Graphical Schematic illustration of the key elements in 3D printed OC scaffolds. Figure created with BioRender.com.

Metal-based additive manufacturing has gained significant attention in the field of medical implants over the past decade. The application of 3D-printing technology in medical implants offers several advantages over traditional manufacturing methods, including increased design flexibility for implant customization, reduced lead time for emergency cases, and the ability to create complex geometry shapes for patient-specific implants. In this review study, the working principles and conditions of metal 3D-printing technologies such as selective laser sintering, selective laser melting, and electron beam melting, as well as their applications and advantages in the medical field, are investigated in detail. The application scenarios and research status of non-degradable metals including titanium alloy, medical stainless steel, etc., and degradable metals like magnesium alloy are introduced as printing materials. We discuss the improvement of mechanical properties and biocompatibility of implants through surface modification, porous structure design, and the optimization of molding processes. Finally, the biocompatibility issues and challenges caused by the accuracy of CT imaging, fabrication, implant placement, and other aspects are summarized.

The commonly used titanium alloy dental implants currently apply solid structures. However, issues such as stress shielding and stress concentration may arise due to the significant difference in elastic modulus between the implant and host. In order to address these problems, this paper proposes five porous structures based on the Gibson-Ashby theoretical model. We utilized selective laser melting technology to shape a porous structure using Ti-6Al-4V material precisely. The mechanical properties of the porous structure were verified through simulation and compression experiments. The optimal porous structure, which best matched the human bone, was a circular ring structure with a pillar diameter of 0.6 mm and a layer height of 2 mm. The stress and strain of the porous implant on the surrounding cortical and cancellous bone under different biting conditions were studied to verify the effectiveness of the optimal circular ring porous structure in alleviating stress shielding in both standard and osteoporotic bone conditions. The results confirm that the circular ring porous structure meets implant requirements and provides a theoretical basis for clinical dental implantation.

Microextrusion 3D bioprinting is a comparatively easy method to fabricate structures in tissue engineering. But high viscosity and wall shear stress in the tube and nozzle often lead to low cell survival rate of printed tissue. To reduce the viscosity and shear stress of materials in biological 3D printing, a multidimension microvibration assisted hydrogel 3D printing method was proposed. The compliant mechanism driven by piezoceramic was applied to 3D printing of hydrogels. The shear stress and viscosity of hydrogels could be effectively reduced by multidimension microvibration. Simulation analysis of the extrusion device was carried out to study the influence of vibration parameters on viscosity and shear stress, and optimized multidimension vibration forms and vibration parameters were selected for experiments. The experiment results show that multidimension microvibration can effectively reduce the viscosity of hydrogels and improve printing resolution and print speed.

The stress shielding effect is a critical issue for implanted prosthesis due to the difference in elastic modulus between the implanted material and the human bone. The adjustment of the elastic modulus of implants by modification of the lattice structure is the key to the research in the field of implanted prosthesis. Our work focuses on the basic unit structure of octahedron Ti6Al4V. The equivalent elastic modulus and equivalent density of porous structure are optimized according to the mechanical properties of human bone tissue by adjusting the edge diameter and side length of octahedral lattice. Macroscopic long-range ordered arrangement of lattice structures is fabricated by selective laser melting (SLM) technology. Finite element simulation is performed to calculate the mechanical property of octahedron Ti6Al4V. Scanning electronic microscopy is applied to observe the microstructure of octahedron alloy and its cross section morphology of fracture. Standard compression test is performed for the stress–strain behavior of the specimen. Our results show that the octahedral lattice with the edge diameter of 0.4 mm and unit cell length of 1.5 mm has the best mechanical property which is close to the human bone. The value of equivalent elastic modulus increases with the increase in the edge diameter. The SLM technology proves to be an effective processing way for the fabrication of complex microstructures with porosity. In addition, the specimen exhibits isotropic mechanical performance and homogeneity which significantly meet the requirement of implanted prosthetic medical environment.