Mechanical response of a gravity cast Mg-9Al-1Zn-0.2Sc alloy at strain rates from 10-4 to 10 3 /s

A magnesium alloy of nominal composition Mg-9Al-lZn-0.2Sc was formed into plates by die casting and underwent annealing and T4 condition heat treatments to investigate the mechanical response of varying microstructures at strain rates from 10-4-103/s in tension and compression. Full microstructural characterization was performed using optical microscopy, electron backscatter diffraction and energy dispersive x-ray spectroscopy. Quasi-static and dynamic testing was performed using a universal testing machine and a Split Hopkinson Pressure Bar in conjunction with digital image correlation for strain field mapping. Characterization and mechanical testing indicates that the T4 condition has the highest overall strength due to small equiaxed grains, a decrease in the size of ß-Mg17Al12 phase at the grain boundaries, and an increase in the size of scandium intermetallics. Testing indicates an increase in strain hardening for dynamic compression and strain rate dependence in tension; failing suddenly due to casting defects dominating the fracture mechanics. Copyright © 2016 by The Minerals, Metals & Materials Society. All rights reserved

Near-infrared-emissive polymersomes: Self-assembled soft matter for in vivo optical imaging

We demonstrate that synthetic soft materials can extend the utility of natural vesicles, from predominantly hydrophilic reservoirs to functional colloidal carriers that facilitate the biomedical application of large aqueous-insoluble compounds. Near-infrared (NIR)-emissive polymersomes (50-nm- to 50-μm-diameter polymer vesicles) were generated through cooperative self assembly of amphiphilic diblock copolymers and conjugated multi(porphyrin)-based NIR fluorophores (NIRFs). When compared with natural vesicles comprised of phospholipids, polymersomes were uniquely capable of incorporating and uniformly distributing numerous large hydrophobic NIRFs exclusively in their lamellar membranes. Within these sequestered compartments, long polymer chains regulate the mean fluorophore–fluorophore interspatial separation as well as the fluorophore-localized electronic environment. Porphyrin-based NIRFs manifest photophysical properties within the polymersomal matrix akin to those established for these high-emission dipole strength fluorophores in organic solvents, thereby yielding uniquely emissive vesicles. Furthermore, the total fluorescence emanating from the assemblies gives rise to a localized optical signal of sufficient intensity to penetrate through the dense tumor tissue of a live animal. Robust NIR-emissive polymersomes thus define a soft matter platform with exceptional potential to facilitate deep-tissue fluorescence-based imaging for in vivo diagnostic and drug-delivery applications