Additive manufacturing of metallic implants: a comprehensive review of material selection, porous architecture, and hybrid surface engineering

Abstract

Additive manufacturing (AM) of metallic implants is shifting from geometry replication toward integrated control of load transfer, tissue interaction, and surface stability. Nevertheless, the literature remains fragmented, often optimizing biomaterials, architectures, AM processes, and bioactive coatings as separate components despite their coupled performance. This review proposes an integrated design framework that connects patient anatomy, material selection, architected porosity, AM technology, and hybrid surface engineering into a unified development pathway. CT/MRI-based design and topology optimization are presented for a lattice topology, with the aim of achieving precise volumetric porosity levels between 50% and 85% to bring effective stiffness into the physiological range of human bone, approximately 0.01–20 GPa. Titanium, Co-Cr alloys, and 316L stainless steel, as well as magnesium alloys, are critically compared with hydroxyapatite, bioactive glass, and hierarchical hybrid coatings to demonstrate how multilayer functionality can overcome limitations of metallic substrates. Coating performance correlates with adhesion, degradation, and cellular response, which treats biological evaluation as an interconnected metric rather than an isolated endpoint. It discusses critical trade-offs where increased porosity improves mechanical compatibility, but retention of fatigue strength above cortical bone thresholds of 40–60 MPa remains a profound manufacturing challenge; increased coating complexity increases the risk of interfacial failure, and accelerated degradation compromises retention of structural integrity. The review concludes by identifying manufacturing reproducibility, coating durability on complex lattices, and regulatory qualification as the leading barriers to clinical translation.