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.

Novel protein blends have been prepared by mixing gelatin (G) with Bombyx mori silk fibroin (SF) and using aqueous methanol (MeOH) to post-induce SF crystallization. When co-cast from solution, amorphous blends of these polymers appear homogeneous, as discerned from visual observation, microscopy, and Fourier-transform infrared (FTIR) spectroscopy. Upon subsequent exposure to aqueous MeOH, SF undergoes a conformational change from random coil to beta sheet. This transformation occurs in pure SF, as well as in each of the G/SF blends, according to X-ray diffractometry and thermal calorimetry. The influence of MeOH-induced SF crystallization on structure and property development has been ascertained in terms of preparation history and blend composition. Thermal gravimetric analysis reveals that the presence of beta sheets in SF and G/SF blends improves thermal stability, while extensional rheometry confirms that SF crystallization enhances the tensile properties of the blends. By preserving a support scaffold above the G helix-to-coil transition temperature, the formation of crystalline SF networks in G/SF blends can be used to stabilize G-based hydrogels for biomaterial and pharmaceutical purposes. The present study not only examines the properties of G/SF blends before and after SF crystallization, but also establishes the foundation for future research into thermally responsive G/SF bioconjugates.

Environmentally‐responsible materials processing is becoming an important global consideration in a wide variety of technologies, especially those wherein volatile and/or residual organic solvents cannot be tolerated. In this context, polymer processing has benefited tremendously from advances achieved using high‐pressure CO2 as a viscosity modifier, plasticizing agent, foaming agent, and reaction medium. Pressurized CO2 is environmentally benign, inexpensive, sustainable, and versatile owing to its gas‐like viscosity and liquid‐like solubility, which can be tuned through judicious choice of temperature and pressure. The addition of high‐pressure CO2 to homopolymer blends and block copolymers can have a profound impact on polymer thermodynamics and kinetic processes since the number of interacting species increases. As a result, the compressibility as well as plasticization and intermolecular screening effects become non‐negligible. In this work, we review how these factors influence such polymeric systems, and discuss commercial polymer processes and applications that benefit from the use of high‐pressure CO2.

Highly asymmetric metal‐containing block copolymers are capable of forming nanotubes in solutions containing a nonpolar solvent. In this study, the time‐dependent formation of these nanotubes is investigated and reveals how the aggregate nanostructures develop (see figure for an example at an early stage). These nanotubes are semicrystalline (see the diffraction pattern in the inset), suggesting that crystallization is at least partially responsible for the unique morphology formed by these block copolymers.