Figure 2.

Schematic illustration of the preparation of alginate multilayer hydrogels. The partly crosslinked layer (membrane) formed with the egg-box structure in the sodium alginate solution (a). The completely or incompletely crosslinked hydrogels (b). The second layer formed at the periphery of either completely or incompletely crosslinked hydrogel (c). The finally obtained double-membrane hydrogel with or without inter-membrane space (d). Photographs of the multi-membrane alginate hydrogels without (e) and with (f) inter-layer space. (Reproduced with permission from [24]. Royal Society of Chemistry, 2009).