Rheology-guided experimental design of dynamically crosslinked keratin/ι-carrageenan hydrogels as potential drug delivery systems.

This study establishes a deterministic framework for designing 3D-printable, dynamically crosslinked hydrogel inks for controlled drug delivery via Direct Ink Writing (DIW). By blending cysteine-S-sulfonated keratin with ι-carrageenan through Ca2+ ionotropic gelation, shear-responsive networks were created. A Design of Experiments (DoE) approach generated a predictive rheology-to-printability map correlating composition with storage modulus (G'), flow stress (τf), and printability index (Pr). Advanced Large Amplitude Oscillatory Shear (LAOS) profiling revealed a transition from ductile, entanglement-driven networks in keratin-rich blends to brittle yielding via cooperative ionic junction rupture in crosslinked systems. Sequence of Physical Processes (SPP) analysis further identified an intracycle recovery loss factor (tanδrec) that dictates post-deposition shape retention. Structural analyses verified that Ca2+ drives network compaction and crystalline β-sheet reorganization. Crucially, dexamethasone (Dex) loading acts as a dual-functional modulator via supramolecular hydrogen bonding: behaving as an interfacial sliding agent that reduces interchain friction within densely crosslinked matrices, while acting as a secondary physical crosslinker in weakly crosslinked networks, which amplifies elastic energy storage and induces viscous Lissajous-Bowditch loop expansions. Finally, mathematical modeling confirmed that ionic crosslinking shifts drug transport from anomalous diffusion to a relaxation-controlled Super Case II regime governed by the relaxation rate (kr).