Lignin-based additive materials: A review of current status, challenges, and future perspectives

Additive manufacturing, using three-dimensional (3D) printing technology, is considered revolutionary in manufacturing, pharmaceutical, food, and biomedical industries, as it provides a platform for constructing a wide range of tailored object geometries. This rapidly growing technology mainly uses renewable natural polymers combined with synthetic materials to achieve the printability with desired features of the printed 3D structures. Among different polymers, lignin is receiving immense consideration as a renewable bio-based raw material for manufacturing high-performance 3D printed products owing to its amorphous macromolecular structure and antioxidative, antimicrobial, and other beneficial properties. Lignin is a natural organic polymer found in all plants, particularly wood and tree bark, with few exceptions like bryophytes. It accounts for about 30% of the total biomass worldwide, ranking it as the second most abundant renewable material after cellulose. Despite such advantages, the complex polymeric and amorphous structure of lignin is a great challenge to its utilization in 3D printing for the manufacturing of high-value-added products. This review summarizes the use of lignin in the preparation of ink for the 3D printing of different materials, such as degradable composites, hydrogels, and 3D thermoplastic materials. This review discusses the potential merits and limitations of different types of lignin and their innate features in the preparation of 3D printed materials. The challenges and future perspectives for use of lignin in the preparation of ink for 3D printing are also discussed to underscore the critical issues and opportunities.