Research and Clinical Applications of Selective Laser Melted Tantalum Bone Plates

Academic Background

In the field of orthopedic implants, titanium (Ti)-based alloys and tantalum (Ta) are widely used due to their high biocompatibility. Titanium-based alloys are typically used to manufacture load-bearing implants, such as bone plates and femoral stems, while tantalum, due to its high density and excellent bone tissue affinity, is often used in porous forms or as a coating material. However, traditional manufacturing methods, such as chemical vapor deposition (CVD), cannot precisely control the topological characteristics of porous structures, limiting the application of tantalum in orthopedic implants. In recent years, additive manufacturing (AM) technology, particularly selective laser melting (SLM), has provided new possibilities for manufacturing personalized implants with complex porous structures. This study aims to fabricate tantalum bone plates using SLM technology and evaluate their performance as internal fixation materials for fractures.

Source of the Paper

This paper was authored by a research team from the Department of Orthopedics at the Affiliated Zhongshan Hospital of Dalian University. The main authors include Dewei Zhao, Baoyi Liu, Feng Wang, Zhijie Ma, and Junlei Li. The paper was published online on December 27, 2024, in the journal Bio-design and Manufacturing, with the DOI 10.1631/bdm.2300321.

Research Process

1. Sample Preparation

The research team used spherical Ti6Al4V (extra low impurity, ELI) and tantalum powder with a purity of >99.95% to fabricate Ti6Al4V and tantalum disk samples (20 mm in diameter, 2 mm in thickness) via selective laser melting (SLM). The manufacturing parameters for Ti6Al4V were: layer thickness of 30 μm, laser power of 150 W, exposure time of 40 μs, spot pitch of 50 μm, and hatch distance of 60 μm. For tantalum, the parameters were: exposure interval of 100 μs, laser power of 260 W, layer thickness of 30 μm, spot pitch of 50 μm, and hatch distance of 65 μm. The samples were sandblasted to remove surface metal particles, polished with SiC sandpaper up to 2000 grit, and finally ultrasonically cleaned and dried.

2. Material Characterization

The surface morphology and elemental composition of the samples were observed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Phase composition was analyzed using X-ray diffraction (XRD). Contact angle tests were used to characterize surface energy, and surface roughness was measured using confocal laser scanning microscopy (CLSM). Tensile tests were conducted to evaluate mechanical properties, including yield strength, ultimate tensile strength, and elongation at break.

3. Cell Culture

Mouse calvaria-derived osteogenic cells (MC3T3-E1 cells) were used for cell proliferation, morphology, and differentiation experiments. The cells were cultured in α-MEM medium supplemented with 10% fetal bovine serum. Cell proliferation was assessed using the CCK-8 kit, cell viability was evaluated using live/dead cell staining, and cell morphology was observed using CLSM. The expression levels of osteogenic-related genes (Runx2, ALP, OCN, OPN, Col-1) were detected using quantitative real-time PCR (qPCR).

4. In Vitro Macrophage Response

RAW 264.7 macrophages were used to evaluate the effects of SLM Ti6Al4V, SLM Ti6Al4V with Ta coating, and SLM Ta on macrophage polarization. Immunofluorescence staining was used to detect the expression of iNOS and CD206, flow cytometry was used to analyze the surface markers of M1 and M2 macrophages (CCR7 and CD206), and a mouse cytokine array panel was used to detect the expression levels of inflammatory factors.

5. Animal Experiments

SLM Ti6Al4V, SLM Ti6Al4V with Ta coating, and SLM Ta rods were implanted into the femoral condyle of New Zealand rabbits. Bone integration performance was evaluated after 6 weeks. Bone-implant contact (BIC) and new bone formation were observed using Van Gieson (VG) staining, and the stability of the implants was assessed using push-out force tests.

6. Clinical Trial

From September 2021 to February 2023, 20 patients with limb fractures (14 males and 6 females) were selected for internal fixation surgery using SLM porous tantalum bone plates. Postoperative fracture healing was evaluated using X-rays.

Main Results

1. Material Characterization

The surface roughness of SLM Ti6Al4V and SLM Ta was similar, at 2.000 μm and 2.046 μm, respectively, while the surface roughness of SLM Ti6Al4V with Ta coating was 2.208 μm. SLM Ti6Al4V had the highest surface energy (40.6 mN/m), followed by SLM Ta (35.3 mN/m), and SLM Ti6Al4V with Ta coating had the lowest surface energy (33.1 mN/m). Tensile tests showed that SLM Ta had the highest plastic deformation ability, while SLM Ti6Al4V had the highest tensile strength.

2. Cell Culture

MC3T3-E1 cells exhibited significantly better proliferation, adhesion, and osteogenic differentiation on SLM Ta and SLM Ti6Al4V with Ta coating surfaces compared to SLM Ti6Al4V. qPCR results showed that the expression levels of osteogenic-related genes were significantly higher on SLM Ta and SLM Ti6Al4V with Ta coating surfaces than on SLM Ti6Al4V.

3. Macrophage Response

SLM Ta significantly promoted macrophage polarization toward the M2 phenotype and inhibited the secretion of inflammatory factors. Flow cytometry showed that the proportion of M2 macrophages in the SLM Ta group was significantly higher than in the SLM Ti6Al4V group.

4. Animal Experiments

The SLM Ta group had the highest bone-implant contact (BIC) and new bone formation area. Push-out force tests showed that the stability of SLM Ta implants was significantly better than that of SLM Ti6Al4V.

5. Clinical Trial

All patients achieved good fracture healing, with an average surgery time of 56 minutes and an average blood loss of 145.6 ml. X-rays showed that the fracture line completely disappeared 3-6 months after surgery.

Conclusion

This study fabricated porous tantalum bone plates using SLM technology and verified their superior performance as internal fixation materials for fractures. SLM Ta exhibited excellent mechanical properties, anti-inflammatory activity, and bone integration ability, promoting fracture healing and avoiding the need for secondary surgery. This research provides new insights into the personalized design and manufacturing of orthopedic implants, with significant scientific and application value.

Research Highlights

1. Innovative Manufacturing Technology: For the first time, porous tantalum bone plates were fabricated using SLM technology, enabling precise control of complex porous structures.
2. Excellent Biocompatibility: SLM Ta demonstrated superior cell affinity and osteogenic activity, significantly outperforming traditional titanium alloys.
3. Clinical Application Prospects: SLM porous tantalum bone plates showed excellent fracture healing effects in clinical trials, indicating broad application prospects.