Carboxyl-activated silk fibroin nano-fiber microcarrier@sodium alginate as a probiotic colony delivery system

Oral probiotic efficacy is often limited by poor bioavailability and restricted intestinal colonization due to harsh and variable gastrointestinal conditions, as well as complex gut microbiota. To address this, a core-shell delivery system was developed based on carboxyl-activated silk fibroin nano-fiber microcarriers (SFMs) coated with sodium alginate. Bacillus subtilis (Bs) was loaded onto SFMs, followed by carboxyl group activation via EDC/NHS chemistry and coating with a sodium alginate out-layer (Bs-SFMs@SA). As expected, the SFMs successfully supported the loading and proliferation of the probiotics and carboxyl activation enhanced the intestinal adhesion of SFMs. The sodium alginate coating provided protection against gastric fluid degradation in vitro/vivo, thereby significantly enhancing probiotic viability. Compared to individual probiotics, these probiotic-loaded microcarriers formed colonies, which enhanced colonization efficiency and functionality within the gastrointestinal tract through synergistic interactions and the creation of a protective, cooperative niche. Bs-SFMs@SA system increased Firmicutes D (Bacilli) abundance, enhanced metabolic synergy and microbial connectivity, and promoted host commensal bacterial growth, thereby alleviating pathological progression in enterohemorrhagic Escherichia coli & Dextran sulfate sodium-induced colitis. The Bs-SFMs@SA system harnessed silk fibroin microcarriers to form robust probiotic colonies, resulting in significantly higher gut colonization efficiency compared to the dispersed probiotics typically found in other delivery systems or commercialized capsules.