nanoMAG (United States)

Magnesium (Mg) alloys are gaining interest for biodegradable medical implant devices due to a good combination of mechanical properties and biocompatibility. Nevertheless, the fast degradation rates of Mg and its biocompatible alloys in the aggressive physiological environment impose limitations on their clinical applications. This necessitates the development of Mg based implants with controlled degradation rates to match the kinetics of the bone and tissue healing process and to avoid any complications or issues that might negatively impact surrounding tissues. The current study presents alloy design and thermomechanical processing to optimize the mechanical and biological properties of a new proprietary Mg based alloy. Its corrosion profiles have been evaluated by a combination of in vitro and in vivo experimental studies. The corrosion rates of laboratory samples and prototype devices have been examined via long term immersion studies by measuring the cumulative amount of hydrogen (H2) that is emitted by samples. The cumulative H2 measurements have a direct correlation to the mass loss that the Mg alloy samples undergo during the duration of the tests. The results of the current in vitro corrosion studies are compared to 52 week small animal studies to develop predictive models for designing future biomedical devices.

Lightweight, recyclable, and plentiful Mg alloys are receiving increased attention due to an exceptional combination of strength and ductility not possible from pure Mg. Yet, due to their alloying elements, such as rare-earths or aluminum, they are either not economical or biocompatible. Here we present a new rare-earth and aluminum-free magnesium-based alloy, with trace amounts of Zn, Ca, and Mn (≈ 2% by wt.). We show that the dilute alloy exhibits outstanding high strength and high ductility compared to other dilute Mg alloys. By direct comparison with annealed material of the same chemistry and using transmission electron microscopy (TEM), high-resolution TEM (HR-TEM) and atom probe tomography analyses, we show that the high strength can be attributed to a number of very fine, Zn/Ca-containing nanoscale precipitates, along with ultra-fine grains. These findings show that forming a hierarchy of nanometer precipitates from just miniscule amounts of solute can invoke simultaneous high strength and ductility, producing an affordable, biocompatible Mg alloy.

Ag5-induced formation of surface polarons at the Ag5–TiO2 interface enables to reveal a general polarization phenomenon.

The alloy development of bioabsorbable BioMg® 250 is described in terms of design of mechanical properties, biocorrosion rate and biocompatibility. The basic mechanistic role of microalloyig elements Zn, Ca and Mn is discussed as related to microstructures. In vitro corrosion and in vivo animal studies are reported. Finally, we list potential orthopedic applications in bone fixation devices fabricated from BioMg 250.

A wide variety of Mg alloysAlloys have been processed by ThixomoldingThixomolding ® followed by thermomechanical processingThermomechanical processing (TMP)—to increase tensile, creep and fatigue strength, ductility and formability. These alloys encompass variations in Al, Zn, Ca, Mn, Sr, Y, Zr and Rare Earths (RE) in the Mg base. Due to the fine microstructure and low porosity rendered by Thixomolding, TMP has been feasible using high strain warm rolling and warm pressing. Thus, grain size is further reduced and texture can be moderated. Data is presented on the above alloys along with more extensive information on the commercial alloys AM60 and AZ61; but also the newly developed AZ70L-TH and AXJ810-TH alloys. In discussing the above processing, properties are related to microstructures.

Microstructure evolution is studied in Thixomolded® Thermomechanical Processed (TTMP) AZ61L sheet at various stages of processing. Transmission electron microscopy (TEM) is utilized to examine (1) grain refinement and recrystallization and (2) refinement and re-distribution of the β-Mg17Al12 phase in the as-Thixomolded, as-TTMP, and annealed conditions. Electron backscatter diffraction (EBSD) is used to study texture evolution through TTMP and annealing. The influence of microstructure produced by TTMP and annealing on the mechanical properties will be discussed.