Biofabrication techniques such as extrusion-based 3D bioprinting have transformed tissue engineering by enabling the precise deposition of biomaterials bioinks, which can be used to create complex structures. However, the development of biomaterial bioinks that exhibit mechanical integrity, biocompatibility, and functional properties such as electrical conductivity remains a major challenge. In this study, a sustainable colloidal formulation strategy is proposed for incorporating reduced graphene oxide (rGO) into cellulose nanofiber (CNF) suspensions. This strategy eliminates the need for in situ chemical reduction and reduces the resulting toxicity. By leveraging electrostatic interactions and the intrinsic colloidal stability of the system, the method enhances control over the formulation process and facilitates the development of reproducible, efficient, and cytocompatible bioinks suitable for extrusion-based 3D bioprinting. For its validation, comprehensive rheological and printability analyses were carried out. Formulations containing 0.05 % and 0.1 % rGO were identified as the optimal for extrusion-based 3D bioprinting, demonstrating high structural fidelity and resolution. Preliminary biological assays using human astrocyte stem cells have confirmed excellent cytocompatibility, thereby promoting cell adhesion, proliferation, and survival, while minimizing cytotoxic effects. The incorporation of rGO into the hydrogels resulted in the enhancement of electrical conductivity, thereby expanding their application potential in the field of electrically active tissue regeneration. In summary, the CNF-rGO hybrid bioinks developed herein represent a promising, scalable, and cytocompatibility platform for advanced neural tissue engineering and other biomedical applications requiring electrically conductive scaffolds.
