Lesion-targeted probiotic delivery via ROS-activated gelation and mucoadhesion for transanal treatment of colitis

• • The s-BSA-Fe+EcN enema solution achieves high fluidity (viscosity < 10 mPa·s) enabling full coverage of the colorectal mucosa, while Fe2+ triggers rapid gelation (< 5 min) in ROS-rich environments (H2O2 concentration ≥ 100 μM), forming a conformal hydrogel that adheres to lesions for > 24 h, significantly improving probiotic retention compared to PBS or PEG controls. • • The hydrogel scavenges H2O2 with an efficiency of > 85% within 30 min, reducing oxidative stress in the colonic tissue by 70% (p < 0.01) as measured by malondialdehyde levels, while maintaining probiotic viability at > 80% after 4 h exposure to oxidative conditions, outperforming free EcN which drops below 20%. • • In a DSS-induced colitis mouse model, treatment with h-BSA-Fe+EcN reduced the Disease Activity Index (DAI) from 8.5 ± 0.5 to 2.0 ± 0.3 (p < 0.001) and restored colon length from 4.2 ± 0.3 cm to 6.8 ± 0.2 cm, comparable to healthy controls, demonstrating superior therapeutic efficacy over free EcN or BSA-Fe alone. • • The system exhibits excellent biocompatibility: no significant systemic toxicity was observed in mice (body weight change < 5%, serum ALT/AST within normal range), and the porcine model confirmed endoscopic visibility of gelation, supporting translational potential for clinical enema formulations.