Medicinal horizons of lignin: A bioactive polymer beyond waste – A review

As aromatic biopolymer naturally occurring, lignin consists of approximately 15–30% of plant biomass, with an estimated annual global production of 50–70 million tons. Despite its abundance, most industrial lignin is still burned for energy recovery, limiting its value added utilization and contributing to emissions. Consisting of its intrinsic antioxidant, antimicrobial, UV-protective, and biodegradable properties, lignin has emerged as a promising renewable biomaterial for biomedical, pharmaceutical, and cosmetic applications. Its antimicrobial effects involve membrane disruption and inhibition of biofilm formation, supporting applications in wound healing and infection control while its antioxidant activity is primarily linked to phenolic hydroxyl groups that scavenge reactive oxygen species. This review comprehensively discusses lignin structure, occurrence, extraction methods, characterization techniques, and chemical modification strategies, with particular emphasis on emerging biomedical applications including wound dressings, hydrogels, drug delivery systems, tissue engineering, and bioactive composites. Furthermore, it highlights how lignin source and extraction method influence chemical composition, functional group distribution, reactivity, and biological performance. Current literature demonstrates increasing interest in environmentally friendly extraction processes and lignin-based biomaterials however, clinical translation remains constrained by structural heterogeneity, batch-to-batch variability, limited reproducibility, insufficient long-term biocompatibility and cytotoxicity studies, inadequate in vivo and clinical evaluations, and the absence of standardized extraction, characterization, sterilization, and biological testing protocols for medical applications.