Engineering lignin-incorporated hydrogels for agricultural and environmental applications: From synthesis to...

Petroleum-based hydrogels dominate agriculture and environmental remediation, but their fossil dependence and environmental persistence raise sustainability concerns. Lignin, comprising approximately 15-30% of lignocellulosic biomass with global production exceeding 50 million tons annually, remains largely underutilized with over 95% burned as low-value fuel. This review examines lignin-incorporated hydrogels from an engineering and agricultural implementation perspective, focusing on translating molecular design into scalable manufacturing and field deployment. Common synthesis approaches include physical self-assembly, enzymatic crosslinking, chemical grafting, and additive manufacturing. Lignin incorporation enhances mechanical strength and introduces functional capabilities for controlled-release fertilizers, soil conditioning, water retention, and pollutant remediation. Unlike previous reviews emphasizing synthesis methods, we critically analyze lignin-polymer interfacial interactions, network topology control, and process robustness from agricultural implementation standpoints to clarify the distinctive engineering challenges and opportunities. Emerging advances including AI-driven formulation optimization, microfluidic synthesis platforms, and real-time process monitoring are integrated with emphasis on their relevance to scalable production. Key barriers include lignin heterogeneity causing property variations, limited solubility, and challenges. This review emphasizes practical solutions including controlled chemical modification, hybrid material design, standardized production routes, and circular biorefinery integration, thereby establishing an engineering-oriented framework to advance lignin-based hydrogels toward sustainable agricultural and environmental applications.