Degree of deacetylation governs gelation mechanism, rheology, and 3D printability of chitosan ionogels

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Abstract
Chitosan-based ionogels are promising materials for extrusion-based processing, yet the influence of degree of deacetylation (DDA) on gelation and printability remains poorly understood. Here, chitosans with different DDA and molecular weight were dissolved in 1-ethyl-3-methylimidazolium acetate (EMImAc) to establish structure–network–processing relationships through rheology and 3D printing. Oscillatory rheology revealed distinct DDA-dependent pathways toward network formation. Chitosan with 76% DDA developed elastic domains at lower concentrations, consistent with associations involving residual acetylated units, hydrogen bonding, hydrophobic interactions, and residual ordered regions. These domains remained weakly interconnected until increasing chain overlap established long-range connectivity. In contrast, 90% DDA chitosan exhibited delayed but highly cooperative network development. Despite comparable complex viscosities, only the 90% DDA ionogels exhibited homogeneous extrusion and high printing fidelity. Nonlinear rheology revealed that lower-DDA ionogels generated larger first normal stress differences and greater structural recovery, indicating a resilient network that accumulated recoverable elastic stresses and hindered stable extrusion. The best printing performance was achieved with 4.5 wt.% 890 kDa chitosan (90% DDA). Overall, DDA governs network formation and the resulting nonlinear rheological response, ultimately determining extrusion stability and printability.

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