From waste to wealth: Advancing sustainability with state-of-the-art progress of cellulose nanocrystals and its composites for biomedical applications: A review

• Circular economy principles can help in reducing the impact on natural resources. • Summarizes recent advances in the extraction and functionalization of cellulose nanocrystals (CNCs) from agricultural and industrial waste. • Reviews the development of CNC-based composites for drug delivery, tissue engineering, wound healing, and biosensing. • Sustainability and circular bioeconomy perspectives by valorizing lignocellulosic waste into high-value biomedical materials. Recent advances in cellulose nanocrystals (CNCs) have significantly expanded their potential in biomedical applications, driven by their high surface area, biodegradability, and ability to be functionalized for specific biological interactions. The CNC market is projected to reach approximately USD 1 billion by 2030. This review critically examines the latest developments in CNC extraction methods, highlighting conversion of waste to wealth hydrolysis-based techniques that offer improved yield and reduced environmental impact. It also explores innovative surface modification strategies, such as peptide conjugation and polymer grafting, which have enhanced CNCs’ performance in targeted drug delivery and tissue scaffolding. Particular emphasis is placed on CNC-based hydrogels and aerogels, which have demonstrated improved cell adhesion, controlled drug release profiles, and antimicrobial efficacy in recent in vitro and in vivo studies. Despite this progress, issues such as batch variability and cytotoxicity in long-term implantation remain. To address these issues, the review highlights promising directions, including the development of standardized protocols for biological testing, scalable green synthesis pathways, and the integration of CNCs with other nanomaterials. Overall, the review synthesizes emerging evidence that positions CNCs as a viable, multifunctional platform for next-generation biomedical technologies, while outlining practical strategies to bridge the gap between experimental promise and clinical implementation.