|Thursday, August 26|
Open porous, biodegradable Mg fiber scaffolds as cancellous bone replacement
* Frank witte, Charité Medical University, Germany
R Bonithon, University of Portsmouth
K Karali, University of Portsmouth
G Tozzi, University of Portsmouth
INTRODUCTION: Magnesium (Mg) alloys are of particular interest for application as degradable bone substitutes due to their appropriate mechanical properties, closer to bone than any other biomaterials (1). 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 employ high-resolution X-ray computed tomography (XCT) to assess the bone regeneration pattern at 4, 8 and 16 weeks following the implantation of Mg-based fibres into critical-sized defects, compared to that induced by natural bovine bone grafts (BBG) and empty controls. METHODS: Critical size defects of 5mm diameter and 5mm deep were drilled in chronic bone defects (3months after teeth extraction, PM2-M1) bilateral into the mandibula of beagle dogs. The defects were either filled with Mg scaffold, BBG or left empty. After sample retrieval, high-resolution XCT has been performed. Mechanical characterisation was also performed on 16-weeks newly formed bone-biomaterial tissues by means of in situ XCT mechanics coupled with digital volume correlation (DVC). RESULTS: Mg promoted higher bone formation (0.77 ± 0.15, 0.53 ± 0.07 and 0.45± 0.06 at 16 weeks for Mg, empty and BBG, respectively) up to full restoration of critical-sized defects, with closer interaction between bone and Mg fibres, as well as adequate corrosion rate. The newly formed bone seemed to undergo mineralization (541 ± 50 mg HA.cm-3), physiological remodelling (osteocytes cavities 426 ± 221 μm3) and angiogenesis after 16 weeks, enabling the Mg-bone system to gain sufficient mechanical strength (3.32 ± 0.92 MPa and 152 ± 1 MPa for apparent yield stress and Young’s modulus, respectively). Fig. 1: XCT cross-sections of the 6-7μm voxel size images at 16 weeks post-implantation for (a) Mg, (b) empty and (c) BBG. Red arrows indicate corroded Mg fibres (a) or BBG granules (c). Fig. 2: Bone volume fraction (Bvf) for Mg, empty and BBG at 4, 8 and 16 weeks after implantation. # p<0.001 significant difference between 4 and 16 weeks for Mg; *p<0.05 significant difference compared to Mg at 16 weeks. DISCUSSION & CONCLUSIONS: This study provides evidence that these Mg-based fibres has the ability to promote osteointegration, conduction and promotion allowing the reconstruction of critical-sized defects while maintaining the mechanical integrity of the injured site. REFERENCES: 1 R. Bonithon, A.P. Kao, M.P. Fernandez, et al (2021) Acta Biomater 127:338-352.
Enhancing nerve regeneration with a zinc-iron alloy
* Sarah Pixley, University of Cincinnati College of Medicine, United States
Avi Leon, Ben-Gurion University of the Negev
Tomer Ron, Ben-Gurion University of the Negev
Kevin Little, University of Cincinnati College of Medicine
Eli Aghion, Ben-Gurion University of the Negev
Microfilaments were made of a novel Zn-2%Fe alloy to give physical support for regenerating nerves to bridge nerve gaps made by injury. Microfilaments (0.3 mm diameter, 10 mm long) of the alloy were prepared by extrusion followed by drawing. They were placed inside hollow silicone nerve conduits to make scaffolds that were used to repair six mm gaps in adult rat sciatic nerves. Controls were empty conduits or autografts. The Zn group showed improved health in the first week after surgery and similar functional recovery as other groups. After 17 weeks, no significant toxicity or inflammation were seen with the Zn alloy and axons had used the filaments for guidance. Axon density with Zn was as high as in positive controls. Only a thin, poorly organized fibrous capsule separated Zn from healthy axons. Thus, Zn based alloys show excellent promise for use in nerve regeneration and repair.
X-Ray Fluorescence study of the influence of Mg-10Gd implant on the bone ultrastructure
* Kamila Iskhakova, Helmholtz-Zentrum Geesthacht, Germany
Berit Zeller-Plumhoff, Helmholtz-Zentrum Geesthacht
Florian Wieland, Helmholtz-Zentrum Geesthacht
Regine Willumeit-Römer, Helmholtz-Zentrum Geesthacht
Biodegradable magnesium (Mg) implants gained a high interest due to high biocompatibility and good mechanical properties similar to the bone itself. Magnesium-Gadolinium alloy Mg-10Gd as an implant material not only shows the improved mechanical properties and the degradation rate but also enhances bone osseointegration. During the healing process, newly formed bone ultrastructure can be affected by implant degradation, e.g. ionic substitution or change in crystal lattice parameters. Due to this, the mechanical properties of the bone matrix might change resulting in failure of the implant. In this study, we have looked into how the Mg-10Gd screw-shaped implant affects the newly formed bone ultrastructure. For that, we have studied the atomic distribution in the rat bone tissue the implant at different healing times. X-ray Fluorescence analysis (XRF) has shown that the ultrastructure is not affected by the Mg-10Gd implant and Gd stays in the degradation layer without being incorporated into the bone.
Discussion - Short Oral Presentation