Swelling behavior and morphological evolution of mixed gelatin/silk fibroin hydrogels

Mixed protein-based hydrogels have been prepared by blending gelatin (G) with amorphous Bombyx mori silk fibroin (SF) and promoting beta-crystallization of SF via subsequent exposure to methanol or methanol/water solutions. The introduction of beta crystals in SF serves to stabilize the hydrogel network and extend the solidlike behavior of these thermally responsive materials to elevated temperatures beyond the helix-->coil (h-->c) transition of G. In this work, we investigate the swelling and protein release kinetics of G/SF hydrogels varying in composition at temperatures below and above the G h-->c transition. At 20 degrees C, G and G-rich mixed hydrogels display evidence of moderate swelling with negligible mass loss in aqueous solution, resulting in porous polymer matrixes upon solvent removal according to electron microscopy. When the solution temperature is increased beyond the G h-->c transition to body temperature (37 degrees C), these gels exhibit much higher swelling with considerable mass loss due to dissolution and release of G. The extent to which these properties respond to temperature decreases systematically with increasing SF content. The unique temperature- and composition-dependent properties of G/SF hydrogels dictate the efficacy of these novel materials as stimuli-responsive delivery vehicles.