Valorisation of collagen and keratin from animal hides and skins for sustainable functional and smart leather applications: A review

Leather material is essential for crafting items such as shoes, clothing, gloves, leather goods, and car interiors. Conventional leather manufacturing is facing environmental, sustainability, and low value addition challenges. Leather manufacturing generates substantial collagen- and keratin-rich residues that remain underutilized despite their potential as renewable feedstocks for high-value materials. This review critically examines the valorisation of collagen and keratin from hides, skins, and associated tannery wastes for the development of sustainable functional and smart leather. The review links the molecular structure and physicochemical characteristics of these proteins with their roles in leather functionalization and emerging electronic applications. Recent studies demonstrate that functionalization can impart antibacterial, flame-retardant, hydrophobic, self-cleaning and thermal properties, while incorporation of conductive nanomaterials enables sensing, energy harvesting and electronic functionality. For example, leather-based strain sensors have achieved gauge factors as high as 7238.92, while MXene/leather triboelectric systems have generated output voltages of 199.56 V and power densities of 0.469 mW cm⁻². Natural sheepskin-based electronic skins have further demonstrated multimodal human-health monitoring, while leather-based tactile sensor arrays coupled with machine-learning algorithms have achieved 93.75% accuracy for object-hardness recognition and 92.29% accuracy for human-interaction-intention recognition. These advances indicate a transition from passive functional leather toward sensing and intelligent leather systems. However, challenges remain in conductive-network uniformity, sensor durability, multimodal integration, power management, signal processing, manufacturing scalability and long-term environmental stability. The review therefore identifies key material, technological and system-level requirements for converting tannery-derived collagen and keratin into sustainable, multifunctional and intelligent leather platforms, while highlighting research priorities for industrial translation and circular leather.