Additive Manufacturing for Functional Coatings and Surface-Engineered Materials: Advances, Strategies, and Applications

Additive manufacturing (AM) enables the fabrication of complex three-dimensional architectures, yet the performance of many printed components is ultimately governed by their surfaces and interfaces. Functional coatings and surface-engineering strategies can introduce tailored chemical, physical, electrical, catalytic, optical, or biological properties while preserving the bulk characteristics of the printed material. This review focuses primarily on polymer-based AM, where surface engineering is particularly important because of limited intrinsic surface functionality, process-dependent morphology, and widespread use in microfluidics, sensing, and other functional devices. Metallic, ceramic, and hybrid systems are also considered to illustrate how substrate morphology, porosity, microstructure, and chemical and thermal stability influence coating formation and performance. The review critically examines functional composite feedstocks, chemical and plasma modification, wet-chemical and sol–gel deposition, vapor-phase processes, metallization, laser processing, and hybrid approaches. Particular emphasis is placed on the relationships among AM processing, surface morphology, coating–substrate interfaces, three-dimensional architecture, and application-level performance. Applications in microfluidics and microreactors, catalytic and environmental processes, energy and electrochemical systems, sensing, biomedical technologies, and industrial surfaces are discussed. Key challenges include functionalization of complex geometries, interfacial durability, reproducibility, standardized evaluation, scale-up, and sustainability. Emerging directions in surface-architecture co-design, flow-assisted functionalization, multiphysics modelling, and data-driven optimization are highlighted.