Dynamic covalent network encapsulation of probiotics: A facile strategy for freeze-drying stability and controlled colon delivery

Developing hydrogels capable of safeguarding probiotics against harsh upper gastrointestinal (GI) tract (stomach and small intestine) remains a pivotal challenge for effective colon delivery. Herein, we engineer imine cross-linked hydrogels by integrating oxidized konjac glucomannan (OKGM) into gelatin networks, creating mechanically robust and upper GI-tolerant carriers for probiotic protection. The dynamic covalent networks synergistically enhance mechanical robustness (elastic modulus: 5970 Pa, rupture stress: 13700 Pa) and tolerance to upper GI environments, alongside thermotolerance at 37 °C and self-healing properties. The hydrogel demonstrates minimal swelling in simulated gastric fluid (SGF) and programmed degradation in simulated small intestinal fluid (SIF), effectively shielding probiotics from acidic inactivation and enzymatic attack. With only 7.7 % OKGM, the system achieves 96 % encapsulation efficiency and sustains exceptional probiotic viability: 89 % survival post-SGF and 85 % post-SIF, outperforming conventional gelatin carriers. Notably, scanning electron microscopy (SEM) confirms that the hydrogel network preserves probiotic structural integrity even after freeze-drying—a critical advancement for industrial storage and scalability. The synergy between dynamic imine networks and OKGM/gelatine biopolymers ensures dual functionality: (1) buffering mechanical stresses during SGF and SIF transit, and (2) programmed degradation for colon-specific payload release. This work establishes a rational strategy to engineer gelatin-based hydrogels with spatially resolved GI resistance, addressing the core limitation of current oral delivery systems—premature probiotic inactivation in the upper GI tract. By enabling controlled colon delivery of viable probiotics, our findings advance the development of functional foods and therapeutic formulations requiring localized microbial activity.