Jessica Borges-Vilches, Tuuli Virkkala, Valentina Guccini, Marko Crivaro, Thaddeus Maloney, Tekla Tammelin, Eero Kontturi
Abstract: Stimuli-responsive hydrogels are interesting, particularly in the realm of biomedicals, but often the fundamental response of their key physical properties is not simultaneously monitored. Here, we investigated the pH response on the porosity, rheological behavior, mechanical performance, and molecular diffusivity of a hydrogel system composed of two bio-based components: gelatin and rod-like cellulose nanocrystals (CNCs). By leveraging the pH-responsive nature of gelatin, we systematically examined the structural properties of these hydrogels formed under three pH conditions: below (pH 5), above (pH 11), and at the isoelectric point (pH 8) of type A gelatin. All hydrogels exhibited a distinct cellular architecture, characterized by micron-scale tubular pores with embedded mesopores. Increasing pH upon the hydrogel crosslinking promoted the formation of more porous structures with significantly enhanced mechanical performance. The effect on the Young's modulus was significant: with a 3-fold increase compared to its counterparts, the hydrogel fabricated at pH 11 exhibited the stiffest structure. This improvement in hydrogel stiffness with pH further restricted the molecular diffusivity within the hydrogels to some extent, as evidenced by Fluorescence Recovery After Photobleaching analysis using fluorescein isothiocyanate-dextran as a diffusion probe. Overall, this study presents a straightforward and effective strategy for fabricating pH-tunable hydrogels, providing valuable insights for the design of responsive biomaterials with potential applications in soft tissue engineering and drug delivery.
