The effect of poly(vinyl alcohol) (PVA) on the swelling behavior of chitosan (CS) cryogel under simulated digestion

Chitosan (CS) porous gels (e.g. aerogel, cryogels, and xerogels) are promising carriers for nutrients and bioactive compounds in the gastrointestinal tract, but their poor stability under digestive conditions limits their application. This study investigated the effects of 0-5 wt% poly(vinyl alcohol) (PVA) on the microstructure, mechanical properties, and swelling behavior of CS cryogels under simulated gastrointestinal conditions. PVA incorporation increased the effective crosslinking density (ν_eff), bulk density (ρ_b), and Young's modulus (E). However, SEM suggested increased pore heterogeneity, accompanied by pore collapse and shrinkage at CS-P5. Under acidic conditions (pH 3.0), PVA significantly reduced the swelling ratio at 120 min (4.13 ± 1.13 to 1.06 ± 0.29). Gastric-phase swelling followed the Weibull model, with τ and β indicating rapid initial swelling for CS-P0 but a more gradual approach to equilibrium for the CS-PVA cryogels. In the intestinal phase, CS-P0 exhibited a dry mass gain after digestion (-0.28 ± 0.03 to 0.22 ± 0.20), suggesting entrapment of digestive components. Overall, moderate PVA incorporation decelerated hydration and improved structural stability, whereas excessive PVA increased pore heterogeneity. These findings establish a structure-swelling relationship under simulated gastrointestinal conditions, providing a structural basis for the rational design of CS-based cryogels delivery systems.