Fig. 4. Synthesis of photoresponsive hydrogels enabled by the integrated use of split CarH_C and Spy chemistries.

(A and B) Schematic showing the synthesis of AdoB₁₂- and MeB₁₂-dependent photoresponsive protein hydrogels, Ado gel (A) and Me gel (B), of which the mechanics can be photoweakened and photostrengthened, respectively. Insets are photographs of corresponding materials. (C and D) Evolution of storage (G′) and loss (G″) modulus of the reaction of SpyTag-ELP-CarH_CC-ELP-SpyTag (ACCA) + SpyCatcher-ELP-CarH_CN-ELP-SpyCatcher (BCNB) in the dark after addition of AdoB₁₂ (C) or MeB₁₂ (D) as a function of time. (E and F) Normalized storage modulus (G′/G′₀) of photoweakening Ado gel (E) and photostrengthening Me gel (F) monitored by time sweep tests at a fixed frequency of 1 rad/s and strain of 5% at 23°C. Data are presented as means ± SD (n = 3). (G and H) Frequency sweep tests of the Ado (G) and Me (H) gels at a fixed strain of 10% at 23°C before and after photolysis with 30-klux light.