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

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.

In Vitro Degradation and In Vivo Biocompatibility of Strontium-Doped Magnesium Phosphate-Reinforced Magnesium Composites.

Magnesium is projected for use as a degradable orthopedic biomaterial. However, its fast degradation in physiological media is considered as a significant challenge for its successful clinical applications. Bioactive reinforcements containing Mg-based composites constitute one of the promising approaches for developing degradable metallic implants because of their adjustable mechanical behaviors, corrosion resistance, and biological response. Strontium is a trace element known for its role in enhancing osteoblast activity. In this study, bioactive SrO-doped magnesium phosphate (MgP)-reinforced Mg composites containing 1, 3, and 5 wt % MgP were developed through the casting route. The influence of the SrO-doped MgP reinforcement on degradation behaviors of the composites along with its cell-material interactions and in vivo biocompatibility was investigated. The wt % and distribution of MgP particles significantly improved the mechanical properties of the composite. HBSS immersion study indicated the least corrosion rate (0.56 ± 0.038 mmpy) for the Mg-3MgP composite. The higher corrosion resistance of Mg-3MgP leads to a controlled release of Sr-containing bioactive reinforcement, which eventually enhanced the cytotoxicity as measured using MG-63 cell-material interactions. The in vivo biocompatibility of the composite was evaluated using the rabbit femur defect model. Micro-computed tomography (µ-CT) and histological analysis supported the fact that Mg-3MgP maintained its structural integrity and enhanced osteogenesis (50.36 ± 2.03%) after 2 months of implantation. The results indicated that the Mg-MgP composite could be used as a degradable internal fracture fixation device material.