Additive manufacturing of sustainable bio-based composites: Challenges and new opportunities

Additive manufacturing (AM) enables the fabrication of complex, customized structures with efficient material use. In parallel, the global imperative for sustainable materials has intensified interest in bio-based composite materials derived from renewable biological sources and often reinforced with natural fibers or fillers. This review critically examines the convergence of AM and bio-based composites, offering a comprehensive analysis of current advancements, technical challenges, and future directions. It explores the suitability of various AM techniques, such as material extrusion (ME), vat photopolymerization, powder-based methods, etc., for processing bio-based polymers including cellulose, lignin, chitosan (CS), polylactic acid (PLA), etc. Key challenges such as poor thermal stability, low crosslinking density, and printability limitations are discussed alongside emerging strategies for overcoming them, including chemical modification, hybrid composite design, and parameter optimization. The review further delves into the evolution of 4D printing with bio-based stimuli-responsive materials, enabling applications in soft robotics, smart packaging, regenerative medicine, etc. By synthesizing interdisciplinary advances from materials science, mechanical engineering, and environmental design, this article highlights both the promise and complexity of integrating sustainability and functionality in AM. The insights provided serve as a roadmap for developing high-performance, eco-conscious systems that align with global sustainability goals.