| RESEARCH HIGHLIGHTS |


players are needed for the one-step activation to work, with no additional cues besides LPS. Notably, all of the experiments were


conducted with human monocytes, not mouse cells as most previous studies had done, and as Mortellaro notes: “There are considerable differences between human and mouse immunity.”


Since septic shock results from the flood


of cytokines like IL-1β that can follow an infection, Mortellaro hopes that blocking the one-step activation pathway she teased apart could have therapeutic value in patients with sepsis. And there could be applications in other disease contexts, too. “It would be interesting to investigate this pathway in a


context of metabolic and chronic inflamma- tory diseases,” Mortellaro says.


1. Viganò, E., Diamond, C. E., Spreafico, R., Balachander, A., Sobota, R. M. & Mortellaro, A. Human caspase-4 and caspase-5 regulate the one-step non-canonical inflammasome activation in monocytes. Nature Communications 6, 8761 (2015).


Materials:


STRESSED OUT COATINGS


FINE-GRAINED MICROSTRUCTURE COULD TOUGHEN PROTECTIVE COATINGS


Hard materials like chromium nitride are used as wear and corrosion protection coatings in a wide range of applications, including metal cutting. Now, A*STAR researchers have discovered exactly how such materials behave when used in high-stress situations, paving the way to producing even better coatings1. One way to improve a material's


resistance to wear is to increase its hardness. This depends mainly on the force it can withstand before it starts to permanently deform. In most crystalline materials, this deformation occurs when defects, known as dislocations, start to move through a materi- al’s crystal structure. Currently used coating materials are


very brittle, with a toughness only a little more than that of window glass. Also, previous research has shown that it is very difficult to break crystals that are extremely small. So Shiyu Liu of the A*STAR Singapore Institute of Manufacturing Technology and co-workers have used this effect to study


46 A*STAR RESEARCH


Scanning electron microscope images show pristine (left) and compressed (right) micropillars of (top) chromium nitride, (middle) chromium aluminum ni- tride, and (bottom) chromium aluminum nitride / silicon nitride nanocomposite.


how coatings based on chromium nitride might deform. The researchers first made microscopic pillars


of the material, roughly 380 nanometers across. Then they compressed them using a diamond flat punch in a scanning electron microscope at temperatures up to 500 degrees Celsius, and studied their responses (see image). They found that if the chromium-ni-


tride-based coatings are made with very fine grains, each roughly 10 nanometers across, with each grain separated by a thin grain boundary phase, the force required to deform such materials increased dramatically. Indeed, deformation began at stresses very


much higher than expected, and close to the theoretical maximum value from calculations. Liu's team has shown that this increase happened when the grains became so small that they did not contain dislocations, so that the applied forces had to be sufficiently large to form new dislocations within the grains. It had long been thought that the thin


grain boundary phase would be the main factor in determining the material’s proper- ties. However, the researchers have shown this was not the case, providing a way to reliably make a hard material. The results show that the formation of a fine-grained microstructure could provide a


ISSUE 5 | OCTOBER – DECEMBER 2016


Reprinted from Ref. 2, with the permission of AIP Publishing.


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