Robust gelatin/dialdehyde starch biofoams via yeast-induced in situ foaming: fabrication and properties

Bio-based porous carriers are widely used for controlled release, but pores formed under mild conditions in natural polymer matrices often come at the cost of structural integrity. In addition, conventional chemical foaming and crosslinking can introduce safety concerns. Here we couple yeast fermentation-driven foaming with Schiff-base crosslinking between gelatin and dialdehyde starch (DAS), so that the evolving bubble-derived pore structure can be progressively retained while pore walls consolidate into a three-dimensionally porous composite (GDS). FT-IR indicated imine formation between DAS aldehydes and gelatin ε-amino groups, with strong hydrogen-bonding interactions also evidenced. SEM showed an open, honey_comb-like network with a maximum porosity of 72.6%, whereas the yeast-free control reached only ∼19%. Even at high porosity, the crosslinked walls preserved shape after swelling, and the GDS samples showed improved thermal stability, reflected by a shift of the main degradation region toward higher temperatures. Aspirin (ASP) loading in the optimized matrix (ASP@GDS-4/70/6) produced biphasic release in PBS (pH 7.4): an early fraction (M_1h = 35.4%), close to a commercial 75 mg sustained-release aspirin tablet (30.6%), followed by a longer sustained-release phase (t₉₅ = 8 h vs 6 h). Overall release followed a first-order model (R² = 0.993). For M_t/M_∞ ≤ 0.60, Korsmeyer-Peppas fitting gave n = 0.66 (R² = 0.967), consistent with non-Fickian transport arising from coupled diffusion and polymer relaxation. This coupled foaming-and-crosslinking approach offers a mild route to interconnected porosity in natural polymer matrices.