Fig. 2: Synthesis procedure and structure characterization.

a BC-g-PNCl dense layer towards the soft tissue was prepared by grafting of PAM on nanofibrils of BC membrane, followed by N-Cl functionalization of PAM chains. CS and HAP were introduced into the surface of BC-g-PNCl dense layer through drop-coating and lyophilization to form CS-HAP loose layer facing the bone defect. b, c FTIR spectra of BC, BC-g-PAM, and BC-g-PNCl (b) and XPS spectra of BC and BC-g-PNCl (c), proving that the N-halamine functionalized BC-g-PNCl layer is successfully constructed. d Side view macroscopic image showing asymmetric bilayer structure and thickness of BC-g-PNCl/CS-HAP (scale bar = 200 μm). e–g Top view SEM images of BC-g-PNCl layer (scale bar = 1 μm) (e), CS-HAP layer of BC-g-PNCl/CS-HAP (upper scale bar = 50 μm, lower scale bar = 5 μm) (f) and dense layer of the commercial CM (scale bar = 1 μm) (g). h, i SEM images of BC-g-PNCl layer of BC-g-PNCl/CS-HAP (h) and dense layer of CM (i) after 4 weeks of simulated clinical immersion (scale bars = 1 μm). SEM observation was repeated three times independently, yielding similar results.