Fig. 1. (A) Synthesis steps of CEC and OHA. (B) Schematic of the double networks of SC and SS hydrogels.

Fig. 2. (A) FTIR spectra of CS, CEC, HA and OHA, the arrows indicate the characteristic peaks. (B) 1H NMR spectra in D2O of CEC, the peaks labeled by 1, 2 were the methyl protons of acetamido and the methylene protons of carboxyethyl, respectively.

Fig. 3. The macroscopic self-healing property of PEGDA, SC and SS hydrogels. (A) Two pieces of each kind of hydrogels were prepared and one was stained with rhodamine B. (B) All the hydrogels were cut into 4 pieces and recombined with alternate colors. (C) After healing for 2 h, all the hydrogels turned red. (D, E) When PBS was added, PEGDA hydrogel was separated into 4 pieces immediately, while SC and SS hydrogels still remained integrity, even after immersing in PBS for 24 h.

Fig. 4. The rheological measurements of SC and SS hydrogels. (A) G' and G” of SS hydrogel on strain sweep. G' and G” in continuous step strain (1% strain → 100% strain → 1% strain) measurements: (B) SC hydrogel and (C) SS hydrogel.

Fig. 5. (A) Preparation of the bilayered osteochondral scaffold and (B) its micro and macro (inserted image) morphology after lyophilization. Scale bar: 100 μm. (C) The macroscopic self-healing property of the osteochondral scaffold.

Fig. 6. (A) Weight swelling ratio and (B) volume swelling ratio of SC and SS hydrogels.

Fig. 7. (A) Compressive stress-strain curves and (B) compressive modulus of SC and SS hydrogels before and after healing for 30 min. (C) The healing efficiency of SC and SS hydrogels.

Fig. 8. (A) Compressive stress-strain curve and (B) compressive modulus of SO hydrogel. (C) Schematic of the push-out experiment evaluating interfacial integration performance of SO hydrogel. (D) Interfacial integration stress of SO hydrogel enhanced by prolonging the healing time.

Fig. 9. Live/dead staining of the rabbit BMSCs encapsulated in (A) SC and (B) SS hydrogels after 3 days of cultivation. (C) Cell viability at day 1, 3, 5, 7 detected by CCK-8 assay.

Fig. 10. Histological observation of the (A, C) SC hydrogel and (B, D) SS hydrogel being implanted subcutaneously, on (A, B) day 10 and (C, D) day 20 post-implanting. The right of the red dash lines, the implant. Scale bar: 100 μm.