Sprayable dynamic Schiff-base hydrogel engineers an oxygen-limited microenvironment for viable Bifidobacterium bifidum delivery and accelerated oral ulcer healing.

Oral ulcers affect over 25% of the global population, substantially impairing quality of life. Current therapeutic approaches are limited by challenges such as drug resistance and treatment dependency. Although probiotics have shown promise in mucosal repair, local delivery of anaerobic strains such as Bifidobacterium bifidum remains challenging because oxygen exposure rapidly reduces bacterial viability. Here, we report a sprayable, dynamic Schiff-base gelatin/cellulose hydrogel capable of in situ gelation and microenvironment engineering for the viable delivery of Bifidobacterium bifidum. The reversible imine crosslinking network forms an oxygen-limited, moisture-retaining niche that preserves bacterial viability while enabling uniform mucosal adhesion and deformation tolerance. B. bifidum embedded in the hydrogel exhibited sustained release over 2 h and maintained high activity throughout gelation and degradation. In vitro, the hydrogel and B. bifidum synergistically enhanced fibroblast migration, reduced LPS-induced TNF-α and IL-6 expression, and promoted macrophage polarization toward the M2 phenotype. In vivo, the B. bifidum-loaded hydrogel markedly accelerated oral ulcer closure, improved epithelial regeneration, increased collagen deposition, and elevated α-SMA and collagen I expression. Cytokine profiling confirmed a transition toward a pro-healing microenvironment characterized by decreased TNF-α/IL-6 and increased IL-10 levels. No systemic toxicity was observed. This work demonstrates a microbe-material synergy strategy, where a dynamic covalent hydrogel enables anaerobic probiotic therapy by engineering a protective oxygen-limited microenvironment. The platform offers a clinically translatable approach for managing oral mucosal wounds under complex wet conditions.