Figure 13. Design principle for strong hydrogels – synchronize stiffening and fracture of multiple polymer chains:

a. definition and measurement of the tensile strength. A and a are the cross-section areas of the sample in the undeformed and deformed states, and F is applied tensile force. b. the simultaneous stiffening and fracture of substantial polymer chains give a high tensile strength⁷⁵⁹. F_f is the tensile force at the failure of the sample. c. the nominal tensile strength s_c increases with the decrease of the defect size D up to a critical value D_c, below which the tensile strength is defect-insensitive^760,761.