Research on 3D Bioprinted Scaffolds Promoting Bone Regeneration

Academic Background

In recent years, the incidence of head and craniofacial injuries has significantly increased due to the development of industries and transportation, as well as the frequent occurrence of wars and conflicts. These injuries and related treatments (such as decompressive craniectomy) may lead to cranial defects, which can impair brain function recovery, trigger psychological disorders, and impose socio-economic burdens. Therefore, the successful implementation of cranioplasty is crucial. Traditional autologous bone grafting has been considered the ideal method for cranioplasty. However, in clinical practice, the acquisition of autologous bone marrow-derived mesenchymal stem cells (auto-BMSCs) faces many limitations, such as bone marrow senescence and hematopoietic system diseases. As a result, allogeneic bone marrow-derived mesenchymal stem cells (allo-BMSCs) have emerged as a potential alternative. Nevertheless, the role of allo-BMSCs in bone regeneration remains unclear. This study aims to explore the bone regeneration-promoting effects of allo-BMSCs in 3D-printed autologous bone particle (ABP) scaffolds.

Source of the Paper

This paper was co-authored by Yu Huan, Hongqing Chen, Dezhi Zhou, and others, with the research team affiliated with multiple institutions, including the Department of Neurosurgery at Xijing Hospital of the Air Force Medical University in Xi’an, China, and the Department of Mechanical Engineering at Tsinghua University. The paper was published online on January 10, 2025, in the journal Bio-design and Manufacturing, with the DOI 10.1631/bdm.2400011.

Research Process and Results

1. Research Design and Experimental Process

This study was divided into in vitro and in vivo experiments to validate the bone regeneration capacity of allo-BMSCs in 3D-printed ABP scaffolds.

1.1 In Vitro Experiments

• Experimental Design: The research team first used 3D bioprinting technology to simultaneously print polycaprolactone (PCL), ABP, and allo-BMSCs into a multi-layer composite scaffold. PCL provided mechanical support, ABP released bioactive factors, and allo-BMSCs served as seed cells to promote osteogenesis.
• Cell Culture and Differentiation: Allo-BMSCs were cultured in 2D and 3D systems, and their osteogenic differentiation capacity was evaluated through alkaline phosphatase (ALP) staining and quantitative real-time PCR (qPCR) analysis.
• Results: ABP significantly promoted the osteogenic differentiation of allo-BMSCs, with more pronounced effects in the 3D culture system. ALP activity and the expression of osteogenesis-related genes (such as OCN, BMP2, and RUNX2) were higher in the ABP/allo group compared to the control groups.

1.2 In Vivo Experiments

• Animal Model: Beagle dogs aged 18–20 months were used as experimental subjects. A full-thickness cranial defect model with a diameter of 2 cm was created. Three months later, 3D-printed PCL/ABP/allo scaffolds were used for cranioplasty.
• Histological and Imaging Analysis: Bone regeneration was assessed at three and nine months post-surgery through histological staining, immunohistochemical analysis, and micro-computed tomography (micro-CT).
• Results: The PCL/ABP/allo group showed higher collagen volume and expression of chondrogenesis markers (such as ACAN and COL2) at three months post-surgery. At nine months, the new bone formation in this group was significantly higher than in other groups, and differences in trabecular bone number (Tb.N) and spacing (Tb.Sp) further confirmed the synergistic effects of ABP and allo-BMSCs.

2. Key Findings and Mechanisms

• Differentiation and Survival of Allo-BMSCs: Using green fluorescent protein (GFP) labeling, the study found that only a small portion of the implanted allo-BMSCs survived and differentiated into vascular endothelial cells, chondrocytes, and osteocytes.
• Paracrine Signaling and Recruitment of Native BMSCs: The implanted allo-BMSCs released stromal cell-derived factor 1 (SDF1) through paracrine signaling, recruiting native BMSCs into the defect area, thereby promoting bone regeneration.
• Immune Response Evaluation: The study also found that the implantation of allo-BMSCs did not significantly increase local inflammatory responses, indicating their safety and reliability in bone tissue engineering.

Conclusions and Significance

This study successfully designed a novel 3D bioprinted scaffold combining ABP and allo-BMSCs, which significantly promoted bone regeneration. The results demonstrated that allo-BMSCs recruit native BMSCs by releasing SDF1 through paracrine signaling, playing a crucial role in bone defect repair. This finding provides a theoretical basis for the application of allo-BMSCs in bone tissue engineering and offers new insights for the clinical treatment of cranial defects.

Research Highlights

1. Innovative Scaffold Design: This study is the first to combine PCL, ABP, and allo-BMSCs using 3D bioprinting technology to create a composite scaffold with both mechanical strength and bone regeneration potential.
2. Revealing Paracrine Mechanisms: The study clarified the molecular mechanism by which allo-BMSCs recruit native BMSCs through SDF1 release, providing a new perspective for bone regeneration research.
3. Clinical Application Potential: The results offer important references for the clinical application of allo-BMSCs in bone defect repair, especially in cases where autologous BMSCs are difficult to obtain.

Additional Valuable Information

• Future Research Directions: The research team suggests further exploration of the most effective components in ABP for promoting bone regeneration and validating the potential of allo-BMSCs in other bioactive scaffolds.
• Technical Limitations: This study did not directly compare the osteogenic effects of auto-BMSCs and allo-BMSCs. Future comparative experiments could further validate the substitutive value of allo-BMSCs.

Through this study, scientists have deepened their understanding of the mechanisms of allo-BMSCs and provided new tools and methods for bone tissue engineering and clinical treatment.