Figure 12.

Steps in making robust, tougher, and stretchable hydrogels and their mechanical properties. (A) The transition from soft to rigid materials. (B) Young’s modulus of various materials. Biocompatible soft hydrogel stiffness fits in the cellular and human skin zone. LCEs: Liquid-crystal polymer elastomers; LCNs: Liquid-crystal polymer networks; LCPs: Liquid-crystal polymers; SMPs: Shape-memory polymers. (C) An example of morphing of various “frozen” shapes of tough gels. (D) Three-dimensional folding of the Fe${}^{3+}$ ion-patterned Ca–alginate/polyacrylamide (PAAm) tough hydrogels. Adapted with permission from [305]. Copyright 2017, The Royal Society of Chemistry.