Synthesis, Structural Characterization, Degradation Rate, and Biocompatibility of Magnesium-Carbonate Apatite (Mg-Co₃Ap) Composite and Its Potential as Biodegradable Orthopaedic Implant Base Material

Suitable biomechanical properties with a degradation rate parallel to normal bone healing time are vital characteristics for biodegradable implant material in orthopaedics. Magnesium (Mg) is a natural micronutrient as well as biodegradable metal with biomechanical characteristics close to that of the human bone, while carbonate apatite (CO3Ap) is a biological apatite with good osteoconductivity which allows bone healing without forming fibrotic tissue. We fabricated a Mg-CO3Ap composite with various content ratios by powder metallurgy, various milling times (3, 5, and 7 hours) at 200 RPM, warm compaction at 300°C and pressure of 265 MPa, sintering at 550°C, holding time of 1 hour, heating rate of 5°C/minutes, and room atmosphere cooling. Specimens were successfully created and had a density comparable to that of the human bone (1.95-2.13 g/cm3). Good biocompatibility was found on Mg-10% CO3Ap composite (66.67% of viable cells). Nevertheless, its biomechanical properties and corrosion resistance were inferior to the human bone. Additionally, the materials of the composites make the surrounding environment alkaline. Interparticle consolidation and grain size were dissatisfactory due to microstructural pores presumably formed by the Mg(OH)2 layer and oxidation process during sintering. However, alkaline condition caused by the material corrosion by-product might be beneficial for bone healing and wound healing process. Modifications on fabrication parameters are needed to improve interparticle consolidation, refine grain size, improve biomechanical strength, reduce corrosion products, and improve the degradation rate.