Comparison of microstructure, mechanical property, and degradation rate of Mg-1Li-1Ca and Mg-4Li-1Ca alloys.

Mg-1 wt.% Li-1 wt.% Ca (LX11) and Mg-4 wt.% Li-1 wt.% Ca (LX41) alloys share the same hexagonal closed-packed crystalline structure. However, the differences in microstructure, mechanical properties, and degradation rates between the two alloys are not well understood. Hereby, the above three aspects of LX11 and LX41 alloys were studied via optical microscopy, tensile tests, and electrochemical polarization and electrochemical impedance spectroscopy, together with hydrogen evolution. The concentration of the released Mg2+, Ca2+, and Li+ ions was analyzed using a flame atomic absorption spectrophotometer. Results demonstrated that the LX11 alloy was composed of finer α-Mg grains, fewer twins, and smaller volume fractions of the intermetallic phases Mg2Ca than the LX41 alloy. The increasing Li concentration generated a weak decrease in the yield strength of the Mg-Li-Ca alloys, a remarkable increase in elongation to failure, and a stable ultimate tensile strength. The LX11 alloy had better corrosion resistance than the LX41 alloy. The release rate of the cations (Mg2+, Ca2+, and Li+) varied significantly with time. The release rate of metallic ions in Hank's solution cannot reflect the true corrosion rate of Mg-Li-Ca alloys due to the formation of the precipitated corrosion products and their difference in solubility. The dealloying corrosion mechanism of the Mg2Ca phase in Mg-Li-Ca alloys was proposed.

In Vitro Degradation and Photoactivated Antibacterial Activity of a Hemin-CaP Microsphere-Loaded Coating on Pure Magnesium.

Photoactivated sterilization has received more attention in dealing with implant-associated infections due to its advantages of rapid and effective bacteriostasis and broad-spectrum antibacterial activity. Herein, a micro-arc oxidation (MAO)/polymethyltrimethoxysilane (PMTMS)@hemin-induced calcium-bearing phosphate microsphere (Hemin-CaP) coating was prepared on pure magnesium (Mg) via MAO processing and dipping treatments. The morphology and composition of the coating were characterized via scanning electron microscopy, Fourier transform infrared spectrometer, X-ray diffractometer and X-ray photoelectron spectrometer. Corrosion behavior was evaluated through electrochemical and hydrogen evolution tests. The release of Fe3+ ions at different immersion times was measured with an atomic absorption spectrophotometer. Antibacterial performance and cytotoxicity were assessed using the spread plate method, MTT assay and live/dead staining experiment. The results showed that the corrosion current density of the MAO/PMTMS@(Hemin-CaP) coating (4.41 × 10-8 A·cm-2) was decreased by two orders of magnitude compared to that of pure Mg (3.12 × 10-6 A·cm-2). Photoactivated antibacterial efficiencies of the Hemin-CaP microspheres and MAO/PMTMS@(Hemin-CaP) coating reached about 99% and 92%, respectively, which we attributed to the photothermal and photodynamic properties of hemin with a porphyrin ring. Moreover, based on the release of Fe3+ ions, the MC3T3-E1 pre-osteoblasts' viability reached up to 125% after a 72 h culture, indicating a positive effect of the coating in promoting cell growth. Thus, this novel composite coating holds a promising application as bone implants.