Potential use of Friction Welding for Fabricating Semi-Biodegradable Bone Screws

Certain surgical interventions, such as fractures, may require implants that have a combination of external and internal parts made of inert and biodegradable biomaterials, respectively. This implant design can be fabricated using specific fabrication methods such as friction welding that are able to efficiently combine two biomaterials. This study reports the utilization of the direct friction welding technique for the fabrication of semi-biodegradable bone screws using two parent metals of low carbon steel and austenitic stainless steel 202. The welding parameters were optimized to obtain welded joints for bone screw fabrication. The mechanical properties of metals that have been welded were identified through tensile and three-point bending analyses. The corrosion test was then conducted on the welded metals through the measurement of corrosion rate, changes in pH value, morphology visualization, and element release, while the cytotoxicity effect was evaluated through a cell viability test. Screw implant materials with a diameter of up to 12.7 mm were successfully fabricated using a continuous friction drive welding machine at 4000 rpm and 24.5 MPa hydraulic pressure. The results of mechanical testing show that the tensile strength of weld joints decreased by 3.6% from low carbon steel and 20.4% from stainless steel. Fractures were observed at the welding interface after being subjected to flexural testing. The pH value of the Saline solution decreased from 7.13±0.06 to 6.73±0.06 after the welded metals were immersed for up to 8 weeks. Evaluation of the surface morphology in all welding zones at week eight samples obtained that almost all types of corrosion that occurred were uniform corrosion, except in the PZ zone where galvanic corrosion was formed. The concentrations of Cr and Ni ions (ppm level) were very low, namely 0.058 ppm for Cr and 0.199 ppm for Ni. The viability of human fibroblast cells was maintained at higher than 75% viability after the cell incubation at 1, 3, and 5 days with different parts of welded joints.