Figure 7.

Representative examples of SMHs. A) Formation of injectable SMHs: i) cryogelation process: 1) alginate is chemically modified to allow radical polymerization; 2) MA-alginate is added to a chemical initiator at −20 °C to allow ice crystal formation; 3) cryogelation takes place followed by thawing of ice crystals; and 4) conventional needle–syringe injection of preformed cryogels; ii) Photographs showing placement of a cryogel in a syringe (before injection) and hydrogel recovery (after injection); iii) MA-alginate gels with various sizes and shapes. Fluorescent square-shaped gels were syringe injected and showed complete geometric restoration after injection; iv) Cryogels prepared with different geometric shapes. Reproduced with permission.^[235] Copyright 2012, National Academy of Sciences. B) Shape-memory behavior of highly stretchable hydrogels: i) The original length of the hydrogel is 26.3 mm; ii) The hydrogel heated in 65 °C water and stretched to 45.2 mm; iii) The shape of the hydrogel immediately after cooling to 10 °C; iv) After 24 h soaking in 10 °C water, the length of hydrogel decreased to 43.0 mm; v) After reheating hydrogel in 65 °C water without any external stress, the length recovered to 26.0 mm. Reproduced with permission.^[239] Copyright 2009, American Chemical Society.