Polydopamine-Coating Nanoarchitectonics of Cellulose Hydrogels with Promoted Sustainable and Alkali-Resistant Natures for 3D Cell Culture Application

Sustainable and chemically resilient hydrogels are critically needed in biointerface engineering, particularly for 3D cell culture systems and surface modification under physiological to mildly alkaline conditions. However, physically cross-linked cellulose nanofiber (CNF) hydrogels─despite their renewable origin and biocompatibility─typically disintegrate at pH > 8, limiting their use in polydopamine (PDA)-based surface functionalization. Here, we present a simple and scalable physical treatment strategy to fabricate alkali-resistant, physically cross-linked hydrogels from carboxymethyl cellulose nanofibers (CMCF). By combining freeze-drying with mild thermal annealing (70 °C), the hydrogel network undergoes partial dehydration and ester bond formation via mild thermal condensation between carboxyl and hydroxyl groups, resulting in enhanced internal densification while preserving porosity and rehydration capacity. The resulting hydrogels remain structurally intact in Tris buffer (pH 9.7) and allow uniform in situ PDA coating at pH 8.5 on a physically cross-linked CMCF scaffold. The PDA-functionalized hydrogels exhibit interconnected porous microstructures, high water content (∼97 wt %), and robust mechanical and chemical stability. They support long-term 3D culture of EGFP-expressing human dermal fibroblasts for over 30 days, demonstrating excellent cytocompatibility and deep cell infiltration. This sustainable platform bridges green material design with functional surface engineering under alkaline conditions, and offers a versatile foundation for applications in regenerative medicine, selective ion adsorption, and environmental remediation.