Advances in multi-material polymer 3D printing depositions: techniques, materials combinations, challenges, and emerging applications

Multi-material polymer additive manufacturing enables the fabrication of components with spatially varied mechanical, thermal, electrical, and functional properties within a single build, overcoming the intrinsic limitations of single-material 3D printing. By combining thermoplastics, elastomers, photopolymers, and functional polymer composites, this approach allows material composition to be programmed alongside geometry, enabling monolithic fabrication of multifunctional and heterogeneous polymer systems. This review critically surveys recent advances in multi-material polymer additive manufacturing across major process families, including material extrusion, vat photopolymerization, material jetting, powder bed fusion, and emerging hybrid platforms. Key material systems and deposition strategies are examined with particular emphasis on interfacial adhesion, thermal-mechanical compatibility, and process reliability, which collectively govern the performance of multi-material printed parts. The review further synthesizes current challenges related to material integration, hardware and software complexity, and post-processing, and highlights representative application domains such as soft robotics, biomedical devices, embedded electronics, aerospace tooling, and functionally graded structures. By consolidating fabrication strategies, material considerations, and application-driven insights, this work provides a structured reference for advancing the design and implementation of multi-material polymer additive manufacturing.