (A, B and C); lower panel: gel is formed (indicated by arrow) in the channel A upon UV exposure; (b) electrodeposition of calcium-crosslinked alginate film triggered by the release of Ca²⁺ ions from insoluble CaCO₃ particles; (c) preparation of patterned calcium crosslinked alginate hydrogel by photochemical patterning of iron (III) crosslinked alginate hydrogel, dissolution of the exposed areas and photochemical reductive cation exchange. See text for details. Part (a) is adapted with permission from Oh et al. [49], Copyright (2016), American Chemical Society; part (b) is reproduced by permission from Liu et al. [50], Copyright (2017), Springer Nature; part (c) is adapted from Bruchet and Melman [51], Copyright (2015), with permission from Elsevier.