Nanoscale Mechanosensing of Natural Killer Cells is Revealed by Antigen‐Functionalized Nanowires

Cells sense their environment by transducing mechanical stimuli into biochemical signals. Commonly used tools to study cell mechanosensing provide limited spatial and force resolution. Here, a novel nanowire‐based platform for monitoring cell forces is reported. Nanowires are functionalized with ligands for cell immunoreceptors, and they are used to explore the mechanosensitivity of natural killer (NK) cells. In particular, it is found that NK cells apply centripetal forces to nanowires, and that the nanowires stimulate cell contraction. Based on the nanowire deformation, it is calculated that cells apply forces of down to 10 pN, which is the smallest value demonstrated so far by microstructured platforms for cell spreading. Furthermore, the roles of: i) nanowire topography and ii) activating ligands in the cell immune function are studied and it is found that only their combination produces enhanced population of activated NK cells. Thus, a mechanosensing mechanism of NK cells is proposed, by which they integrate biochemical and mechanical stimuli into a decision‐making machinery analogous to the AND logic gate, whose output is the immune activation. This work reveals unprecedented mechanical aspects of NK cell immune function and introduces an innovative nanomaterial for studying cellular mechanics with unparalleled spatial and mechanical resolution.     

Evaluation of the fatigue defect population in an elastomer using X‐ray computed micro‐tomography

As elastomeric materials are heterogeneous by nature, their fatigue behavior is strongly driven by the initiation and the growth of cavities. In this study, X‐ray micro‐tomography is used to describe the fatigue mechanisms at a microscale. This non destructive method has already been widely applied to elastomeric materials to control the fillers size and dispersion or to analyze the cavitation induced under high hydrostatic pressure fatigue loading, for example. Here, this technique is used with a good resolution to analyze the evolution of the defects population during a fatigue campaign on hourglass shaped axisymmetric specimens. The initiation and propagation mechanisms are clearly shown on 3D observations, and the influences of the maximum principal strain and of the number of cycles on several parameters (size repartition, porosity, and defect volumic density) are investigated. A scenario for the fatigue damage evolution is proposed and some fatigue initiation criteria are finally discussed, using the results obtained at the microscopic scale. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers.     

Depuration and Relaying: A Review on Potential Removal of Norovirus from Oysters

Pollution of coastal waters can result in contamination of bivalve shellfish with human enteric viruses, including norovirus (NoV), and oysters are commonly implicated in outbreaks. Depuration is a postharvest treatment involving placement of shellfish in tanks of clean seawater to reduce contaminant levels; this review focuses on the efficacy of depuration in reducing NoV in oysters. There have been many NoV outbreaks from depurated oysters containing around 10³ genome copies/g oyster tissue, far exceeding the median infectious dose (ID50). Half of the published NoV reduction experiments showed no decrease in NoV during depuration, and in the remaining studies it took between 9 and 45.5 d for a 1‐log reduction—significantly longer than commercial depuration time frames. Surrogate viruses are more rapidly depurated than NoV; the mean number of days to reduce NoV by 1 log is 19, and 7.5 d for surrogates. Thus, surrogates do not appear to be suitable for assessing virological safety of depurated oysters; data on reduction of NoV infectivity during depuration would assist evaluations on surrogate viruses and the impact of methods used. The longer persistence of NoV highlights its special relationship with oysters, which involves the binding of NoV to histo‐blood group‐like ligands in various tissues. Given the persistence of NoV and on‐going outbreaks, depuration as currently performed appears ineffective in guaranteeing virologically safe oysters. Conversely, relaying oysters for 4 wk is more successful, with low NoV concentrations and no illnesses associated with products. The ineffectiveness of depuration emphasizes the need for coastal water quality to be improved to ensure oysters are safe to eat.     

Behavior and failure of uniformly hydrided Zircaloy-4 fuel claddings between 25 °C and 480 °C under various stress states,including RIA loading conditions

The anisotropic plastic behavior and the fracture of as-received and hydrided Cold-Worked Stress Relieved Zircaloy-4 cladding tubes are investigated under thermal–mechanical loading conditions representative of Pellet–Clad Mechanical Interaction during Reactivity Initiated Accidents in Pressurized Water Reactors. In order to study the combined effects of temperature, hydrogen content, loading direction and stress state, Axial Tensile, Hoop Tensile, Expansion Due to Compression and hoop Plane Strain Tensile tests are performed at room temperature, 350 °C and 480 °C on the material containing various hydrogen contents up to 1200 wt. ppm (hydrides are circumferential and homogeneously distributed). These tests are combined with digital image correlation and metallographic and fractographic observations at different scales. The flow stress of the material decreases with increasing temperature. The material is either strengthened or softened by hydrogen depending on temperature and hydrogen content. Plastic anisotropy depends on temperature but not on hydrogen content. The ductility of the material decreases with increasing hydrogen content at room temperature due to damage nucleation by hydride cracking. The plastic strain that leads to hydride fracture at room temperature decreases with increasing hydrogen content. The influence of stress triaxiality on hydride cracking is negligible in the studied range. The influence of hydrogen on material ductility is negligible at 350 °C and 480 °C since hydrides do not crack at these temperatures. The ductility of the material increases with increasing temperature. The evolution of material ductility is associated with a change in both the macroscopic fracture mode of the specimens and the microscopic failure mechanisms.     

Cell adhesion molecules and pharmacologic applications. Round Table No 3 at Giens XIII]

The mature ovary contains a large number of macrophages. In the present study, the distribution of macrophages in murine ovaries at various developmental stages was immunohistochemically studied using a monoclonal antibody against F4/80, a highly specific antigen of murine macrophages. The results showed that definite F4/80-positive stains were hardly detectable in ovaries on day 0 after birth. On day 7, a few F4/ 80-positive cells could be identified between the developing follicles. The positive stains were irregular in shape and showed little physical contact with the primordial or primary follicles. By days 14 and 21, when the theca cell layers of growing follicles were developing, the positive cells had extended or elongated to surround the cell layer. On day 28, besides the presence of elongating positive cells surrounding the growing follicles, irregularly shaped F4/80-positive cells became apparent in the interstitium between the growing follicles and also in the capsular tissues. Thereafter, positive cells with stellate appearance were detected in the corpora lutea, which first developed around 6 weeks of age. Although the positive cells were homogenously distributed in the corpora lutea in virgin adults, only a few sporadic positive cells were found there in pregnant mice. However, the positive cells infiltrated into the corpora lutea again in the postpartum period. These results show that ovarian macrophages exhibit dramatical changes in their distribution from neonatal to postpartum periods.     

Thermometric investigations for the characterization of fatigue crack initiation and propagation in Wire and Arc Additively Manufactured parts with as-built surfaces

Metal Additive Manufacturing (AM) allows for the fabrication of complex shapes with high added value at low costs. Indeed, as-built structures are near net shape: they require few to no finishing operations. However, as-built AM parts present significant roughness caused by the layer discretization. In the case of the Wire and Arc Additive Manufacturing (WAAM) process, used for large-scale structures, the as-built roughness is estimated to several hundreds of micrometers. For complex geometries, a complete machining of the surfaces is not necessarily possible. In this study, an experimental method is proposed, relying on thermoelastic stress analysis, to characterize the effect of as-built WAAM surface roughness on high-cycle fatigue properties. Using an infrared camera, multiple cracks can be detected and monitored over a large surface on rough WAAM samples under cyclic bending. The collected data constitutes valuable information for the identification of a fatigue model dedicated to as-built WAAM structures.