Study of Printable and Biocompatible Alginate–Carbon Hydrogels for Sensor Applications: Mechanical, Electrical, and Cytotoxicity Evaluation

The development of printable, conductive, and biocompatible hydrogels has emerged as a promising strategy for the next generation of flexible and soft sensor platforms. In this study, we present a systematic investigation of alginate-based hydrogels incorporating different carbonaceous materials, natural graphite, carbon black (Vulcan V3), and activated carbon (PCO1000C), to evaluate their suitability for sensor applications. Hydrogels were formulated with varying concentrations of sodium alginate and a fixed loading of carbon additives. Each composite was characterized in terms of electrical conductivity under compression, rheological behavior, and mechanical strength. Printability was assessed using a custom-designed extrusion platform that allowed for the precise determination of the minimum force and optimal conditions required to extrude each formulation through a standard 20G nozzle. Among all tested systems, the alginate-graphite hydrogel demonstrated superior extrudability, shear-thinning behavior, and shape fidelity, making it well-suited for 3D printing or direct ink writing. A simple conductivity-testing device was developed to verify the electrical response of each hydrogel in the hydrated state. The effects of different drying methods on the final conductivity were also analyzed, showing that oven drying at 50 °C yielded the highest restoration of conductive pathways. Mechanical tests on printed structures confirmed their ability to maintain shape and resist compressive forces. Finally, the biocompatibility of the printed alginate-graphite hydrogel was validated using a standard cytotoxicity assay. The results demonstrated high cell viability, confirming the material's potential for use in biomedical sensing environments. This work offers a robust framework for the development of sustainable, printable, and biocompatible conductive hydrogels. The combined performance in printability, mechanical integrity, electrical conductivity, and cytocompatibility highlights their promise for flexible biosensors and wearable sensor technologies.