Waste-derived carbon scaffolds and carbon-hydrogel composites for sustainable regenerative engineering: From circular bioeconomy to clinical translation

The convergence of regenerative engineering and circular bioeconomy principles has stimulated growing interest in waste-derived carbon materials as candidates for sustainable scaffold design. This review critically examines porous carbon scaffolds and carbon-hydrogel composites derived from agricultural residues, food-processing byproducts, and polymeric waste for applications in bone, cartilage, wound, and neural tissue engineering. Particular emphasis is placed on feedstock selection, fabrication routes, purification requirements, structure-property-function relationships, and biological performance in vitro and in vivo. Waste-derived carbons offer tunable porosity, large surface area, electrical functionality, and adaptable surface chemistry, which together can support cell attachment, mineralization, angiogenesis, and electroactive tissue responses. Carbon-hydrogel systems further improve mechanical stability, swelling control, and multifunctionality, especially in soft and osteochondral tissue applications. At the same time, their translational promise is constrained by precursor heterogeneity, impurity removal, batch-to-batch reproducibility, long-term biosafety, and regulatory qualification. The review, therefore, evaluates these materials not only from a performance perspective but also through the lenses of standardization, sustainability, and clinical manufacturability. Overall, waste-derived carbon biomaterials are promising but remain preclinical platforms, and their future clinical relevance will depend on rigorous purification, quality control, and evidence-based translational pathways. This review aligns with Sustainable Development Goals (SDGs) 3, 9, and 12 by linking regenerative healthcare materials to sustainable waste valorization.