Advanced collagen nanofibers-based functional bio-composites for high-value utilization of leather: A review

Natural leather with outstanding biomimetic properties is the main application of animal skin. However, the traditional tannery industry is facing serious issues of sustainability, such as low value addition and high environmental pollution. Upscaled functional leather (UFL) inherits all the natural properties of leather and combines it with other cross-domain functions, due to which it has gained considerable attention as advanced functional bio-based materials. This review briefly introduces the multi-hierarchical structure and preponderant properties of leather as a natural biomass. Further emphasis is on UFL, which includes electromagnetic (EM) wave absorbing leather, infrared absorbing leather, X-ray shielding leather, flexible conductive leather, flame-retardant leather, antibacterial leather, self-cleaning leather as well as water-, oil-, and soil-repellent leather. Furthermore, the fabrication methods of these UFLs, their merits and their respective applications are comprehensively discussed. Moreover, possible challenges and outlooks for the development of UFL are proposed. This review describes how UFL will expand the scope of applications and significantly improve the ontological value of natural leather. Significantly, UFL is expected to boost the sustainable development of conventional leather industry and the next-generation of advanced functional bio-based materials.