Combination of 3D Printing with Traditional Fabrication Techniques in Bone Tissue Engineering Scaffolds: A Review

Large bone defects that fail to heal require scaffolds that combine load transfer, interconnected multiscale porosity and bioactivity, and no single fabrication route currently provides all three. 3D printing controls macro-architecture and patient-specific geometry but cannot readily produce the sub-100 µm and nanoscale features that govern cell attachment. Conventional methods such as particulate leaching, freeze-drying, gas foaming, phase separation and electrospinning create such features but offer little control over global architecture. Previous reviews have covered combined additive manufacturing across tissue types or focused on single pairings, mainly with electrospinning. This review focuses on bone and examines hybrid routes technique by technique. We first review the main 3D printing technologies and how each has been combined with other fabrication methods. We then analyse the rationale for integration and extend an established three-level integration framework with the role of the printed part (permanent framework or sacrificial template) and the processing sequence. Representative studies are compared using consistent metrics for material composition, processing sequence, pore size, porosity, mechanical properties and level of biological evidence, and are benchmarked against native cortical and trabecular bone. Most hybrid scaffolds reproduce trabecular-like porosity and stiffness but remain well below cortical bone in strength, and the evidence comes largely from in vitro and small-animal studies. We close with a structured map of research gaps, including interfacial integrity, standardised characterisation, cell-compatible processing, scalability and large-animal validation, and outline the studies needed to address them.