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The present work aims to understand the effect of zinc and rare-earth element addition (i.e., 2 wt% Gd, 2 wt% Dy, and 2 wt% of Gd and Nd individually) on the microstructure evolution, mechanical properties, in vitro corrosion behavior, and cytotoxicity of Mg for biomedical application. The microstructure results indicate that the Mg–Zn–Gd alloy consists of the lamellar long period stacking ordered phase. The electrochemical and immersion corrosion behavior were studied in Hanks balanced salt solution. Enhanced corrosion resistance with reduced hydrogen evolution volume and magnesium (Mg2+) ion release were estimated for the Mg–Zn–Gd alloy as compared to the other two alloy systems. At the early stage of corrosion, formation of the oxide film inhibited the corrosion propagation. However, at the later stages, the breaking of the oxide film leads to shallow pitting mode of corrosion. The ultimate tensile strength of Mg–Zn–Gd–Nd is better than the other two alloys due to the uniform distribution of the Mg12Nd precipitate phase. The moderate strength in the Mg–Zn–Gd alloy is due to the low volume fraction of the secondary phase. The MTT (methylthiazoldiphenyl-tetrazolium bromide) assay study was carried out to understand the cell cytotoxicity on the alloy surfaces. Studies revealed that all three alloys had significant cellular adherence and no adverse effect on cells.
In this investigation, an electron beam melting-processed γ-TiAl alloy (Ti–48Al–2Cr–2Nb, at.%) was oxidized in air to improve its in vitro tribological, electrochemical, and biocompatibility properties. The γ-TiAl alloy samples were oxidized at 400, 600, and 800 °C for 1 and 4 h. The oxidized layer thickness, composition, and surface morphology found to change with oxidation temperature. The oxidation thickness varied between 1.29 ± 0.2 and 2.18 ± 0.2 μm. The primary oxides on the surface were Al2O3 and TiO2 with minor concentrations of Cr2O3, Nb2O5, and nitrides of Ti. The surface hardness of the alloy increased by 1.7-fold with increasing temperature from 400 to 800 °C with 1 h soaking, and at 4 h, the maximum hardness was 12.26 GPa. The high hardness of the oxidized γ-TiAl alloy resulted in two orders of magnitude lower wear rate than the bare γ-TiAl alloy. Oxidation at 800 °C for 4 h resulted in significant reduction in corrosion current and no passivity breakdown was observed. In vitro cell culture experiments, using mouse preosteoblast cells, revealed high cell density on the oxidized γ-TiAl alloy, suggesting its enhanced cell proliferation compared to the bare γ-TiAl alloy and CP-Ti.
Surface modification by the bioactive material is a potential way to overcome the poor osseoconductivity of titanium (Ti)-based implants. A continuous wave laser source was used to deposit strontium titanate (SrTiO3)-reinforced Ti coating on the Ti substrate using the laser engineered net shaping (LENS™) process. The maximum of 10 wt% SrTiO3 could be incorporated into Ti using laser without cracking of the deposit. This study investigated the constituent phases, microstructure, compositional analysis, wettability, and electrochemical behavior of the composite coatings. XRD and EDX analyses confirmed the presence of the SrTiO3 phase in the coatings. The composite coatings also exhibited superior mechanical properties, corrosion resistance, and bioactivity compared to that of commercially pure Ti. In vitro ion release study confirmed the sustain release of Sr2+ from the composite coatings. In summary, the excellent mechanical bonding with the substrate and high in vitro bioactivity make these SrTiO3-incorporated composite coatings as a potential material to enhance osseoconductivity of Ti-based orthopedic implants.
Drug delivery systems (DDSs) have been developed to target tumor cells by releasing active biomolecules at the specific site of infection, thus eliminating the side effects of anticancer drugs. However, DDSs are generally limited by high drug dosage, biobarriers, poor target recognition, etc. To address these deficiencies, we propose a new noninvasive method consisting of exposing the cancer cells to a combination of low-intensity pulsed ultrasound (LIPUS) and static magnetic field (SMF). This combined treatment found to negatively regulate colon cancer cell (HCT116) activities in vitro by altering their cell membrane potential and permeability thus increased the DDS efficacy by 40%. The treated cancer cell membrane became hyperpolarized leading to cancer cell death. The combination treatment (LIPUS + SMF) restricted the cancer cell proliferation to 16 and 5% in the presence of bare anticancer drug and DDS, respectively, in 72 h, which is almost 40% higher than that observed without the treatment. The acceleration of cancer cellular inhibition was confirmed by the significant increase in the apoptosis of the cell exposed to the LIPUS + SMF treatment. The observed improvement is believed to be due to changes in the cell membrane stability/permeability as a result of mechanical (20–22 kPa) and electrical (19–23 µV/cm) stimuli generated during the LIPUS + SMF treatment.
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