Additive manufacturing of chitosan and its derivatives: Advancing safe and sustainable by design (SSbD) materials

Chitosan is one of the most versatile bio-based polymers explored for additive manufacturing (AM) due to its biocompatibility, tunable chemistry, and ability to form hydrogels with controlled architecture. Over the past two decades, a rapidly expanding body of literature has investigated AM routes to process chitosan-based formulations into three-dimensional constructs with predefined shape and porosity, primarily for biomedical applications. This review provides a critical and up-to-date overview of recent advances in the AM of chitosan and its derivatives, emphasizing structure-process-property relationships linking chitosan chemistry, processing routes, and the performance of 3D-printed hydrogels. After outlining industrial production routes and market-related aspects, key scientific and technological challenges for chitosan AM are discussed through the lens of the Safe and Sustainable by Design (SSbD) framework, as a representative approach to circular economy-driven materials innovation. The review systematically analyzes AM strategies based on chitosan deprotonation/desolvation, ionotropic gelation, polyelectrolyte complexation, and covalent stabilization. Emerging formulations based on chemically modified derivatives (e.g., carboxymethyl chitosan or chitosan methacryloyl) and their stabilization in aqueous media via ionic interactions or photoreactions are also examined. Finally, current limitations and future perspectives are highlighted, focusing on reproducibility, safety, sustainability, and translational pathways for advanced biomedical applications.