Hydrothermal treatment and butylphosphonic acid derived self-assembled monolayers for improving the surface chemistry and corrosion resistance of AZ61 magnesium alloy.

The hydrothermal treatment followed by a self-assembled monolayer (SAM) of 1-butylphosphonic acid through the tethering by aggregation and growth (T-BAG) method was employed to produce protective surface coatings on the Mg-6Al-1Zn alloy (AZ61) for reducing the degradation rate in physiological environments. Potentiodynamic polarization measurements revealed that the organic self-assembled monolayer and Mg(OH)2 coating can further enhance the surface chemical stability and corrosion resistance of Mg alloys. SAM-treated Mg(OH)2 coatings can be served as a more passive surface layer as a result of their much higher charge transfer resistance and the presence of Warburg impedance in electrochemical impedance spectroscopy measurement.

Phenolic Modified Ceramic Coating on Biodegradable Mg Alloy: The Improved Corrosion Resistance and Osteoblast-Like Cell Activity.

Magnesium alloys have great potential for developing orthopedic implants due to their biodegradability and mechanical properties, but the rapid corrosion rate of the currently-available alloys limits their clinical applications. To increase the corrosion resistance of the substrate, a protective ceramic coating is constructed by a micro-arc oxidation (MAO) process on ZK60 magnesium alloy. The porous ceramic coating is mainly composed of magnesium oxide and magnesium silicate, and the results from cell cultures show it can stimulate osteoblastic cell growth and proliferation. Moreover, gallic acid, a phenolic compound, was successfully introduced onto the MAO coating by grafting on hydrated oxide and chelating with magnesium ions. The gallic acid and rough surface of MAO altered the cell attachment behavior, making it difficult for fibroblasts to adhere to the MAO coating. The viability tests showed that gallic acid could suppress fibroblast growth and stimulate osteoblastic cell proliferation. Overall, the porous MAO coating combined with gallic acid offered a novel strategy for increasing osteocompatibility.

Dramatically decreased magnetoresistance in non-stoichiometric WTe2 crystals.

Recently, the layered semimetal WTe2 has attracted renewed interest owing to the observation of a non-saturating and giant positive magnetoresistance (~10(5)%), which can be useful for magnetic memory and spintronic devices. However, the underlying mechanisms of the giant magnetoresistance are still under hot debate. Herein, we grew the stoichiometric and non-stoichiometric WTe2 crystals to test the robustness of giant magnetoresistance. The stoichiometric WTe2 crystals have magnetoresistance as large as 3100% at 2 K and 9-Tesla magnetic field. However, only 71% and 13% magnetoresistance in the most non-stoichiometry (WTe1.80) and the highest Mo isovalent substitution samples (W0.7Mo0.3Te2) are observed, respectively. Analysis of the magnetic-field dependent magnetoresistance of non-stoichiometric WTe2 crystals substantiates that both the large electron-hole concentration asymmetry and decreased carrier mobility, induced by non-stoichiometry, synergistically lead to the decreased magnetoresistance. This work sheds more light on the origin of giant magnetoresistance observed in WTe2.

Microstructure-modified biodegradable magnesium alloy for promoting cytocompatibility and wound healing in vitro.

The microstructure of biomedical magnesium alloys has great influence on anti-corrosion performance and biocompatibility. In practical application and for the purpose of microstructure modification, heat treatments were chosen to provide widely varying microstructures. The aim of the present work was to investigate the influence of the microstructural parameters of an Al-free Mg-Zn-Zr alloy (ZK60), and the corresponding heat-treatment-modified microstructures on the resultant corrosion resistance and biological performance. Significant enhancement in corrosion resistance was obtained in Al-free Mg-Zn-Zr alloy (ZK60) through 400 °C solid-solution heat treatment. It was found that the optimal condition of solid-solution treatment homogenized the matrix and eliminated internal defects; after which, the problem of unfavorable corrosion behavior was improved. Further, it was also found that the Mg ion-release concentration from the modified ZK60 significantly induced the cellular activity of fibroblast cells, revealing in high viability value and migration ability. The experimental evidence suggests that this system can further accelerate wound healing. From the perspective of specific biomedical applications, this research result suggests that the heat treatment should be applied in order to improve the biological performance.

Heat treatment mechanism and biodegradable characteristics of ZAX1330 Mg alloy.

Heat treatments are key processes in the development of biodegradable magnesium implants. The aim of this study is to investigate the factors of microstructures and metallurgical segregation on the functionality of biodegradable magnesium alloy. The solid solution heat treatment and strain induced melting activation heat treatment were employed to alter the microstructures of ZAX1330 alloy in this study. Heat treatments caused a significant change on grain size and distribution of secondary phases. The fine-grained microstructure enhanced the mechanical strength, corrosion resistance and achieved the lowest degradation rate in simulated body fluid solution. In coarse-grained microstructure systems, grain growth followed liquid phase formation. The corrosion rate increased due to a larger cathodic region. The status of micro-alloyed calcium (in solid solution or segregated) influenced the microstructural evolution mechanisms, mechanical strength, and degradation properties. A cytotoxicity test and a live/dead assay showed that ZAX1330 had good cytocompatibility, which varied with heat treatment, and no cell toxicity. The results suggest that heat treatment should be controlled precisely in order to improve the cytocompatibility of magnesium alloys for application in orthopedic implants.

The effect of dynamic culture conditions on endothelial cell seeding and retention on small diameter polyurethane vascular grafts.

Due to the limited number of cells available in endothelial cell (EC) seeding of small diameter vascular grafts, high seeding rate and ideal proliferation are normally required and can be achieved by optimizing the EC seeding and culture procedures. In this study, by using rotational seeding at 0.16 rpm for 12 h in an incubator, 90% cells were successfully seeded on the polyurethane vascular grafts. Following a period of 72 h of static culture, the cell retention after 6 h of flushing could reach 90%. The retention was further enhanced after perfuse culture (9 cm/s). The optimal procedures to prepare a polyurethane vascular graft (4-mm i.d., 4 cm long) populated with firmly attached EC were therefore: (1) seeding the graft with 0.5 ml of cell suspension containing approximately 10(5) cells rotated at 0.16 rpm for 12 h; (2) culturing the seeded graft in static for 72 h; and (3) culturing the graft by perfusion (9 cm/s) for another 72 h to 7 days. These procedures consistently resulted in a graft covered with confluent vein EC that fully retained on the surface after 6 h of in vitro flushing.