Research on Magnesium and Gallium Co-loaded Microspheres Accelerating Bone Repair

Academic Background

Bone defects are a common clinical challenge, often caused by infection, tumor resection, or mechanical trauma. Bone defects not only affect patients’ quality of life but may also lead to functional loss. Although bone grafting is currently the primary method for treating bone defects, it faces issues such as limited donor availability, high infection risks, and immune rejection. Additionally, the high cost of bone grafting and the need for multiple surgeries impose socioeconomic burdens. Therefore, developing a biomaterial that can both promote bone regeneration and prevent infection is of great significance.

In recent years, bioresorbable microspheres have garnered significant attention as drug delivery carriers. These microspheres can not only fill irregular bone defects but also provide a suitable microenvironment for cells, promoting bone regeneration. However, existing biomaterials have limited effectiveness in promoting osteogenesis and antibiosis. To address this, researchers have attempted to combine magnesium ions (Mg²⁺), which promote bone formation, with gallium ions (Ga³⁺), which have antibacterial properties, to develop a new type of bone repair material.

Source of the Paper

This paper was co-authored by Jin Bai, Si Shen, Yan Liu, and other researchers from the Tianjin Institute of Environmental and Operational Medicine and the School and Hospital of Stomatology at Tianjin Medical University. The paper was published online on December 17, 2024, in the journal Bio-design and Manufacturing, titled “Magnesium and gallium-coloaded microspheres accelerate bone repair via osteogenesis and antibiosis.”

Research Process and Results

1. Preparation and Characterization of Microspheres

The researchers used a modified water-in-oil-in-water (W1/O/W2) emulsion method to prepare poly(lactic acid-co-glycolic acid) (PLGA) microspheres, co-loading magnesium ions (Mg²⁺) and gallium ions (Ga³⁺) into the microspheres to form Mg-Ga@PLGA microspheres. Scanning electron microscopy (SEM) observations revealed that the microspheres had a rough surface with a diameter of approximately 50 micrometers, making them suitable for filling irregular bone defects. X-ray photoelectron spectroscopy (XPS) analysis showed that the atomic percentages of magnesium and gallium in the microspheres were 6.99% and 0.44%, respectively, indicating successful loading of magnesium and gallium into the microspheres.

2. Release Kinetics of Magnesium and Gallium

To evaluate the release behavior of Mg²⁺ and Ga³⁺, the researchers immersed Mg-Ga@PLGA microspheres in phosphate-buffered saline (PBS) and stirred them magnetically at 37°C. Inductively coupled plasma optical emission spectroscopy (ICP-OES) detection revealed that Mg²⁺ and Ga³⁺ were released rapidly within the first 10 days, after which the release stabilized. This slow-release characteristic helps maintain the local concentration of bioactive components, promoting osteogenesis and antibacterial effects.

3. Biocompatibility Testing

The researchers assessed the biocompatibility of Mg-Ga@PLGA microspheres through cytotoxicity experiments. The results showed that the microspheres had no significant cytotoxicity toward mouse embryo osteoblast precursor cells (MC3T3-E1) or bone marrow-derived macrophages (BMMs). Additionally, cytoskeleton staining and Transwell migration experiments demonstrated that Mg-Ga@PLGA microspheres promoted the migration and adhesion of MC3T3-E1 cells, indicating good biocompatibility and cell support capabilities.

4. Effects on Osteogenesis and Osteoclast Differentiation

Through alkaline phosphatase (ALP) staining and alizarin red S (ARS) staining, the researchers found that Mg-Ga@PLGA microspheres significantly promoted the osteogenic differentiation of MC3T3-E1 cells and increased calcium deposition. Western blot and immunofluorescence experiments further confirmed that Mg-Ga@PLGA microspheres upregulated the expression of osteogenesis-related proteins, such as BMP2 and Runx2. Moreover, tartrate-resistant acid phosphatase (TRAP) staining showed that Mg-Ga@PLGA microspheres inhibited osteoclast differentiation, indicating their dual role in promoting osteogenesis and inhibiting bone resorption.

5. Evaluation of Antibacterial Properties

The researchers assessed the antibacterial properties of Mg-Ga@PLGA microspheres through inhibition zone experiments and live/dead bacterial staining. The results showed that Mg-Ga@PLGA microspheres exhibited significant antibacterial effects against Staphylococcus aureus and Escherichia coli. Gallium ions exert their antibacterial effects by competing with iron ions, disrupting bacterial iron metabolism. Additionally, the presence of magnesium ions further enhanced the antibacterial effect of gallium ions.

6. In Vivo Bone Repair Experiments

In a rat cranial defect model, the researchers implanted Mg-Ga@PLGA microspheres into 8-mm bone defects. After 12 weeks, micro-computed tomography (micro-CT) and histological analysis revealed that Mg-Ga@PLGA microspheres significantly promoted new bone formation, with a bone volume fraction (BV/TV) of 33.41%, significantly higher than that of the control group. Furthermore, immunohistochemical analysis showed that Mg-Ga@PLGA microspheres upregulated the expression of osteogenesis-related proteins, such as BMP2, collagen type I, osteocalcin, and osteopontin, further confirming their potential in bone repair.

7. In Vivo Antibacterial Experiments

To verify the antibacterial effect of Mg-Ga@PLGA microspheres in vivo, the researchers inoculated Staphylococcus aureus into rat cranial defects and implanted the microspheres. After 3 days, colony counting and quantitative real-time PCR (qRT-PCR) analysis revealed that Mg-Ga@PLGA microspheres significantly reduced bacterial survival and decreased the expression levels of inflammatory factors, such as TNF-α and IL-6, demonstrating their good antibacterial and anti-inflammatory effects.

Conclusions and Significance

This study successfully developed a novel Mg-Ga@PLGA microsphere with dual functions of promoting osteogenesis and antibiosis. Through in vitro and in vivo experiments, the researchers confirmed the potential of Mg-Ga@PLGA microspheres in bone repair, particularly in the treatment of infected bone defects. This research not only provides new insights into the treatment of bone defects but also offers important experimental evidence for the development of biomaterials.

Research Highlights

1. Dual Functionality: Mg-Ga@PLGA microspheres simultaneously promote osteogenesis and exhibit antibacterial properties, addressing the limitations of traditional bone repair materials in infection control.
2. Slow Release: The slow-release characteristics of Mg²⁺ and Ga³⁺ in the microspheres help maintain the local concentration of bioactive components, promoting bone repair.
3. Biocompatibility: The microspheres are non-toxic to cells and support cell migration and adhesion, demonstrating good biocompatibility.
4. In Vivo Validation: Through a rat cranial defect model, the researchers validated the bone repair and antibacterial effects of Mg-Ga@PLGA microspheres in vivo, laying the foundation for their clinical application.

Additional Valuable Information

The study also explored the antibacterial mechanism of gallium ions, finding that they compete with iron ions to disrupt bacterial iron metabolism, thereby exerting antibacterial effects. This discovery provides theoretical support for the development of new antibacterial materials. Additionally, the researchers analyzed the expression levels of inflammatory factors through qRT-PCR, further validating the anti-inflammatory effects of Mg-Ga@PLGA microspheres.

This research offers a new solution for the treatment of bone defects, with significant scientific value and clinical application prospects.