Mg-based alloys as biodegradable materials have several advantages. However, the extensive applications of Mg-based alloys are limited mainly by their high corrosion rate and loss in structural integrity in a physiological environment. In order to improve the corrosion resistance and biocompatibility of biomedical magnesium, fluorine (F) ions are doped in hydroxyapatite (HA) to form fluorohydroxyapatite (FHA) surface coatings on the Mg-8.5Al-0.5Zn (AZ80) Mg alloy by the hydrothermal synthesizing process. Experimental evidence confirmed that FHA coatings with nanoscaled needle-like crystals can be uniformly deposited without rupture on the entire surface of AZ80 Mg alloy by the hydrothermal synthesizing process. The hydrothermal deposition coating on AZ80 is composed of a Mg(OH) 2 intermediate layer and a FHA top coat. X-ray photoelectron spectroscopy results show that fluorine ions are successfully substituted into the HA crystal structure. Potentiodynamic polarization and immersion tests in the Kokubo's simulated body fluid (SBF) show that the corrosion resistance of AZ80 is significantly improved and the dissolution rate is decreased with the deposition of hydrothermal FHA coatings. The in vitro cell culture studies, using human osteosarcoma MG63 osteoblast-like cell, demonstrated that significant cell viability and proliferation on the surface of FHA-coated AZ80 Mg alloy after 6 to 48 h cell culture. The results suggest that the hydrothermally synthesized FHA coating is effective to improve the in vitro biocompatibility of the Mg-based alloys.
Electric cell–substrate impedance sensing (ECIS) is an attractive method for monitoring cell behaviors in tissue culture in real time. The time series impedance fluctuations of the cell-covered electrodes measured by ECIS are the phenomena accompanying cellular micromotion as cells continually rearrange their cell–cell and cell–substrate adhesion sites. Accurate assessment of these fluctuations to extract useful information from raw data is important for both scientific and practical purposes. In this study, we apply discrete wavelet transform (DWT) to analyze the concentration-dependent effect of cytochalasin B on human umbilical vein endothelial cells (HUVECs). The sampling rate of the impedance time series is 1 Hz and each data set consists of 2048 points. Our results demonstrate that, in the Daubechies (db) wavelet family, db1 is the optimal mother wavelet function for DWT-based analysis to assess the effect of cytochalasin B on HUVEC micromotion. By calculating the energy, standard deviation, variance, and signal magnitude area of DWT detail coefficients at level 1, we are able to significantly distinguish cytotoxic concentrations of cytochalasin B as low as 0.1 μM, and in a concentration-dependent manner. Furthermore, DWT-based analysis indicates the possibility to decrease the sampling rate of the micromotion measurement from 1 Hz to 1/16 Hz without decreasing the discerning power. The statistical measures of DWT detail coefficients are effective methods for determining both the sampling rate and the number of individual samples for ECIS-based micromotion assays.
Magnesium alloys with coatings have the potential to be used for bone substitute alternatives since their mechanical properties are close to those of human bone. However, the surface modification of magnesium alloys to increase the surface biocompatibility and reduce the degradation rate remains a challenge. Here, FHA-Mg scaffolds were made of magnesium alloys and coated with fluorohydroxyapatite (FHA). Human mesenchymal stem cells (hMSCs) were cultured on FHA-Mg scaffolds and cell viability, proliferation, and osteogenic differentiation were investigated. The results showed that FHA-Mg scaffolds display a nano-scaled needle-like structure of aggregated crystallites on their surface. The average Mg2+ concentration in the conditioned media collected from FHA-Mg scaffolds (5.8–7.6 mM) is much lower than those collected from uncoated, Mg(OH)2-coated, and hydroxyapatite (HA)-coated samples (32.1, 17.7, and 21.1 mM, respectively). In addition, compared with hMSCs cultured on a culture dish, cells cultured on FHA-Mg scaffolds demonstrated better proliferation and comparable osteogenic differentiation. To eliminate the effect of osteogenic induction medium, hMSCs were cultured on FHA-Mg scaffolds in culture medium and an approximate 66% increase in osteogenic differentiation was observed three weeks later, indicating a significant effect of the nanostructured surface of FHA-Mg scaffolds on hMSC behaviors. With controllable Mg2+ release and favorable mechanical properties, porous FHA-Mg scaffolds have a great potential in cell-based bone regeneration.
Novel diphoshinoamine(PNRNP) ligands have been used in ethylene oligomerization with Cr(III) compounds and cocatalyst. The results indicate that the catalyst system can yield 1-octene in selectivities up to 80%. Another novel diphoshinoamine ligands (((Ar2P)2N)2R)(R=cyclopropylamine) also were synthesized and characterized. Factors which affect the result of ethylene tetramerisation, such as cocatalyst, temperature, pressure and the molar ratio of Al/Cr were examined. Steric effects and electric effects were also considered in this report.
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