Macroporous Hydrogels Prepared By Ice Templating: Developments And Challenges^†

Comprehensive Summary Macroporous hydrogels are water‐swollen polymer networks with porous structures beyond the mesh size. They provide high specific surface areas and hieratical mass transfer channels which are desired for emerging applications including cell culturing, bio‐separation, and drug delivery. A variety of approaches have been developed to fabricate macroporous hydrogels, including gas foaming, porogen templating, phase separation, 3D printing, etc . Alternatively, ice templating utilizes the crystallization of water as the porogenation mechanism which doesn't need the leaching of porogens. The porous structures can be easily manipulated by controlling the morphology of ice (size, orientation, etc .) upon freezing. In addition, mechanical properties of obtained porous hydrogels are commonly better than those of other macroporous hydrogels since the pore walls are made up of concentrated polymers through the freezing step. These three characteristics, that is, the green process, the highly tunable morphology, and the enhanced mechanical strength make the ice templating a superior porogenation method. This review expects to give an overview on macroporous hydrogels prepared by the ice templating, namely, cryogels. Recent progresses on emerging cryo‐porogenation methods are introduced. Fundamental understanding concerning the behavior of the polymer chains during the formation of ice is proposed. Future opportunities on the application of cryogels are prospected.