Search

Despite various strategies to address sticking failure in stainless steels (STSs), difficulties in understanding its fundamental mechanisms hinder precise solutions during STS fabrication. This study investigated the effect of chromium (Cr) content on the microstructures and failure modes of oxide scales under a tensile load, simulating the hot-rolling process. The dynamic, real-time behavior of crack initiation, propagation, and interfacial delamination in the oxide scales under tension was analyzed using an in situ scanning electron microscopy (SEM) tensile test. With a high Cr content, iron (Fe) oxide and chromium(III) oxide (Cr2O3) form a layered structure, which is delaminated along the interfaces between the thin Cr2O3 layer and the bulk after perpendicular cracking. The saturated crack densities obtained from in situ SEM provide interfacial strength, while the elastic modulus and hardness obtained from nanoindentation provide vertical fracture strength. In combination with an ex situ elemental image analysis, the in situ SEM results reveal three different failure modes of the four different STSs. The results confirm that sticking failure is more likely to occur as the Cr content increases.

This study aimed to assess the skin-related anti-photoaging activities of the 2 epimeric forms of protopanaxadiol (PPD), 20(S)-PPD and 20(R)-PPD, in cultured human keratinocytes (HaCaT cells). The anti-photoaging activity was evaluated by analyzing the levels of reactive oxygen species (ROS) and matrix metalloproteinases (MMPs), as well as cell viability for HaCaT cells under UV-B irradiation. The activities for MMP-2 and -1 in conditioned medium were determined using gelatin zymography, and MMP-2 protein in the conditioned medium was detected using Western blot analysis. 20(S)-PPD, but not 20(R)-PPD, suppressed UV-B-induced ROS elevation. Neither of the epimers, at the concentrations used, exhibited cytotoxicity, irrespective of UV-B irradiation. 20(S)-PPD, but not 20(R)-PPD, exhibited an inhibitory effect on UV-B-induced MMP-2 activity and expression in HaCaT cells. In brief, only 20(S)-PPD, a major metabolic product of PPD-type ginsenosides, inhibits UV-B-induced ROS and MMP-2 elevation, implying its stereospecific anti-photoaging activity on the skin. Key words: saponin, aglycone, anti-photoaging, ginseng, HaCaT. Cette etude visait a evaluer les activites anti-photovieillissement de deux epimeres du protopanaxadiol (PPD), le 20(S)-PPD et le 20(R)-PPD, sur des keratinocytes humains en culture. L'activite anti-photovieillissement a ete evaluee en analysant les niveaux d'especes reactives d'oxygene (ERO), des metalloproteases de la matrice (MMP) et la viabilite cellulaire des cellules HaCaT soumises a une irradiation aux UV-B. L'activite de la MMP-2 et de la MMP-1 dans le milieu conditionne a ete determinee par une zymographie sur gelatine, et la MMP-2 presente dans le milieu conditionne a ete detectee par buvardage Western. Le 20(S)-PPD supprimait l'elevation d'ERO induite par les UV-B, contrairement au 20(R)-PPD. Les deux epimeres, aux concentrations utilisees, n'etaient pas cytotoxiques, peu importe l'irradiation aux UV-B. Le 20(S)-PPD exer^ait un effet inhibiteur sur l'activite et l'expression de la MMP-2 induites par les UV-B chez les cellules HaCaT, contrairement au 20(R)-PPD. En bref, seul le 20(S)-PPD, un metabolite majeur des ginsenosides de type PPD, exerce des effets inhibiteurs sur la production des ERO et l'elevation de MMP-2 induites par les UV-B, ce qui implique que son activite anti-photovieillissement soit stereospecifique. [Traduit par la Redaction] Mots-cles: saponine, aglycone, anti-photovieillissement, ginseng, HaCaT., Introduction UV-B (280-315 nm) radiation is primarily involved in skin photoaging, the signs of which are wrinkles, laxity, coarseness, mottled pigmentation, epidermal thickening, degradation of matrix macromolecules, vascularization, and immunosuppression [...]