Application of Double Gyroid Titanium Alloy Scaffolds Based on Triply Periodic Minimal Surface Structures in Bone Repair

Academic Background

Bone defect repair is a significant challenge in the field of orthopedics, especially in cases of critical-size bone defects caused by trauma, tumors, inflammation, and other diseases. Currently, the commonly used clinical methods for bone repair include autologous bone grafting and allogeneic bone grafting. However, autologous bone grafting is limited by donor site damage and limited bone availability, while allogeneic bone grafting carries risks of immune rejection and disease transmission. Therefore, bone tissue engineering (BTE) has become an important strategy to replace traditional treatment methods. Titanium alloys are widely used in clinical bone repair due to their excellent mechanical properties, biocompatibility, and corrosion resistance. However, the elastic modulus of titanium alloys is higher than that of natural bone, which may lead to the stress shielding effect, resulting in bone resorption and implant loosening. To address this issue, researchers have introduced porous designs to reduce the elastic modulus of implants, thereby avoiding the stress shielding effect and providing effective space for bone ingrowth.

In recent years, porous scaffolds based on triply periodic minimal surface (TPMS) structures have attracted widespread attention due to their similarity to cancellous bone structures. TPMS structures feature smooth and continuous surfaces that promote cell adhesion and proliferation, and they exhibit excellent mechanical properties and osteoconductivity. However, research on the optimal porosity for specific TPMS structures remains limited. This study aims to design and fabricate double gyroid (DG) titanium alloy scaffolds based on TPMS structures, exploring the effects of different porosities on osseointegration and angiogenesis, and providing new design ideas and experimental evidence for bone defect repair.

Source of the Paper

This paper was authored by Hao Liu, Hao Chen, and other researchers from the Department of Orthopedic Surgery, The Second Hospital of Jilin University, and was published online on December 21, 2024, in the journal Bio-design and Manufacturing. The study was supported by multiple funding sources, including the National Natural Science Foundation of China and the Department of Science and Technology of Jilin Province.

Research Process and Results

1. Design and Preparation of Porous Titanium Alloy Scaffolds

The research team used computer-aided design software Rhinoceros 6 and the Grasshopper plugin to design DG titanium alloy scaffolds based on TPMS structures. By adjusting mathematical function parameters, four DG scaffolds with different porosities (40%, 55%, 70%, and 85%) were designed and named DG40, DG55, DG70, and DG85, respectively. The control group consisted of traditional cubic scaffolds with 70% porosity, named Cube. The scaffolds were fabricated using electron beam melting (EBM) technology, with Ti6Al4V ELI powder as the raw material. After fabrication, residual powder was removed from the scaffolds using sandblasting and ultrasonic cleaning, followed by sterilization.

2. Characterization and Mechanical Testing of Scaffolds

The surface morphology and chemical composition of the scaffolds were analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results showed that Ti6Al4V metal particles were uniformly distributed on the scaffold surfaces, and the elemental composition was consistent with standard Ti6Al4V. Micro-computed tomography (micro-CT) revealed that the porous structures of the scaffolds were well-formed, with no visible cracks or impurities. Compression tests indicated that the elastic modulus and compressive strength of the DG scaffolds decreased with increasing porosity, and the DG55 scaffold exhibited mechanical properties most suitable for orthopedic implants.

3. In Vitro Cell Experiments

The research team evaluated the biocompatibility and ability of the scaffolds to promote angiogenesis and osteogenic differentiation through in vitro cell experiments. Rabbit bone marrow mesenchymal stem cells (BMSCs) and human umbilical vein endothelial cells (HUVECs) were used as the research subjects.

• Cell Proliferation Experiment: The proliferation of BMSCs on the scaffolds was assessed using live/dead cell staining and CCK-8 assays. The results showed that the cell proliferation capacity on the DG70 scaffold was significantly better than that on the Cube scaffold, with the DG55 scaffold exhibiting the best performance.
• Angiogenesis Experiment: The migration and tube formation abilities of HUVECs were evaluated using scratch healing assays, Transwell migration assays, and tube formation assays. The results demonstrated that the DG70 scaffold significantly promoted HUVEC migration and tube formation, with the DG55 scaffold showing the best results.
• Osteogenic Differentiation Experiment: The osteogenic differentiation ability of BMSCs was assessed using alkaline phosphatase (ALP) staining and alizarin red S (ARS) staining. The results indicated that the DG55 scaffold performed best in promoting osteogenic differentiation.

4. In Vivo Animal Experiments

The research team implanted the scaffolds into a critical bone defect model in the femoral condyle of New Zealand rabbits to evaluate their ability to promote angiogenesis and bone regeneration in vivo. Micro-CT and histological analyses revealed that the DG55 scaffold performed best in promoting new bone formation and angiogenesis, with higher maturity of the newly formed bone tissue.

Conclusions and Significance

This study designed and fabricated DG titanium alloy scaffolds based on TPMS structures, systematically exploring the effects of different porosities on osseointegration and angiogenesis. The results demonstrated that the DG55 scaffold performed best in promoting cell proliferation, angiogenesis, and osteogenic differentiation, and its mechanical properties were suitable for orthopedic implants. Compared to traditional cubic scaffolds, DG scaffolds exhibited a larger specific surface area and more uniform fluid distribution characteristics, which better promoted cell adhesion and growth.

The scientific value of this study lies in providing new scaffold design ideas for bone defect repair, optimizing the pore structure design of titanium alloy scaffolds, and offering important experimental evidence for clinical bone repair applications. Additionally, the study revealed the unique advantages of TPMS structures in promoting angiogenesis and bone regeneration, providing new directions for future research in bone tissue engineering.

Research Highlights

1. Innovative Scaffold Design: For the first time, the double gyroid structure was combined with TPMS to design porous titanium alloy scaffolds with excellent biocompatibility and mechanical properties.
2. Systematic Research: The osteointegration and angiogenesis capabilities of scaffolds with different porosities were comprehensively evaluated through in vitro cell experiments and in vivo animal experiments.
3. Optimal Porosity Determination: The study found that the DG scaffold with 55% porosity performed best in promoting bone regeneration and angiogenesis, providing important references for clinical bone repair.
4. Fluid Dynamics Analysis: Computational fluid dynamics analysis revealed the advantages of DG scaffolds in cell adhesion and growth.

Additional Valuable Information

The research team also compared the specific surface area and fluid distribution characteristics of traditional gyroid structures and double gyroid structures, finding that the double gyroid structure had greater advantages in cell adhesion and growth. Additionally, the study explored the role of TPMS structures in activating the YAP/TAZ signaling pathway, providing new insights for future research.