Synergistic Effects of Cerium and Hot Forging on Biodegradation, Antibacterial Properties, and In Vivo Biocompatibility of Microalloyed Mg–Zr–Sr Alloys

Abstract

Biodegradable magnesium (Mg)-based alloys are potential candidates for orthopedic applications. In the present study, we have discussed the effect of cerium (Ce) addition and hot forging on mechanical properties, in vitro–in vivo corrosion, antibacterial activity, and cytocompatibility of microalloyed Mg-0.2Zr-0.1Sr-xCe (x = 0 [MZS], 0.5 wt % [MZS-Ce]) alloys. Addition of 0.5 wt % Ce to forged MZS alloys leads to strengthening of the basal texture as well as formation of a higher fraction of dynamic recrystallized (DRX) grains. Hot forging and addition of cerium to the MZS alloy improve both the yield strength and ultimate tensile strength of the forged MZS-Ce alloy by 1.39 and 1.21 times, respectively, compared to those of the forged MZS alloy. The potentiodynamic polarization test in Hank’s solution indicates that the corrosion resistance of the forged MZS alloy improves with addition of 0.5 wt % Ce. Uniform distribution of Mg12Ce precipitates, a higher DRX fraction, strengthened texture, and formation of a compact CeO2 passive layer result in 1.68 times reduction in the immersion corrosion rate of the forged MZS-Ce alloy compared to that of the forged MZS alloy. Addition of Ce to the MZS alloy shows excellent antibacterial activity. The forged MZS-Ce alloy exhibited the highest antibacterial efficacy (76.73%). All the alloys show favorable cytocompatibility and alkaline phosphatase (ALP) activity with MC3T3-E1 cells. The improved corrosion resistance of the forged MZS-Ce alloy (95%) leads to higher cell viability compared to that of the forged MZS alloy (85%). In vivo biodegradation and the ability to generate new bones were analyzed by implanting cylindrical samples in the rabbit femur. Histological analysis showed no adverse effects around the implants. Gradual degradation of the implants and higher new bone formation around the forged MZS-Ce sample were confirmed by micro-CT analysis. Bone regeneration around the implants (58.21%) was validated by flurochrome labeling. After 60 days, the forged MZS-Ce alloy showed controlled corrosion and better bone–implant integration, presenting it as a potential candidate for internal fracture fixation materials.

Synergistic Improvement of Antibacterial and Osteogenic Differentiation of Thermomechanically Processed Mg–Zr–Sr-Ce Alloy: Insights into the Role of Precipitate Evolution Supported by AIMD Simulation Study

“…The lower value of R p corresponds to inferior corrosion resistance and vice versa. The polarization resistance for the circuit R S + (CPE f || ( R f + (CPE dl || R ct || ( R l + L )))) can be determined following basic electricity theory …”

“…Antibacterial efficacy was characterized by exposing the specimen extracts with Pseudomonas aeruginosa, Gram-negative bacterium E. coli (DH5α), and Gram-positive bacterium Staphylococcus aureus , retaining specimen extracts to bacterial solution at a ratio of 9:1. , The autoclaved specimens were immersed in HBSS for 24 h at 37 °C to prepare the extract. The surface area of specimen to HBSS volume was maintained at 3 cm 2 /mL following the ISO-10993:12 protocol.…”