Asymmetric Hydrogel Membranes from Cationized Chitosan and Chitin Whiskers via Direct Ink Writing for Advanced Wound Care

Skin wounds pose significant clinical and economic challenges, driving the need for advanced dressing materials capable of protecting the injury, supporting tissue regeneration, maintaining moisture, and preventing infection. Polysaccharide-based hydrogels have gained attention for these applications due to their hydrophilicity, biocompatibility, and repair-promoting properties. In this work, we developed a fully aqueous ink for direct ink writing (DIW) 3D printing composed of N-(2-hydroxy)-propyl-3-trimethylammonium chitosan chloride (HTCC), beta-chitin whiskers (ChW), and genipin as a nontoxic cross-linker. HTCC, a cationic and water-soluble chitosan derivative, was synthesized via reaction with glycidyltrimethylammonium chloride, while ChW were produced by acidolysis of beta-chitin, yielding high-aspect-ratio nanocrystals. Their combination generated a composite ink with synergistic features: HTCC provided cationic functionality and solubility, whereas ChW imparted mechanical reinforcement and anisotropy. Notably, ChW significantly strengthened the hydrogel network, increasing the compressive modulus from 5.9 to 24.1 kPa and the tensile strength from 19.3 to 78.0 kPa, representing a 4-fold improvement. The formulation displayed rheological properties suitable for DIW, including viscoelasticity, shear-thinning behavior, and rapid thixotropic recovery. Such features enabled high-resolution 3D printing of asymmetric membranes with a dense outer layer (OL) and a porous inner layer (IL) with a honeycomb-like microarchitecture. The membranes were effectively cross-linked by genipin, remained stable in physiological buffer, and exhibited controlled enzymatic degradation in lysozyme. Besides, both OL and IL demonstrated contact-active antibacterial activity against Staphylococcus aureus and Escherichia coli, arising from the polyelectrolytic nature of HTCC. Importantly, assays using mouse fibroblast assays confirmed that the material extracts were noncytotoxic. Taken together, these results demonstrate that HTCC/ChW-based asymmetric hydrogels constitute a sustainable and multifunctional platform for wound dressings, integrating structural asymmetry, biodegradability, mechanical robustness, and intrinsic antibacterial properties.