Improved in vivo bone regeneration and mechanical stability in critical-sized defects using WZM211 fluorine coated...

Magnesium (Mg) alloys are promising for application as degradable bone substitutes due to their appropriate elastic modulus, which is closer to bone than that of permanent metallic biomaterials. Once implanted, Mg implants must provide adequate mechanical support to maintain the integrity of the injured site while promoting bone ingrowth to ensure optimal tissue healing. The aim of this study was to assess the quality of bone regeneration in a dog model via high-resolution X-ray computed tomography (XCT) at 4, 8 and 16 weeks following the implantation of Mg-based fibres into critical-sized defects. These results were compared to those induced by a commercially available bovine bone graft (BBG) and empty (E) controls. At 16 weeks, mechanical characterisation was also performed using digital volume correlation (DVC). Mg promoted greater bone formation (bone volume fraction of 0.77 ± 0.15, 0.53 ± 0.07 and 0.45± 0.06 at 16 weeks for Mg, E and BBG, respectively). New bone formation combined with homogenous and tight integration of the Mg fibres led to the complete restoration of the defect. The newly formed bone showed signs of increasing mineralization (541 ± 50 mg HA.cm^-3), remodelling and angiogenesis after 16 weeks, enabling the Mg fibres to facilitate complete tissue healing and provide sufficient mechanical strength (3.32 ± 0.92 MPa and 152 ± 1 MPa for apparent yield stress and Young's modulus, respectively) to support loading. This study suggests that Mg-based fibres can promote osteointegration and osteoconduction enabling the reconstruction of critical-sized defects while maintaining the mechanical integrity of the injured site. STATEMENT OF SIGNIFICANCE: Magnesium is a highly promising biomaterial for bone regeneration; however, its rapid corrosion in physiological environments can compromise mechanical integrity and lead to treatment failure. This study investigates an innovative strategy designed to slow corrosion, combining 1) a magnesium alloy without aluminium, neodymium or gadolinium, elements commonly present in AZ31 or WE24 alloys but associated with poor biocompatibility and 2) a fluorine coating. The biological and mechanical performance of this composite biomaterial were assessed after implantation in a critical-size bone defect, using histological analyses, X‑ray computed tomography, and digital volume correlation to evaluate bone healing. The findings will contribute to the advancement of safe and effective biomaterials that can be translated to clinical solutions for bone tissue regeneration.