Advances and challenges in 3D-Printed microporous titanium alloy implants for reconstruction of humeral segmental bone defects

Segmental defects of the humerus often result from high-energy trauma, infectious osteonecrosis, or tumor resection. These defects lead to significant disability and functional loss, posing ongoing challenges for orthopedic reconstruction. Autografts, allografts, and conventional metallic fixations have limitations, including graft scarcity, immunogenicity, and stress shielding. These challenges underscore the need for alternative solutions. In the past decade, 3D-printed microporous titanium (Ti) alloy implants have gained attention due to their customizable mechanical properties and inherent bioactivity. This review summarizes recent advancements in materials science, manufacturing technologies, and biomedical applications of microporous Ti alloys for humeral reconstruction. First, we discuss their excellent biocompatibility and how pore architecture influences elastic modulus and fatigue life. We emphasize gradient porosity as a design principle that balances mechanical integrity with osteogenesis. Second, evidence from animal models and finite-element analyses is presented, showing enhanced osteoconduction, angiogenesis, and mechanobiological signaling. The osteoinductive and anti-infective potential of surface functionalization, including BMP-2 or VEGF immobilization and bioactive coatings, is also evaluated. In clinical practice, we explore patient-specific scaffold design workflows, intraoperative considerations, and representative case outcomes. Persistent challenges, such as residual unmelted powder, fatigue crack initiation and propagation, non-standardized manufacturing protocols, and economic barriers, are also identified. We recommend fatigue-testing protocols tailored to humeral loading patterns, multicenter randomized controlled trials, and longitudinal follow-up for at least five years to accelerate the intelligent, functional, and standardized translation of this technology. With these advancements, 3D-printed microporous Ti alloy implants offer promise as a key strategy for reconstructing large segmental defects in long bones.