Schematic for hydrogel swelling–modulated flow control via smart channels and valves: (A) and (B) represent smart channel designs—with a hydrogel strip (A), with a patterned array of hydrogel posts (B); (C)—(E) represent smart valve designs—with a single post (C), multiple posts (D), and multiple jacketed posts (E); (F) represents a hybrid hydrogel–flexible diaphragm (e.g., PDMS) valve where the expansion of the hydrogel deforms the diaphragm, reminiscent of the deformation of a bimetallic strip on heating (Modified from [281]).